Rahim Tafazolli

Professor Rahim Tafazolli FREng


Head of the Institute for Communication Systems (ICS)
Regius, FREng, FIET, WWRF Fellow
+44 (0)1483 689834
03 CII 02
Personal assistant: Samantha Hayward

Academic and research departments

Institute for Communication Systems.

Biography

Affiliations and memberships

Innovate UK (since September 2014)
On the ICT Industry Advisory Board.
UK Smart Cities (since November 2013)
On the forum.
Business, Innovation and Skills (BIS) UK (since March 2012)
Advisory working group to the National Measurement Office for NPL Programmes.
Wireless World Research Forum (WWRF)
In 2011, I was appointed as Fellow in recognition of his personal contributions to the wireless world.
IET Communications
On the policy panel

News

Indicators of esteem

  • Professor Tafazolli was awarded the 28th KIA Laureate Award in 2015 for his contribution to communications technology.

    The laureates of the KIA, Khwarizmi International Award (KIA) of Iran, are selected from the internationally distinguished scientists and researchers whose contributions to the advancement of science and technology are confirmed by the Iranian Research Organisation of Science and Technology (IROST) scientific committee.

    My publications

    Publications

    Wei D, Navaratnam P, Gluhak A, Tafazolli R (2010) Energy-efficient Clustering for Wireless Sensor
    Networks with Unbalanced Traffic Load,
    IEEE Wireless Communications and Networking conference IEEE
    Clustering algorithms have been extensively applied
    for energy conservation in wireless sensor networks (WSNs).
    Cluster-heads (CHs) play an important role and drain energy
    more rapidly than other member nodes. Numerous mechanisms
    to optimize CH selection and cluster formation during the set-up
    phase have been proposed for extending the stable operation
    period of the network until any node depletes its energy. However,
    the existing mechanisms assume that the traffic load contributed
    by each node is the same, in other words, same amount of data are
    sent to CH from the member nodes during each scheduled round.
    This paper assumes the nodes contribute traffic load at different
    rates, and consequently proposes an energy-efficient clustering
    algorithm by considering both the residual node energy and the
    traffic load contribution of each node during the set-up phase.
    The proposed algorithm makes nodes with more residual energy
    and less traffic load contribution get more chances to become CHs.
    Furthermore, clusters are adaptively organized in a way that the
    deviation of ratio between the total cluster energy and the total
    cluster traffic load (ETRatio) is limited, in order to balance the
    energy usage among the clusters. Performance evaluation shows
    that the proposed algorithm extends the stable operation period of
    the network significantly
    Jaber M, Imran MA, Tafazolli R, Tukmanov A (2016) A Distributed SON-based User-Centric Backhaul Provisioning Scheme,IEEE Access 4 pp. 2314-2330 IEEE
    5G definition and standardization projects are well underway, and governing characteristics and major challenges have been identified. A critical network element impacting the potential performance of 5G networks is the backhaul, which is expected to expand in length and breadth to cater to the exponential growth of small cells while offering high throughput in the order of Gbps and less than one-millisecond latency with high resilience and energy efficiency. Such performance may only be possible with direct optical fibre connections which are often not available countrywide and are cumbersome and expensive to deploy. On the other hand, a prime 5G characteristic is diversity, which describes the radio access network, the backhaul, and also the types of user applications and devices. Thus, we propose a novel, distributed, selfoptimized, end-to-end user-cell-backhaul association scheme that intelligently associates users with potential cells based on corresponding dynamic radio and backhaul conditions while abiding by users? requirements. Radio cells broadcast multiple bias factors, each reflecting a dynamic performance indicator (DPI) of the endto-end network performance such as capacity, latency, resilience, energy consumption, etc. A given user would employ these factors to derive a user-centric cell ranking that motivates it to select the cell with radio and backhaul performance that conforms to the user requirements. Reinforcement learning is used at the radio cell to optimize the bias factors for each DPI in a way that maximizes the system throughput while minimizing the gap between the users? achievable and required end-to-end quality of experience (QoE). Preliminary results show considerable improvement in users QoE and cumulative system throughput when compared to state-of-theart user-cell association schemes.
    Nikitopoulos K, Chatzipanagiotis D, Jayawardena C, Tafazolli R (2016) MultiSphere: Massively Parallel Tree Search for Large Sphere Decoders,IEEE GLOBECOM 2016 Proceedings
    ?This work introduces MultiSphere, a method to massively parallelize the tree search of large sphere decoders in a nearly-independent manner, without compromising their maximum-likelihood performance, and by keeping the overall processing complexity at the levels of highly-optimized sequential sphere decoders. MultiSphere employs a novel sphere decoder tree partitioning which can adjust to the transmission channel with a small latency overhead. It also utilizes a new method to distribute nodes to parallel sphere decoders and a new tree traversal and enumeration strategy which minimize redundant computations despite the nearly-independent parallel processing of the subtrees. For an 8 × 8 MIMO spatially multiplexed system with 16-QAM modulation and 32 processing elements MultiSphere can achieve a latency reduction of more than an order of magnitude, approaching the processing latency of linear detection methods, while its overall complexity can be even smaller than the complexity of well-known sequential sphere decoders. For 8×8 MIMO systems, MultiSphere?s sphere decoder tree partitioning method can achieve the processing latency of other partitioning schemes by using half of the processing elements. In addition, it is shown that for a multi-carrier system with 64 subcarriers, when performing sequential detection across subcarriers and using MultiSphere with 8 processing elements to parallelize detection, a smaller processing latency is achieved than when parallelizing the detection process by using a single processing element per subcarrier (64 in total).
    Zhang L, Ijaz A, Xiao P, Tafazolli R (2017) Channel Equalization and Interference Analysis for Uplink Narrowband Internet of Things (NB-IoT),IEEE communications Letters 21 (10) pp. 2206-2209 IEEE
    We derive the uplink system model for In-band
    and Guard-band narrowband Internet of Things (NB-IoT). The
    results reveal that the actual channel frequency response (CFR) is
    not a simple Fourier transform of the channel impulse response,
    due to sampling rate mismatch between the NB-IoT user and
    Long Term Evolution (LTE) base station. Consequently, a new
    channel equalization algorithm is proposed based on the derived
    effective CFR. In addition, the interference is derived analytically
    to facilitate the co-existence of NB-IoT and LTE signals. This
    work provides an example and guidance to support network
    slicing and service multiplexing in the physical layer.
    Zhang L, Ijaz A, Xiao P, Tafazolli R (2017) Multi-service System: An Enabler of Flexible 5G Air-Interface,IEEE Communications Magazine 55 (10) pp. 152-159 IEEE
    Multi-service system is an enabler to flexibly support diverse communication requirements for the next generation wireless communications. In such a system, multiple types of services co-exist in one baseband system with each service having its optimal frame structure and low out of band emission (OoBE) waveforms operating on the service frequency band to reduce the inter-service-band-interference (ISvcBI). In this article, a framework for multi-service system is established and the challenges and possible solutions are studied. The multi-service system implementation in both time and frequency domain is discussed. Two representative subband filtered multicarrier (SFMC) waveforms: filtered orthogonal frequency division multiplexing (F-OFDM) and universal filtered multi-carrier (UFMC) are considered in this article. Specifically, the design methodology, criteria, orthogonality conditions and prospective application scenarios in the context of 5G are discussed. We consider both single-rate (SR) and multi-rate (MR) signal processing methods. Compared with the SR system, the MR system has significantly reduced computational complexity at the expense of performance loss due to inter-subband-interference (ISubBI) in MR systems. The ISvcBI and ISubBI in MR systems are investigated with proposed low-complexity interference cancelation algorithms to enable the multi-service operation in low interference level conditions.
    He Z, Ma Y, tafazolli R (2012) Posterior Cramér-Rao Bound for Inertial Sensors Enhanced Mobile Positioning Under The Random Walk Motion Model,IEEE Wireless Communications Letters (99) pp. 1-4 IEEE
    This letter presents a new posterior Cramér-Rao bound (PCRB) for inertial sensors enhanced mobile positioning, which performs hybrid data fusion of parameters including position estimates, pedestrian step size, pedestrian heading, and the knowledge of random walk motion model. Moreover, a non-matrix closed form of the PCRB is derived without position estimates. Finally, our numerical results show that when the accuracy of step size and heading measurements is high enough, the knowledge of random walk model becomes redundant.
    Shariat M, Quddus AU, Ghorashi SA, Tafazolli R (2009) Scheduling as an Important Cross-Layer Operation for Emerging Broadband Wireless Systems,IEEE COMMUNICATIONS SURVEYS AND TUTORIALS 11 (2) pp. 74-86 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Bennis M, Kermoal J-P, Ojanen P, Lara J, Abedi S, Pintenet R, Thilakawardana S, Tafazolli R (2009) Advanced Spectrum Functionalities for Future Radio Networks, WIRELESS PERSONAL COMMUNICATIONS 48 (1) pp. 175-191 SPRINGER
    Mohamed A, Onireti O, Imran M, Imran A, Tafazolli R (2015) Correlation-based Adaptive Pilot Pattern in Control/Data Separation Architecture,2015 IEEE International Conference on Communications (ICC) pp. 2233-2238
    Most of the wireless systems such as the long term evolution (LTE) adopt a pilot symbol-aided channel estimation approach for data detection purposes. In this technique, some of the transmission resources are allocated to common pilot signals which constitute a significant overhead in current standards. This can be traced to the worst-case design approach adopted in these systems where the pilot spacing is chosen based on extreme condition assumptions. This suggests extending the set of the parameters that can be adaptively adjusted to include the pilot density. In this paper, we propose an adaptive pilot pattern scheme that depends on estimating the channel correlation. A new system architecture with a logical separation between control and data planes is considered and orthogonal frequency division multiplexing (OFDM) is chosen as the access technique. Simulation results show that the proposed scheme can provide a significant saving of the LTE pilot overhead with a marginal performance penalty.
    Tang W, Shakir M, Imran MA, Tafazolli R, Alouini M (2012) Throughput Analysis for Cognitive Radio Networks with Multiple Primary Users and Imperfect Spectrum Sensing,IET Communications 6 (17) pp. 2787-2795 IEEE
    In cognitive radio networks, the licensed frequency bands of the primary users (PUs) are available to the secondary user (SU) provided that they do not cause significant interference to the PUs. In this study, the authors analysed the normalised throughput of the SU with multiple PUs coexisting under any frequency division multiple access communication protocol. The authors consider a cognitive radio transmission where the frame structure consists of sensing and data transmission slots. In order to achieve the maximum normalised throughput of the SU and control the interference level to the legal PUs, the optimal frame length of the SU is found via simulation. In this context, a new analytical formula has been expressed for the achievable normalised throughput of SU with multiple PUs under prefect and imperfect spectrum sensing scenarios. Moreover, the impact of imperfect sensing, variable frame length of SU and the variable PU traffic loads, on the normalised throughput has been critically investigated. It has been shown that the analytical and simulation results are in perfect agreement. The authors analytical results are much useful to determine how to select the frame duration length subject to the parameters of cognitive radio network, such as network traffic load, achievable sensing accuracy and number of coexisting PUs.
    Qi Y, Hoshyar R, Tafazolli R (2009) Efficient hybrid relaying schemes with limited feedback, Proceedings of the 2009 ACM International Wireless Communications and Mobile Computing Conference, IWCMC 2009 pp. 754-758
    We noticed that in a relay system, the assumption of global Channel State Information (CSI) knowledge is unrealistic and normally, only the receiver but not the transmitter side has CSI knowledge. In this paper, we analyzed, with receive CSI, the performance of hybrid relaying scheme in the half-duplex relay channel in terms of the outage probability and expected throughput, where the relay switches between decode-and-forward (DF) and compress-and-forward (CF) modes adaptively according to the current channel realizations. Moreover, since the original CF technique requires global CSI at the relay to calculate the optimal compression rate, we established a restricted feedback link to convey extremely limited CSI (only 3 bits in our results) from the destination to the relay and develop a more practical hybrid relaying scheme. Simulation results revealed that the hybrid relaying scheme with restricted feedback outperforms DF especially when the link between source and relay is of low quality. Copyright © 2009 ACM.
    Quddus AU, Yang X, Tafazolli R (2008) Link-level analysis of downlink handover regions in UMTS,2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7 pp. 2527-2531 IEEE
    Yi N, Ma Y, Tafazolli R (2009) Coexistence Strategies and Capacity Theorems of Interference Awareness Cognitive Radio,2009 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATION WORKSHOPS, VOLS 1 AND 2 pp. 644-648 IEEE
    Salami G, Quddus AU, Thilakawardana D, Tafazolli R (2008) Nonpool based spectrum sharing for two UMTS operators in the UMTS extension band,IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC
    This paper investigates spectrum sharing (in the form of code sharing) between two Universal Mobile Telecommunication System (UMTS) operators in the UMTS extension band (2500-2690MHz) with equal and unequal number of proprietary carriers, respectively. The paper proposes a Dynamic Spectrum Allocation (DSA) algorithm to address the problem of spectrum sharing between two operators on a non-pool basis. It also investigates the impact of Adjacent Channel Interference (ACI) on the spectrum sharing gain. Additionally, an architecture that enables spectrum sharing to take place between two or more UMTS operators is presented. The simulated performance of the proposed DSA algorithm shows that under peak-hour loading, up to 32% increase in capacity can be obtained when compared to currently used Fixed Spectrum Allocation (FSA). © 2008 IEEE.
    Imran A, Tafazolli R (2009) Performance & capacity of mobile broadband WiMax (802.16e) deployed via high altitude platform, 2009 European Wireless Conference, EW 2009 pp. 319-323
    This paper investigates the performance and capacity of a WiMAX 802.16e cellular system deployed via High Altitude Platform (HAP WiMAX) through extensive simulations. HAP WiMAX link performance is evaluated for a wide range of channel conditions in terms of elevation angle and signal to noise ratio (SNR) through a comprehensive link level simulator based on 802.16e. The obtained results are then used to investigate HAP WiMAX cellular system performance in terms of user capacity, cell throughput and Grade of Service (GoS) by modelling a multi cellular scenario. The performance is evaluated for frequency reuse of 1 and 3 with and without Adaptive Coding and Modulations (ACM) for two different user data rates. Simulation results show that, cell throughputs as high as 3.6 Mbps per cell can be achieved for 5MHz channel bandwidth while attaining an acceptable GoS with a minimum frequency reuse of 3 in a HAP WiMAX 802.16e system.
    Movahedian M, Ma Y, Tafazolli R (2008) An MUI resilient approach for blind CFO estimation in OFDMA uplink, IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC
    This paper presents a novel blind method to estimate carrier frequency offsets (CFOs) in OFDMA uplink. The major idea is employing a linear precoder to establish time correlation, which offers a second-order moments based blind CFO estimation for each user. With a careful precoder design, the interference from adjacent users can be considerably mitigated in CFO estimation. Since the majority of interference power is from adjacent users, the proposed method shows significant robustness to multiuser interference (MUI) even without the aid of virtual subcarriers. Simulation results show that the proposed approach offers significant performance improvement in comparison with state-of-the-art approaches in multiuser environments. © 2008 IEEE.
    Mirzadeh S, Tafazolli R, Armknecht F, Pallares J, Afifi H (2008) CPFP: An efficient key management scheme for large scale personal networks,2008 3RD INTERNATIONAL SYMPOSIUM ON WIRELESS PERVASIVE COMPUTING, VOLS 1-2 pp. 743-747 IEEE
    This paper provides an efficient key management scheme for large scale personal networks (PN) and introduces the Certified PN Formation Protocol (CPFP) based on a personal public key infrastructure (personal PKI) concept and Elliptic Curve Cryptography (ECC) techniques.
    Salami G, Thilakawardana S, Tafazolli R (2009) The impact of queuing and call setup delays on UMTS spectrum sharing algorithm, WTS: 2009 WIRELESS TELECOMMUNICATIONS SYMPOSIUM pp. 402-406 IEEE
    Wathan F, Hoshyar R, Tafazolli R (2008) Dynamic grouped chip-level iterated multiuser detection based on Gaussian forcing technique,IEEE COMMUNICATIONS LETTERS 12 (3) pp. 167-169 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Liu H, Ma Y, Tafazolli R (2007) Optimum pilot placement for chunk-based OFDMA uplink: Single chunk scenario, 2007 IEEE 66TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5 pp. 2194-2198 IEEE
    Vural S, Navaratnam P, Tafazolli R (2012) Transmission Range Assignment for Backbone Connectivity in Clustered Wireless Networks, IEEE Wireless Communications Letters
    Liu H, Ma Y, Tafazolli R (2008) On efficiency gain of joint pilot and data adaptation for OFDM based systems, IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC
    in OFDM-based systems, data symbols are usually transmitted together with pilots, which are used for channel estimation or prediction. More pilots in use can further improve the accuracy of channel estimation or prediction. However, this can also result in the efficiency loss of channel gain allocated for data transmission. In this paper, we investigate the joint pilot and data adaptation regarding pilot allocation, payload power and bits. Three different implementation approaches are proposed, the performance is evaluated and shows joint pilot and data adaptation can considerably improve system overall performance, and the efficiency gain related to the pilot-allocation adaptation can be significant. © 2008 IEEE.
    Wang Y, Fan L, He D, Tafazolli R (2008) Solution to weight-adaptive fair queuing, ELECTRON LETT 44 (5) pp. 385-387 INST ENGINEERING TECHNOLOGY-IET
    Liu H, Ma Y, Tafazolli R (2009) Enhanced linear interpolation schemes for chunk-based OFDMA uplink, IEEE Vehicular Technology Conference
    Linear interpolation is often employed for chunk-based OFDMA uplink because of its low complexity and good performance. However, the linear interpolation error induced by the mismatch between the linear interpolation model and the actual channel can be detrimental to high-data-rate systems operating in high signal-to-noise-ratio (SNR) range or high mobility scenario. In this paper, enhanced linear interpolation schemes with small time-direction interpolation error are proposed, particularly for the chunk-based OFDMA uplink. Unlike the conventional linear interpolation, which is based on the assumption that the real and imaginary parts of channel coefficients are separately linearly varying, the proposed schemes are based on an interesting observation that the amplitude and phase of a communication channel are also linearly varying within a short time duration, e.g. a chunk duration. Simulation results show the proposed schemes can effectively improve the performance. © 2009 IEEE.
    Li Z, Tafazolli R (2007) Location management for packet switched services in 3G partnership project networks, IET COMMUNICATIONS 1 (4) pp. 562-569 INST ENGINEERING TECHNOLOGY-IET
    Pateromichelakis E, Shariat M, Quddus A, Tafazolli R (2012) On the Evolution of Multi-cell Scheduling in 3GPP LTE / LTE-A, IEEE Communcations Surveys & Tutorials
    Heliot F, Imran MA, tafazolli R (2011) On the Energy Efficiency Gain of MIMO Communication under Various Power Consumption Models,
    Akbari I, Onireti O, Imran A, Imran MA, Tafazolli R (2015) Impact of Inaccurate User and Base Station Positioning on Autonomous Coverage Estimation,2015 IEEE 20TH INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELLING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD) pp. 114-118 IEEE
    Ul Mustafa HA, Imran MA, Shakir MZ, Imran A, Tafazolli R (2015) Separation Framework: An Enabler for Cooperative and D2D Communication for Future 5G Networks, IEEE COMMUNICATIONS SURVEYS AND TUTORIALS 18 (1) pp. 419-445 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Mirzadeh S, Tafazolli R (2005) Secure Service Discovery for Personal Networks,
    Forum WWR (2006) Technologies for the wireless future, John Wiley & Sons
    This is a comprehensive single point of reference, focusing on the specifications and requirements of 4G and identifying potential business models, the research ...
    Imran A, Imran MA, Tafazolli R (2010) A new performance characterization framework for deployment architectures of next generation distributed cellular networks, IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC pp. 2046-2051
    Performance of next generation OFDM/OFDMA based Distributed Cellular Network (ODCN) where no cooperation based interference management schemes are used, is dependent on four major factors: 1) spectrum reuse factor, 2) number of sectors per site, 3) number of relay station per site and 4) modulation and coding efficiency achievable through link adaptation. The combined effect of these factors on the overall performance of a Deployment Architecture (DA) has not been studied in a holistic manner. In this paper we provide a framework to characterize the performance of various DA's by deriving two novel performance metrics for 1) spectral efficiency and 2) fairness among users. These metrics are designed to include the effect of all four contributing factors. We evaluate these metrics for a wide set of DA's through extensive system level simulations. The results provide a comparison of various DA's for both cellular and relay enhanced cellular systems in terms of spectral efficiency and fairness they offer and also provide an interesting insight into the tradeoff between the two performance metrics. Numerical results show that, in interference limited regime, DA's with highest spectrum efficiency are not necessarily those that resort to full frequency reuse. In fact, frequency reuse of 3 with 6 sectors per site is spectrally more efficient than that with full frequency reuse and 3 sectors. In case of relay station enhanced ODCN a DA with full frequency reuse, six sectors and 3 relays per site is spectrally more efficient and can yield around 170% higher spectrum efficiency compared to counterpart DA without RS. ©2010 IEEE.
    Heliot F, Fazel S, Hoshyar R, Tafazolli R (2009) RECEIVE KNOWLEDGE ONLY POWER ALLOCATION FOR NONREGENERATIVE COOPERATIVE MIMO COMMUNICATION,SPAWC: 2009 IEEE 10TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS pp. 524-528 IEEE
    Gluhak A, Inoue M, Moessner K, Tafazolli R (2007) Signaling channel for coordinated multicast service delivery in next generation wireless networks, IEICE TRANSACTIONS ON COMMUNICATIONS E90B (7) pp. 1780-1790 IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG
    Salami G, Tafazolli R (2009) A two stage genetically inspired algorithm for spectrum sharing between two UMTS operators, International Conference on Ultra Modern Telecommunications & Workshops
    This paper proposes a two stage algorithm to address spectrum sharing between two Universal Mobile Telecommunication System (UMTS) operators. The two stage algorithm uses both genetic algorithm and load balancing techniques. The first stage uses genetic algorithm as a solution to optimize the allocation when the correlation of traffic is low. The second stage uses load balancing scheme in the highly correlated traffic region. The simulation result shows that significant spectrum sharing gains up to 26 percent and 20 percent respectively, can be obtained on both networks using the proposed algorithm.
    Heliot F, Hoshyar R, Tafazolli R (2009) A CLOSED-FORM APPROXIMATION OF THE OUTAGE PROBABILITY FOR DISTRIBUTED MIMO SYSTEMS,SPAWC: 2009 IEEE 10TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS pp. 529-533 IEEE
    Salami G, Thilakawardana S, Tafazolli R (2009) Dynamic spectrum sharing algorithm between two UMTS operators in the UMTS Extension Band, 2009 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATION WORKSHOPS, VOLS 1 AND 2 pp. 338-343 IEEE
    Wei D, Jin Y, Vural S, Moessner K, Tafazolli R (2011) An Energy-efficient Clustering Solution for Wireless Sensor Networks,Transactions on Wireless Communications PP (99) pp. 1-11 IEEE
    Hot spots in a wireless sensor network emerge
    as locations under heavy traffic load. Nodes in such areas quickly deplete energy resources, leading to disruption in network services. This problem is common for data collection scenarios in
    which Cluster Heads (CH) have a heavy burden of gathering and relaying information. The relay load on CHs especially intensifies as the distance to the sink decreases. To balance the traffic load and the energy consumption in the network, the CH role should be rotated among all nodes and the cluster sizes should be carefully determined at different parts of the network.
    This paper proposes a distributed clustering algorithm, Energy-efficient Clustering (EC), that determines suitable cluster sizes depending on the hop distance to the data sink, while achieving approximate equalization of node lifetimes and reduced energy consumption levels. We additionally propose a simple
    energy-efficient multihop data collection protocol to evaluate the effectiveness of EC and calculate the end-to-end energy consumption of this protocol; yet EC is suitable for any data collection protocol that focuses on energy conservation. Performance results demonstrate that EC extends network lifetime and achieves energy equalization more effectively than two well-known clustering algorithms, HEED and UCR.
    Fazel Falavarjani MS, Hoshyar R, Tafazolli R (2010) Performance evaluation of a flexible amplify and forward (AF) combined with HARQ,IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC pp. 488-493
    A Hybrid ARQ (HARQ) scheme employing a flexible amplify and forward (AF) relaying is considered for a cooperative relay channel. Two phase types with flexible length: one phase for relay reception and another phase for relay forwarding are assumed to accommodate half duplex relaying. We assume two types of encoding: repetition coding (RC) and unconstrained coding (UC). The outage performance of the considered flexible AF scheme is analytically derived for any number of retransmissions, and both RC and UC encoding used by the considered HARQ. The state transition models of the considered protocols are presented and then the HARQ throughput and latency performance are analytically calculated; As a result time consuming Monte Carlo based evaluations are avoided. The provided analysis enables us to predict the performance and adjust transmission rate and frame structure for any combination of the signal to noise ratio (SNR) of the involved links. Performance gains of up to 1 and 1.5 dB are observed for the considered simulation scenarios thanks to the flexible AF combined with properly designed HARQ protocols. Also the flexible AF is able to attain its performance over all the range of SNRs of the constituent links while the conventional AF is only efficient on a restricted range of SNRs. ©2010 IEEE.
    Zhang Y, Ma Y, Tafazolli R (2010) Modulation-adaptive cooperation in Rayleigh fading channels with imperfect CSI, IWCMC 2010 - Proceedings of the 6th International Wireless Communications and Mobile Computing Conference pp. 148-152
    Adaptive modulation can improve the throughput of cooperative communications, which has been shown in previous research. So far the adaptive modulation is applied with respect to perfect transmitter side Channel State Information (CSI) in most current work. In this paper we have investigated the modulation-adaptive cooperation in Rayleigh fading channels providing imperfect CSI at senders. The adaptive modulation scheme with rate adaptation at the relay proposed in our previous work has been extended here first. Then a new adaptive modulation scheme with adaptation at both the source and relay is proposed. Simulation results show the proposed two schemes can provide significant improvement in throughput over the fixed DF relaying cooperation even with imperfect feedback; the throughput can be further improved with the proposed scheme allowing adaptive modulation at both the source and relay. Copyright © 2010 © ACM.
    Wathan FP, Hoshyar R, Tafazolli R (2007) Iterated SISO MUD for synchronous uncoded CDMA systems over AWGN channel: Performance evaluation in overloaded condition,2007 INTERNATIONAL SYMPOSIUM ON COMMUNICATIONS AND INFORMATION TECHNOLOGIES, VOLS 1-3 pp. 397-402 IEEE
    Sali A, Widiawan A, Thilakawardana S, Tafazolli R, Evans BG (2005) Cross-layer design approach for multicast scheduling over satellite networks,2nd International Symposium on Wireless Communications Systems 2005 (ISWCS 2005) pp. 701-705 IEEE
    Imran MA, Imran A, tafazolli R (2011) Relay Station Access Link Spectral Efficiency Optimization through SO of Macro BS Tilts,IEEE Communications Letters 15 (12) pp. 1326-1328 IEEE
    In this paper we present a novel framework for spectral efficiency enhancement on the access link between relay stations and their donor base station through Self Organization (SO) of system-wide BS antenna tilts. Underlying idea of framework is inspired by SO in biological systems. Proposed solution can improve the spectral efficiency by upto 1 bps/Hz.
    Hoshyar R, Tafazolli R (2008) Soft decode and forward of MQAM modulations for cooperative relay channels, 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7 pp. 639-643 IEEE
    Auer G, Godor I, Hevizi L, Imran M, Tafazolli R (2010) Enablers for Energy Efficient Wireless Networks,Green Wireless Communications and Networks Workshop ý GreeNet, Proc. IEEE VTC Fall 2010 pp. 1-5 IEEE
    Mobile communications are increasingly contributing to global energy consumption. The EARTH (Energy Aware Radio and neTworking tecHnologies) project tackles the important issue of reducing CO emissions by enhancing the energy efficiency of cellular mobile networks. EARTH is a holistic approach to develop a new generation of energy efficient products, components, deployment strategies and energy-aware network management solutions. In this paper the holistic EARTH approach to energy efficient mobile communication systems is introduced. Performance metrics are studied to assess the theoretical bounds of energy efficiency as well as the practical achievable limits. A vast potential for energy savings lies in the operation of radio base stations. In particular, base stations consume a considerable amount of the available power budget even when operating at low load. Energy efficient radio resource management (RRM) strategies need to take into account slowly changing daily load patterns, as well as highly dynamic traffic fluctuations. Moreover, various deployment strategies are examined focusing on their potential to reduce energy consumption, whilst providing uncompromised coverage and user experience. This includes heterogeneous networks with a sophisticated mix of different cell sizes, which may be further enhanced by energy efficient relaying and base station cooperation technologies. Finally, scenarios leveraging the capability of advanced terminals to operate on multiple radio access technologies (RAT) are discussed with respect to their energy savings potential. ©2010 IEEE.
    Akbari A, Imran MA, Tafazolli R, Dianati M (2011) Energy Efficiency Contours for Single-Carrier Downlink Channels,IEEE Communications Letters 15 (12) pp. 1307-1309 IEEE
    Energy efficiency has become an important aspect of wireless communication, both economically and environmentally. This letter investigates the energy efficiency of downlink AWGN channels by employing multiple decoding policies. The overall energy efficiency of the system is based on the bits-per-joule metric, where energy efficiency contours are used to locate the optimal operating points based on the system requirements. Our novel approach uses a linear power model to define the total power consumed at the base station, encompassing the circuit and processing power, and amplifier efficiency, and ensures that the best energy efficiency value can be achieved whilst satisfying other system targets such as QoS and rate-fairness.
    Dianati M, Tafazolli R, Shen X, Naik K (2010) Per-user service model for opportunistic scheduling scheme over fading channels,WIRELESS COMMUNICATIONS & MOBILE COMPUTING 10 (1) pp. 87-100 JOHN WILEY & SONS INC
    Georgiades M, Akhtar N, Ghader M, Li Z, Gultchev S, Tafazolli R (2005) Surrey's Next Generation Wireless Network Testbed,
    Heliot F, Imran MA, Tafazolli R (2012) Energy-efficient Power Allocation for Point-to-point MIMO System over the Rayleigh Fading Channel, IEEE Wireless Communications Letters 1 (4) pp. 304-307 IEEE
    It is well-established that transmitting at full power is the most spectral-efficient power allocation strategy for point-to-point (P2P) multi-input multi-output (MIMO) systems, however, can this strategy be energy efficient as well? In this letter, we address the most energy-efficient power allocation policy for symmetric P2P MIMO systems by accurately approximating in closed-form their optimal transmit power when a realistic MIMO power consumption model is considered. In most cases, being energy efficient implies a reduction in transmit and overall consumed powers at the expense of a lower spectral efficiency.
    Ma Y, De Luna Ducoing Juan Carlos, Yi N, Tafazolli R (2015) Using Real Constellations in Fully- and Over-loaded Large MU-MIMO Systems with Simple Detection,IEEE Wireless Communications Letters PP (99) pp. 92-95 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    The aim of this letter is to exhibit some advantages of using real constellations in large multi-user (MU) MIMO systems. It is shown that a widely linear zero-forcing (WLZF) receiver with M-ASK modulation enjoys a spatial-domain diversity gain, which linearly increases with the MIMO size even in fully- and over-loaded systems. Using the decision of WLZF as the initial state, the likelihood ascent search (LAS) achieves nearoptimal BER performance in fully-loaded large MIMO systems. Interestingly, for coded systems, WLZF shows a much closer BER to that of WLZF-LAS with a gap of only 0:9-2 dB in SNR.
    Xiao P, Tafazolli R, Moessner K, Gluhak A (2012) Codebook Based Single-User MIMO System Design with Widely Linear Processing,IEEE Transactions on Communications
    This work addresses joint transceiver optimization for multiple-input, multiple-output (MIMO) systems. In practical systems the complete knowledge of channel state information (CSI) is hardly available at transmitter. To tackle this problem, we resort to the codebook approach to precoding design, where the receiver selects a precoding matrix from a finite set of pre-defined precoding matrices based on the instantaneous channel condition and delivers the index of the chosen precoding matrix to the transmitter via a bandwidth-constraint feedback channel. We show that, when the symbol constellation is improper, the joint codebook based precoding and equalization can be designed accordingly to achieve improved performance compared to the conventional system.
    Hoshyar R, Shariat M, Tafazolli R (2010) Subcarrier and Power Allocation with Multiple Power Constraints in OFDMA Systems, IEEE COMMUNICATIONS LETTERS 14 (7) pp. 644-646 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Katranaras E, Imran MA, Dianati M, Tafazolli R (2014) Green inter-cluster interference management in uplink of multi-cell processing systems,IEEE Transactions on Wireless Communications 13 (12) pp. 6580-6592
    © 2014 IEEE.This paper examines the uplink of cellular systems employing base station cooperation for joint signal processing. We consider clustered cooperation and investigate effective techniques for managing inter-cluster interference to improve users' performance in terms of both spectral and energy efficiency. We use information theoretic analysis to establish general closed form expressions for the system achievable sum rate and the users' Bit-per-Joule capacity while adopting a realistic user device power consumption model. Two main inter-cluster interference management approaches are identified and studied, i.e., through: 1) spectrum re-use; and 2) users' power control. For the former case, we show that isolating clusters by orthogonal resource allocation is the best strategy. For the latter case, we introduce a mathematically tractable user power control scheme and observe that a green opportunistic transmission strategy can significantly reduce the adverse effects of inter-cluster interference while exploiting the benefits from cooperation. To compare the different approaches in the context of real-world systems and evaluate the effect of key design parameters on the users' energy-spectral efficiency relationship, we fit the analytical expressions into a practical macrocell scenario. Our results demonstrate that significant improvement in terms of both energy and spectral efficiency can be achieved by energy-aware interference management.
    Quddus AU, Guo T, Shariat M, Hunt B, Imran A, Ko Y, Tafazolli R (2010) Next Generation Femtocells: An Enabler for High Efficiency Multimedia Transmission, IEEE Comsoc MMTC E-Letters 5 (5) pp. 27-31 IEEE
    The first generation of femtocells is evolving to the next generation with many more capabilities in terms of better utilisation of radio resources and support of high data rates. It is thus logical to conjecture that with these abilities and their inherent suitability for home environment, they stand out as an ideal enabler for delivery of high efficiency multimedia services. This paper presents a comprehensive vision towards this objective and extends the concept of femtocells from indoor to outdoor environments, and strongly couples femtocells to emergency and safety services. It also presents and identifies relevant issues and challenges that have to be overcome in realization of this vision.
    Akbari A, Imran MA, Hoshyar R, Amich A, Tafazolli R (2011) Average Energy Efficiency Contours with Multiple Decoding Policies,IEEE Communications Letter 15 (5) pp. 506-508 IEEE
    This letter addresses energy-efficient design in multi-user, single-carrier uplink channels by employing multiple decoding policies. The comparison metric used in this study is based on average energy efficiency contours, where an optimal rate vector is obtained based on four system targets: Maximum energy efficiency, a trade-off between maximum energy efficiency and rate fairness, achieving energy efficiency target with maximum sum-rate and achieving energy efficiency target with fairness. The transmit power function is approximated using Taylor series expansion, with simulation results demonstrating the achievability of the optimal rate vector, and negligible performance difference in employing this approximation.
    Ma Y, Yi N, Tafazolli R (2008) Bit and power loading for OFDM-based three-node relaying communications,IEEE TRANSACTIONS ON SIGNAL PROCESSING 56 (7) pp. 3236-3247 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Mostafavi SM, Hamadani E, Tafazolli R (2010) Delay minimization in multipath routing, IWCMC 2010 - Proceedings of the 6th International Wireless Communications and Mobile Computing Conference pp. 711-715
    A key component of an efficient multipath routing is the optimal resource allocation strategy that deals with how the traffic should be distributed amongst the multiple paths. In this paper, intelligent traffic distribution policies that minimise the experienced delay by the user are proposed. For such delay minimisation, we investigate and evaluate traffic distribution policies in a multipath environment that minimize the average delay and the bottleneck path delay over all the paths.
    Wang M, Georgiades M, Tafazolli R (2008) Signalling cost evaluation of mobility management schemes for different core network architectural arrangements in 3GPP LTE/SAE, 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7 pp. 2253-2258 IEEE
    Qi Y, Hoshyar R, Tafazolli R (2006) Capacity of Intelligent Quadrifiliar Helix Antenna (IQHA) based MIMO system,2006 IEEE International Workshop on Antenna Technology: Small Antennas and Novel Metamaterials (IWAT) pp. 365-368 IEEE
    Vural S, Navaratnam P, Wang N, Tafazolli R (2014) Asynchronous Clustering of Multihop Wireless Sensor Networks, IEEE International Conference on Communications (ICC), 2014 pp. 472-477 IEEE
    Node clustering has been widely studied in recent years for Wireless Sensor Networks (WSN) as a technique to form a hierarchical structure and prolong network lifetime by reducing the number of packet transmissions. Cluster Heads (CH) are elected in a distributed way among sensors, but are often highly overloaded, and therefore re-clustering operations should be performed to share the resource intensive CH-role. Existing protocols involve periodic network-wide re-clustering operations that are simultaneously performed, which requires global time synchronisation. To address this issue, some recent studies have proposed asynchronous node clustering for networks with direct links from CHs to the data sink. However, for large-scale WSNs, multihop packet delivery to the sink is required since longrange transmissions are costly for sensor nodes. In this paper, we present an asynchronous node clustering protocol designed for multihop WSNs, considering dynamic conditions such as residual node energy levels and unbalanced data traffic loads caused by packet forwarding. Simulation results demonstrate that it is possible to achieve similar levels of lifetime extension by re-clustering a multihop WSN via independently made decisions at CHs, without a need for time synchronisation required by existing synchronous protocols.
    Ghader M, Moessner K, Tafazolli R (2004) Service Discovery and Provision Protocols for Wireless Networks,
    Imran A, Shateri M, Tafazolli R (2009) On the Comparison of Performance, Capacity and Economics of Terrestrial Base Station and High Altitude Platform Based Deployment of 4G, PE-WASUN09: PROCEEDINGS OF THE SIXTH ACM INTERNATIONAL SYMPOSIUM ON PERFORMANCE EVALUATION OF WIRELESS AD-HOC, SENSOR, AND UBIQUITOUS NETWORKS pp. 58-62 ASSOC COMPUTING MACHINERY
    Qi Y, Hoshyar R, Tafazolli R (2010) A novel decoding structure in compress-and-forward systems, IWCMC 2010 - Proceedings of the 6th International Wireless Communications and Mobile Computing Conference pp. 412-416
    A novel joint decompression and forward error correction (FEC) decoding structure for a compress-and-forward relay system is proposed. We notice the possibility of iterative processing between the decompressor and the FEC decoder for the original source information and propose a turbo-like structure to allow interaction and extrinsic information exchange between these two parts. Simulation results show considerable gains through this interaction Copyright © 2010 ACM.
    Shariat M, Pateromichelakis E, Quddus A, Tafazolli R (2014) Joint TDD Backhaul and Access Optimization in Dense Small Cell Networks,IEEE Transactions on Vehicular Technology (99) IEEE
    This paper addresses the problem of joint backhaul and access links optimization in dense small cell networks with special focus on time division duplexing (TDD) mode of operation in backhaul and access links transmission. Here, we propose a framework for joint radio resource management where we systematically decompose the problem in backhaul and access links. To simplify the analysis, the procedure is tackled in two stages. At the first stage, the joint optimization problem is formulated for a point-to-point scenario where each small cell is simply associated to a single user. It is shown that the optimization can be decomposed into separate power and subchannel allocation in both backhaul and access links where a set of rate-balancing parameters in conjunction with duration of transmission governs the coupling across both links. Moreover, a novel algorithm is proposed based on grouping the cells to achieve rate-balancing in different small cells. Next in the second stage, the problem is generalized for multi access small cells. Here, each small cell is associated to multiple users to provide the service. The optimization is similarly decomposed into separate sub-channel and power allocation by employing auxiliary slicing variables. It is shown that similar algorithms as previous stage are applicable by slight change with the aid of slicing variables. Additionally, for the special case of line-of-sight backhaul links, simplified expressions for sub-channel and power allocation are presented. The developed concepts are evaluated by extensive simulations in different case studies from full orthogonalization to dynamic clustering and full reuse in the downlink and it is shown that proposed framework provides significant improvement over the benchmark cases.
    Ghader M, Tafazolli R (2004) Performance of Service Discovery Protocols in Personal Networks,
    Dianati M, Tafazolli R, Moessner K (2010) Enabling Tussle-Agile Inter-networking Architectures by Underlay Virtualisation, FUTURE INTERNET - FIS 2009 6152 pp. 81-95 SPRINGER-VERLAG BERLIN
    Chatzimisios P, Dagiuklas T, Tafazolli R, Verikoukis C (2010) Message from ConWire'10 co-chairs, Proceedings - International Conference on Computer Communications and Networks, ICCCN
    Dianati M, Tafazolli R, Shen X, Naik K (2009) A markov model for per-user service of opportunistic scheduling, Proceedings of the 2009 ACM International Wireless Communications and Mobile Computing Conference, IWCMC 2009 pp. 681-686
    In this paper, we consider maximum rate opportunistic scheduling from a single wireless base station with a single antenna to multiple mobile users, each equipped with a single antenna. We show that a finite-state Markovian model can capture the dynamics of a single user's service, namely peruser service. We consider a saturated scenario, where the base station always has buffered data for transmission. Copyright © 2009 ACM.
    Hoshyar R, Heliot F, Tafazolli R (2009) A Novel Multi-layer Cooperative Decode and Forward Scheme,2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5 pp. 1248-+ IEEE
    Yarmohammad A, Abaii M, Thilakawardana S, Tafazolli R (2009) Inter-operator Dynamic Spectrum Selection in UMTS, 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5 pp. 504-508 IEEE
    Huang L, Liu Y, Thilakawardana S, Tafazolli R (2006) Network-centric user assignment in the next generation mobile networks,IEEE COMMUNICATIONS LETTERS 10 (12) pp. 822-824 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Heliot F, Chu X, Hoshyar R, Tafazolli R (2009) A Tight Closed-Form Approximation of the Log-Normal Fading Channel Capacity,IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 8 (6) pp. 2842-2847 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Yi N, Ma Y, Tafazolli R (2008) Rate-adaptive bit and power loading for OFDM based DF relaying, 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7 pp. 1340-1344 IEEE
    Touheed H, Quddus AU, Tafazolli R (2008) An improved link adaptation scheme for High Speed Downlink Packet Access,2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7 pp. 2051-2055 IEEE
    Nourizadeh H, Nourizadeh S, Tafazolli R (2006) Impact of the Inter-relay Handoff on the Relaying System Performance,2006 IEEE 64TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-6 pp. 2529-2533 IEEE
    Presser M, Gluhak A, Babb D, Tafazolli R, Herault L (2006) E-SENSE - Capturing ambient intelligence for mobile communications through wireless sensor networks, WINSYS 2006: Proceedings of the International Conference on Wireless Information Networks and Systems pp. 341-346 INSTICC-INST SYST TECHNOLOGIES INFORMATION CONTROL & COMMUNICATION
    Ma Y, Tafazolli R (2005) Exploiting hidden pilots for carrier frequency offset estimation for generalized MC-CDMA systems,2005 IEEE/SP 13th Workshop on Statistical Signal Processing (SSP), Vols 1 and 2 pp. 1237-1241 IEEE
    Khalily M, Tafazolli R, Rahman TA, Kamarudin MR (2016) Design of Phased Arrays of Series-Fed Patch Antennas With Reduced Number of the Controllers for 28-GHzmm-Wave Applications,IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS 15 pp. 1305-1308 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    He Z, Ma Y, Tafazolli R (2012) Training Convergence in Range-based Cooperative Positioning with Stochastic Positional Knowledge, IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences E95.A (7) pp. 1200-1204 IEICE
    This letter investigates the training convergence in range-based cooperative positioning with stochastic positional knowledge. Firstly, a closed-form of squared position-error bound (SPEB) is derived with error-free ranging. Using the derived closed-form, it is proved that the SPEB reaches its minimum when at least 2 out of N(>2) agents send training sequences. Finally, numerical results are provided to elaborate the theoretical analysis with zero-mean Gaussian ranging errors.
    Han C, Dianati M, Tafazolli R, Kernchen R (2010) Throughput Analysis of the IEEE 802.11p Enhanced Distributed Channel Access Function in Vehicular Environment, pp. 1-5
    This paper proposes an analytical model for the throughput of the Enhanced Distributed Channel Access (EDCA)mechanism in IEEE 802.11p MAC sub-layer. Features in EDCA such as different Contention Windows (CW) and Arbitration Interframe Space (AIFS) for each Access Category (AC), and internal collisions are taken into account. The analytical model is suitable for both basic access and the Request-To-Send/Clear-To-Send (RTS/CTS) access mode. The proposed analytical model is validated against simulation results to demonstrate its accuracy
    Puschmann D, Barnaghi P, Tafazolli R (2016) Adaptive Clustering for Dynamic IoT Data Streams, IEEE Internet of Things IEEE
    The emergence of the Internet of Things (IoT) has
    led to the production of huge volumes of real-world streaming
    data. We need effective techniques to process IoT data streams
    and to gain insights and actionable information from realworld
    observations and measurements. Most existing approaches
    are application or domain dependent. We propose a method
    which determines how many different clusters can be found
    in a stream based on the data distribution. After selecting the
    number of clusters, we use an online clustering mechanism
    to cluster the incoming data from the streams. Our approach
    remains adaptive to drifts by adjusting itself as the data changes.
    We benchmark our approach against state-of-the-art stream
    clustering algorithms on data streams with data drift. We show
    how our method can be applied in a use case scenario involving
    near real-time traffic data. Our results allow to cluster, label and
    interpret IoT data streams dynamically according to the data
    distribution. This enables to adaptively process large volumes of
    dynamic data online based on the current situation. We show
    how our method adapts itself to the changes. We demonstrate
    how the number of clusters in a real-world data stream can be
    determined by analysing the data distributions.
    Tang SY, Thilakawardana S, Tafazolli R, Qian Y (2005) Performance analysis of predictive scalable resource allocation for integrated wireless networks, 2005 INTERNATIONAL CONFERENCE ON WIRELESS NETWORKS, COMMUNICATIONS AND MOBILE COMPUTING, VOLS 1 AND 2 pp. 745-750 IEEE
    Yi N, Ma Y, Tafazolli R (2008) Multi-tone transmissions over two-user cognitive radio channel with weak interference, IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC
    A transmitter with cognitive capability can sense talk between the other transmitter-receiver pairs. When this transmitter knows full or partial message of the others, it can choose an efficient strategy to access the transmission medium. This is referred to as cognitive radio channel. This work aims to investigate multi-tone transmission over two-user cognitive radio channels where cross-talk interference is weak. Cognitive transmitter (Tx1) is assumed to have full knowledge of message that is sent by the other transmitter (Tx2) to its corresponding receiver (Rx2). Channel capacity is carefully analyzed for frequency-selective scenarios. Efficient power-allocation strategies at Txl are investigated for various wireless environments. It is shown that Tx1 can find an efficient resource-accessing strategy if the channel gain of Tx1-Rx1 (the corresponding receiver) link is larger than the channel gain of Tx2-Rx2 link. In this case, the cognitive transmitter Tx1 can offer better performance by employing equal power allocation approach. Otherwise, it is not worthy for Txl to access transmission medium of Tx2-Rx2 link. © 2008 IEEE.
    Georgoulas S, Moessner K, Mcaleer B, Tafazolli R (2010) Using Formal Verification Methods and Tools for Protocol Profiling and Performance Assessment in Mobile and Wireless Environments, 2010 IEEE 21st International Symposium on Personal Indoor and Mobile Radio Communications pp. 2471-2476 IEEE
    The most common use of formal verification methods and tools so far has been in identifying whether livelock and/or deadlock situations can occur during protocol execution, process, or system operation. In this work we aim to show that an additional equally important and useful application of formal verification tools can be in protocol design and protocol selection in terms of performance related metrics. This can be achieved by using the tools in a rather different context compared to their traditional use. That is not only as model checking tools to assess the correctness of a protocol in terms of lack of livelock and deadlock situations but rather as tools capable of building profiles of protocol operations, assessing their performance, and identifying operational patterns and possible bottleneck operations. This process can provide protocol designers with an insight about the protocols' behavior and guide them towards further protocol design optimizations. It can also assist network operators and service providers in selecting the most suitable protocol for specific network and service configurations. We illustrate these principles by showing how formal verification tools can be applied in this protocol profiling and performance assessment context using some existing protocols as case studies.
    Dohler M, McLaughlin S, Lee Y, Tafazolli R (2007) Implementable wireless access for B3G networks - Part IV: Resource management issues,IEEE COMMUNICATIONS MAGAZINE 45 (3) pp. 106-111 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Guo T, Quddus AU, Wang N, Tafazolli R (2012) Local Mobility Management for Networked Femtocells Based on X2 Traffic Forwarding, IEEE Transactions on Vehicular Technology IEEE
    Femtocell is becoming a promising solution to face the explosive growth of mobile broadband usage in cellular networks. While each femtocell only covers a small area, a massive deployment is expected in the near future forming networked femtocells. An immediate challenge is to provide seamless mobility support for networked femtocells with minimal support from mobile core networks. In this paper, we propose efficient local mobility management schemes for networked femtocells based on X2 traffic forwarding under the 3GPP Long Term Evolution Advanced (LTE-A) framework. Instead of implementing the path switch operation at core network entity for each handover, a local traffic forwarding chain is constructed to use the existing Internet backhaul and the local path between the local anchor femtocell and the target femtocell for ongoing session communications. Both analytical studies and simulation experiments are conducted to evaluate the proposed schemes and compare them with the original 3GPP scheme. The results indicate that the proposed schemes can significantly reduce the signaling cost and relieve the processing burden of mobile core networks with the reasonable distributed cost for local traffic forwarding. In addition, the proposed schemes can enable fast session recovery to adapt to the self-deployment nature of the femtocells.
    Han C, Muhaidat S, Abualhaol I, Dianati M, Tafazolli R (2013) Intrusion Detection in Vehicular Ad-Hoc Networks on Lower Layers, In: Security, Privacy, Trust, and Resource Management in Mobile and Wireless Communications 8 IGI Global
    Vehicular Ad-Hoc Networks (VANETs) are a critical component of the Intelligent Transportation Systems (ITS), which involve the applications of advanced information processing, communications, sensing, and controlling technologies in an integrated manner to improve the functionality and the safety of transportation systems, providing drivers with timely information on road and traffic conditions, and achieving smooth traffic flow on the roads. Recently, the security of VANETs has attracted major attention for the possible presence of malicious elements, and the presence of altered messages due to channel errors in transmissions. In order to provide reliable and secure communications, Intrusion Detection Systems (IDSs) can serve as a second defense wall after prevention-based approaches, such as encryption. This chapter first presents the state-of-the-art literature on intrusion detection in VANETs. Next, the detection of illicit wireless transmissions from the physical layer perspective is investigated, assuming the presence of regular ongoing legitimate transmissions. Finally, a novel cooperative intrusion detection scheme from the MAC sub-layer perspective is discussed.
    Zhang Y, Ma Y, Tafazolli R (2007) Tighter bounds of symbol error probability for amplify-and-forward cooperative protocol over rayleigh fading channels, 2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9 pp. 1920-1924 IEEE
    Rodriguez V, Moessner K, Tafazolli R (2006) Market driven dynamic spectrum allocation over space and time among radio-access networks: DVB-T and B3G CDMA with heterogeneous terminals, MOBILE NETWORKS & APPLICATIONS 11 (6) pp. 847-860 SPRINGER
    Kosta C, Sodunke T, Shateri M, Tafazolli R (2010) Two-stage call admission control policy for LTE Systems, IWCMC 2010 - Proceedings of the 6th International Wireless Communications and Mobile Computing Conference pp. 1101-1105
    In this paper, we evaluate a two-stage call admission control (CAC) policy for Long Term Evolution (LTE) Systems working along with packet scheduler (PS). The proposed twostage admission scheme uses the quality the received signal as an indicator to estimate the amount of resources for each call in order to improve the performance of the overall network. Unlikely with other CAC approaches we use a SINR-based estimator to clarified the connection quality, and thereafter quantize the user demand in term of physical resources. However, for scheduling, we use an algorithm where highest priority is assigned for guaranteed bit rate (GBR) proportional to their packet delays. Simulations results show that the proposed CAC scheme combined with proposed Packet Scheduling policy greatly improves performance of non-GBR service, while also maintaining quite well the Quality of Service (QoS) of delay sensitive traffic (GBR) and ends up with reduction in Packet Drop Ratio (PDR) for Copyright © 2010 ACM.
    Liu H, Ma Y, Tafazolli R (2007) Sub-optimum pilot placement for chunk-based OFDMA uplink: Consecutive chunks scenario, 2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9 pp. 1925-1929 IEEE
    Qi Y, Imran MA, Demo Souza R, Tafazolli R (2015) On the Optimization of Distributed Compression in Multi-Relay Cooperative Networks,IEEE Transactions on Vehicular Technology IEEE
    In this paper, we consider multi-relay cooperative networks for the Rayleigh fading channel, where each relay, upon receiving its own channel observation, independently compresses it and forwards the compressed information to the destination. Although the compression at each relay is distributed using Wyner-Ziv coding, there exists an opportunity for jointly optimizing compression at multiple relays to maximize the achievable rate. Considering Gaussian signalling, a primal optimization problem is formulated accordingly. We prove that the primal problem can be solved by resorting to its Lagrangian dual problem and an iterative optimization algorithm is proposed. The analysis is further extended to a hybrid scheme, where the employed forwarding scheme depends on the decoding status of each relay. The relays that are capable of successful decoding perform decode-and-forward and the rest conduct distributed compression. The hybrid scheme allows the cooperative network to adapt to the changes of the channel conditions and benefit from an enhanced level of flexibility. Numerical results from both spectrum and energy efficiency perspectives show that the joint optimization improves efficiency of compression and identify the scenarios where the proposed schemes outperform the conventional forwarding schemes. The findings provide important insights into the optimal deployment of relays in a realistic cellular network.
    Acar G, Thilakawardana S, Tafazolli R, Evans B (2006) Performance of Multicast File Transfer Protocol (MFTP) over geostationary satellite systems with DAMA uplinks, Collection of Technical Papers - 24th AIAA International Communications Satellite Systems Conference, ICSSC 1 pp. 61-74
    Their inherent broadcasting capabilities over very large geographical areas make satellite systems one of the most effective vehicles for multicast service delivery. Recent advances in spotbeam antennas and high-power platforms further accentuate the suitability of satellite systems as multicasting tools. The focus of this article is reliable multicast service delivery via geostationary satellite systems. Starburst MFTP is a feedback-based multicast transport protocol that is distinct from other such protocols in that it defers the retransmission of lost data until the end of the transmission of the complete data product. In contrast to other multicast transport protocols, MFTP retransmission strategy does not interrupt the fresh data transmission with the retransmissions of older segments. Thanks to this feature, receivers enjoying favourable channel conditions do not suffer from unnecessarily extended transfer delays due to those receivers that experience bad channel conditions. Existing research studies on MFTP's performance over satellite systems assume fixed-capacity satellite uplink channels dedicated to individual clients on the return link. Such fixed-assignment uplink access mechanisms are considered to be too wasteful uses of uplink resources for the sporadic and thin feedback traffic generated by MFTP clients. Indeed, such mechanisms may prematurely limit the scalability of MFTP as the multicast client population size grows. In contrast, the reference satellite system considered in this article employs demand-assignment multiple access (DAMA) with contention-based request signalling on the uplink. DAMA MAC (Medium Access Control) protocols in satellite systems are well-known in the literature for their improved resource utilisation and scalability features. Moreover, DAMA forms the basis for the uplink access mechanisms in prominent satellite networks such as Inmarsat's BGAN (Broadband Global Area Network), and return link specifications such as ETSI DVB-RCS, However, in comparison with fixed-assignment uplink access mechanisms, DAMA protocols may introduce unpredictable delays for MFTP feedback messages on the return link. Collisions among capacity requests on the contention channel, temporary lack of capacity on the reservation channel, and random transmission errors on the uplink are the potential causes of such delays, This article presents the results of a system-level simulation analysis of MFTP over a DAMA GEO satellite system with conten
    Ijaz A, Zhang L, ul Quddus A, Tafazolli R (2016) HARQ in Relay-Assisted Transmission for Machine Type Communications,IEEE WIRELESS COMMUNICATIONS LETTERS 5 (2) pp. 172-175 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Heliot F, Imran MA, Tafazolli R (2012) On the Energy Efficiency-Spectral Efficiency Trade-Off over the MIMO Rayleigh Fading Channel, IEEE Transactions on Communications 60 (5) pp. 1345-1356 IEEE
    Along with spectral efficiency (SE), energy efficiency (EE) is becoming one of the key performance evaluation criteria for communication system. These two criteria, which are conflicting, can be linked through their trade-off. The EE-SE trade-off for the multi-input multi-output (MIMO) Rayleigh fading channel has been accurately approximated in the past but only in the low-SE regime. In this paper, we propose a novel and more generic closed-form approximation of this trade-off which exhibits a greater accuracy for a wider range of SE values and antenna configurations. Our expression has been here utilized for assessing analytically the EE gain of MIMO over single-input single-output (SISO) system for two different types of power consumption models (PCMs): the theoretical PCM, where only the transmit power is considered as consumed power; and a more realistic PCM accounting for the fixed consumed power and amplifier inefficiency. Our analysis unfolds the large mismatch between theoretical and practical MIMO vs. SISO EE gains; the EE gain increases both with the SE and the number of antennas in theory, which indicates that MIMO is a promising EE enabler; whereas it remains small and decreases with the number of transmit antennas when a realistic PCM is considered.
    Movahhedian M, Ma Y, Tafazolli R (2010) Blind CFO Estimation for Linearly Precoded OFDMA Uplink, IEEE TRANSACTIONS ON SIGNAL PROCESSING 58 (9) pp. 4698-4710 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Presser M, Brown T, Goulianos A, Stavrou S, Tafazolli R (2007) Body centric context aware application scenarios, IET Seminar Digest 2007 (11803) pp. 19-25
    This paper describes several communication categories for personal and body centric communications. It uses several application scenarios to give examples of these categories and therefore to concretise these categories. Further, the paper presents a first set of analysis for off-body communications.
    Ma Y, Tafazolli R, Zhang Y, Qian C (2011) Adaptive Modulation for Opportunistic Decode-and-Forward Relaying, IEEE Transactions on Wireless Communications 10 (7) pp. 2017-2022 IEEE
    Orthogonal relay based cooperative communication enjoys distributed spatial diversity gain at the price of spectral efficiency. This work aims at improving the spectral efficiency for orthogonal opportunistic decode-and-forward (DF) relaying through employment of novel adaptive modulation scheme. The proposed scheme allows source and relay to transmit information in different modulation formats, while the MAP receiver is employed at destination for the diversity combining. Given the individual power constraint and target bit-error-rate (BER), the proposed scheme can significantly improve the spectral efficiency in comparison with the non-adaptive DF relaying and adaptive direct transmission.
    Mach T, Tafazolli R (2010) Battery life idle parameter optimization of UE in self organizing network, IEEE 21st International Symposium on Personal, Indoor and Mobile Radio Communications pp. 1332-1336
    This paper presents a novel mechanism which increases mobile terminal battery performance. It supports a cell reselection algorithm which decides on which cell, user equipment (UE) is camped on when in idle mode (there is no active radio connection with a mobile network). Study is based on real 3G UTRA network measurements. Authors propose a technique to reduce UE current consumption in idle mode based on dynamic Sintrasearch neighbour cell measurements threshold optimization. System analysis covers both UTRA and E-UTRA - Long Term Evolution (LTE) technology.
    Yi N, Ma Y, Tafazolli R (2011) Cooperative iterative water-filling for two-user Gaussian frequency-selective interference chanels,
    In this paper, a cooperative iterative water-filling approach is investigated for two-user Gaussian interference channel. State-of-the-art approaches only maximize the individual user's own rate and always model interference as noise. Our proposed approach establishes user cooperation through sharing network side information. It iteratively maximizes the sum-rate of both users subject to distributed power constraint. Interference is optimally regarded as message or noise. Three efficient rate-sharing schemes are also investigated between two users based on priority. Numerical results are performed in frequency-selective environment. It is observed that the proposed approach offers significantly performance improvement in comparison with conventional iterative water-filling approaches.
    Grandblaise D, Moessner K, Vivier G, Tafazolli R (2007) Credit token based rental protocol for dynamic channel allocation,1st International Conference on Cognitive Radio Oriented Wireless Networks and Communications 2006, CROWNCOM
    This paper describes a distributed, cooperative and real time rental protocol for DCA operations in a multi system and mult) cell context for OFDMA systems. A credit token based rental protocol using auctioning Is proposed in support of dynamic spectrum sharing between cells. The proposed scheme can be tuned adaptively as a function of the context by specifying the credit tokens usage in the radio etiquette. The application of the rental protocol is illustrated with an ascending bid auctioning. The paper also describes two approaches for BS-BS communications in support of the rental protocol. Finally, it is described how the proposed mechanisms contribute to the current approaches followed in the IEEE 802.16h and IEEE 802.22 standards efforts addressing cognitive radio, © 2006 IEEE.
    Zhang L, Quddus A, Katranaras E, Dubben W, Qi Y, Tafazolli R (2016) Performance Analysis and Optimal Cooperative Cluster Size for Randomly Distributed Small Cells under Cloud RAN,IEEE Access 4 pp. 1925-1939 IEEE
    One major advantage of cloud/centralized radio access network (C-RAN) is the ease of implementation of multicell coordination mechanisms to improve the system spectrum efficiency (SE). Theoretically, large number of cooperative cells lead to a higher SE, however, it may also cause significant delay due to extra channel state information (CSI) feedback and joint processing computational needs at the cloud data center, which is likely to result in performance degradation. In order to investigate the delay impact on the throughput gains, we divide the network into multiple clusters of cooperative small cells and formulate a throughput optimization problem. We model various delay factors and the sum-rate of the network as a function of cluster size, treating it as the main optimization variable. For our analysis, we consider both base stations? as well as users? geometric locations as random variables for both linear and planar network deployments. The output SINR (signal-tointerference-plus-noise ratio) and ergodic sum-rate are derived based on the homogenous Poisson point processing (PPP) model. The sum-rate optimization problem in terms of the cluster size is formulated and solved. Simulation results show that the proposed analytical framework can be utilized to accurately evaluate the performance of practical cloud-based small cell networks employing clustered cooperation.
    Pateromichelakis E, Shariat M, Quddus A, Tafazolli R (2015) Joint Routing and Scheduling in Dense Small Cell Networks using 60GHz backhaul,
    Mirzadeh S, Cruickshank H, Tafazolli R (2008) An efficient key management solution for personal network federations,Proceedings - The 2nd International Conference on Mobile Ubiquitous Computing, Systems, Services and Technologies, UBICOMM 2008 pp. 401-406
    Personal Network Federation (PN-F) aims to provide secure interactions between a subset of devices of different Personal Networks (PN) for achieving a common goal or providing some services in collaborative environments. Security and privacy is one of the major concerns in the development and acceptance of PN-F like collaborative networks and as any other security architecture, the key management is the corner stone of any possible solution. In this paper, we provide security mechanisms and protocols for key exchange and key management in PN Federations and specify how the established keys can be used to secure communications in different layers. © 2008 IEEE.
    Rodriguez V, Moessner K, Tafazolli R (2006) Market driven dynamic spectrum allocation over space and time among radio-access networks: DVB-T and B3G CDMA with heterogeneous terminals, Multibody System Dynamics 16 (4) pp. 847-860
    The radio frequency spectrum is a naturally limited resource of extraordinary value as the key to the provision of important communication and information services. Traditionally spectrum has been allocated first to specific access technologies and then sub-allocated to specific access networks on very long term basis (up to decades). The traditional scheme can be very inefficient when demand patterns ("loads") exhibit high temporal and spatial variations. Dynamic spectrum allocation (DSA) improves radio spectrum efficiency by adjusting the allocation as demand changes in time and/or space. In previous work we introduced a DSA scheme in which a spectrum manager periodically auctions short-term spectrum licenses. The scheme can be supported by a realistic "pooling" business model and can work with many radio-access technologies. But our previous analysis only considers a code-division multiple access (CDMA) technology; and DSA provides the greatest benefits with the participation of networks having complementary "busy hours" such as video entertainment services and cellular telephony. Here a digital video broadcast (DVB) terrestrial network joins the scheme. A typical DVB terrestrial cell is (much) larger than a UMTS cell. This brings to the forefront inter-cell interference and inter-related auctions in different cells. To capture the essence of these issues we focus first on a situation where one DVB terrestrial cell overlays two adjacent CDMA cells. Subsequently we discuss extensions to richer scenarios. The contributions of the present work over our previous publications include to : (i) address the impact of inter-cell interference among several CDMA cells (ii) introduce the DVB access technology into the DSA scheme (iii) modify the auction scheme to consider that a DVB cell overlays several CDMA cells (iv) characterise analytically the marketing and bidding behaviour of the DVB network. © Springer Science + Business Media LLC 2006.
    Liu Y, Hoshyar R, Yang X, Tafazolli R (2006) Integrated radio resource allocation for multihop cellular networks with fixed relay stations,IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 24 (11) pp. 2137-2146 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Qi YA, Hoshyar R, Tafazolli R (2009) A New ARQ Protocol for Hybrid DF/CF Relay Scheme, 69th IEEE VEHICULAR TECHNOLOGY CONFERENCE pp. 1356-1360 IEEE
    Automatic Repeat re-Quest (AQR) is implemented to ensure reliable transmission when channel state information (CSI) is not available to the source and the selected transmission rate is not supported by the current channel realization. We consider a relay system with hybrid relay scheme, where the relay switches between decode-and-forward (DF) and compress-and-forward (CF) adapting to the decoding status. In such case, we propose new ARQ strategy and analyze its performance in terms of maximum throughput, average reward and inter-renewal time. Compared with pure DF, the hybrid relay schemes show considerable gain.
    Hamadani E, Mostafavi M, Tafazolli R, Rakocevic V (2009) Analysis of IEEE802.11 DCF Parameters on Achievable Throughput in Ad hoc Networks, 2009 IEEE 70TH VEHICULAR TECHNOLOGY CONFERENCE FALL, VOLS 1-4 pp. 465-470 IEEE
    Thilakawardana S, Acar G, Hale B, Tafazolli R (2007) Impact of status retry timer values on MFTP performance over bgan satellite multicast,2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9 pp. 4089-4094 IEEE
    Zhang Y, Ma Y, Tafazolli R (2008) Modulation-adaptive cooperation schemes for wireless networks,2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7 pp. 1320-1324 IEEE
    Qi Y, Hoshyar R, Tafazolli R (2010) A novel hybrid relaying scheme using multilevel coding, IEEE Vehicular Technology Conference
    In this paper, multilevel coding is tailored for cooperative communication, where the source deploys a layered encoding structure. Due to the BER difference for different coding levels, there is some possibility that the relay, despite of successful decoding in upper coding levels, might not be able to correctly decode in lower levels. We propose a hybrid relaying scheme to cope with this problem, where the relay deploys decode-and-forward in upper levels and compress-and-forward in lower levels. Simulation results demonstrate that this hybrid technique approaches a fine balance among the complexity, BER performance and transmission efficiency. © 2010 IEEE.
    Li Z, Akhtar N, Tafazolli R (2007) Seamless IP multimedia service continuity support in inter-worked UMTS and WLAN, 2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9 pp. 1478-1482 IEEE
    Hoshyar R, Tafazolli R (2009) Performance evaluation Of HARQ schemes for Cooperative Regenerative Relaying, 2009 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-8 pp. 3355-3360 IEEE
    Cheraghi P, Ma Y, Tafazolli R, Lu Z (2012) Cluster based differential energy detection for spectrum sensing in multi-carrier systems,IEEE Transactions on Signal Processing 60 (12) pp. 6450-6464 IEEE
    Mustafa HA, Shakir MZ, Imran MA, Imran A, Tafazolli R (2015) Coverage Gain and Device-to-Device User Density: Stochastic Geometry Modeling and Analysis, IEEE COMMUNICATIONS LETTERS 19 (10) pp. 1742-1745 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Imran A, Imran MA, Tafazolli R (2010) A novel self organizing framework for adaptive frequency reuse and deployment in future cellular networks, 21st IEEE International Symposium on Personal, Indoor and Mobile Radio Communications pp. 2354-2359
    Recent research on Frequency Reuse (FR) schemes for OFDM/OFDMA based cellular networks (OCN) suggest that a single fixed FR cannot be optimal to cope with spatiotemporal dynamics of traffic and cellular environments in a spectral and energy efficient way. To address this issue this paper introduces a novel Self Organizing framework for adaptive Frequency Reuse and Deployment (SO-FRD) for future OCN including both cellular (e.g. LTE) and relay enhanced cellular networks (e.g. LTE Advance). In this paper, an optimization problem is first formulated to find optimal frequency reuse factor, number of sectors per site and number of relays per site. The goal is designed as an adaptive utility function which incorporates three major system objectives; 1) spectral efficiency 2) fairness, and 3) energy efficiency. An appropriate metric for each of the three constituent objectives of utility function is then derived. Solution is provided by evaluating these metrics through a combination of analysis and extensive system level simulations for all feasible FRD's. Proposed SO-FRD framework uses this flexible utility function to switch to particular FRD strategy, which is suitable for system's current state according to predefined or self learned performance criterion. The proposed metrics capture the effect of all major optimization parameters like frequency reuse factor, number of sectors and relay per site, and adaptive coding and modulation. Based on the results obtained, interesting insights into the tradeoff among these factors is also provided.
    Georgoulas S, Moessner K, Mcaleer B, Tafazolli R (2010) Towards efficient protocol design through protocol profiling and verification of performance and operational metrics,Proceedings of the 6th International Wireless Communications and Mobile Computing Conference pp. 848-852
    Formal verification tools have been extensively used in the past to assess the correctness of protocols, processes, and systems in general. Their most common use so far has been in identifying whether livelock or deadlock situations can occur during protocol execution, process, or system operation. In this paper we aim to showcase that an additional equally important and useful application of formal verification tools can be in protocol design and optimization itself. This can be achieved by using the tools in a rather different context compared to their traditional use. That is not only as means to assess the correctness of a protocol in terms of lack of livelock and deadlock situations but rather as tools capable of building profiles of protocols, associating performance related metrics, and identifying operational patterns and possible bottleneck operations in terms of metrics of interest. This process can provide protocol designers with an insight about the protocols' behavior and guide them towards further protocol design optimizations. We illustrate these principles using some existing protocol implementations as case studies. Copyright © 2010 ACM.
    Hanzo II L, Tafazolli R (2011) The effects of shadow-fading on QoS-aware routing and admission control protocols designed for multi-hop MANETs, Wireless Communications and Mobile Computing 11 (1) pp. 1-22
    Ma Y, Tafazolli R (2007) Channel estimation for OFDMA uplink: a hybrid of linear and BEM interpolation approach,IEEE TRANSACTIONS ON SIGNAL PROCESSING 55 (4) pp. 1568-1573 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Yarmohammad A, Tafazolli R (2009) Decentralized inter-radio access network dynamic spectrum selection scheme, 2009 International Conference on Wireless Communications and Signal Processing, WCSP 2009
    Many radio access networks (RAN) operate in various bands, providing both common and distinct services. Currently the fixed allocation of spectrum (FSA) to various RANs creates inflexibility that leads to inefficient use of the spectrum. In this work a robust, technology neutral, decentralized, Inter-RAN dynamic spectrum selection (DSS) scheme is proposed. This work has sought to establish the basis for a generic method of DSS, wherein user equipment (UE) can obtain the most appropriate RAN for operation. Low complexity and low signaling overhead have been two important factors in designing this scheme. The impact of the proposed scheme on spectral efficiency and signaling load has been investigated. The results show an improvement in spectral efficiency with considerably low signaling overhead. Fairness in sharing, which is one of the important issues in spectrum sharing, can be easily achieved with this scheme. © 2009 IEEE.
    Movahedian M, Ma Y, Tafazolli R (2008) Iterative carrier frequency offset estimation and compensation for OFDMA uplink, IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC
    This paper presents a method to counteract the detrimental effects of carrier frequency offsets (CFOs) in the uplink of OFDMA-based wireless networks. The CFO values of different users are first estimated from the received decomposed signal using the best linear unbiased estimator (BLUE). The CFOs effects are then compensated based on the estimated values and also taking advantage of an iterative parallel interference cancelation (PIC) scheme. A novel contribution of this paper is introducing an iterative concatenated estimation and compensation algorithm for suppressing the residual interference due to imperfect estimators. The introduced method is successful where the estimator converges after only one iteration with a significant improvement in estimation accuracy. Also very close BER performance results can be achieved to that of systems with perfect knowledge or without CFOs particularly at practical SNRs. © 2008 IEEE.
    Zhang YY, Ma Y, Tafazolli R (2008) Improved Coded Cooperation Schemes for Wireless Communications,2008 6TH INTERNATIONAL SYMPOSIUM ON MODELING AND OPTIMIZATION IN MOBILE, AD HOC AND WIRELESS NETWORKS AND WORKSHOPS, VOLS 1 AND 2 pp. 507-512 IEEE
    Cooperative communications can exploit distributed spatial diversity gain to improve link performance. When the message is coded at a low rate, source and relay can send different parts of a codeword to destination. This is referred to as the coded cooperation. In this paper, we propose two novel coded cooperation schemes for three-node relay networks, i.e., adaptive coded cooperation and ARQ-based coded cooperation. The former one needs the channel quality information available at source. The codeword splits adaptively to minimize the overall BER. The latter one is devised for relay network with erasure. In the first time slot, source sends a high-rate sub-codeword. Once destination reports the decoding errors, either source or relay can send one or two new bits selected from the mother codeword. Unlike random rateless erasure codes, such as Fountain code, the proposed scheme is based on the deterministic code generator and puncture pattern. It is experimentally shown that the proposed scheme can offer improved throughput in comparison with the conventional approach.
    Héliot F, Hoshyar R, Tafazolli R (2011) An accurate closed-form approximation of the distributed MIMO outage probability, IEEE Transactions on Wireless Communications 10 (1) pp. 5-11
    Hoseinitabatabaei SA, Gluhak A, Tafazolli R (2011) uDirect: A novel approach for pervasive observation of user direction with mobile phones,2011 IEEE International Conference on Pervasive Computing and Communications, PerCom 2011 pp. 74-83
    In this paper we present the uDirect algorithm as a novel approach for mobile phone centric observation of a user's facing direction, through which the device and user orientations relative to earth coordinate are estimated. While the device orientation estimation is based on accelerometer and magnetometer measurements in standing mode, the unique behavior of measured acceleration during stance phase of a human's walking cycle is used for detecting user direction. Furthermore, the algorithm is independent of initial orientation of the device which gives the user higher space of freedom for long term observations. As the algorithm only relies on embedded accelerometer and magnetometer sensors of the mobile phone, it is not susceptible to shadowing effect as GPS. In addition, by performing independent estimations during each step of walking the model is robust to error accumulation. Evaluating the algorithm with 180 data samples from 10 participates has empirically confirmed the assumptions of our analytical model about the unique characteristics of the human stance phase for direction estimation. Moreover, our initial inspection has shown a system based on our algorithm outperforms conventional use of GPS and PCA analysis based techniques for walking distances more than 2 steps. © 2011 IEEE.
    Wang Y, Fan L, He D, Tafazolli R (2008) Performance comparison of scheduling algorithms in network mobility environment, COMPUTER COMMUNICATIONS 31 (9) pp. 1727-1738 ELSEVIER SCIENCE BV
    Sand S, Mensing C, Ma Y, Tafazolli R, Yin X, Figueiras J, Nielsen J, Fleury BH (2008) Hybrid data fusion and cooperative schemes for wireless positioning, IEEE Vehicular Technology Conference
    The Wireless Hybrid Enhanced Mobile Radio Estimators (WHERE) consortium researches radio positioning techniques to improve various aspects of communications systems. In order to provide the benefits of position information available to communications systems, hybrid data fusion (HDF) techniques estimate reliable position information. Within this paper, we first present the scenarios and radio technologies evaluated by the WHERE consortium for wireless positioning. We compare conventional HDF approaches with two novel approaches developed within the framework of WHERE. Yet, HDF may still provide insufficient localization accuracy and reliability. Hence, we will research and develop new cooperative positioning algorithms, which exploit the available communications links among mobile terminals of heterogeneous wireless networks, to further enhance the positioning accuracy and reliability. ©2008 IEEE.
    Ghader M, Tafazolli R (2007) Enhanced Service Location Protocol in Personal Network,
    Liu H, Ma Y, Tafazolli R (2008) Optimum pilot placement for chunk-based OFDMA uplink: Time direction scenario, 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7 pp. 2547-2551 IEEE
    Chen H, Maunder RG, Ma Y, Tafazolli R, Hanzo L (2015) Hybrid-ARQ-Aided Short Fountain Codes Designed for Block-Fading Channels,IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 64 (12) pp. 5701-5712 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Abaii M, Liu Y, Tafazolli R (2008) An efficient resource allocation strategy for future wireless cellular systems, IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 7 (8) pp. 2940-2949 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Vural S, Wang N, Navaratnam P, Tafazolli R (2016) Caching Transient Data in Internet Content Routers,IEEE/ACM Transactions on Networking
    The Internet-of-Things (IoT) paradigm envisions billions
    of devices all connected to the Internet, generating low-rate
    monitoring and measurement data to be delivered to application
    servers or end-users. Recently, the possibility of applying innetwork
    data caching techniques to IoT traffic flows has been
    discussed in research forums. The main challenge as opposed to
    the typically cached content at routers, e.g. multimedia files, is
    that IoT data are transient and therefore require different caching
    policies. In fact, the emerging location-based services can also
    benefit from new caching techniques that are specifically designed
    for small transient data. This paper studies in-network caching
    of transient data at content routers, considering a key temporal
    data property: data item lifetime. An analytical model that
    captures the trade-off between multihop communication costs and
    data item freshness is proposed. Simulation results demonstrate
    that caching transient data is a promising information-centric
    networking technique that can reduce the distance between
    content requesters and the location in the network where the
    content is fetched from. To the best of our knowledge, this is
    a pioneering research work aiming to systematically analyse the
    feasibility and benefit of using Internet routers to cache transient
    data generated by IoT applications.
    Touheed H, Quddus AU, Tafazolli R (2008) Predictive CQI reporting for HSDPA, IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC
    One of the key features of High-Speed Downlink Packet Access (HSDPA) is Adaptive Modulation and Coding (AMC). Link Adaptation at Node-B is done on the basis of Channel Quality Indicator (CQI) reports sent by the User Equipment (IE). However there is a delay of about 10 ms between computation of a CQI report at UE and the corresponding Transport Format and Resource Indicator (TFRI) selection at the Node-B. This delay significantly degrades the performance of link adaptation process. In order to compensate for this loss of performance, we propose predictive CQI reporting by the UE. A simple linear predictor based on NLMS (Normalized Least Mean Square) adaptation is shown through simulations to provide substantial gain in HSDPA link throughput. Results show that predictive CQI reporting provides larger gain in channel environments with medium to high Doppler and lack of multipath diversity. © 2008 IEEE.
    Nourizadeh H, Nourizadeh S, Tafazolli R (2006) Performance evaluation of Cellular Networks with Mobile and Fixed Relay Station, 2006 IEEE 64TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-6 pp. 2434-2438 IEEE
    Onireti OS, Akbari I, Imran MA, Imran A, Tafazolli R (2014) Effect of Inaccurate Position Estimation on Self-Organising Coverage Estimation in Cellular Networks,pp. 176-180 VDE
    Requirement for low operating and deployment costs of cellular networks motivate the need for self-organisation in cellular networks. To reduce operational costs, self-organising networks are fast becoming a necessity. One key issue in this context is self-organised coverage estimation that is done based on the signal strength measurement and reported position information of system users. In this paper, the effect of inaccurate position estimation on self-organised coverage estimation is investigated. We derive the signal reliability expression (i.e. probability of the received signal being above a certain threshold) and the cell coverage expressions that take the error in position estimation into consideration. This is done for both the shadowing and non-shadowing channel models. The accuracy of the modified reliability and cell coverage probability expressions are also numerically verified for both cases.
    Hoshyar R, Tafazolli R (2009) Optimum Decoding of Full Decode and Forward Scheme over Cooperative Relay Channels, 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5 pp. 1054-1058 IEEE
    Shariat M, Quddus AU, Tafazolli R (2009) Distance-incorporated opportunistic scheduling, Proceedings of the 2009 ACM International Wireless Communications and Mobile Computing Conference, IWCMC 2009 pp. 675-680
    This paper highlights the deficiencies of classical figures of merit such as throughput and fairness index to evaluate different scheduling algorithms and proposes a new complementary figure of merit called as transport-throughput, which has been inspired from information theory literature to better represent trade-offs among throughput, fairness and coverage associated with a given scheduling algorithm. Furthermore, new objective functions for opportunistic scheduling are proposed that utilize the knowledge about the geographic distance of mobile terminals from the base station. The proposed concept can be easily integrated as an extension to classical scheduling algorithms and provides the ability to control the effective distribution of throughput across the network Copyright © 2009 ACM.
    Ghader M, Olsen RL, Giro-Genet M, Tafazolli R (2005) Service Management Platform for Personal Networks,
    He Z, Ma Y, Tafazolli R (2012) Opportunistic Cooperative Positioning in OFDMA Systems, IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences Vol.E95-A (9) pp. 1642-1645 IEICE
    This letter presents a novel opportunistic cooperative positioning approach for orthogonal frequency-division multiple access (OFDMA) systems. The basic idea is to allow idle mobile terminals (MTs) opportunistically estimating the arrival timing of the training sequences for uplink synchronization from active MTs. The major advantage of the proposed approach over state-of-the-arts is that the positioning-related measurements among MTs are performed without the paid of training overhead. Moreover, Cramer-Rao lower bound (CRLB) is utilized to derive the positioning accuracy limit of the proposed approach, and the numerical results show that the proposed approach can improve the accuracy of non-cooperative approaches with the a-priori stochastic knowledge of clock bias among idle MTs.
    Lu Z, Ma Y, Tafazolli R (2010) A first-order cyclostationarity based energy detection approach for non-cooperative spectrum sensing,IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC pp. 554-559
    Spectrum sensing is one of key enabling techniques to advanced radio technologies such as cognitive radios and ALOHA. This paper presents a novel non-cooperative spectrum sensing approach that can achieve a good trade-off between latency, reliability and computational complexity. Our major idea is to exploit the first-order cyclostationarity of the primary user's signal to reduce the noise-uncertainty problem inherent in the conventional energy detection approach. It is shown that the proposed approach is suitable for detecting the primary user's activity in the interweave paradigm of cognitive spectrum sharing, while the active primary user is periodically sending training sequence. Computer simulations are carried out for the typical IEEE 802.11g system. It is observed that the proposed approach outperforms both the energy detection and the second-order cyclostationarity approach when the observation period is more than 10 frames corresponding to 0.56 ms. ©2010 IEEE.
    Hoshyar R, Wathan FP, Tafazolli R (2006) Novel Low-Density Signature structure for synchronous DS-CDMA systems,GLOBECOM - IEEE Global Telecommunications Conference
    Novel Low-Density Signature (LDS) structure is proposed for synchronous Code Division Multiple Access (CDMA) systems for an uplink communication over AWGN channel. It arranges the system such that the interference pattern being seen by each user at each received sampled chip is different. Furthermore, new near-optimum chip-level iterative multiuser decoder is suggested to exploit the proposed structure. It is shown via computer simulations that, without forward error correction (FEC) coding, the proposed LDS structure could achieve near single-user performance with up to 200% loading condition. As the proposed iterative decoding converges relatively fast, the complexity is kept much more affordable than that of optimum multiuser detection (MUD) with conventional structure. © 2006 IEEE.
    Hanzo L, Tafazolli R (2009) Admission Control Schemes for 802.11-Based Multi-Hop Mobile Ad hoc Networks: A Survey, IEEE COMMUNICATIONS SURVEYS AND TUTORIALS 11 (4) pp. 78-108 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Al Kiyumi R, Vural S, Foh CH, Tafazolli R (2015) A Distributed Sleep Mechanism for Energy-Efficiency in Non-Beacon-Enabled IEEE 802.15.4 Networks, 2015 IEEE 20TH INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELLING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD) pp. 237-241 IEEE
    Shariat M, Ul Quddus A, Tafazolli R (2009) IEEE Wireless Communications and Networking Conference, WCNC
    In this paper, a novel framework is proposed to integrate spectrum (resource) sharing into multihop scheduling in relay-assisted systems. This approach provides an effective solution to minimize the effect of extra resources that are required in multihop transmission. Particularly, this approach can be combined with different topologies of resource scheduling to provide better performance in terms of throughput and coverage compared to benchmark non-sharing algorithms. © 2009 IEEE.
    Qi Y, Imran MA, Hoshyar R, Tafazolli R (2011) H2-ARQ Relaying: Spectrum and Energy Efficiency Analysis,IEEE Journal on Selected Areas in Communications 29 (8) pp. 1547-1558 IEEE
    In this paper, we propose novel Hybrid Automatic Repeat re-Quest (HARQ) strategies used in conjunction with hybrid relaying schemes, named as H^2-ARQ-Relaying. The strategies allow the relay to dynamically switch between amplify-and-forward/compress-and-forward and decode-and-forward schemes according to its decoding status. The performance analysis is conducted from both the spectrum and energy efficiency perspectives. The spectrum efficiency of the proposed strategies, in terms of the maximum throughput, is significantly improved compared with their non-hybrid counterparts under the same constraints. The consumed energy per bit is optimized by manipulating the node activation time, the transmission energy and the power allocation between the source and the relay. The circuitry energy consumption of all involved nodes is taken into consideration. Numerical results shed light on how and when the energy efficiency can be improved in cooperative HARQ. For instance, cooperative HARQ is shown to be energy efficient in long distance transmission only. Furthermore, we consider the fact that the compress-and-forward scheme requires instantaneous signal to noise ratios of all three constituent links. However, this requirement can be impractical in some cases. In this regard, we introduce an improved strategy where only partial and affordable channel state information feedback is needed.
    Mozaffaripour M, Tafazolli R (2007) Suboptimal search algorithm in conjunction with polynomial-expanded linear multiuser detector for FDD WCDMA mobile uplink, IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 56 (6) pp. 3600-3606 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Heliot F, Imran MA, Tafazolli R (2012) A Very Tight Approximation of the SISO Energy Efficiency-Spectral Efficiency Trade-Off,IEEE Communications Letters
    Beside the well-established spectral-efficiency (SE), energy-efficiency (EE) is currently becoming an important performance evaluation metric, which in turn makes the EE-SE trade-off as a prominent criterion for efficiently designing future communication systems. In this letter, we propose a very tight closed-form approximation (CFA) of this trade-off over the single-input single-output (SISO) Rayleigh flat fading channel. We first derive an improved approximation of the SISO ergodic capacity by means of a parametric function and then utilize it for obtaining our novel EE-SE trade-off CFA, which is also generalized for the symmetric multi-input multi-output channel. We compare our CFA with existing CFAs and show its improved accuracy in comparison with the latter.
    Ma Y, Tafazolli R (2007) Estimation of carrier frequency offset for multicarrier CDMA uplink,IEEE TRANSACTIONS ON SIGNAL PROCESSING 55 (6) pp. 2617-2627 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Ko Y, Quddus AU, Tafazolli R (2016) Multi-Device Selection Scheduling in Non-Identically Distributed Fading Channels,IET Communications
    Multiuser selection scheduling concept has been recently proposed in the literature in order to
    increase the multiuser diversity gain and overcome the significant feedback requirements for the opportunistic
    scheduling schemes. The main idea is that reducing the feedback overhead saves per-user
    power that could potentially be added for the data transmission. In this work, we propose to integrate the
    principle of multiuser selection and the proportional fair scheduling scheme. This is aimed especially at
    power-limited, multi-device systems in non-identically distributed fading channels. For the performance
    analysis, we derive closed-form expressions for the outage probabilities and the average system rate of the
    delay-sensitive and the delay-tolerant systems, respectively, and compare them with the full feedback
    multiuser diversity schemes. The discrete rate region is analytically presented, where the maximum
    average system rate can be obtained by properly choosing the number of partial devices. We optimize
    jointly the number of partial devices and the per-device power saving in order to maximize the average
    system rate under the power requirement. Through our results, we finally demonstrate that the proposed
    scheme leveraging the saved feedback power to add for the data transmission can outperform the full
    feedback multiuser diversity, in non-identical Rayleigh fading of devices? channels.
    Navaratnam P, Akhtar N, Tafazolli R (2006) On the performance of DCCP in wireless mesh networks,MobiWAC 2006 - Proceedings of the 2006 ACM International Workshop on Mobility Management and Wireless Access 2006 pp. 144-147
    The Datagram Congestion Control Protocol (DCCP) has been recently proposed as a new transport protocol, suitable for use by applications such as multimedia streaming. Wireless mesh networks have promising commercial potential for a large variety of applications. In this paper, we evaluate the performance of DCCP with TCP Friendly Rate Control (TFRC) in wireless mesh networks using ns2 simulations, in terms of fairness and throughput smoothness. Our results show that in wireless mesh networks DCCP shares the limited wireless channel bandwidth fairly with the competing flows and provides better throughput smoothness than TCP flows in isolation i.e. with no competing flows. However, DCCP loses its ability to maintain the smoothness for streaming media applications with competing flows in the network. Copyright 2006 ACM.
    Wathan FP, Hoshyar R, Tafazolli R (2008) PERFORMANCE ANALYSIS OF GROUPED CHIP-LEVEL ITERATED MULTIUSER DETECTION FOR OVERLOADED CDMA SYSTEMS, 2008 IEEE 9TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS, VOLS 1 AND 2 pp. 131-135 IEEE
    Hanzo L, Mostafavi SM, Tafazolli R (2008) Connectivity-related properties of mobile nodes obeying the random walk and random waypoint mobility models,2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7 pp. 133-137 IEEE
    Wei D, Jin Y, Gluhak A, Tafazolli R, Moessner K (2010) Hot-spot issue aware clustering for WSNs to extend stable operation period, 2010 Future Network and Mobile Summit
    In existing energy-efficient clustering algorithms for Wireless Sensor Networks (WSNs), individual nodes usually experience significant differences in lifetime. The issue of some nodes depleting energy earlier than other is usually referred to as hot-spot issue in WSNs, which dramatically shortens the stable operation period of a network when all nodes are live with residual energy. This paper addresses hot-spot issue through equalizing individual node's lifetime throughout the network. The probability of nodes to become cluster-head (CH) in this algorithm is relevant to node distance to the sink and is subject to the individual node-lifetime equalization. When selecting CHs, the residual node energy is considered as well. Performance evaluation illustrates the effectiveness of our algorithm in terms of extending the stable operation period of the clustered WSNs. Copyright © 2010 The authors.
    Psaras I, Dianati M, Tafazolli R (2009) Why Rely on Blind AIMDs? (Work in Progress),NETWORKING 2009 5550 pp. 404-415 SPRINGER-VERLAG BERLIN
    Akbari I, Onireti O, Imran A, Imran MA, Tafazolli R (2016) How Reliable is MDT-Based Autonomous Coverage Estimation in the Presence of User and BS Positioning Error?,IEEE WIRELESS COMMUNICATIONS LETTERS 5 (2) pp. 196-199 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Qi Y, Hoshyar R, Tafazolli R (2008) Soft multilevel Slepian-Wolf decoding in systems using Turbo joint decoding and decompressing, 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7 pp. 1514-1518 IEEE
    Hoshyar R, Tafazolli R (2009) A Pre-BSC Model for Distributed Turbo Codes, 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5 pp. 1936-1940 IEEE
    Akbari A, Hoshyar R, Tafazolli R (2010) Energy-efficient resource allocation in wireless OFDMA systems, IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC pp. 1731-1735
    Reducing the consumed energy in wireless communication systems has a direct impact on operational expenditure as well as CO2 emissions. With increasing interest in multimedia applications and high data rate services, environmentally sustainable communications networks must reduce the energy per delivered bit at an equal rate, if not better. This paper addresses downlink energy-efficient transmission in OFDMA systems and maximizes the overall bits transmitted per joule of energy. In addition to the transmit power, circuit power is also accounted for in the energy-efficient design, which is tackled using both standard optimization techniques and a frame work based on time-sharing. Simulation results show similar performances for both cases with the latter having lower complexity and taking less CPU time to run. ©2010 IEEE.
    Hanzo L, Tafazolli R (2011) QoS-aware routing and admission control in shadow-fading environments for multirate MANETs, IEEE Transactions on Mobile Computing 10 (5) pp. 622-637
    Hoshyar R, Tafazolli R (2008) BER performance analysis of a cooperative BICM system based on post-BSC model, IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC
    A Generic Cooperative BICM system is described and an analytical model capturing relay error through a binary symmetric channel (BSC) is presented. The analytical model is called Post-BSC model as the BSC channel is placed after encoder of the relay node. Tight BER upper bound is derived for the presented model and close match between simulation and analysis for the presented model is observed. However it is also observed that the proposed model is optimistic and fails to effectively model the original system at low SNR conditions of the source to relay link. Despite this fact the incorporation of the Post-BSC model based maximum likelihood decoding greatly improves the system BER with respect to the original DF scheme. © 2008 IEEE.
    Fazel MS, Hoshyar R, Tafazolli R (2009) Flexible Amplify and Forward Relaying Protocol with optimized duplexing,2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5 pp. 3176-3180 IEEE
    Qi Y, Hoshyar R, Tafazolli R (2008) Performance evaluation of soft decode-and-forward in fading relay channels, 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7 pp. 1286-1290 IEEE
    Zhang L, liu W, quddus A, Dianati M, tafazolli R (2015) Adaptive Distributed Beamforming for Relay Networks based on Local Channel State Information,IEEE Transactions on Signal and Information Processing over Networks 1 (2) pp. 117-128 IEEE
    Most of the existing distributed beamforming algorithms for relay networks require global channel state information (CSI) at relay nodes and the overall computational complexity is high. In this paper, a new class of adaptive algorithms is proposed which can achieve a globally optimum solution by employing only local CSI. A reference signal based (RSB) scheme is first derived, followed by a constant modulus (CM) based scheme when the reference signal is not available. Considering individual power transmission constraint at each relay node, the corresponding constrained adaptive algorithms are also derived as an extension. An analysis of the overhead and stepsize range for the derived algorithms are then provided and the excess mean square error (EMSE) for the RSB case is studied based on the energy reservation method. As demonstrated by our simulation results, a better performance has been achieved by our proposed algorithms and they have a very low computational complexity and can be implemented on low cost and low processing power devices.
    Katsaros K, Dianati M, Tafazolli R, Guo X (2016) End-to-End Delay Bound Analysis for Location-Based Routing in Hybrid Vehicular Networks, IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 65 (9) pp. 7462-7475 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Akbari A, Imran MA, Hoshyar R, Amich A, Tafazolli R (2011) Average energy efficiency contours with multiple decoding policies, IEEE Communications Letters 15 (5) pp. 506-508
    Yi N, Ma Y, Tafazolli R (2008) Bit and power loading for OFDM with an amplify-and-forward cooperative relay,IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC
    In this paper, we propose a rate-adaptive bit and power loading approach for the OFDM-based relaying communications. The cooperative relay operates in the half-duplex amplify-and-forward mode. The source and the relay has the separate power constraints. The maximum-ratio combining is employed at -the destination for maximizing the received SNR. Assuming the perfect channel knowledge available at all nodes, the proposed approach is to maximize the throughput (the number of bits/symbol) at the given power constraint and the target link performance. Unlike the water-filling method, the proposed approach does not need the iterative loading process, and can otTer the sub-optimum performance. Computer simulations are used to test the proposed approach for various scenarios with respect to the relay location or the distributed power allocation. © 2008 IEEE.
    Mohamed A, Onireti O, Qi Y, Imran A, Imran M, Tafazolli R (2014) Physical Layer Frame in Signalling-Data Separation Architecture: Overhead and Performance Evaluation,Proceedings of European Wireless 2014; 20th European Wireless Conference pp. 820-825
    Conventional cellular systems are dimensioned according to a worst case scenario, and they are designed to ensure ubiquitous coverage with an always-present wireless channel irrespective of the spatial and temporal demand of service. A more energy conscious approach will require an adaptive system with a minimum amount of overhead that is available at all locations and all times but becomes functional only when needed. This approach suggests a new clean slate system architecture with a logical separation between the ability to establish availability of the network and the ability to provide functionality or service. Focusing on the physical layer frame of such an architecture, this paper discusses and formulates the overhead reduction that can be achieved in next generation cellular systems as compared with the Long Term Evolution (LTE). Considering channel estimation as a performance metric whilst conforming to time and frequency constraints of pilots spacing, we show that the overhead gain does not come at the expense of performance degradation.
    Ghader M, Olsen RL, Prasad V, Jacobsson M, Sanchez L, Lanza J, Louati W, Girod-Genet M, Zeghlache D, Tafazolli R (2006) Service Discovery in Personal Networks; design, implementation and analysis,
    Qi Y, Imran M, Tafazolli R (2010) On the energy aware deployment strategy in cellular systems, IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC pp. 363-367
    The rapid evolution of telecoms industry is accompanied by a huge increase of energy consumption of mobile networks, which forces the operators to exploit the potential of new techniques to save energy. In this paper, we propose a novel deployment strategy which is able to adapt itself to the spatial variation of the traffic by enhancing the cell radius in the low traffic areas, while the target quality of service (QoS) is still satisfied. Thus, the number of base stations deployed in the low traffic areas is reduced. Since the base station is the most energy-intensive equipment in cellular networks, this reduction naturally leads to significant energy savings for the entire cellular system. ©2010 IEEE.
    Qi Y, Hoshyar R, Tafazolli R (2009) On the Performance of HARQ with Hybrid Relaying Schemes, 2009 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-8 pp. 4357-4362 IEEE
    Jaber M, Imran MA, Tafazolli R, Tukmanov A (2016) 5G Backhaul Challenges and Emerging Research Directions: A Survey, IEEE Access 4 pp. 1743-1766
    5G is the next cellular generation and is expected to quench the growing thirst for taxing data
    rates and to enable the Internet of Things. Focused research and standardization work have been addressing
    the corresponding challenges from the radio perspective while employing advanced features, such as network
    densi cation, massive multiple-input-multiple-output antennae, coordinated multi-point processing, intercell
    interference mitigation techniques, carrier aggregation, and new spectrum exploration. Nevertheless,
    a new bottleneck has emerged: the backhaul. The ultra-dense and heavy traf c cells should be connected
    to the core network through the backhaul, often with extreme requirements in terms of capacity, latency,
    availability, energy, and cost ef ciency. This pioneering survey explains the 5G backhaul paradigm, presents
    a critical analysis of legacy, cutting-edge solutions, and new trends in backhauling, and proposes a novel
    consolidated 5G backhaul framework. A new joint radio access and backhaul perspective is proposed for the
    evaluation of backhaul technologies which reinforces the belief that no single solution can solve the holistic
    5G backhaul problem. This paper also reveals hidden advantages and shortcomings of backhaul solutions,
    which are not evident when backhaul technologies are inspected as an independent part of the 5G network.
    This survey is key in identifying essential catalysts that are believed to jointly pave the way to solving
    the beyond-2020 backhauling challenge. Lessons learned, unsolved challenges, and a new consolidated 5G
    backhaul vision are thus presented.
    Touheed H, Quddus AU, Tafazolli R (2009) Impact of MMSE equalization on adaptive modulation and coding in HSDPA, Proceedings of 6th International Bhurban Conference on Applied Sciences and Technology, IBCAST-2009 2 pp. 127-131
    High Speed Downlink Packet Access (HSDPA) is the front-line technology within the 3rd Generation Partnership Project (3GPP) and represents mid term evolution of the standard. This paper presents simple equalizer structures based on Minimum Mean Square Error criterion that are suitable for Adaptive Modulation and Coding (AMC), which is one of the key features of HSDPA. Performance of equalizer structures in AMC has been shown to provide significant gain over Rake receiver, in terms of HSDPA throughput, by enabling the use of higher CQI (Channel Quality Indicator) indices whilst showing stability against changing input signal statistics caused by AMC. LMMSE equalizer has been found to roughly double the HSDPA throughput in a variety of radio channels with relatively small increase in complexity. © 2009 IEEE.
    Salami G, Tafazolli R (2009) On the Performance evaluation of spectrum sharing algorithms between two UMTS operators, 2009 INTERNATIONAL CONFERENCE ON TELECOMMUNICATIONS (ICT) pp. 260-265 IEEE
    Heliot F, Tafazolli R (2016) Optimal Energy-efficient Joint Resource Allocation for Multi-hop MIMO-AF Systems,IEEE Transactions on Communications 64 (9) pp. 3655-3668 IEEE
    Energy ef?ciency (EE) is a key enabler for the next generation of communication systems. Equally, resource allocation and cooperative communication are effective tech-niques for improving communication system performance. In this paper, we propose an optimal energy-ef?cient joint resource allocation method for the multi-hop multiple-input-multiple-output (MIMO) amplify-and-forward (AF) system. We de?ne the joint source and multiple relays optimization problem and prove that its objective function, which is not generally quasiconvex, can be lower-bounded by a convex function. Moreover, all the minima of this objective function are strict minima. Based on these two properties, we then simplify the original multivariate optimization problem into a single variable problem and design a novel approach for optimally solving it in both the unconstraint and power constraint cases. In addition, we provide a sub-optimal approach with reduced complexity; the latter reduces the computational complexity by a factor of up to 40 with near-optimal performance. We ?nally utilize our novel approach for comparing the optimal energy-per-bit consumption of multi-hop MIMO-AF and MIMO systems; results indicate that MIMO-AF can help to save energy when the direct link quality is poor.
    Pateromichelakis E, Shariat M, Quddus A, Tafazolli R (2014) Graph-Based Multicell Scheduling in OFDMA-Based Small Cell Networks,IEEE Access 2 pp. 897-908
    This paper proposes a novel graph-based multicell scheduling framework to efficiently mitigate downlink intercell interference in OFDMA-based small cell networks. We define a graph-based optimization framework based on interference condition between any two users in the network assuming they are served on similar resources. Furthermore, we prove that the proposed framework obtains a tight lower bound for conventional weighted sum-rate maximization problem in practical scenarios. Thereafter, we decompose the optimization problem into dynamic graph-partitioning-based subproblems across different subchannels and provide an optimal solution using branch-and-cut approach. Subsequently, due to high complexity of the solution, we propose heuristic algorithms that display near optimal performance. At the final stage, we apply cluster-based resource allocation per subchannel to find candidate users with maximum total weighted sum-rate. A case study on networked small cells is also presented with simulation results showing a significant improvement over the state-of-the-art multicell scheduling benchmarks in terms of outage probability as well as average cell throughput.
    Ma Y, Yi N, Tafazolli R (2006) Channel estimation for PIRP-OFDM in slowly time-varying channel: First-order or second-order statistics?,IEEE SIGNAL PROCESSING LETTERS 13 (3) pp. 129-132 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Mach T, Tafazolli R (2009) Mass Mobility Signaling Congestion Avoidance Mechanism Using Randomized Time Distribution of Cell Reselections, 2009 INTERNATIONAL CONFERENCE ON TELECOMMUNICATIONS (ICT) pp. 238-242 IEEE
    Héliot F, Hoshyar R, Tafazolli R (2010) Weighted Sum-Rate based Power Allocation for the Uplink of Nonregenerative Cooperative Multi-User MIMO Communication System,Proc. ICT Future Network & Mobile Summit
    Ma Y, Yamani A, Yi N, Tafazolli R (2016) Low-Complexity MU-MIMO Nonlinear Precoding Using Degree-2 Sparse Vector Perturbation,IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 34 (3) pp. 497-509 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    He Z, Ma Y, Tafazolli R (2012) A High Accuracy Mobile Positioning Approach in IEEE 802.11a WLANs, IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences E95-A (10) pp. 1776-1779 IEICE
    This paper presents a novel approach for mobile positioning in IEEE 802.11a wireless LANs with acceptable computational complexity. The approach improves the positioning accuracy by utilizing the time and frequency domain channel information obtained from the orthogonal frequency-division multiplexing (OFDM) signals. The simulation results show that the proposed approach outperforms the multiple signal classification (MUSIC) algorithm, Ni's algorithm and achieve a positioning accuracy of 1 m with a 97% probability in an indoor scenario.
    Pilloni V, Navaratnam P, Vural S, Atzori L, Tafazolli R (2013) TAN: a Distributed Algorithm for Dynamic Task Assignment in WSNs, IEEE Sensor Networks
    Schott W, Gluhak A, Presser M, Hunkeler U, Tafazolli R (2007) e-SENSE protocol stack architecture for wireless sensor networks, 2007 PROCEEDINGS OF THE 16TH IST MOBILE AND WIRELESS COMMUNICATIONS, VOLS 1-3 pp. 464-468 IEEE
    Huy DTP, Rodriguez J, Gameiro A, Tafazolli R (2007) Dynamic resource allocation for beyond 3G cellular networks, WIRELESS PERSONAL COMMUNICATIONS 43 (4) pp. 1727-1740 SPRINGER
    Hoseinitabatabaei SA, barnaghi P, tafazolli R, wang C Method and apparatus for scalable data discovery in IoT systems,
    This patent is based on our novel data discovery mechanism for large scale, highly distributed and heterogeneous data networks. Managing Big Data harvested from IoT environments is an example application
    Salami G, Tafazolli R (2009) On the Impact of Varying Bandwidth on the Performance of UMTS Spectrum Sharing Algorithm, CONTEL 2009: PROCEEDINGS OF THE 10TH INTERNATIONAL CONFERENCE ON TELECOMMUNICATIONS pp. 319-324 UNIV ZAGREB, FAC ELECT ENGN COMP
    Zhang Y, Hoshyar R, Tafazolli R (2008) Timing and frequency offset estimation scheme for the uplink of OFDMA systems, IET COMMUNICATIONS 2 (1) pp. 121-130 INST ENGINEERING TECHNOLOGY-IET
    Al-Imari M, Xiao P, Imran MA, Tafazolli R (2014) Radio Resource Allocation for Uplink OFDMA Systems with Finite Symbol Alphabet Inputs,IEEE Transactions on Vehicular Technology 63 (4) pp. 1917-1921 IEEE
    In this paper, we consider the radio resource allocation problem for uplink OFDMA system. The existing algorithms have been derived under the assumption of Gaussian inputs due to its closed-form expression of mutual information. For the sake of practicality, we consider the system with Finite Symbol Alphabet (FSA) inputs, and solve the problem by capitalizing on the recently revealed relationship between mutual information and Minimum Mean-Square Error (MMSE). We first relax the problem to formulate it as a convex optimization problem, then we derive the optimal solution via decomposition methods. The optimal solution serves as an upper bound on the system performance. Due to the complexity of the optimal solution, a low-complexity suboptimal algorithm is proposed. Numerical results show that the presented suboptimal algorithm can achieve performance very close to the optimal solution and outperforms the existing suboptimal algorithms. Furthermore, using our proposed algorithm, significant power saving can be achieved in comparison to the case when Gaussian input is assumed.
    Qi YA, Hoshyar R, Tafazolli R (2009) A Novel Quantization Scheme in Compress-and-Forward Relay System, IEEE 69th VEHICULAR TECHNOLOGY CONFERENCE pp. 1854-1858 IEEE
    In this paper, we extend a well-developed quantization scheme to block fading relay system using compress-and-forward and propose a new achievable rate based quantization scheme (ARBQS). A new signal combination scheme with less complexity is also proposed accordingly. Based on the scalar quantizer obtained, vector quantizer with Trellis coded quantization (TCQ) scheme is provided. While many quantization schemes have concentrated on minimization of quantization distortion, our simulations results indicate that the new scheme achieves better performance in both AWGN case and block fading case without distortion minimization and achieve higher compression efficiency and reduced complexity simultaneously.
    Ghader M, Prasad N, Olsen RL, Mirzadeh S, Tafazolli R (2004) Secure Resource and Service Discovery in Personal Networks Wireless,
    Akbari A, Heliot F, Imran MA, Tafazolli R (2012) Energy Efficiency Contours for Broadcast Channels Using Realistic Power Models, IEEE Transactions on Wireless Communications 11 (11) pp. 4017-4025 IEEE
    Energy savings are becoming a global trend, hence the importance of energy efficiency (EE) as an alternative performance evaluation metric. This paper proposes an EE based resource allocation method for the broadcast channel (BC), where a linear power model is used to characterize the power consumed at the base station (BS). Having formulated our EE based optimization problem and objective function, we utilize standard convex optimization techniques to show the concavity of the latter, and thus, the existence of a unique globally optimal energy-efficient rate and power allocation. Our EE based resource allocation framework is also extended to incorporate fairness, and provide a minimum user satisfaction in terms of spectral efficiency (SE). We then derive the generic equation of the EE contours and use them to get insights about the EE-SE trade-off over the BC. The performances of the aforementioned resource allocation schemes are compared for different metrics against the number of users and cell radius. Results indicate that the highest EE improvement is achieved by using the unconstrained optimization scheme, which is obtained by significantly reducing the total transmit power. Moreover, the network EE is shown to increase with the number of users and decrease as the cell radius increases. © 2012 IEEE.
    Bennis M, Wijting C, Abedi S, Thilakawardana S, Tafazolli R (2009) Performance evaluation of advanced spectrum functionalities for future radio networks, WIRELESS COMMUNICATIONS & MOBILE COMPUTING 9 (11) pp. 1532-1542 JOHN WILEY & SONS INC
    Hanzo L, Tafazolli R (2008) Mobile Ad Hoc Networks: Challenges and Solutions for Providing Quality of Service Assurances, In: Kyriazakos S, Soldatos I, Karetsos G (eds.), 4g Mobile and Wireless Communications Technologies River Publishers
    Mobile Ad Hoc Networks: Challenges and Solutions for Providing Quality of
    Service Assurances Lajos Hanzo (II.)1 and Rahim Tafazolli University of Surrey,
    ...
    Shariat M, Quddus AU, Tafazolli R (2008) On the efficiency of interference coordination schemes in emerging cellular wireless networks,IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC
    In this paper, the efficiencies of different interference coordination schemes are evaluated for emerging wireless networks and the possible impact on intra-cell scheduling is studied through extensive simulations. The results show that pure fractional frequency reuse can provide similar improvement in the cell-edge throughput compared to power coordinated counterpart at a less cost in terms of overall throughput. Moreover, it can provide fairer distribution of throughput in both central as well as cell-edge areas. However, this scheme can not mange asymmetrical changes in the distribution of users across different cells in the entire system. As a result, a power coordination mechanism would be still necessary on top of such flexible frequency reuse schemes. © 2008 IEEE.
    Salami GK, Tafazolli R (2009) A framework for UMTS inter-operator spectrum sharing in the UMTS extension band, 9th International Symposium on Communications and Information Technology pp. 193-198 IEEE
    This paper proposes a framework for spectrum sharing between multiple Universal Mobile Telecommunication System (UMTS) operators in the UMTS extension band. An algorithm is proposed, and the performance of the algorithm is investigated under uniform and non-uniform traffic conditions. The impact of call setup messages on the overall performance of the algorithm show that DSA gains in the region of 7% and 2% can be obtained under uniform and non-uniform traffic conditions.
    Reategui Del Aguila F, Imran MA, Tafazolli R (2013) On The Three-Receiver Multilevel Broadcast Channel with Random Parameters,VDE Verlag GmBh 9
    In this paper we extend the analysis of two-receiver broadcast channels with random parameters to the three-receivers case. Specifically we base our work on Nair and El Gamal's results for the three-receiver discrete memoryless multilevel broadcast channel and assume that state information is available non-causally at the transmitter. We provide an achievable rate region for this setting and acknowledge its importance in the study of multiuser cognitive radio configurations.
    Yi N, Ma Y, Tafazolli R (2011) Incremental Decode-Forward Relaying over Asymmetric Fading Channels: Outage Probability and Location-Aided Relay Selection, pp. 181-184
    This paper presents two contributions towards incremental decode-forward relaying over asymmetric fading channels. One is about the outage probability of incremental relay network accommodating i.n.d. cooperative paths. Our contribution is mainly on formulating a closed-form of the outage probability through employment of the Inverse Laplace Transform and Eular Summation. The other is about the proposal of transmit-power efficient relay-selection strategy through exploitation of the relationship between position of relays and the outage probability.
    Grandblaise D, Moessner K, Vivier G, Tafazolli R (2006) Rental protocol for automated spectrum sharing negotiation between base stations, FREQUENZ 60 (9-10) pp. 162-166 FACHVERLAG SCHIELE SCHON
    Quddus AU, Evans BG, Tafazolli R (2009) Blind adaptive multiuser detection for code division multiple access using Cimmino's reflection method, Proceedings of 6th International Bhurban Conference on Applied Sciences and Technology, IBCAST-2009 2 pp. 118-120
    This paper investigates adaptive implementation of the linear minimum mean square error (MMSE) detector in code division multiple access (CDMA). From linear algebra, Cimmino's reflection method is proposed as a possible way of achieving the MMSE solution blindly. Simulation results indicate that the proposed method converges four times faster than the blind least mean squares (LMS) algorithm and has roughly the same convergence performance as the blind recursive least squares (RLS) algorithm. Moreover the proposed algorithm is numerically more stable than the RLS algorithm and also exhibits parallelism for pipelined implementation. © 2009 IEEE.
    Thilakawardana D, Moessner K, Tafazolli R (2008) Darwinian approach for dynamic spectrum allocation in next generation systems, IET COMMUNICATIONS 2 (6) pp. 827-836 INST ENGINEERING TECHNOLOGY-IET
    Yi N, Ma Y, Tafazolli R (2010) Underlay Cognitive Radio with Full or Partial Channel Quality Information, International Journal of Navigation and Observation 2010 105723
    Georgiades M, Akhtar N, Politis C, Tafazolli R (2007) Enhancing mobility management protocols to minimise AAA impact on handoff performance, COMPUTER COMMUNICATIONS 30 (3) pp. 608-618 ELSEVIER SCIENCE BV
    Qi Y, Hoshyar R, Tafazolli R (2010) The error-resilient compression of correlated binary sources and EXIT chart based performance evaluation, Proceedings of the 2010 7th International Symposium on Wireless Communication Systems, ISWCS'10 pp. 741-745
    Vural S, Navaratnam P, Wang N, Tafazolli R (2013) Asynchronous Clustering of Multihop Wireless Sensor Networks,ACM Transactions on Sensor Networks
    Abangar H, Ghader M, Gluhak A, Tafazolli R (2010) Improving the Performance of Web Services in Wireless Sensor Networks,
    Hoshyar R, Tafazolli R (2008) Achievable full decode and forward rates for cooperative MIMO BICM systems, IEEE International Symposium on Personal, Indoor and Mobile Radio Communications IEEE
    A generic cooperative MIMO BICM system is described. Achievable rates are computed based on the extended equivalent binary input channel model of the original BICM system. Full decode and forward is assumed at the relay node. Two types of two-phased transmission/reception protocols are employed to establish orthogonal transmission/reception of the relay node. The achievable rate results are provided for different combinations of modulation orders and the number of antennas used at the source and relay nodes. Quantitative results provided in this paper could serve as a guide on when to engage cooperative transmission and how to choose proper constellations and puncturing ratios for the practical BICM coded systems. Comparison of the considered BICM system with other possible cooperative coded systems is also crucial that this paper due to lack of space for exposition misses to address.
    Imran A, Tafazolli R (2009) Evaluation and Comparison of Capacities and Costs of Multihop Cellular Networks, 2009 INTERNATIONAL CONFERENCE ON TELECOMMUNICATIONS (ICT) pp. 160-165 IEEE
    Rodriguez J, Marques P, Radwan A, Moessner K, Tafazolli R, Raspopoulos M, Stavrou S, Trapps P, Noquet D, Sithamparanathan K, Gomes A, Piesiewicz R, Mokrani H, Foglar A, Verikoukis C (2010) Cognitive radio and cooperative strategies for power saving in multi-standard wireless devices, 2010 Future Network and Mobile Summit
    Energy is a critical resource in the design of wireless networks since wireless devices are usually powered by batteries. Without any new approaches for energy saving, 4G mobile users will relentlessly be searching for power outlets rather than network access, and becoming once again bound to a single location. To avoid the so called 4G "energy trap" and to help wireless devices become more environment friendly, there is a clear need for disruptive strategies to address all aspects of power efficiency from the user devices through to the core infrastructure of the network and how these devices and equipment interact with each other. The ICT-C2POWER project is the vehicle that will address these issues through cognitive techniques and cooperation. The C2POWER case study is to research, develop and demonstrate energy saving technologies for multi-standard wireless mobile devices, exploiting the combination of cognitive radio and cooperative strategies, while still enabling the required performance in terms of data rate and QoS to support active applications. Copyright © 2010 The authors.
    He Z, Ma Y, Tafazolli R, Liu H (2010) An oversampling approach for LoS-ToA estimation in interleaved OFDMA, IWCMC 2010 - Proceedings of the 6th International Wireless Communications and Mobile Computing Conference pp. 580-584
    Line-of-sight (LoS) time-of-arrival (ToA) is one of key parameters for network-based localization techniques. Its estimation accuracy depends on the bandwidth of transmitted signals. This paper aims to investigate the LoS-ToA estimation for an interleaved OFDMA based network, where the signal bandwidth is not sufficiently wide to offer the acceptable estimation accuracy. In this situation, an oversampling approach is proposed to improve the resolution. Moreover, the proposed scheme does not require modification of mobile communications systems. It is found that the proposed approach can significantly improve the ToA estimationperformance, and offer adequate accuracy even for the low signal-to-noise ratio (SNR) range. Copyright 2010 ACM.
    Hanzo L, Tafazolli R (2007) Throughput assurances through admission control for multi-hop MANETs, 2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9 pp. 1945-1949 IEEE
    Héliot F, Chut X, Hoshyar R, Tafazolli R (2008) An accurate closed-form approximation of the ergodic capacity over log-normal fading channels,IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC
    The log-normal probability distribution is commonly used in wireless communications to model the shadowing and, more recently, the small-scale fading for indoor ultra-wide-band communications. In this paper, an accurate closed-form approximation of the ergodic capacity over log-normal fading channels is derived. This expression can be easily used to evaluate and compare the ergodic capacity of communication systems operating over log-normal fading channels. © 2008 IEEE.
    Dianati M, Tafazolli R, Shen XS, Naik K (2010) Call admission control with opportunistic scheduling scheme,WIRELESS COMMUNICATIONS & MOBILE COMPUTING 10 (3) pp. 372-382 JOHN WILEY & SONS INC
    Zhang Y, Ma Y, Tafazolli R (2010) Power Allocation for Bidirectional AF Relaying over Rayleigh Fading Channels, IEEE COMMUNICATIONS LETTERS 14 (2) pp. 145-147 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Ghader M, Tafazolli R (2009) Efficient Employment of Service Location Protocol in Multi-cluster Networks,
    Imran M, Mohamed A, Tafazolli R (2014) Splitting the data and control functionality: Scalable deployment solution for 5G cellular networks, Proceedings of International Wireless Industry Consortium (IWPC) Workshop 2014 IWPC - The International Wireless Industry Consortium
    Akbari A, Imran MA, Tafazolli R (2011) Maximising Average Energy efficiency for Two-user AWGN Broadcast Channel,Future Network and Mobile Summit IEEE
    Energy consumption has become an increasingly important aspect of wireless communications, from both an economical and environmental point of view. New enhancements are being placed on mobile networks to reduce the power consumption of both mobile terminals and base stations. This paper studies the achievable rate region of AWGN broadcast channels under Time-division, Frequency-division and Superposition coding, and locates the optimal energy-efficient rate-pair according to a comparison metric based on the average energy efficiency of the system. In addition to the transmit power, circuit power and signalling power are also incorporated in the energy efficiency function, with simulation results verifying that the Superposition coding scheme achieves the highest energy efficiency in an ideal, but non-realistic scenario, where the signalling power is zero. With moderate signalling power, the Frequency-division scheme is the most energy-efficient, with Superposition coding and Time-division becoming second and third best. Conversely, when the signalling power is high, both Time-division and Frequency-division schemes outperform Superposition coding. On the other hand, the Superposition coding scheme also incorporates rate-fairness into the system, which allows both users to transmit whilst maximising the energy efficiency.
    Georgiades M, Dagiuklas T, Tafazolli R (2006) Middlebox context transfer for multimedia session support in all-IP networks, IWCMC 2006 - Proceedings of the 2006 International Wireless Communications and Mobile Computing Conference 2006 pp. 389-394
    This paper describes a mechanism of forwarding secure state information associated to communication sessions, between middleboxes belonging to different Radio Access Networks (RANs). The transfer of state information among RANs could support service integrity and continuity by maintaining a mobile user's multimedia sessions which may otherwise be dropped and also minimize security vulnerabilities. The paper demonstrates how the context transfer protocol could be employed for this purpose to forward certain security information from the old to the new middlebox to support multimedia session maintenance during mobility and also at the same time notify the previous middlebox to close unnecessary open ports for improved security and resolve vulnerability. A number of test scenarios are used to demonstrate how middleboxes could intervene with multimedia sessions during mobility and show how context transfer can provide a solution for improving the performance in the multimedia session re-establishment as well as enhancing middlebox security. Copyright 2006 ACM.
    Hamid A, Hoshyar R, Tafazolli R (2008) Joint rate and power adaptation for MC-CDMA over tempo-spectral domain,WCNC 2008: IEEE WIRELESS COMMUNICATIONS & NETWORKING CONFERENCE, VOLS 1-7 pp. 969-973 IEEE
    Pilloni V, Navaratnam P, Vural S, Atzori L, Tafazolli R (2013) Cooperative Task Assignment for Distributed Deployment of Applications in WSNs,
    Mirzadeh S, Tafazolli R, Pallares JJ, Armknecht F, Afifi H (2008) CPFP: An efficient key management scheme for large scale personal networks,3rd International Symposium on Wireless Pervasive Computing, ISWPC 2008, Proceedings pp. 744-748
    This paper provides an efficient key management scheme for large scale personal networks (PN) and introduces the Certified PN Formation Protocol (CPFP) based on a personal public key infrastructure (personal PKI) concept and Elliptic Curve Cryptography (ECC) techniques. © 2008 IEEE.
    Navaratnam P, Cruickshank H, Tafazolli R (2008) A link adaptive transport protocol for multimedia streaming applications in multi hop wireless networks, MOBILE NETWORKS & APPLICATIONS 13 (3-4) pp. 246-258 SPRINGER
    Qi Y, Hoshyar R, Tafazolli R (2009) Efficient ARQ Protocol for Hybrid Relay Schemes with Limited Feedback, 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5 pp. 1849-1853 IEEE
    Prammanee S, Moessner K, Tafazolli R (2006) Discovering modalities for adaptive multimodal interfaces, Interactions 13 (3) pp. 66-70
    A scheme for discovering modalities for adaptive multimodal interfaces, is discussed. One of the features of miultimodal applications is to provide the possibility of interfacing through different interface devices. This means that the user should be able to interact through any modality available, even if the environment is mobile. Making user interfaces adaptable extends the user friendliness and usability of mobile terminals and applications. A three party model for multimodal interface discovery is suggested for extending the functionality of the discovery mechanisms. The interface and modality description are based on a script for private as well as public interface devices.
    Jung J, Abaii M, Tafazolli R (2008) Load Matrix optimization in mobile cellular networks,2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7 pp. 2016-2020 IEEE
    Widiawan AK, Tafazolli R (2007) High altitude platform station (HAPS): A review of new infrastructure development for future wireless communications, WIRELESS PERSONAL COMMUNICATIONS 42 (3) pp. 387-404 SPRINGER
    Hanzo L, Tafazolli R (2007) Quality of Service routing and admission control for mobile ad-hoc networks with a contention-based MAC layer, 2006 IEEE International Conference on Mobile Adhoc and Sensor Systems, Vols 1 and 2 pp. 451-454 IEEE
    Guo T, Wang N, Tafazolli R, Moessner K (2010) Policy-Aware Virtual relay placement for inter-domain path diversity, Proc. IEEE Symp. Computers and Communications (ISCC) pp. 38-43
    Onireti OS, Imran A, Imran M, Tafazolli R (2016) Impact of Positioning Error on Achievable Spectral Efficiency in Database-aided Networks,
    Database-aided user association, where users are associated with data base stations (BSs) based on a database which stores their geographical location with signal-to-noise-ratio tagging, will play a vital role in the futuristic cellular architecture with separated control and data planes. However, such approach can lead to inaccurate user-data BS association, as a result of the inaccuracies in the positioning technique, thus leading to sub-optimal performance. In this paper, we investigate the impact of database-aided user association approach on the average spectral efficiency (ASE). We model the data plane base stations using its fluid model equivalent and derive the ASE for the channel model with pathloss only and when shadowing is incorporated. Our results show that the ASE in database-aided networks degrades as the accuracy of the user positioning technique decreases. Hence, system specifications for database-aided networks must take account of inaccuracies in positioning techniques.
    Abbas Fathy Abbas Y, Barnaghi P, Enshaeifar S, Tafazolli R (2017) A Distributed In-network Indexing Mechanism for the Internet of Things,IEEE World Forum on Internet of Things pp. 585-590 IEEE
    The current Web and data indexing and search mechanisms are mainly tailored to process text-based data and are limited in addressing the intrinsic characteristics of distributed, large-scale and dynamic Internet of Things (IoT) data networks. The IoT demands novel indexing solutions for large-scale data to create an ecosystem of system; however, IoT data are often numerical, multi-modal and heterogeneous. We propose a distributed and adaptable mechanism that allows indexing and discovery of real-world data in IoT networks. Comparing to the state-of-the-art approaches, our model does not require any prior knowledge about the data or their distributions. We address the problem of distributed, efficient indexing and discovery for voluminous IoT data by applying an unsupervised machine learning algorithm. The proposed solution aggregates and distributes the indexes in hierarchical networks. We have evaluated our distributed solution on a large-scale dataset, and the results show that our proposed indexing scheme is able to efficiently index and enable discovery of the IoT data with 71% to 92% better response time than a centralised approach.
    Puschmann D, Barnaghi P, Tafazolli R (2017) Using LDA to Uncover the Underlying Structures and Relations in Smart City Data Streams,IEEE Systems Journal 12 (2) pp. 1755-1766 Institute of Electrical and Electronics Engineers (IEEE)

    Recent advancements in sensing, networking technologies
    and collecting real-world data on a large scale and from various environments
    have created an opportunity for new forms of real-world services
    and applications. This is known under the umbrella term of the Internet
    of Things (IoT). Physical sensor devices constantly produce very large
    amounts of data. Methods are needed which give the raw sensor measurements
    a meaningful interpretation for building automated decision
    support systems. To extract actionable information from real-world data,
    we propose a method that uncovers hidden structures and relations
    between multiple IoT data streams. Our novel solution uses Latent
    Dirichlet Allocation (LDA), a topic extraction method that is generally
    used in text analysis. We apply LDA on meaningful abstractions that
    describe the numerical data in human understandable terms. We use
    Symbolic Aggregate approXimation (SAX) to convert the raw data into
    string-based patterns and create higher level abstractions based on
    rules.

    We finally investigate how heterogeneous sensory data from multiple
    sources can be processed and analysed to create near real-time intelligence
    and how our proposed method provides an efficient way to
    interpret patterns in the data streams. The proposed method uncovers
    the correlations and associations between different pattern in IoT data
    streams. The evaluation results show that the proposed solution is able
    to identify the correlation with high efficiency with an F-measure up to
    90%.

    Yi N, Ma Y, Tafazolli R (2008) Doubly differential communication assisted with cooperative relay,2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING 1 - 7 pp. 644-647 IEEE
    Doubly differential modem turns out to be a promising
    technology for coping with unknown frequency offsets with
    the pay of signal-to-noise ratio (SNR). In this paper, we propose to compensate the SNR loss by employing the detection-forward cooperative relay. The receiver can employ two kind of combiners to attain the achievable spatial diversity-gain. Performance analysis is carefully investigated for the Rayleigh-fading channel. It is
    shown that the SNR-compensation is satisfied for the large-SNR range.
    Zhang L, Ijaz A, Mao J, Xiao P, Tafazolli R (2017) Multi-service Signal Multiplexing and Isolation for
    Physical-Layer Network Slicing (PNS)
    ,
    VTC2017-Fall Proceedings
    Network slicing has been identified as one of the
    most important features for 5G and beyond to enable operators
    to utilize networks on an as-a-service basis and meet the wide
    range of use cases. In physical layer, the frequency and time
    resources are split into slices to cater for the services with
    individual optimal designs, resulting in services/slices having
    different baseband numerologies (e.g., subcarrier spacing) and
    / or radio frequency (RF) front-end configurations. In such a
    system, the multi-service signal multiplexing and isolation among
    the service/slices are critical for the Physical-Layer Network
    Slicing (PNS) since orthogonality is destroyed and significant
    inter-service/ slice-band-interference (ISBI) may be generated.
    In this paper, we first categorize four PNS cases according to the
    baseband and RF configurations among the slices. The system
    model is established by considering a low out of band emission
    (OoBE) waveform operating in the service/slice frequency band to
    mitigate the ISBI. The desired signal and interference for the two
    slices are derived. Consequently, one-tap channel equalization
    algorithms are proposed based on the derived model. The
    developed system models establish a framework for further
    interference analysis, ISBI cancelation algorithms, system design
    and parameter selection (e.g., guard band), to enable spectrum
    efficient network slicing.
    Vural S, Wang N, Foster G, Tafazolli R (2017) Success Probability of Multiple-Preamble Based Single-Attempt Random Access to Mobile Networks,IEEE Communications Letters 21 (8) pp. 1755-1758 IEEE
    In this letter, we analyse the trade-off between collision probability and code-ambiguity, when devices transmit a sequence of preambles as a codeword, instead of a single preamble, to reduce collision probability during random access to a mobile network. We point out that the network may not have sufficient resources to allocate to every possible codeword, and if it does, then this results in low utilisation of allocated uplink resources. We derive the optimal preamble set size that maximises the probability of success in a single attempt, for a given number of devices and uplink resources.
    Molu M, Xiao P, Khalily M, Zhang L, Tafazolli R (2017) A Novel Equivalent Definition of Modified Bessel Functions for Performance Analysis of Multi-Hop Wireless Communication Systems,IEEE Access 5 pp. 7594-7605 IEEE
    A statistical model is derived for the equivalent signal-to-noise ratio of the Source-to-Relay-to-Destination (S-R-D) link for Amplify-and-Forward (AF) relaying systems that are subject to block Rayleigh-fading. The probability density function and the cumulated density function of the S-R-D link SNR involve modified Bessel functions of the second kind. Using fractional-calculus mathematics, a novel approach is introduced to rewrite those Bessel functions (and the statistical model of the S-R-D link SNR) in series form using simple elementary functions. Moreover, a statistical characterization of the total receive-SNR at the destination, corresponding to the S-R-D and the S-D link SNR, is provided for a more general relaying scenario in which the destination receives signals from both the relay and the source and processes them using maximum ratio combining (MRC). Using the novel statistical model for the total receive SNR at the destination, accurate and simple analytical expressions for the outage probability, the bit error probability, and the ergodic capacity are obtained. The analytical results presented in this paper provide a theoretical framework to analyze the performance of the AF cooperative systems with an MRC receiver.
    Onireti OS, Imran Ali, Imran Muhammad, Tafazolli Rahim (2015) Energy Efficient Inter-Frequency Small Cell Discovery in Heterogeneous Networks,IEEE Transactions on Vehicular Technology 65 (9) pp. 7122-7135 IEEE
    In this paper, using stochastic geometry, we investigate the average energy efficiency (AEE) of the user terminal (UT) in the uplink of a two-tier heterogeneous network (HetNet), where the two tiers are operated on separate carrier frequencies. In such a deployment, a typical UT must periodically perform inter-frequency small cell discovery (ISCD) process in order to discover small cells in its neighborhood and benefit from the high data rate and traffic offloading opportunity that small cells present. We assume that the base stations (BSs) of each tier and UTs are randomly located and we derive the average ergodic rate and UT power consumption, which are later used for our AEE evaluation. The AEE incorporates the percentage of time a typical UT missed small cell offloading opportunity as a result of the periodicity of the ISCD process. In addition to this, the additional power consumed by the UT due to the ISCD measurement is also included. Moreover, we derive the optimal ISCD periodicity based on the UT?s average energy consumption (AEC) and AEE. Our results reveal that ISCD periodicity must be selected with the objective of either minimizing UT?s AEC or maximizing UT?s AEE.
    Heliot F, Hoshyar R, Tafazolli R (2011) An Accurate Closed-Form Approximation of the Distributed MIMO Outage Probability,IEEE Transactions on Wireless Communications 10 (1) pp. 5-11 IEEE
    The mutual information (MI) of multiple-input multiple-output (MIMO) system over Rayleigh fading channel is known to asymptotically follow a normal probability distribution. In this paper, we first prove that the MI of distributed MIMO (DMIMO) system is also asymptotically equivalent to a Gaussian random variable (RV) by deriving its moment generating function (MGF) and by showing its equivalence with the MGF of a Gaussian RV. We then derive an accurate closed-form approximation of the outage probability for DMIMO system by using the mean and variance of the MI and show the uniqueness of its formulation. Finally, several applications for our analysis are presented.
    Multi-user (MU) massive multiple-input-multiple-output (MIMO) is one of the promising technologies for the 5th Generation of wireless communication systems. However, as an emerging technology, various technical challenges that hinder practical use of massive MIMO need to be addressed, e.g., imperfections on channel estimation and channel reciprocity. The overall objective of the proposed research is to investigate some of the key practical challenges of implementation of the massive MIMO system and propose effective solutions for those problems.
    First, in order to realise promised benefits of massive MIMO, there is a need for a highly accurate technique for provisioning of channel state information (CSI). However, the acquisition of CSI can be considerably influenced by imperfect channel estimation in practice. We therefore analyse the impact of channel estimation error on the performance of massive MIMO uplinks with the considerations of the channel correlation over space. We then propose a novel antenna selection scheme by exploiting the sparsity of the channel gain matrix at the received end, which significantly reduces implementation overhead and complexity compared to the well-adopted scheme, without degrading the system performance.
    Second, it is known that channel reciprocity in time-division duplexing (TDD) massive MIMO systems can be exploited to reduce the overhead required for the acquisition of CSI. However, perfect reciprocity is unrealistic in practical systems due to random radio-frequency (RF) circuit mismatches in uplink and downlink channels. We model and analyse the impact of the RF mismatches by taking into account the channel estimation error. We derive closed-form expressions of the output signal-to-interference-plus- noise ratio for typical linear precoding schemes, and further investigate the asymptotic performance of the considered precoding schemes to provide insights into the practical system designs, including guidelines for the selection of the effective precoding schemes.
    Third, our theoretical model for analysing the effect of channel reciprocity error on massive MIMO systems reveals that the imperfections in channel reciprocity might become a performance limiting factor. In order to compensate for these imperfections, we present and investigate two calibration schemes for TDD-based MU massive MIMO systems, namely, relative calibration and inverse calibration. In particular, the design of the proposed inverse calibration takes into account a compound effect of channel reciprocity error and channel estimation error. To compare two calibration schemes, we derive closed-form expressions for the ergodic sum-rate and the receive mean-square error for downlinks. We demonstrate that the proposed inverse calibration outperforms the relative calibration, thanks to its greater robustness to the compound effect of both errors.
    Pateromichelakis E, Shariat M, Quddus AU, Dianati M, Tafazolli R (2013) Dynamic Clustering Framework for Multi-Cell Scheduling in Dense Small Cell Networks,IEEE Communications Letters 17 (9) pp. 1802-1805 IEEE
    This letter proposes a novel graph-based multi-cell scheduling framework to efficiently mitigate downlink inter-cell interference in small cell OFDMA networks. This framework incorporates dynamic clustering combined with channel-aware resource allocation to provide tunable quality of service measures at different levels. Our extensive evaluation study shows that a significant improvement in user's spectral efficiency is achievable, while also maintaining relatively high cell spectral efficiency via empirical tuning of re-use factor across the cells according to the required QoS constraints.
    Hasanpour M, Shariat S, Barnaghi P, Hoseinitabatabaei S, Vahid S, Tafazolli R (2017) Quantum Load Balancing in Ad Hoc Networks,Quantum Information Processing 16 (148) Springer Verlag
    this paper presents a novel approach in targeting load balancing in ad hoc networks utilizing the properties of quantum game theory. This approach benefits from the instantaneous and information-less capability of entangled particles to synchronize the load balancing strategies in ad hoc networks. The Quantum Load Balancing (QLB) algorithm proposed by this work is implemented on top of OLSR as the baseline routing protocol; its performance is analyzed against the baseline OLSR, and considerable gain is reported regarding some of the main QoS metrics such as delay and jitter. Furthermore, it is shown that QLB algorithm supports a solid stability gain in terms of throughput which stands a proof of concept for the load-balancing properties of the proposed theory.
    Huang L, Chew K, Thilakawardana S, Liu Y, Moessner K, Tafazolli R (2006) Efficient group-based multimedia-on-demand service delivery in wireless networks,IEEE TRANSACTIONS ON BROADCASTING 52 (4) pp. 492-504 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    Recently, an upsurge of interest has been observed in providing multimedia on-demand (MoD) services to mobile users over wireless networks. Nevertheless, due to the rapidly varying nature of mobile networks and the scarcity of radio resources, the commercial implementation is still limited. This paper presents an efficient group-based multimedia-on-demand (GMoD) service model over multicast-enabled wireless infrastructures, where users requesting the same content are grouped and served simultaneously with a single multicast stream. The grouping is fulfilled through a process named "batching". An analytical model is derived to analyse a timeout-based hatching scheme with respect to the tradeoff between user blocking probability and reneging probability. Based on the deduced analytical model, an optimal timeout-based hatching scheme is proposed to dynamically identify the optimal tradeoff point that maximizes the system satisfaction ratio given a particular system status. The proposed scheme is evaluated by means of simulation and compared with two basic hatching schemes (timeout-based, size-based), and two hybrid ones (combined-for-profit, combined-for-loss). The simulation results demonstrate the proposed approach can ensure significant gains in terms of user satisfaction ratio, with low reneging and blocking probabilities.

    Onireti OS, Imran A, Imran Muhammad, Tafazolli Rahim (2015) On Energy Efficient Inter-Frequency Small Cell Discovery in Heterogeneous Networks,2015 IEEE International Conference on Communications (ICC) pp. 13-18
    In this paper, we investigate the optimal inter- frequency small cell discovery (ISCD) periodicity for small cells deployed on carrier frequency other than that of the serving macro cell. We consider that the small cells and user terminals (UTs) positions are modeled according to a homogeneous Poisson Point Process (PPP). We utilize polynomial curve fitting to approximate the percentage of time the typical UT misses small cell offloading opportunity, for a fixed small cell density and fixed UT speed. We then derive analytically, the optimal ISCD periodicity that minimizes the average UT energy consumption (EC). Furthermore, we also derive the optimal ISCD periodicity that maximizes the average energy efficiency (EE), i.e. bit- per-joule capacity. Results show that the EC optimal ISCD periodicity always exceeds the EE optimal ISCD periodicity, with the exception of when the average ergodic rate in both tiers are equal, in which the optimal ISCD periodicity in both cases also becomes equal.
    Zhang L, Ijaz A, Xiao P, Quddus AU, Tafazolli R (2017) Subband Filtered Multi-carrier Systems for Multi-service Wireless Communications,IEEE Transactions on Wireless Communications 16 (3) pp. 1893-1907 IEEE
    Flexibly supporting multiple services, each with
    different communication requirements and frame structure, has
    been identified as one of the most significant and promising
    characteristics of next generation and beyond wireless communication
    systems. However, integrating multiple frame structures
    with different subcarrier spacing in one radio carrier may
    result in significant inter-service-band-interference (ISBI). In this
    paper, a framework for multi-service (MS) systems is established
    based on subband filtered multi-carrier system. The subband
    filtering implementations and both asynchronous and generalized
    synchronous (GS) MS subband filtered multi-carrier (SFMC)
    systems have been proposed. Based on the GS-MS-SFMC system,
    the system model with ISBI is derived and a number of properties
    on ISBI are given. In addition, low-complexity ISBI cancelation
    algorithms are proposed by precoding the information symbols
    at the transmitter. For asynchronous MS-SFMC system in the
    presence of transceiver imperfections including carrier frequency
    offset, timing offset and phase noise, a complete analytical
    system model is established in terms of desired signal, intersymbol-interference,
    inter-carrier-interference, ISBI and noise.
    Thereafter, new channel equalization algorithms are proposed
    by considering the errors and imperfections. Numerical analysis
    shows that the analytical results match the simulation results,
    and the proposed ISBI cancelation and equalization algorithms
    can significantly improve the system performance in comparison
    with the existing algorithms.
    Mohamed A, Onireti O, Imran M, Imran A, Tafazolli R (2016) Predictive and Core-network Efficient RRC Signalling for Active State Handover in RANs with Control/Data Separation,IEEE Transactions on Wireless Communications 16 (3) pp. 1423-1436 IEEE
    Frequent handovers (HOs) in dense small cell deployment scenarios could lead to a dramatic increase in signalling overhead. This suggests a paradigm shift towards a signalling conscious cellular architecture with intelligent mobility management. In this direction, a futuristic radio access network with a logical separation between control and data planes has been proposed in research community. It aims to overcome limitations of the conventional architecture by providing high data rate services under the umbrella of a coverage layer in a dual connection mode. This approach enables signalling efficient HO procedures, since the control plane remains unchanged when the users move within the footprint of the same umbrella. Considering this configuration, we propose a core-network efficient radio resource control (RRC) signalling scheme for active state HO and develop an analytical framework to evaluate its signalling load as a function of network density, user mobility and session characteristics. In addition, we propose an intelligent HO prediction scheme with advance resource preparation in order to minimise the HO signalling latency. Numerical and simulation results show promising gains in terms of reduction in HO latency and signalling load as compared with conventional approaches.
    Chandrasekaran G, Wang N, Jun J, Xu M, Tafazolli R (2016) Towards D2D-based Opportunistic Data Relay Service in Partial Not-spots,Proceedings of WiMob'2016
    With the recent development of Device-toDevice (D2D) communication technologies, mobile devices will no longer be treated as pure ?terminals?, but they could become an integral part of the network in specific application scenarios. In this paper, we introduce a novel scheme of using D2D communications for enabling data relay services in partial Not-Spots, where a client without local network access may require data relay by other devices. Depending on specific social application scenarios that can leverage on the D2D technology, we consider tailored algorithms in order to achieve optimised data relay service performance on top of our proposed networkcoordinated communication framework. The approach is to exploit the network?s knowledge on its local user mobility patterns in order to identify best helper devices participating in data relay operations. This framework also comes with our proposed helper selection optimization algorithm based on reactive predictability of individual user. According to our simulation analysis based on both theoretical mobility models and real human mobility data traces, the proposed scheme is able to flexibly support different service requirements in specific social application scenarios.
    Kuzminskiy A, Abramovich Y, Xiao P, Tafazolli R (2016) Spectrum Sharing Efficiency Analysis in Rule Regulated Networks with Decentralized Occupation Control,IEEE PIMRC 2016 Proceedings
    Decentralized dynamic spectrum allocation (DSA) that exploit adaptive antenna array interference mitigation (IM) diversity at the receiver, is studied for interference-limited environments with high level of frequency reuse. The system consists of base stations (BSs) that can optimize uplink frequency allocation to their user equipments (UEs) to minimize impact of interference on the useful signal, assuming no control over band allocation of other BSs sharing the same bands. To this end, ?good neighbor? (GN) rules allow effective trade off between the equilibrium and transient decentralized DSA behavior if the performance targets are adequate to the interference scenario. In this paper, we extend the GN rules by including a spectrum occupation control that allows adaptive selection of the performance targets corresponding to the potentially ?interference free? DSA; define the semi-analytic absorbing Markov chain model for the GN DSA with occupation control and study the convergence properties including effects of possible breaks of the GN rules; and for higher-dimension networks, develop the simplified search GN algorithms with occupation and power control (PC) and demonstrate their efficiency by means of simulations in the scenario with unlimited requested network occupation.
    Qi Y, Heliot Fabien, Imran Muhammad, Tafazolli Rahim (2012) Green Relay Techniques in Cellular Systems,In: Yu FR, Leung V-C, Zhang X (eds.), Green Communications and Networking CRC Press
    Zhang Lei, Xiao Pei, Zafar Adnan, Quddus Atta, Tafazolli Rahim (2016) FBMC System: An Insight into Doubly Dispersive Channel Impact,IEEE Transactions on Vehicular Technology 66 (5) pp. 3942-3956 IEEE
    It has been claimed that the filter bank multicarrier (FBMC) systems suffer from negligible performance loss caused by moderate dispersive channels in the absence of guard time protection between symbols. However, a theoretical and systematic explanation/analysis for the statement is missing in the literature to date. In this paper, based on one-tap minimum mean square error (MMSE) and zero-forcing (ZF) channel equalizations, the impact of doubly dispersive channel on the performance of FBMC systems is analyzed in terms of mean square error (MSE) of received symbols. Based on this analytical framework, we prove that the circular convolution property between symbols and the corresponding channel coefficients in the frequency domain holds loosely with a set of inaccuracies. To facilitate analysis, we first model the FBMC system in a vector/matrix form and derive the estimated symbols as a sum of desired signal, noise, inter-symbol interference (ISI), inter-carrier interference (ICI), inter-block interference (IBI) and estimation bias in the MMSE equalizer. Those terms are derived one-by-one and expressed as a function of channel parameters. The numerical results reveal that in harsh channel conditions, e.g., with large Doppler spread or channel delay spread, the FBMC system performance may be severely deteriorated and error floor will occur.
    Chen G, Xiao Pei, Kelly James, Li B, Tafazolli Rahim (2017) Full-Duplex Wireless-Powered Relay in Two Way Cooperative Networks,IEEE Access 5 pp. 1548-1558 IEEE
    This paper investigates a full duplex wirelesspowered two way communication networks, where two hybrid access points (HAP) and a number of amplify and forward (AF) relays both operate in full duplex scenario. We use time switching (TS) and static power splitting (SPS) schemes with two way full duplex wireless-powered networks as a benchmark. Then the new time division duplexing static power splitting (TDD SPS) and full duplex static power splitting (FDSPS) schemes as well as a simple relay selection strategy are proposed to improve the system performance. For TS, SPS and FDSPS, the best relay harvests energy using the received RF signal from HAPs and uses harvested energy to transmit signal to each HAP at the same frequency and time, therefore only partial self-interference (SI) cancellation needs to be considered in the FDSPS case. For the proposed TDD SPS, the best relay harvests the energy from the HAP and its self-interference. Then we derive closed-form expressions for the throughput and outage probability for delay limited transmissions over Rayleigh fading channels. Simulation results are presented to evaluate the effectiveness of the proposed scheme with different system key parameters, such as time allocation, power splitting ratio and residual SI.
    Qian P, Wang N, Foster G, Tafazolli R (2017) Enabling Context-aware HTTP with Mobile Edge Hint,Proceedings of IEEE CCNC 2017 IEEE
    Due to dynamic wireless network conditions and heterogeneous mobile web content complexities, web-based content services in mobile network environments always suffer from long loading time. The new HTTP/2.0 protocol only adopts one single TCP connection, but recent research reveals that in real mobile environments, web downloading using single connection will experience long idle time and low bandwidth utilization, in particular with dynamic network conditions and web page characteristics. In this paper, by leveraging the Mobile Edge Computing (MEC) technique, we present the framework of Mobile Edge Hint (MEH), in order to enhance mobile web downloading performances. Specifically, the mobile edge collects and caches the meta-data of frequently visited web pages and also keeps monitoring the network conditions. Upon receiving requests on these popular webpages, the MEC server is able to hint back to the HTTP/2.0 clients on the optimized number of TCP connections that should be established for downloading the content. From the test results on real LTE testbed equipped with MEH, we observed up to 34.5% time reduction and in the median case the improvement is 20.5% compared to the plain over-the-top (OTT) HTTP/2.0 protocol.
    Dawoud DWM, Heliot F, Imran MA, Tafazolli R (2017) Spatial Quadrature Modulation for Visible Light Communication in Indoor Environment,2017 IEEE ICC Conference Proceedings
    In this paper, a novel low-complexity and spectrally efficient modulation scheme for visible light communication (VLC) is proposed. Our new spatial quadrature modulation (SQM) is designed to efficiently adapt traditional complex modulation schemes to VLC; i.e. converting multi-level quadrature amplitude modulation (M-QAM), to real-unipolar symbols, making it suitable for transmission over light intensity. The proposed SQM relies on the spatial domain to convey the orthogonality and polarity of the complex signals, rather than mapping bits to symbol as in existing spatial modulation (SM) schemes. The detailed symbol error analysis of SQM is derived and the derivation is validated with link level simulation results. Using simulation and derived results, we also provide a performance comparison between the proposed SQM and SM. Simulation results demonstrate that SQM could achieve a better symbol error rate (SER) and/or data rate performance compared to the state of the art in SM; for instance a Eb/No gain of at least 5 dB at a SER of 10 4.
    Abbas Fathy Abbas Y, Barnaghi P, Tafazolli R (2017) Distributed Spatial Indexing for the Internet of Things Data Management,Proceedings of IM 2017 pp. 1246-1251 IEEE
    The Internet of Things (IoT) has become a new enabler for collecting real-world observation and measurement data from the physical world. The IoT allows objects with sensing and network capabilities (i.e. Things and devices) to communicate with one another and with other resources (e.g. services) on the digital world. The heterogeneity, dynamicity and ad-hoc nature of underlying data, and services published by most of IoT resources make accessing and processing the data and services a challenging task. The IoT demands distributed, scalable, and efficient indexing solutions for large-scale distributed IoT networks. We describe a novel distributed indexing approach for IoT resources and their published data. The index structure is constructed by encoding the locations of IoT resources into geohashes and then building a quadtree on the minimum bounding box of the geohash representations. This allows to aggregate resources with similar geohashes and reduce the size of the index. We have evaluated our proposed solution on a large-scale dataset and our results show that the proposed approach can efficiently index and enable discovery of the IoT resources with 65% better response time than a centralised approach and with a high success rate (around 90% in the first few attempts).
    Guo T, Quddus AU, Wang N, Tafazolli R Local Mobility Management for Networked Femtocells Based on X2 Traffic Forwarding,IEEE Transactions on Vehicular Technology Institute of Electrical and Electronics Engineers
    Femtocell is becoming a promising solution to face the explosive growth of mobile broadband usage in cellular networks. While each femtocell only covers a small area, a massive deployment is expected in the near future forming networked femtocells. An immediate challenge is to provide seamless mobility support for networked femtocells with minimal support from mobile core networks. In this
    paper, we propose efficient local mobility management schemes for networked femtocells based on X2 traffic forwarding under the 3GPP Long Term Evolution Advanced (LTE-A) framework. Instead of implementing the path switch operation at core network entity for each handover, a local traffic forwarding chain is constructed to use the existing Internet backhaul and the local path between the local
    anchor femtocell and the target femtocell for ongoing session communications. Both analytical studies and simulation experiments are conducted to evaluate the proposed schemes and compare them with the original 3GPP scheme. The results indicate that the proposed schemes can significantly reduce the signaling cost and relieve the processing burden of mobile core networks with the reasonable distributed cost for local traffic forwarding. In addition, the proposed schemes can enable fast session recovery to adapt to the self-deployment nature of the femtocells.
    Gluhak A, Chew K, Moessner K, Tafazolli R (2005) Multicast bearer selection in heterogeneous wireless networks,Proc. IEEE Int. Conf. Communications ICC 2005 2 pp. 1372-1377
    Network scenarios beyond 3G assume the cooperation of operators with wireless access networks of different technologies in order to improve scalability and provide enhanced services to their mobile customers. While the selection of an optimised delivery path in such scenarios with multiple access networks is already a challenging task for unicast delivery, the problem becomes more severe for multicast services, where a potentially large group of heterogeneous receivers has to be served simultaneously via shared resources. In this paper we study the problem of selecting the optimal bearer paths for multicast services with groups of heterogeneous receivers in wireless networks with overlapping coverage. We propose an algorithm for bearer selection with different optimisation goals, demonstrating the existing tradeoff between user preference and resource efficiency.
    Peyvandi H, Imran MA, Tafazolli R (2012) On Performance Optimization in Self-Organizing Network using Enhanced Simulated Annealing with Similarity Measure,International Symposium on Information Theory (ISIT) IEEE
    Network performance optimization is among the most important tasks within the area of wireless communication networks. In a Self- Organizing Network (SON) with the capability of adaptively changing parameters of a network, the optimization tasks are more feasible than static networks. Yet, with an increase of OPEX and CAPEX in new generation telecommunication networks, the optimization tasks are inevitable. In this paper, it is proven that the similarity among target and network parameters can produce lower Uncertainty Entropy (UEN) in a self-organizing system as a higher degree of organizing is gained. The optimization task is carried out with the Adaptive Simulated Annealing method, which is enhanced with a Similarity Measure (SM) in the proposed approach (EASA). The Markov model of EASA is provided to assess the proposed approach. We also show a higher performance through a simulation, based on a scenario in LTE network.
    Hoshyar R, Wathan P, Tafazolli R (2008) Novel low-density signature for synchronous CDMA systems over AWGN channel,IEEE T SIGNAL PROCES 56 (4) pp. 1616-1626 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    Novel low-density signature (LDS) structure is proposed for transmission and detection of symbol-synchronous communication over memoryless Gaussian channel. Given N as the processing gain, under this new arrangement, users' symbols are spread over N chips but virtually only d(v) < N chips that contain nonzero-values. The spread symbol is then so uniquely interleaved as the sampled, at chip rate, received signal contains the contribution from only d(c) < K number of users, where K denotes the total number of users in the system. Furthermore, a near-optimum chip-level iterative soft-in-soft-out (SISO) multiuser decoding (MUD), which is based on message passing algorithm (MPA) technique, is proposed to approximate optimum detection by efficiently exploiting the LDS structure. Given beta = K/N as the system loading, our simulation suggested that the proposed system alongside the proposed detection technique, in AWGN channel, can achieve an overall performance that is close to single-user performance, even when the system has 200% loading, i.e., when beta = 2. Its robustness against near-far effect and its performance behavior that is very similar to optimum detection are demonstrated in this paper. In addition, the complexity required for detection is now exponential to d(c) instead of K as in conventional code division multiple access (CDMA) structure employing optimum multiuser detector.

    Dianati M, Tafazolli R (2008) Opportunistic scheduling over wireless fading channels without explicit feedback,2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7 pp. 1871-1875

    A novel approach for implementation of opportunistic scheduling without explicit feedback channels is proposed in this paper, which exploits the existing, ARQ signals instead of feedback channels to reduce the complexity of implementation. Monte Carlo simulation results demonstrate the efficacy of the proposed approach in harvesting multiuser diversity gain. The proposed approach enables implementation of opportunistic scheduling, in a variety of wireless networks, such as the IEEE 802.11, without feedback facilities for collecting partial channel state information from users.

    Heliot F, Imran MA, Tafazolli R (2012) On the energy efficiency-spectral efficiency trade-off over the MIMO rayleigh fading channel,IEEE Transactions on Communications 60 (5) pp. 1345-1356 IEEE
    Along with spectral efficiency (SE), energy efficiency (EE) is becoming one of the key performance evaluation criteria for communication system. These two criteria, which are conflicting, can be linked through their trade-off. The EE-SE trade-off for the multi-input multi-output (MIMO) Rayleigh fading channel has been accurately approximated in the past but only in the low-SE regime. In this paper, we propose a novel and more generic closed-form approximation of this trade-off which exhibits a greater accuracy for a wider range of SE values and antenna configurations. Our expression has been here utilized for assessing analytically the EE gain of MIMO over single-input single-output (SISO) system for two different types of power consumption models (PCMs): the theoretical PCM, where only the transmit power is considered as consumed power; and a more realistic PCM accounting for the fixed consumed power and amplifier inefficiency. Our analysis unfolds the large mismatch between theoretical and practical MIMO vs. SISO EE gains; the EE gain increases both with the SE and the number of antennas in theory, which indicates that MIMO is a promising EE enabler; whereas it remains small and decreases with the number of transmit antennas when a realistic PCM is considered. © 2012 IEEE.
    Jiang J, Dianati M, Imran MA, Tafazolli R, Chen Y (2013) On the Relation between Energy Efficiency and Spectral Efficiency of Multiple-Antenna Systems,IEEE Transactions on Vehicular Technology 62 (7) pp. 3463-3469 IEEE
    Motivated by increased interests in energy efficient
    communication systems, the relation between energy efficiency
    (EE) and spectral efficiency (SE) for multiple-input multipleoutput
    (MIMO) systems is investigated in this paper. To provide
    insight into the design of practical MIMO systems, we adopt
    a realistic power model, as well as consider both independent
    Rayleigh fading and semicorrelated fading channels. We derive
    a novel and closed-form upper bound for the system EE as a
    function of SE. This upper bound exhibits a great accuracy
    for a wide range of SE values, and thus can be utilized for
    explicitly assessing the influence of SE on EE, and analytically
    addressing the EE optimization problems. Using this tight EE
    upper bound, our analysis unfolds two EE optimization issues:
    Given the number of transmit and receive antennas, an optimum
    value of SE is derived such that the overall EE can be maximized;
    Given a specific value of SE, the optimal number of antennas is
    derived for maximizing the system EE.
    Guo T, Wang N, Tafazolli R, Moessner K (2010) Policy-Aware Virtual Relay Placement for Inter-Domain Path Diversity,IEEE ISCC pp. 38-43
    Exploiting path diversity to enhance communication
    reliability is a key desired property in Internet. While the existing routing architecture is reluctant to adopt changes, overlay routing has been proposed to circumvent the constraints of native routing by employing intermediary relays. However, the selfish interdomain relay placement may violate local routing policies at intermediary relays and thus affect their economic costs and performances. With the recent advance of the concept of network virtualization, it is envisioned that virtual networks should be provisioned in cooperation with infrastructure providers in a holistic view without compromising their profits. In this paper, the problem of policy-aware virtual relay placement is first studied to investigate the feasibility of provisioning policycompliant multipath routing via virtual relays for inter-domain communication reliability. By evaluation on a real domain-level Internet topology, it is demonstrated that policy-compliant virtual
    relaying can achieve a similar protection gain against single link failures compared to its selfish counterpart. It is also shown that the presented heuristic placement strategies perform well to approach the optimal solution.
    Al-Imari M, Imran MA, Tafazolli R, Chen D (2012) Performance Evaluation of Low Density Spreading Multiple Access,2012 8th International Wireless Communications and Mobile Computing Conference (IWCMC) pp. 383-388
    In this paper, we evaluate the performance of Multicarrier-Low Density Spreading Multiple Access (MC-LDSMA) as a multiple access technique for mobile communication systems. The MC-LDSMA technique is compared with current multiple access techniques, OFDMA and SC-FDMA. The performance is evaluated in terms of cubic metric, block error rate, spectral efficiency and fairness. The aim is to investigate the expected gains of using MC-LDSMA in the uplink for next generation cellular systems. The simulation results of the link and system-level performance evaluation show that MC-LDSMA has significant performance improvements over SC-FDMA and OFDMA. It is shown that using MC-LDSMA can considerably reduce the required transmission power and increase the spectral efficiency and fairness among the users.
    It has been envisaged that in future 5G networks user devices will become an integral part of the network by participating in the transmission of mobile content traffic typically through Device-to-device (D2D) technologies. In this context, we promote the concept of Mobility as a Service (MaaS), where the mobile network edge is equipped with necessary knowledge on device mobility in order to meet specific service requirements for clients via a small number of helper devices. In this thesis, we propose a MaaS paradigm based frameworks to address clients? requirement with regards to content offloading service and connectivity relaying service via network assisted D2D communication framework.
    To address content traffic offloading, we present a device-level Information Centric Networking (ICN) architecture that is able to perform intelligent content distribution operations according to necessary context information on mobile user mobility and content characteristics. Based on such an architecture, we further introduce device-level online content caching and offline helper selection algorithms in order to optimise the overall system efficiency. In particular, this piece of work sheds distinct light on the importance of user mobility data analytics based on which helper selection can lead to overall system optimality. Based on representative user mobility models, we conducted realistic simulation experiments and modelling which have proven the efficiency in terms of both network traffic offloading gains and user-oriented performance improvements. In addition, we show how the framework can be flexibly configured to meet specific delay tolerance constraints according to specific context policies.
    With regard to connectivity relaying service, we introduce a novel scheme of using D2D communications for enabling data relay services in partial Not-Spots, where a client without local network access may require data relay by other devices. Depending on specific social application scenarios, this piece of work introduces tailored algorithms in order to achieve optimised data relay service performance. The approach is to exploit the network?s knowledge on its local user mobility patterns to identify best helper devices for participating in data relay operations. This framework is also supported with our proposed helper selection optimisation algorithm based on prediction of individual user mobility. According to our simulation analysis, based on both theoretical mobility models and real human mobility data traces, the proposed scheme is able to flexibly support different service requirements in specific social application scenarios.
    Qian P, Wang N, Oh B, Ge C, Tafazolli R Optimization of Webpage Downloading Performance with Content-aware Mobile Edge Computing,MECOMM '17 Proceedings of the Workshop on Mobile Edge Communications pp. 31-36 Association for Computing Machinery (ACM)
    With increased complexity of webpages nowadays, computation
    latency incurred by webpage processing during downloading operations
    has become a newly identified factor that may substantially
    affect user experiences in a mobile network. In order to tackle this issue,
    we propose a simple but effective transport-layer optimization
    technique which requires necessary context information dissemination
    from the mobile edge computing (MEC) server to user devices
    where such an algorithm is actually executed. The key novelty in
    this case is the mobile edge?s knowledge about webpage content
    characteristics which is able to increase downloading throughput
    for user QoE enhancement. Our experiment results based on a real
    LTE-A test-bed show that, when the proportion of computation
    latency varies between 20% and 50% (which is typical for today?s
    webpages), the downloading throughput can be improved up to
    34.5%, with reduced downloading time by up to 25.1%
    Al-Imari M, Xiao P, Imran MA, Tafazolli R (2014) Uplink Non-Orthogonal Multiple Access for 5G Wireless Networks,11th International Symposium on Wireless Communications Systems (ISWCS) 2014 pp. 781-785 IEEE
    Orthogonal Frequency Division Multiple Access (OFDMA) as well as other orthogonal multiple access techniques fail to achieve the system capacity limit in the uplink due to the exclusivity in resource allocation. This issue is more prominent when fairness among the users is considered in the system. Current Non-Orthogonal Multiple Access techniques (NOMA) introduce redundancy by coding/spreading to facilitate the users' signals separation at the receiver, which degrade the system spectral efficiency. Hence, in order to achieve higher capacity, more efficient NOMA schemes need to be developed. In this paper, we propose a NOMA scheme for uplink that removes the resource allocation exclusivity and allows more than one user to share the same subcarrier without any coding/spreading redundancy. Joint processing is implemented at the receiver to detect the users' signals. However, to control the receiver complexity, an upper limit on the number of users per subcarrier needs to be imposed. In addition, a novel subcarrier and power allocation algorithm is proposed for the new NOMA scheme that maximizes the users' sum-rate. The link-level performance evaluation has shown that the proposed scheme achieves bit error rate close to the single-user case. Numerical results show that the proposed NOMA scheme can significantly improve the system performance in terms of spectral efficiency and fairness comparing to OFDMA.
    Mohamed A, Imran M, Tafazolli R (2015) Energy Efficient 5G Network with Logical Separation of Control and Data Functionality,Proceedings of Ofcom Workshop on 5G and Future Technology
    As soon as 2020, network densification and spectrum extension will be the dominant theme to support enormous capacity and massive connectivity [1]. However, this approach may not guarantee wide area coverage due to the poor propagation capabilities of high frequency bands. In addition, energy efficiency and signalling overhead will become critical considerations in ultra-dense deployment scenarios. This calls for a futuristic two layer RAN architecture with dual connectivity, where the high frequency bands are used for data services, complemented by a coverage layer at conventional cellular bands [2]. This separation of control and data planes will enable a transition from always-on to always-available systems and could result in order of magnitude savings in energy and signalling overhead.
    Mohamed A, Onireti O, Hoseinitabatabaei S, Imran M, Imran A, Tafazolli R (2015) Mobility Prediction for Handover Management in Cellular Networks with Control/Data Separation,2015 IEEE International Conference on Communications (ICC) pp. 3939-3944
    In research community, a new radio access network architecture with a logical separation between control plane (CP) and data plane (DP) has been proposed for future cellular systems. It aims to overcome limitations of the conventional architecture by providing high data rate services under the umbrella of a coverage layer in a dual connection mode. This configuration could provide significant savings in signalling overhead. In particular, mobility robustness with minimal handover (HO) signalling is considered as one of the most promising benefits of this architecture. However, the DP mobility remains an issue that needs to be investigated. We consider predictive DP HO management as a solution that could minimise the out-of band signalling related to the HO procedure. Thus we propose a mobility prediction scheme based on Markov Chains. The developed model predicts the user?s trajectory in terms of a HO sequence in order to minimise the interruption time and the associated signalling when the HO is triggered. Depending on the prediction accuracy, numerical results show that the predictive HO management strategy could significantly reduce the signalling cost as compared with the conventional non-predictive mechanism.
    Mohamed A, Onireti O, Imran M, Pervaiz H, Xiao P, Tafazolli R (2017) Predictive Base Station Activation in Futuristic Energy-Efficient Control/Data Separated RAN,IEEE Globecom 2017 Proceedings IEEE
    Nowadays, system architecture of the fifth generation
    (5G) cellular system is becoming of increasing interest.
    To reach the ambitious 5G targets, a dense base station (BS)
    deployment paradigm is being considered. In this case, the
    conventional always-on service approach may not be suitable due
    to the linear energy/density relationship when the BSs are always
    kept on. This suggests a dynamic on/off BS operation to reduce
    the energy consumption. However, this approach may create
    coverage holes and the BS activation delay in terms of hardware
    transition latency and software reloading could result in service
    disruption. To tackle these issues, we propose a predictive BS
    activation scheme under the control/data separation architecture
    (CDSA). The proposed scheme exploits user context information,
    network parameters, BS sleep depth and measurement databases
    to send timely predictive activation requests in advance before
    the connection is switched to the sleeping BS. An analytical model
    is developed and closed-form expressions are provided for the
    predictive activation criteria. Analytical and simulation results
    show that the proposed scheme achieves a high BS activation
    accuracy with low errors w.r.t. the optimum activation time.
    There has recently been a real demand to design and deploy mobile communication networks
    that consume significantly less energy compared to the existing s ystems. The main thrust of
    this research focuses on investigation of the impacts of radio resource allocation schemes in the
    current state-of-the-art Orthogonal Frequency Division Multiple Access (OFDMA) systems
    on energy efficiency (EE) o f modern Radio Access Networks ( RANs), a s well a s design of
    effective solutions to reduce RAN energy consumption in such networks.
    Due to data traffic fluctuation of communication networks, there are often many unused radio
    resource blocks in OFDMA systems. Efficient allocation of these surplus resource blocks can
    lead to considerable energy savings. One of the key objectives of this thesis is to exploit
    this opportunity by designing practical and effective radio resource allocation techniques that
    exploit fundamental trade-off between energy consumption and bandwidth by reducing energy
    consumption of the RAN while providing the required quality of service (QoS) for the network
    users. The basic concept here is to exploit fluctuations of data traffic in the network.
    Specifically, a novel e nergy e fficient re source al location te chnique, fo r low lo ad tr affic conditions
    is proposed. This technique is then applied to three bespoke scheduling schemes,
    namely Round Robin (RR), Best Channel Quality Indicator (BCQI), and Proportional Fair (PF)
    for performance assessment. Comprehensive evaluation of the proposed scheduling schemes
    demonstrates that adopting the proposed resource allocation technique significantly enhances
    the performance of RAN in terms of energy consumption in comparison with the conventional
    schemes such as the three aforementioned schedulers.
    Finding an optimal method for surplus resource allocation is firstly modelled as an optimisation
    problem which is subsequently solved using dynamic programming. In this context, a
    Knapsack Problem (KP) is adopted to find an optimal solution for a single-cell s cenario. The
    proposed heuristic method is simulated using Equal Power (EP) and Water Filling (WF) algorithms
    for surplus resource allocation. It is shown that the optimal solution is achieved using
    the WF algorithm leading to an EE saving of 60% compared to the greedy KP solution, whilst
    significantly lower computational complexity.
    The optimality of the proposed algorithm is evaluated in a multi-cell scenario to take into
    account reali
    Chen G, Xiao P, Tafazolli R (2016) Dual Antenna Selection in Self-Backhauling Multiple Small Cell Networks,IEEE Communications Letters 20 (8) pp. 1611-1614 IEEE
    This paper investigates self-backhauling with dual antenna selection at multiple small cell base stations. Both half and full duplex transmissions at the small cell base station are considered. Depending on instantaneous channel conditions, the full duplex transmission can have higher throughput than the half duplex transmission, but it is not always the case. Closed-form expressions of the average throughput are obtained, and validated by simulation results. In all cases, the dual receive and transmit antenna selection significantly improves backhaul and data transmission, making it an attractive solution in practical systems.
    Zhang Lei, Ijaz A, Xiao Pei, Quddus Atta, Tafazolli Rahim (2016) Single-rate and Multi-rate Multi-service Systems for Next Generation and Beyond Communications,IEEE 27th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications
    To flexibly support diverse communication requirements (e.g., throughput, latency, massive connection, etc.) for the next generation wireless communications, one viable solution is to divide the system bandwidth into several service subbands, each for a different type of service. In such a multi-service (MS) system, each service has its optimal frame structure while the services are isolated by subband filtering. In this paper, a framework for multi-service (MS) system is established based on subband filtered multi-carrier (SFMC) modulation. We consider both single-rate (SR) and multi-rate (MR) signal processing as two different MS-SFMC implementations, each having different performance and computational complexity. By comparison, the SR system outperforms the MR system in terms of performance while the MR system has a significantly reduced computational complexity than the SR system. Numerical results show the effectiveness of our analysis and the proposed systems. These proposed SR and MR MS-SFMC systems provide guidelines for next generation wireless system frame structure optimization and algorithm design.
    Mi D, Dianati M, Zhang L, Muhaidat S, Tafazolli R (2017) Massive MIMO Performance with Imperfect Channel Reciprocity and Channel Estimation Error,IEEE Transactions on Communications 65 (9) pp. 3734-3749 IEEE
    Channel reciprocity in time-division duplexing (TDD) massive MIMO (multiple-input multiple-output) systems can be exploited to reduce the overhead required for the acquisition of channel state information (CSI). However, perfect reciprocity is unrealistic in practical systems due to random radio-frequency (RF) circuit mismatches in uplink and downlink channels. This can result in a significant degradation in the performance of linear precoding schemes which are sensitive to the accuracy of the CSI. In this paper, we model and analyse the impact of RF mismatches on the performance of linear precoding in a TDD multi-user massive MIMO system, by taking the channel estimation error into considerations. We use the truncated Gaussian distribution to model the RF mismatch, and derive closed-form expressions of the output SINR (signal-to-interference-plus-noise ratio) for maximum ratio transmission and zero forcing precoders. We further investigate the asymptotic performance of the derived expressions, to provide valuable insights into the practical system designs, including useful guidelines for the selection of the effective precoding schemes. Simulation results are presented to demonstrate the validity and accuracy of the proposed analytical results.
    Kamel G, Wang N, Vassilakis V, Sun Z, Navaratnam P, Wang C, Dong L, Tafazolli R (2015) CAINE: A Context-Aware Information-Centric Network Ecosystem,IEEE COMMUNICATIONS MAGAZINE 53 (8) pp. 176-183 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Information-centric networking (ICN) is an emerging
    networking paradigm that places content identifiers rather
    than host identifiers at the core of the mechanisms and protocols
    used to deliver content to end-users. Such a paradigm allows
    routers enhanced with content-awareness to play a direct role
    in the routing and resolution of content requests from users,
    without any knowledge of the specific locations of hosted content.
    However, to facilitate good network traffic engineering
    and satisfactory user QoS, content routers need to exchange
    advanced network knowledge to assist them with their resolution
    decisions. In order to maintain the location-independency tenet
    of ICNs, such knowledge (known as context information) needs
    to be independent of the locations of servers. To this end, we
    propose CAINE ? Context-Aware Information-centric Network
    Ecosystem ? which enables context-based operations to be
    intrinsically supported by the underlying ICN routing and resolution
    functions. Our approach has been designed to maintain the
    location-independence philosophy of ICNs by associating context
    information directly to content rather than to the physical entities
    such as servers and network elements in the content ecosystem,
    while ensuring scalability. Through simulation, we show that
    based on such location-independent context information, CAINE
    is able to facilitate traffic engineering in the network, while not
    posing a significant control signalling burden on the network
    Jaber Mona (2017) Realistic 5G backhaul.,
    The hype surrounding the 5G mobile networks is well justified in view of the explosive increase in mobile traffic and the inclusion of massive ?non-human? users that form the internet of things. Advanced radio features such as network densification, cloud radio access networks (C-RAN), and untapped frequency bands jointly succeed in increasing the radio capacity to accommodate the increasing traffic demand. However, a new challenge has arisen: the backhaul (BH), the transport network that connects radio cells to the core network. The BH needs to expand in a timely fashion to reach the fast spreading small cells. Moreover, the realistic BH solutions are unable to provide the unprecedented 5G performance requirements to every cell. To this end, this research addresses the gap between the 5G stipulated BH characteristics and the available BH capabilities. On the other hand, heterogeneity is a leading trait in 5G networks. First, the RAN is heterogeneous since it comprises different cell types, radio access technologies, and architectures. Second, the BH is composed of a mix of different wired and wireless technologies with different limitations. In addition, 5G users have a broader range of capabilities and requirements than any incumbent mobile network. We exploit this trait and develop a novel scheme, termed User-Centric-BH (UCB). The UCB targets the user association mechanism which is traditionally blind to users? needs and BH conditions. The UCB builds on the existing concept of cell range extension (CRE) and proposes multiple-offset factors (CREO) whereby each reflects the cell's joint RAN and BH capability with respect to a defined attribute (e.g., throughput, latency, resilience, etc.). In parallel, users associate different weights to different attributes, hence, they can make a user-centric decision. The proposed scheme significantly outperforms the state-of-the-art and unlocks the BH bottleneck by availing existing but misused resources to users in need.
    Zhang Lei, Ijaz Ayesha, Molu Mehdi, Tafazolli Rahim (2017) Filtered OFDM Systems, Algorithms and Performance Analysis for 5G and Beyond,IEEE Transactions on Communications 66 (3) pp. 1205-1218 Institute of Electrical and Electronics Engineers (IEEE)
    Filtered orthogonal frequency division multiplexing
    (F-OFDM) system is a promising waveform for 5G and beyond
    to enable multi-service system and spectrum efficient network
    slicing. However, the performance for F-OFDM systems has not
    been systematically analyzed in literature. In this paper, we first
    establish a mathematical model for F-OFDM system and derive
    the conditions to achieve the interference-free one-tap channel equalization.
    In the practical cases (e.g., insufficient guard interval,
    asynchronous transmission, etc.), the analytical expressions for
    inter-symbol-interference (ISI), inter-carrier-interference (ICI)
    and adjacent-carrier-interference (ACI) are derived, where the
    last term is considered as one of the key factors for asynchronous
    transmissions. Based on the framework, an optimal power compensation
    matrix is derived to make all of the subcarriers having
    the same ergodic performance. Another key contribution of the
    paper is that we propose a multi-rate F-OFDM system to enable
    low complexity low cost communication scenarios such as narrow
    band Internet of Things (IoT), at the cost of generating intersubband-
    interference (ISubBI). Low computational complexity
    algorithms are proposed to cancel the ISubBI. The result shows
    that the derived analytical expressions match the simulation
    results, and the proposed ISubBI cancelation algorithms can
    significantly save the original F-OFDM complexity (up to 100
    times) without significant performance loss.
    Fathy Yasmin, Barnaghi Payam, Tafazolli Rahim (2018) Large-Scale Indexing, Discovery and Ranking for the Internet of Things (IoT),ACM Computing Surveys 51 (2) 29 Association for Computing Machinery (ACM)
    Network-enabled sensing and actuation devices are key enablers to connect real-world objects to the cyber
    world. The Internet of Things (IoT) consists of the network-enabled devices and communication technologies
    that allow connectivity and integration of physical objects (Things) into the digital world (Internet). Enormous
    amounts of dynamic IoT data are collected from Internet-connected devices. IoT data is usually multi-variant
    streams that are heterogeneous, sporadic, multi-modal and spatio-temporal. IoT data can be disseminated
    with different granularities and have diverse structures, types and qualities. Dealing with the data deluge
    from heterogeneous IoT resources and services imposes new challenges on indexing, discovery and ranking
    mechanisms that will allow building applications that require on-line access and retrieval of ad-hoc IoT data.
    However, the existing IoT data indexing and discovery approaches are complex or centralised which hinders
    their scalability. The primary objective of this paper is to provide a holistic overview of the state-of-the-art on
    indexing, discovery and ranking of IoT data. The paper aims to pave the way for researchers to design, develop,
    implement and evaluate techniques and approaches for on-line large-scale distributed IoT applications and
    services.
    Heliot F, Tafazolli R (2017) Optimal Energy-efficient Source and Relay Precoder Design for Cooperative MIMO-AF Systems,IEEE Transactions on Signal Processing 66 (3) pp. 573-588 Institute of Electrical and Electronics Engineers (IEEE)
    Energy efficiency (EE) is a key design criterion
    for the next generation of communication systems. Equally,
    cooperative communication is known to be very effective for enhancing
    the performance of such systems. This paper proposes a
    breakthrough approach for maximizing the EE of multiple-inputmultiple-
    output (MIMO) relay-based nonregenerative cooperative
    communication systems by optimizing both the source and
    relay precoders when both relay and direct links are considered.
    We prove that the corresponding optimization problem is at least
    strictly pseudo-convex, i.e. having a unique solution, when the
    relay precoding matrix is known, and that its Lagrangian can
    be lower and upper bounded by strictly pseudo-convex functions
    when the source precoding matrix is known. Accordingly, we
    then derive EE-optimal source and relay precoding matrices that
    are jointly optimize through alternating optimization. We also
    provide a low-complexity alternative to the EE-optimal relay
    precoding matrix that exhibits close to optimal performance,
    but with a significantly reduced complexity. Simulations results
    show that our joint source and relay precoding optimization can
    improve the EE of MIMO-AF systems by up to 50% when
    compared to direct/relay link only precoding optimization.
    Nwankwo C, Zhang L, Quddus A, Imran M, Tafazolli R (2017) A Survey of Self-Interference Management Techniques for Single Frequency Full Duplex Systems,IEEE Access pp. 1-1 Institute of Electrical and Electronics Engineers (IEEE)
    This article presents a comprehensive survey of the literature on self-interference management schemes required to achieve a single frequency full duplex communication in wireless communication networks. A single frequency full duplex system often referred to as in-band full duplex (FD) system has emerged as an interesting solution for the next generation mobile networks where scarcity of available radio spectrum is an important issue. Although studies on the mitigation of self-interference have been documented in the literature, this is the first holistic attempt at presenting not just the various techniques available for handling self-interference that arises when a full duplex device is enabled, as a survey, but it also discusses other system impairments that significantly affect the self-interference management of the system, and not only in terrestrial systems, but also on satellite communication systems. The survey provides a taxonomy of self-interference management schemes and shows by means of comparisons the strengths and limitations of various self-interference management schemes. It also quantifies the amount of self-interference cancellation required for different access schemes from the 1 st generation to the candidate 5 th generation of mobile cellular systems. Importantly, the survey summarises the lessons learnt, identifies and presents open research questions and key research areas for the future. This paper is intended to be a guide and take off point for further work on self-interference management in order to achieve full duplex transmission in mobile networks including heterogeneous cellular networks which is undeniably the network of future wireless systems.
    Molu Mehdi M., Xiao Pei, Khalily Mohsen, Cumanan Kanapathippillai, Zhang Lei, Tafazolli Rahim (2017) Low-Complexity and Robust Hybrid Beamforming Design for Multi-Antenna Communication Systems,IEEE Transactions on Wireless Communications 17 (3) pp. 1445-1459 Institute of Electrical and Electronics Engineers (IEEE)
    This paper proposes a low-complexity hybrid beamforming
    design for multi-antenna communication systems. The
    hybrid beamformer comprises of a baseband digital beamformer
    and a constant modulus analog beamformer in radio frequency
    (RF) part of the system. As in Singular-Value-Decomposition
    (SVD) based beamforming, hybrid beamforming design aims to
    generate parallel data streams in multi-antenna systems, however,
    due to the constant modulus constraint of the analog beamformer,
    the problem cannot be solved, similarly. To address this problem,
    mathematical expressions of the parallel data streams are
    derived in this paper and desired and interfering signals are
    specified per stream. The analog beamformers are designed by
    maximizing the power of desired signal while minimizing the
    sum-power of interfering signals. Finally, digital beamformers are
    derived through defining the equivalent channel observed by the
    transmitter/receiver. Regardless of the number of the antennas
    or type of channel, the proposed approach can be applied to
    wide range of MIMO systems with hybrid structure wherein
    the number of the antennas is more than the number of the
    RF chains. In particular, the proposed algorithm is verified for
    sparse channels that emulate mm-wave transmission as well as
    rich scattering environments. In order to validate the optimality,
    the results are compared with those of the state-of-the-art and
    it is demonstrated that the performance of the proposed method
    outperforms state-of-the-art techniques, regardless of type of the
    channel and/or system configuration.
    Chandrasekaran Ganesh, Wang Ning, hassanpourasheghabadi M., Xu M., Tafazolli Rahim (2017) Mobility as a Service (MaaS): A D2D-based Information Centric Network Architecture for Edge-Controlled Content Distribution,IEEE Access 6 pp. 2110-2129 Institute of Electrical and Electronics Engineers (IEEE)
    It has been envisaged that in future 5G networks user devices will become an integral part by participating in the transmission of mobile content traffic typically through Deviceto- device (D2D) technologies. In this context, we promote the concept of Mobility as a Service (MaaS), where content-aware mobile network edge is equipped with necessary knowledge on device mobility in order to distribute popular mobile content items to interested clients via a small number of helper devices. Towards this end, we present a device-level Information Centric Networking (ICN) architecture that is able to perform intelligent content distribution operations according to necessary context information on mobile user mobility and content characteristics. Based on such a platform, we further introduce device-level online content caching and offline helper selection algorithms in order to optimise the overall system efficiency. In particular, this paper sheds distinct light on the importance of user mobility data analytics based on which helper selection can lead to overall system optimality. Based on representative user mobility models, we conducted realistic simulation experiments and modelling which have proven the efficiency in terms of both network traffic offloading gains and user-oriented performance improvements. In addition, we show how the framework can be flexibly configured to meet specific delay tolerance constraints according to specific context policies.
    Filo Marcin, Foh Chuan, Vahid Seiamak, Tafazolli Rahim (2020) Performance Analysis of Ultra-Dense Networks with Regularly Deployed Base Stations,IEEE Transactions on Wireless Communications Institute of Electrical and Electronics Engineers
    The concept of Ultra Dense Networks (UDNs) is
    often seen as a key enabler of the next generation mobile
    networks. The massive number of BSs in UDNs represents a
    challenge in deployment, and there is a need to understand the performance behaviour and benefit of a network when BS locations are carefully selected. This can be of particular importance to the network operators who deploy their networks
    in large indoor open spaces such as exhibition halls, airports or train stations where locations of BSs often follow a regular pattern. In this paper we study performance of UDNs in downlink
    for regular network produced by careful BS site selection and compare to the irregular network with random BS placement. We first develop an analytical model to describe the performance of regular networks showing many similar performance behaviour
    to that of the irregular network widely studied in the literature. We also show the potential performance gain resulting from proper site selection. Our analysis further shows an interesting finding that even for over-densified regular networks, a nonnegligible
    system performance could be achieved.
    Khalily M, Ghoraishi M, Taheri S, Payami S, Tafazolli R (2018) Millimeter-Wave Directional Path Loss Models in
    the 26 GHz, 32 GHz, and 39 GHz Bands for Small
    Cell 5G Cellular System
    ,
    EuCAP 2018 Proceedings IEEE
    This paper presents empirically-based large-scale
    propagation path loss models for small cell fifth generation (5G)
    cellular system in the millimeter-wave bands, based on practical
    propagation channel measurements at 26 GHz, 32 GHz, and
    39 GHz. To characterize path loss at these frequency bands
    for 5G small cell scenarios, extensive wideband and directional
    channel measurements have been performed on the campus of the
    University of Surrey. Close-in reference (CI), and 3GPP path loss
    models have been studied, and large-scale fading characteristics
    have been obtained and presented.
    Khalily M, Ghoraishi M, Taheri S, Payami S, Tafazolli R (2018) Polarimetric Wideband Directional Channel
    Measurement and Analysis for Outdoor Small Cell
    Scenarios at 32 GHz and 39 GHz
    ,
    EuCAP 2018 Proceedings IEEE
    Wideband millimeter-wave (mmWave) directional
    propagation measurements were conducted in the 32 GHz and
    39 GHz bands in outdoor line-of-sight (LoS) small cell scenarios.
    The measurement provides spatial and temporal statistics that
    will be useful for small-cell outdoor wireless networks for future
    mmWave bands. Measurements were performed at two outdoor
    environments and repeated for all polarization combinations.
    Measurement results show little spread in the angular and delay
    domains for the LoS scenario. Moreover root-mean-squared
    (RMS) delay spread at different polarizations show small difference
    which can be due to specific scatterers in the channel.
    Khalily M, Taheri S, Xiao P, Entezami F, Hill T, Tafazolli R (2018) 26 GHz Indoor Wideband Directional Channel
    Measurement and Analysis in LoS and NLoS
    Scenarios
    ,
    Proceedings of EuCAP 2018 IEEE
    This paper presents details of the indoor wideband
    and directional propagation measurements at 26 GHz in which
    a wideband channel sounder using a millimeter wave (mmWave)
    signal analyzer and vector signal generator was employed. The
    setup provided 2 GHz bandwidth and the mechanically steerable
    directional lens antenna with 5 degrees beamwidth provides 5
    degrees of directional resolution over the azimuth. Measurements
    provide path loss, delay and spatial spread of the channel.
    Angular and delay dispersion are presented for line-of-sight (LoS)
    and non-line-of-sight (NLoS) scenarios.
    Mohamed Abdelrahim, Imran Muhammad, Xiao Pei, Tafazolli Rahim (2018) Memory-full Context-aware Predictive Mobility Management in Dual Connectivity 5G Networks,IEEE Access 6 pp. 9655-9666 Institute of Electrical and Electronics Engineers (IEEE)
    Network densification with small cell deployment
    is being considered as one of the dominant themes in the
    fifth generation (5G) cellular system. Despite the capacity gains,
    such deployment scenarios raise several challenges from mobility
    management perspective. The small cell size, which implies a
    small cell residence time, will increase the handover (HO) rate
    dramatically. Consequently, the HO latency will become a critical
    consideration in the 5G era. The latter requires an intelligent, fast
    and light-weight HO procedure with minimal signalling overhead.
    In this direction, we propose a memory-full context-aware HO
    scheme with mobility prediction to achieve the aforementioned
    objectives. We consider a dual connectivity radio access network
    architecture with logical separation between control and data
    planes because it offers relaxed constraints in implementing the
    predictive approaches. The proposed scheme predicts future HO
    events along with the expected HO time by combining radio
    frequency performance to physical proximity along with the user
    context in terms of speed, direction and HO history. To minimise
    the processing and the storage requirements whilst improving
    the prediction performance, a user-specific prediction triggering
    threshold is proposed. The prediction outcome is utilised to
    perform advance HO signalling whilst suspending the periodic
    transmission of measurement reports. Analytical and simulation
    results show that the proposed scheme provides promising gains
    over the conventional approach.
    Kuzminskiy Alexandr, Xiao Pei, Tafazolli Rahim (2018) Good Neighbor Distributed Beam Scheduling in Coexisting Multi-RAT Networks,Proceedings of WCNC 2018 IEEE
    Spectrum sharing and employing highly directional
    antennas in the mm-wave bands are considered among
    the key enablers for 5G networks. Conventional interference
    avoidance techniques like listen-before-talk (LBT) may not
    be efficient for such coexisting networks. In this paper, we
    address a coexistence mechanism by means of distributed
    beam scheduling with minimum cooperation between spectrum
    sharing subsystems without any direct data exchange
    between them. We extend a ?Good Neighbor? (GN) principle
    initially developed for decentralized spectrum allocation
    to the distributed beam scheduling problem. To do that,
    we introduce relative performance targets, develop a GN
    beam scheduling algorithm, and demonstrate its efficiency
    in terms of performance/complexity trade off compared to
    that of the conventional selfish (SLF) and recently proposed
    distributed learning scheduling (DLS) solutions by means of
    simulations in highly directional antenna mm-wave scenarios.
    Multiuser multiple-input multiple-output (MU-MIMO) has the potential to substantially increase the uplink network efficiency by multiplexing the user terminals' (UTs) transmissions in the spatial domain. However, demultiplexing the transmissions at the network side, known as MU-MIMO detection, can become a considerable signal processing challenge, especially in cases with a high spatial user load. During the last two decades, the MIMO detection problem has been extensively studied, and many receiver designs have been proposed that offer very good tradeoffs in complexity vs. performance. Nevertheless, MU-MIMO detection still presents challenges in signal processing scalability in the system size and modulation order. We revisit this problem but through an alternative method of joint transmitter and receiver design. Two approaches that exhibit near-optimal reliability and low complexity are presented:
    First, a technique that uses real-valued modulation in fully- and over-loaded cases in large MU-MIMO systems, where there are equal or more UTs than service antennas. It is seen that the use of real constellations with a widely linear equaliser benefits from an increased spatial diversity gain over complex constellations with a linear equaliser. Moreover, a likelihood ascent search (LAS) algorithm post-processing stage is applied to further improve the error performance. Computer simulations show remarkable results for large MU-MIMO sizes in uncoded or coded cases.
    Second, recognising that real-valued modulation offers poor modulation efficiency, a real-complex hybrid modulation (RCHM) scheme is proposed, where a mix of real- and complex-valued symbols are interleaved in the spatial and temporal domains. It is seen that RCHM combines the merits of real and complex modulations and enables the adjustment of the diversity-multiplexing tradeoff. Through the system outage probability analysis, the optimal ratio of the number real-to-complex symbols, as well as their optimal power allocation, is found for the RCHM pattern. Furthermore, reliability is improved with a small expense in complexity through the use of a successive interference cancellation (SIC) stage. Results are validated through the mathematical analysis of the average bit error rate and through computer simulations considering single and multiple base station scenarios, which show SNR gains over conventional approaches in excess of 5 dB at 1% BLER.
    The results suggest that an expense in complexity is not the only way to improve error performance, but near-optimal reliability is also possible using simple techniques through a reduction in the multiplexing gain. Therefore, rather than a two-way complexity vs. performance tradeoff in MU-MIMO detection, a three-way tradeoff may be more appropriate, and is roughly expressed in the following statement:
    ?Low complexity, high reliability, high multiplexing gain: choose two.?
    Qian Peng, Wang Ning, Tafazolli Rahim (2018) Achieving Robust Mobile Web Content Delivery Performance Based on Multiple Coordinated QUIC Connections,IEEE Access 6 pp. 11313-11328 Institute of Electrical and Electronics Engineers (IEEE)
    In order to minimize the downloading time of short-lived applications like web browsing,
    web application and short video clips, the recently standardized HTTP/2 adopts stream multiplexing
    on one single TCP connection. However, aggregating all content objects within one single connection
    suffers from the Head-of-Line blocking issue. QUIC, by eliminating such an issue on the basis of UDP,
    is expected to further reduce the content downloading time. However, in mobile network environments,
    the single connection strategy still leads to a degraded and high variant completion time due to the
    unexpected hindrance of congestion window growth caused by the common but uncertain fluctuations in
    round trip time and also random loss event at the air interface. To retain resilient congestion window against
    such network fluctuations, we propose an intelligent connection management scheme based on QUIC
    which not only employs adaptively multiple connections but also conducts a tailored state and congestion
    window synchronization between these parallel connections upon the detection of network fluctuation
    events. According to the performance evaluation results obtained from an LTE-A/Wi-Fi testing network,
    the proposed multiple QUIC scheme can effectively overcome the limitations of different congestion
    control algorithms (e.g. the loss-based New Reno/CUBIC and the rate-based BBR), achieving substantial
    performance improvement in both median (up to 59.1%) and 95th completion time (up to 72.3%). The
    significance of this piece of work is to achieve highly robust short-lived content downloading performance
    against various uncertainties of network conditions as well as with different congestion control schemes.
    Vural S, Wang N, Bucknell P, Foster G, Tafazolli R, Muller J (2018) Dynamic Preamble Subset Allocation for RAN Slicing in 5G Networks,IEEE Access 6 pp. 13015-13032 Institute of Electrical and Electronics Engineers (IEEE)
    The random access (RA) mechanism of Long Term
    Evolution (LTE) networks is prone to congestion when a large
    number of devices attempt RA simultaneously, due to the
    limited set of preambles. If each RA attempt is made by means
    of transmission of multiple consecutive preambles (codewords)
    picked from a subset of preambles, as proposed in [1], collision
    probability can be significantly reduced. Selection of an optimal
    preamble set size [2] can maximise RA success probability in the
    presence of a trade-off between codeword ambiguity and code
    collision probability, depending on load conditions. In light of this
    finding, this paper provides an adaptive algorithm, called Multipreamble
    RA, to dynamically determine the preamble set size
    in different load conditions, using only the minimum necessary
    uplink resources. This provides high RA success probability, and
    makes it possible to isolate different network service classes by
    separating the whole preamble set into subsets each associated
    to a different service class; a technique that cannot be applied
    effectively in LTE due to increased collision probability. This
    motivates the idea that preamble allocation could be implemented
    as a virtual network function, called vPreamble, as part of
    a random access network (RAN) slice. The parameters of a
    vPreamble instance can be configured and modified according
    to the load conditions of the service class it is associated to.
    Abbas Fathy Abbas Y, Barnaghi P, Tafazolli R (2018) An Adaptive Method for Data Reduction in the Internet of Things,Proceedings of IEEE 4th World Forum on Internet of Things IEEE
    Enormous amounts of dynamic observation and
    measurement data are collected from sensors in Wireless
    Sensor Networks (WSNs) for the Internet of Things (IoT)
    applications such as environmental monitoring. However, continuous
    transmission of the sensed data requires high energy
    consumption. Data transmission between sensor nodes and
    cluster heads (sink nodes) consumes much higher energy than
    data sensing in WSNs. One way of reducing such energy
    consumption is to minimise the number of data transmissions.
    In this paper, we propose an Adaptive Method for Data Reduction
    (AM-DR). Our method is based on a convex combination
    of two decoupled Least-Mean-Square (LMS) windowed filters
    with differing sizes for estimating the next measured values
    both at the source and the sink node such that sensor nodes
    have to transmit only their immediate sensed values that
    deviate significantly (with a pre-defined threshold) from the
    predicted values. The conducted experiments on a real-world
    data show that our approach has been able to achieve up to
    95% communication reduction while retaining a high accuracy
    (i.e. predicted values have a deviation of ý+0:5 from real data
    values).
    Dawoud D, Heliot F, Imran M, Tafazolli R (2018) A Novel Coherent Transmission Scheme for Visible Light Communication,2018 IEEE ICC Conference Proceedings Institute of Electrical and Electronics Engineers (IEEE)
    The spatially-incoherent radiators in visible light
    communication (VLC) constrain the optical carrier to be only
    driven by a real electrical sub-carrier, which cannot be quadrature
    modulated as in classic RF-based systems. This restriction,
    in turn, severely limits the transmission throughput of VLC
    systems. To overcome this technical challenge, we propose a
    novel coherent transmission scheme for VLC, in which the
    optical carrier is only treated as a purely amplitude-modulated
    carrier capable of transmitting two-dimensional (2D) symbols
    (e.g. quadrature modulated symbols). The ability of our new
    coherent transmission scheme to transmit 2D symbols is validated
    through analytical symbol error rate derivation and Matlab
    simulations. Results show that our scheme can improve both
    the spectral and energy efficiency of VLC systems, i.e. by either
    doubling the spectral efficiency or achieving more than 45%
    energy efficiency improvement, when compared to its existing
    counterparts.
    Hoseinitabatabaei S, Barnaghi P, Dong L, Wang C, Tafazolli R (2017) Scalable data discovery in an internet of things (iot) system,
    Data discovery for sensor data in an M2M network uses probabilistic models, such as Gaussian Mixing Models (GMMs) to represent attributes of the sensor data. The parameters of the probabilistic models can be provided to a discovery server (DS) that respond to queries concerning the sensor data. Since the parameters are compressed compared to the attributes of the sensor data itself, this can simplify the distribution of discovery data. A hierarchical arrangement of discovery servers can also be used with multiple levels of discovery servers where higher level discovery servers using more generic probabilistic models.
    Al Kiyumi R, Foh C, Vural S, Chatzimisios P, Tafazolli R (2018) Fuzzy Logic-based Routing Algorithm for Lifetime Enhancement in Heterogeneous Wireless Sensor Networks,IEEE Transactions on Green Communications and Networking 2 (2) pp. 517-532 Institute of Electrical and Electronics Engineers (IEEE)
    Energy consumption of sensor nodes is a key factor affecting the lifetime of wireless sensor networks (WSNs). Prolonging network lifetime not only requires energy efficient operation, but also even dissipation of energy among sensor nodes. On the other hand, spatial and temporal variations in sensor activities create energy imbalance across the network. Therefore, routing algorithms should make an appropriate trade-off between energy efficiency and energy consumption balancing to extend the network lifetime. In this paper, we propose a Distributed Energy-aware Fuzzy Logic based routing algorithm (DEFL) that simultaneously addresses energy efficiency and energy balancing. Our design captures network status through appropriate energy metrics and maps them into corresponding cost values for the shortest path calculation. We seek fuzzy logic approach for the mapping to incorporate human logic. We compare the network lifetime performance of DEFL with other popular solutions including MTE, MDR and FA. Simulation results demonstrate that the network lifetime achieved by DEFL exceeds the best of all tested solutions under various traffic load conditions. We further numerically compute the upper bound performance and show that DEFL performs near the upper bound.
    Raza Naqvi Syed Ahsan, Pervaiz Haris, Ali Hassan Syed, Musavian Leila, Ni Qiang, Imran Muhammad Ali, Ge Xiaohu, Tafazolli Rahim (2018) Energy-Aware Radio Resource Management in D2D-Enabled Multi-Tier HetNets,IEEE Access 6 pp. 16610-16622 Institute of Electrical and Electronics Engineers (IEEE)
    Hybrid networks consisting of both millimeter
    wave (mmWave) and microwave (¼W) capabilities are
    strongly contested for next generation cellular communications.
    A similar avenue of current research is deviceto-
    device (D2D) communications, where users establish
    direct links with each other rather than using central base
    stations (BSs). However, a hybrid network, where D2D
    transmissions coexist, requires special attention in terms
    of efficient resource allocation. This paper investigates
    dynamic resource sharing between network entities in a
    downlink (DL) transmission scheme to maximize energy
    efficiency (EE) of the cellular users (CUs) served by either
    (¼W) macrocells or mmWave small cells, while maintaining
    a minimum quality-of-service (QoS) for the D2D
    users. To address this problem, firstly a self-adaptive power
    control mechanism for the D2D pairs is formulated, subject
    to an interference threshold for the CUs while satisfying
    their minimum QoS level. Subsequently, a EE optimization
    problem, which is aimed at maximizing the EE for both
    CUs and D2D pairs, has been solved. Simulation results
    demonstrate the effectiveness of our proposed algorithm,
    which studies the inherent tradeoffs between system EE,
    system sum rate and outage probability for various QoS
    levels and varying density of D2D pairs and CUs.
    Munir Hamnah, Pervaiz Haris bin, Hassan Syed Ali, Musavian Leila, Ni Qiang, Imran Muhammad Ali, Tafazolli Rahim (2018) Computationally Intelligent Techniques for Resource Management in mmWave Small Cell Networks,IEEE Wireless Communications 25 (4) pp. 32-39 Institute of Electrical and Electronics Engineers (IEEE)
    Ultra densification in heterogeneous networks
    (HetNets) and the advent of millimeter wave (mmWave) technology
    for fifth generation (5G) networks have led the researchers
    to redesign the existing resource management techniques. A
    salient feature of this activity is to accentuate the importance
    of computationally intelligent (CI) resource allocation schemes
    offering less complexity and overhead. This paper overviews the
    existing literature on resource management in mmWave-based
    HetNets with a special emphasis on CI techniques and further
    proposes frameworks that ensure quality-of-service requirements
    for all network entities. More specifically, HetNets with mmWavebased
    small cells pose different challenges as compared to an allmicrowave-
    based system. Similarly, various modes of small cell
    access policies and operations of base stations in dual mode, i.e.,
    operating both mmWave and microwave links simultaneously,
    offer unique challenges to resource allocation. Furthermore, the
    use of multi-slope path loss models becomes inevitable for analysis
    owing to irregular cell patterns and blocking characteristics of
    mmWave communications. This paper amalgamates the unique
    challenges posed because of the aforementioned recent developments
    and proposes various CI-based techniques including game
    theory and optimization routines to perform efficient resource
    management.
    Khalily Mohsen, Taheri Sohail, Payami Sohail, Ghoraishi Mir, Tafazolli Rahim (2018) Indoor Wideband Directional Millimeter Wave Channel Measurements and Analysis at 26 GHz, 32 GHz, and 39 GHz,Transactions on Emerging Telecommunications Technologies. Special Issue: Spectrum Extensions for 5G and Beyond 5G Networks 29 (10) e3311 Wiley
    This paper presents details of the wideband directional propagation
    measurements of millimetre-wave (mmWave) channels
    in the 26 GHz, 32 GHz, and 39 GHz frequency bands
    in an indoor typical office environment. More than 14400
    power delay profiles (PDPs) were measured across the 26
    GHz band and over 9000 PDPs have been recorded for the
    32 GHz and 39 GHz bands at each measurement point. A
    mmWave wideband channel sounder has been used, where
    signal analyzer and vector signal generator was employed.
    Measurements have been conducted for both co- and crossantenna
    polarization. The setup provided 2GHz bandwidth
    and the mechanically steerable directional horn antenna with
    8 degrees beamwidth provides 8 degrees of directional resolution
    over the azimuth for 32 GHz and 39 GHz while 26
    GHz measurement setup provides the angular resolution of
    5 degrees. Measurements provide path loss, delay and spatial
    spread of the channel. Large-scale fading characteristics,
    RMS delay spread, RMS angular spread, angular and
    delay dispersion are presented for three mmWave bands
    for the line-of-sight (LoS) scenario.
    Qi Y, Shakir M, Imran M, Qaraqe K, Quddus A, Tafazolli R (2016) Fronthaul Data Compression for Uplink CoMP in Cloud Radio Access Network (C-RAN),Transactions on Emerging Telecommunications Technologies 27 (10) pp. 1409-1425 Wiley
    The design of efficient wireless fronthaul connections for future heterogeneous networks incorporating emerging paradigms such as cloud radio access network (C-RAN) has become a challenging task that requires the most effective utilization of fronthaul network resources. In this paper, we propose to use distributed compression to reduce the fronthaul traffic in uplink Coordinated Multi-Point (CoMP) for C-RAN. Unlike the conventional approach where each coordinating point quantizes and forwards its own observation to the processing centre, these observations are compressed before forwarding. At the processing centre, the decompression of the observations and the decoding of the user message are conducted in a successive manner. The essence of this approach is the optimization of the distributed compression using an iterative algorithm to achieve maximal user rate with a given fronthaul rate. In other words, for a target user rate the generated fronthaul traffic is minimized. Moreover, joint decompression and decoding is studied and an iterative optimization algorithm is devised accordingly. Finally, the analysis is extended to multi-user case and our results reveal that, in both dense and ultra-dense urban deployment scenarios, the usage of distributed compression can efficiently reduce the required fronthaul rate and a further reduction is obtained with joint operation.
    Hoseinitabatabaei Seyed, Fathy Y, Barnaghi Payam, Wang C, Tafazolli Rahim (2018) A Novel Indexing Method for Scalable IoT
    Source Lookup
    ,
    IEEE Internet of Things Journal 5 (3) pp. 2037-2054 IEEE
    When dealing with a large number of devices, the existing indexing solutions for the discovery of IoT sources often fall short
    to provide an adequate scalability. This is due to the high computational complexity and communication overhead that is required to
    create and maintain the indices of the IoT sources particularly when their attributes are dynamic. This paper presents a novel approach
    for indexing distributed IoT sources and paves the way to design a data discovery service to search and gain access to their data. The
    proposed method creates concise references to IoT sources by using Gaussian Mixture Models (GMM). Furthermore, a summary update
    mechanism is introduced to tackle the change of sources availability and mitigate the overhead of updating the indices frequently. The
    proposed approach is benchmarked against a standard centralized indexing and discovery solution. The results show that the proposed
    solution reduces the communication overhead required for indexing by three orders of magnitude while depending on IoT network
    architecture it may slightly increase the discovery time
    Taufique A, Mohamed Abdelrahim, Farooq H, Imran A, Tafazolli Rahim (2018) Analytical Modelling for Mobility Signalling in Ultra-Dense HetNets,IEEE Transactions on Vehicular Technology IEEE
    Multi-band and multi-tier network densification is
    being considered as the most promising solution to overcome the
    capacity crunch problem of cellular networks. In this direction,
    small cells (SCs) are being deployed within the macro cell (MC)
    coverage, to off-load some of the users associated with the MCs.
    This deployment scenario raises several problems. Among others,
    signalling overhead and mobility management will become
    critical considerations. Frequent handovers (HOs) in ultra dense
    SC deployments could lead to a dramatic increase in signalling
    overhead. This suggests a paradigm shift towards a signalling
    conscious cellular architecture with smart mobility management.
    In this regards, the control/data separation architecture (CDSA)
    with dual connectivity is being considered for the future radio
    access. Considering the CDSA as the radio access network
    (RAN) architecture, we quantify the reduction in HO signalling
    w.r.t. the conventional approach. We develop analytical models
    which compare the signalling generated during various HO
    scenarios in the CDSA and conventionally deployed networks.
    New parameters are introduced which can with optimum value
    significantly reduce the HO signalling load. The derived model
    includes HO success and HO failure scenarios along with specific
    derivations for continuous and non-continuous mobility users.
    Numerical results show promising CDSA gains in terms of saving
    in HO signalling overhead.
    Araghi A, Khalily M, Xiao P, Kosari A, Zarrabi H, Tafazolli R (2018) Millimeter-Wave MIMO Balanced Antipodal Vivaldi Antenna Design for Autonomous Cars,IEEE ISNCC 2018 : 2018 IEEE International Symposium on Networks, Computers and Communications Institute of Electrical and Electronics Engineers (IEEE)
    This paper introduces a millimeter-wave multipleinput-
    multiple-output (MIMO) antenna for autonomous (selfdriving)
    cars. The antenna is a modified four-port balanced
    antipodal Vivaldi which produces four directional beams and
    provides pattern diversity to cover 90 deg angle of view. By using
    four antennas of this kind on four corners of the car?s bumper, it
    is possible to have a full 360 deg view around the car. The
    designed antenna is simulated by two commercially full-wave
    packages and the results indicate that the proposed method can
    successfully bring the required 90 deg angle of view.
    De Luna Ducoing Juan Carlos, Ma Yi, Yi Na, Tafazolli Rahim (2018) A Real-Complex Hybrid Modulation Approach for Scaling Up Multiuser MIMO Detection,IEEE Transactions on Communications 66 (9) pp. 3916-3929 Institute of Electrical and Electronics Engineers (IEEE)
    In this paper, a novel approach, namely realcomplex
    hybrid modulation (RCHM), is proposed to scale up
    multiuser multiple-input multiple-output (MU-MIMO) detection
    with particular concern on the use of equal or approximately
    equal service antennas and user terminals. By RCHM, we mean
    that user terminals transmit their data sequences with a mix of
    real and complex modulation symbols interleaved in the spatial
    and temporal domain. It is shown, through the system outage
    probability, RCHM can combine the merits of real and complex
    modulations to achieve the best spatial diversity-multiplexing
    trade-off that minimizes the required transmit-power given a
    sum-rate. The signal pattern of RCHM is optimized with respect
    to the real-to-complex symbol ratio as well as power allocation.
    It is also shown that RCHM equips the successive interference
    canceling MU-MIMO receiver with near-optimal performances
    and fast convergence in Rayleigh fading channels. This result is
    validated through our mathematical analysis of the average biterror-
    rate as well as extensive computer simulations considering
    the case with single or multiple base-stations.
    Ul Quddus Atta, Yang Xinjie, Tafazolli Rahim (2008) Link-Level Analysis of Downlink Handover Regions in UMTS,67th IEEE VTC Vehicular Technology Conference pp. 2527-2531 Institute of Electrical and Electronics Engineers
    This paper investigates the downlink handover (soft/softer/hard) performance of Wideband Code Division
    Multiple Access (WCDMA) based 3rd generation Universal Mobile Telecommunication System (UMTS), as it is known that
    the downlink capacity of UMTS is very sensitive to the extent of overlap area between adjacent cells and power margin between them. Factors influencing the handover performance such as the correlation between the multipath radio channels of the two links, limiting number of Rake fingers in a handset, imperfect channel estimation, etc. that cannot be modeled adequately in system-level simulations are investigated via link-level simulations. It is also shown that the geometry factor has an influence on the handover performance and exhibits a threshold value (which depends on the correlation between the multipath
    channels associated with the two links in a handover) above
    which the performance starts degrading. The variation of the
    handover gain with the closed loop power control (CLPC) stepsize and space-time transmit diversity (STTD) is also quantified. These comprehensive results can be used as guidelines for more accurate coverage and capacity planning of UMTS networks.
    Khalily Mohsen, Tafazolli Rahim, Xiao Pei, Kishk Ahmed A. (2018) Microstrip Array Antenna with Improved Radiation Characteristic for Different 5G Applications,IEEE Transactions on Antennas and Propagation 66 (9) pp. 4641-4647 Institute of Electrical and Electronics Engineers (IEEE)
    A Ka-band inset-fed microstrip patches linear antenna
    array is presented for the fifth generation (5G) applications
    in different countries. The bandwidth is enhanced by stacking
    parasitic patches on top of each inset-fed patch. The array
    employs 16 elements in an H-plane new configuration. The
    radiating patches and their feed lines are arranged in an
    alternating out-of-phase 180-degree rotating sequence to decrease
    the mutual coupling and improve the radiation pattern symmetry.
    A (24.4%) measured bandwidth (24.35 to 31.13 GHz)is achieved
    with -15 dB reflection coefficients and 20 dB mutual coupling
    between the elements. With uniform amplitude distribution, a
    maximum broadside gain of 19.88 dBi is achieved. Scanning the
    main beam to 49.5° from the broadside achieved 18.7 dBi gain
    with -12.1 dB sidelobe level (SLL). These characteristics are in
    good agreement with the simulations, rendering the antenna to
    be a good candidate for 5G applications.
    Chen Hongzhi, Mi De, Chu Zheng, Xiao Pei, Tafazolli Rahim (2018) Rate-Splitting for Multigroup Multicast Beamforming in Multicarrier Systems,Proceedings of 19th IEEE international workshop on signal processing advances in wireless communications (SPAWC) Institute of Electrical and Electronics Engineers (IEEE)
    In this paper, we consider multigroup multicast
    transmissions with different types of service messages in an
    overloaded multicarrier system, where the number of transmitter
    antennas is insufficient to mitigate all inter-group interference.
    We show that employing a rate-splitting based multiuser beamforming
    approach enables a simultaneous delivery of the multiple
    service messages over the same time-frequency resources in a
    non-orthogonal fashion. Such an approach, taking into account
    transmission power constraints which are inevitable in practice,
    outperforms classic beamforming methods as well as current
    standardized multicast technologies, in terms of both spectrum
    efficiency and the flexibility of radio resource allocation.
    Ma Yi, Tafazolli Rahim (2005) Exploiting Hidden Pilots for Carrier Frequency Offset Estimation for Generalized MC-CDMA Systems,IEEE/SP 13th Workshop on Statistical Signal Processing (SSP) Vols 1 and 2 pp. 1318-1323 Institute of Electrical and Electronics Engineers
    This paper proposes a novel carrier frequency offset (CFO)
    estimation method for generalized MC-CDMA systems in unknown frequency-selective channels utilizing hidden pi-
    lots. It is established that CFO is identifiable in the frequency domain by employing cyclic statistics (CS) and linear re-gression (LR) algorithms. We show that the CS-based estimator is capable of mitigating the normalized CFO (NCFO) to a small error value. Then, the LR-based estimator can be employed to offer more accurate estimation by removing the residual quantization error after the CS-based estimator.
    Araghi Ali, Khalily Mohsen, Xiao Pei, Tafazolli Rahim (2020) Multiple-Beam mmW-Slotted-Waveguide
    Leaky Wave Antenna with Control on Polarization
    ,
    2020 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting Institute of Electrical and Electronics Engineers (IEEE)
    By performing the Floquet-mode analysis of a periodic
    slotted waveguide, a multiple-beam leaky wave antenna
    is proposed in the millimetre-wave (mmW) band. Considering
    the direction of surface current lines on the broad/side-walls of
    the waveguide, the polarization of constructed beams are also
    controlled. The simulation results are well matched with the
    initial mathematical analysis.
    WSN applications demand prolonged network operation in which manually replenishing the scarce battery resources of sensor nodes are not usually possible. When the limited energy of sensor nodes is completely exhausted, this leads to reduced coverage and may cause network partitioning, which dramatically reduces the network lifetime. In this respect, network lifetime enhancement is considered the most critical aspect of WSN performance. Prolonging network lifetime requires mechanisms that provide energy consumption balancing (ECB) in addition to energy efficiency (EE).
    This thesis investigates network lifetime maximization problem and proposes solutions to address both EE and ECB. The scope covers two separate but equally important fronts: duty cycling mechanisms and maximum lifetime routing strategies. Duty cycling significantly reduces the energy consumption of sensor nodes resulting from idle listening. Meanwhile, maximum lifetime routing schemes aim at balancing traffic loads and hence energy consumption among sensor nodes across the network.
    In this regard, our contributions are in three-folds. First, a distributed sleep mechanism is proposed for the non-beacon-enabled mode of the IEEE 802.15.4 MAC protocol, to support energy-efficient operation in WSNs. In addition to achieving energy savings, our mechanism helps reshape generated traffic so that the overall channel contention is reduced. This effect in turns improves packet delivery ratio at the data sink.
    Second, we propose a Control-theoretic Duty Cycle Adaptation algorithm (CDCA) to adapt nodes duty cycle based on time-varying and/or spatially non-uniform data traffic loads. The proposed mechanism is distributed; hence each node adjusts its duty cycle independently. We introduce a novel concept called virtual queue, which provides better insight into actual traffic conditions in comparison to existing schemes and prevents excessive packet drop. Using NS-3 simulation, we demonstrate the performance improvements obtained from CDCA in comparison to the state of the art. Furthermore, a stability analysis is conducted to investigate system stability conditions.
    Third, we formulate the maximum lifetime routing problem as a minimax optimization problem, and numerically obtain the upper bound network lifetime. Moreover, we propose a Distributed Energy-aware Fuzzy-Logic based routing algorithm (DEFL). DEFL makes an appropriate trade-off between energy efficiency and energy consumption balancing and successfully extends the network lifetime under different network conditions. The simulation results demonstrate that DEFL outperforms all tested algorithms and performs very close to the upper bound.
    Keywords: Network Lifetime Maximization, Energy Efficiency, Energy Consumption Balancing, MAC, Routing, Wireless Sensor Networks.
    Hamid Asif, Hoshyar Reza, Tafazolli Rahim (2006) Band Based Dynamic Link Adaptation for MC-CDMA Radio Interface,64th IEEE Vehicle Technology Conference pp. 1-5 Institute of Electrical and Electronics Engineers
    This paper studies adaptive power allocation among sub-carriers in MC-CDMA. Due to intrinsic nature of MC-CDMA; Carrier Based power allocation schemes cause MAI (Multiple Access Interference) enhancements, hence fail at higher
    system loads. We propose a Band Based Dynamic Link Adaptation (BBDLA) scheme that preserves orthogonality
    (among users) by spreading user?s signal only over a Band of
    adjacent N sub-carriers (N bandwidth (Bc) of the channel. Hence, it allows Band Based
    power allocation without causing any MAI. However, with only N orthogonal users supported on a particular Band, BBDLA essentially proposes a hybrid of FDMA with MC-CDMA where Bands and transmit powers are optimally assigned to users by Base Station (in accordance with their channel state). Optimum Band allocation for BBDLA is found to be computationally intractable hence a sub-optimal heuristic approach is proposed with equal power distribution among all assigned Bands for each user. Effect of Bc over choice of N is studied and BBDLA with suitably chosen N, is shown to outperform other published Carrier Based power allocation schemes while it maintain almost single user BER performance up to 62% of full system loading
    Heliot Fabien, Tafazolli Rahim (2020) Optimal Energy-ef?cient Source and Relay Precoder Design for Two-way MIMO-AF Relay Systems,Optimal Energy-ef?cient Source and Relay Precoder Design for Two-way MIMO-AF Relay Systems Insitute of Electronic Engineers
    Energy ef?ciency (EE) is a key ?gure of merit for designing the next generation of communication systems. Meanwhile, relay-based cooperative communication, through machine-to-machine and other related technologies, is also playing an important part in the development of these systems. This paper designs an energy ef?cient precoding method for optimizing the EE/energy consumption of two-way multi-input multi-output (MIMO)-amplify-and-forward (AF) relay systems by using pseudo-convexity analysis to design EE-optimal precoding matrices. More precisely, we derive an EE-optimal source precoding matrix in closed-form, design a numerical approach for obtaining an optimal relay precoding matrix, prove the optimality of these matrices, when treated separately, and provide lowcomplexity bespoke algorithms to generate them. These matrices are then jointly optimized through an alternating optimization process that is proved to be systematically convergent. Performance evaluation indicates that our method can be globally optimal in some scenarios and that it is signi?cantly more energy ef?cient (i.e. up to 60% more energy ef?cient) than existing EEbased one-way or two-way MIMO-AF precoding methods.
    Khalily Mohsen, Tafazolli Rahim, Xiao Pei, Kishk Ahmed A. (2018) Broadband mm-Wave Microstrip Array Antenna with Improved Radiation Characteristics for Different 5G Applications,IEEE Transactions on Antennas and Propagation 44 (9) pp. 4641-4647 Institute of Electrical and Electronics Engineers (IEEE)
    A Ka-band inset-fed microstrip patches linear antenna
    array is presented for the fifth generation (5G) applications
    in different countries. The bandwidth is enhanced by stacking
    parasitic patches on top of each inset-fed patch. The array
    employs 16 elements in an H-plane new configuration. The
    radiating patches and their feed lines are arranged in an
    alternating out-of-phase 180-degree rotating sequence to decrease
    the mutual coupling and improve the radiation pattern symmetry.
    A (24.4%) measured bandwidth (24.35 to 31.13 GHz)is achieved
    with -15 dB reflection coefficients and 20 dB mutual coupling
    between the elements. With uniform amplitude distribution, a
    maximum broadside gain of 19.88 dBi is achieved. Scanning the
    main beam to 49.5æ
    from the broadside achieved 18.7 dBi gain
    with -12.1 dB sidelobe level (SLL). These characteristics are in
    good agreement with the simulations, rendering the antenna to
    be a good candidate for 5G applications.
    Chen Hongzhi, Mi De, Fuentes Manuel, Vargas David, Garro Eduardo, Carcel Jose Luis, Mouhouche Belkacem, Xiao Pei, Tafazolli Rahim (2018) Pioneering studies on LTE eMBMS: Towards 5G Point-to-Multipoint Transmissions,Proceedings of The Tenth IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM2018) Institute of Electrical and Electronics Engineers (IEEE)
    The first 5G (5th generation wireless systems) New
    Radio Release-15 was recently completed. However, the specification
    only considers the use of unicast technologies and the extension
    to point-to-multipoint (PTM) scenarios is not yet considered.
    To this end, we first present in this work a technical overview of
    the state-of-the-art LTE (Long Term Evolution) PTM technology,
    i.e., eMBMS (evolved Multimedia Broadcast Multicast Services),
    and investigate the physical layer performance via link-level
    simulations. Then based on the simulation analysis, we discuss
    potential improvements for the two current eMBMS solutions,
    i.e., MBSFN (MBMS over Single Frequency Networks) and SCPTM
    (Single-Cell PTM). This work explicitly focus on equipping
    the current eMBMS solutions with 5G candidate techniques, e.g.,
    multiple antennas and millimeter wave, and its potentials to meet
    the requirements of next generation PTM transmissions.
    Nourizadeh H, Nourizadeh S, Tafazolli Rahim (2006) Impact of the Inter-relay Handoff on the Relaying System Performance,64th IEEE Vehicular Technology Conference pp. 1-5 Institute of Electrical and Electronics Engineers
    It is foreseen that the next generation of cellular network would integrate the relaying or multihop scheme. In a multihop cellular architecture, the users are not only able to communicate directly to the base station (BS) but can also use some relay stations to relay their data to the BS. In such architecture, it may happen that a relayed user handover to another relay station during its communication: this process is called the inter-relay handoff. The main objective of this paper is to study how frequent the inter-relay handoff occurs and its impact on the relaying system performance. For this, different algorithms to decide when a user should inter-relay handover are proposed and tested through a dynamic system level simulator. We compare the capacity gain for the different algorithm with the conventional cellular networks using the UMTS FDD mode.
    The result showed that with an appropriate inter-relay handoff scheme, the uplink capacity gain of 35% is readily achievable.
    Li Ang, Ma Yi, Xue Songyan, Yi Na, Tafazolli Rahim (2018) A Carrier-Frequency-Offset Resilient OFDMA Receiver Designed Through Machine Deep Learning,Proceedings of the 2018 IEEE 29th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC): IEEE PIMRC 2018 Institute of Electrical and Electronics Engineers (IEEE)
    The aim of this paper is to handle the multifrequency
    synchronization problem inherent in orthogonal
    frequency-division multiple access (OFDMA) uplink
    communications, where the carrier frequency offset (CFO)
    for each user may be different, and they can be hardly
    compensated at the receiver side. Our major contribution
    lies in the development of a novel OFDM receiver that
    is resilient to unknown random CFO thanks to the use
    of a CFO-compensator bank. Specifically, the whole CFO
    range is evenly divided into a set of sub-ranges, with
    each being supported by a dedicated CFO compensator.
    Given the optimization for CFO compensator a NP-hard
    problem, a machine deep-learning approach is proposed
    to yield a good sub-optimal solution. It is shown that the
    proposed receiver is able to offer inter-carrier interference
    free performance for OFDMA systems operating at a wide
    range of SNRs.
    Recent advancements in sensing, networking technologies and collecting real-world data on a large scale and from various environments
    have created an opportunity for new forms of services and applications. This is known under the umbrella term of the Internet of
    Things (IoT). Physical sensor devices constantly produce very large amounts of data. Methods are needed which give the raw sensor measurements a meaningful interpretation for building automated decision support systems. One of the main research challenges in this domain is to extract actionable information from real-world data, that is information that can readily be used to make informed automatic
    decisions in intelligent systems. Most existing approaches are application or domain dependent or are only able to deal with specific data
    sources of one kind. This PhD research concerns multiple approaches for analysing IoT data streams. We propose a method which determines how many different clusters can be found in a stream based on the data distribution. After selecting the number of clusters, we use an online clustering mechanism to cluster the incoming data from the streams. Our approach remains adaptive to drifts by adjusting itself as the data changes. The work is benchmarked against state-of-the art stream clustering algorithms on data streams with data drift. We show how our method can be applied in a use case scenario involving near real-time traffic data. Our results allow to cluster, label and interpret IoT data streams dynamically according to the data distribution. This enables to adaptively process large volumes of dynamic data online based on the current situation. We show how our method adapts itself to the changes and we demonstrate how the number of clusters in a real-world data stream can be determined by analysing the data distributions.
    Using the ideas and concepts of this approach as a starting point we designed another novel dynamic and adaptable clustering approach
    that is more suitable for multi-variate time-series data clustering. Our solution uses probability distributions and analytical methods to adjust the centroids as the data and feature distributions change over time. We have evaluated our work against some well-known time-series clustering methods and have shown how the proposed method can reduce the complexity and perform efficient in multi-variate datastreams.
    Finally we propose a method that uncovers hidden structures and relations between multiple IoT data streams. Our novel solution uses Latent Dirichlet Allocation (LDA), a topic extraction method that is generally used in text analysis. We apply LDA on meaningful labels that describe the numerical data in human understandable terms. To create the labels we use Symbolic Aggregate approXimation (SAX), a method that converts raw data into string-based patterns. The extracted patterns are then transformed with a rule engine into the labels.
    The work investigates how heterogeneous sensory data from multiple sources can be processed and analysed to create near real-time intelligence and how our proposed method provides an efficient way to interpret patterns in the data streams. The proposed method provides a novel way to uncover the correlations and associations between different pattern in IoT data streams. The evaluation results show that the proposed solution is able to identify the correlation with high efficiency with an F-measure up to 90%.
    Overall, this PhD research has designed, implemented and evaluated unsupervised adaptive algorithms to analyse, structure and extract information from dynamic and multi-variate sensory data streams. The results of this research has significant impact in designing flexible and scalable solutions in analysing real-world sensory data streams and specially in cases where labelled and annotated data is not available or it is too costly to be collected. Research and advancements in healthcare and smarter cities are two key areas that can directly fr
    Xue Songyan, Ma Yi, Tafazolli Rahim (2018) Unsupervised Deep Learning for MU-SIMO Joint Transmitter and Noncoherent Receiver Design,IEEE Wireless Communications Letters Institute of Electrical and Electronics Engineers (IEEE)
    This work aims to handle the joint transmitter
    and noncoherent receiver optimization for multiuser single-input
    multiple-output (MU-SIMO) communications through unsupervised
    deep learning. It is shown that MU-SIMO can be modeled
    as a deep neural network with three essential layers, which
    include a partially-connected linear layer for joint multiuser
    waveform design at the transmitter side, and two nonlinear layers
    for the noncoherent signal detection. The proposed approach
    demonstrates remarkable MU-SIMO noncoherent communication
    performance in Rayleigh fading channels.
    Pervaiz Haris, Onierti Oluwakayode, Mohamed Abdelrahim, Imran Muhammad, Qiang Ni, Tafazolli Rahim (2018) Energy-Efficient and Load-Proportional eNodeB for 5G User-Centric Networks,IEEE Vehicular Technology Magazine 13 (4) pp. pp 51-59 Institute of Electrical and Electronics Engineers (IEEE)
    Nowadays, dense network deployment is being
    considered as one of the effective strategies to meet capacity
    and connectivity demands of the fifth generation (5G) cellular
    system. Among several challenges, energy consumption will be a
    critical consideration in the 5G era. In this direction, base station
    on/off operation, i.e., sleep mode, is an effective technique to
    mitigate the excessive energy consumption in ultra-dense cellular
    networks. However, current implementation of this technique is
    unsuitable for dynamic networks with fluctuating traffic profiles
    due to coverage constraints, quality-of-service requirements and
    hardware switching latency. In this direction, we propose an
    energy/load proportional approach for 5G base stations with
    control/data plane separation. The proposed approach depends on
    a multi-step sleep mode profiling, and predicts the base station
    vacation time in advance. Such a prediction enables selecting
    the best sleep mode strategy whilst minimizing the effect of
    base station activation/reactivation latency, resulting in significant
    energy saving gains.
    Husmann Christopher, Tafazolli Rahim, Nikitopoulos Konstantinos Antipodal Detection and Decoding for Large Multi-User MIMO with Reduced Base-Station Antennas,Proceedings of the IEEE GLOBECOM 2018 Workshops Institute of Electrical and Electronics Engineers (IEEE)
    To avoid unnecessarily using a massive number of
    base station antennas to support a large number of users spatially
    multiplexed multi-user MIMO systems, optimal detection
    methods are required to demultiplex the mutually interfering
    information streams. Sphere decoding (SD) can achieve this,
    but its complexity and latency becomes impractical for large
    MIMO systems. Low complexity detection solutions such as linear
    detectors (e.g., MMSE) or likelihood ascendant search (LAS)
    approaches, have significantly lower latency requirements than
    SD but their achievable throughput is far from optimal. This
    work presents the concept of Antipodal detection and decoding,
    that can deliver very high throughput with practical latency
    requirements, even in systems where the number of user antennas
    reaches the number of base station antennas. The Antipodal
    detector either results in a highly reliable vector solution, or it
    does not find a vector solution at all (i.e., it results in an erasure),
    skipping the heavy processing load related to finding vector
    solutions that have a very high likelihood to be erroneous. Then,
    a belief-propagation-based decoder is proposed, that restores
    these erasures and further corrects remaining erroneous vector
    solutions. We show that for 32å32, 64-QAM modulated systems,
    and for packet error rates below 10%, Antipodal detection and
    decoding requires 9 dB less transmitted power than systems
    employing soft MMSE or LAS detection and LDPC decoding
    with similar complexity requirements. For the same scenario, our
    Antipodal method achieves practical throughput gains of more
    than 50% compared to soft MMSE and soft LAS-based methods.
    Nikitopoulos Konstantinos, Georgis Georgios, Jayawardena Chathura, Chatzipanagiotis Daniil, Tafazolli Rahim (2018) Massively Parallel Tree Search for High-Dimensional Sphere Decoders,Transactions on Parallel and Distributed Systems IEEE
    The recent paradigm shift towards the transmission of large numbers of mutually interfering information streams, as in the
    case of aggressive spatial multiplexing, combined with requirements towards very low processing latency despite the frequency
    plateauing of traditional processors, initiates a need to revisit the fundamental maximum-likelihood (ML) and, consequently, the
    sphere-decoding (SD) detection problem. This work presents the design and VLSI architecture of MultiSphere; the first method to
    massively parallelize the tree search of large sphere decoders in a nearly-concurrent manner, without compromising their
    maximum-likelihood performance, and by keeping the overall processing complexity comparable to that of highly-optimized sequential
    sphere decoders. For a 10 å 10 MIMO spatially multiplexed system with 16-QAM modulation and 32 processing elements, our
    MultiSphere architecture can reduce latency by 29å against well-known sequential SDs, approaching the processing latency of linear
    detection methods, without compromising ML optimality. In MIMO multicarrier systems targeting exact ML decoding, MultiSphere
    achieves processing latency and hardware efficiency that are orders of magnitude improved compared to approaches employing one
    SD per subcarrier. In addition, for 16å16 both ?hard?- and ?soft?-output MIMO systems, approximate MultiSphere versions are shown to
    achieve similar error rate performance with state-of-the art approximate SDs having akin parallelization properties, by using only one
    tenth of the processing elements, and to achieve up to approximately 9å increased energy efficiency.
    Liu Lifu, Ma Yi, Yi Na, Tafazolli Rahim (2018) An Analogue-Beam Splitting Approach for MmWave D2D Multicast Channel,IEEE PIMRC 2018 Proceedings IEEE
    Considering a densely populated area where
    a mobile device, with a single RF chain, shares its message
    with a set of mobile devices through narrowband mmWave
    channel, an analogue-beam splitting approach is proposed
    to achieve a good capacity and coverage trade-off. The
    proposed approach aims at maximizing the capacity of
    the mmWave multicast channel through antenna-element
    grouping and adaptive phase shifting, which takes into
    account of the inter-beam interference. When receivers are
    randomly distributed on a circle centered at the transmitter,
    according to the uniform distribution, it is found
    that the impact of inter-beam interference on the channel
    capacity can be negligibly small, and thus the analoguebeam
    splitting approach can be largely simplified in practice.
    Computer simulations are carried out to elaborate our
    theoretical study and demonstrate considerable advantages
    of the proposed analogue-beam splitting approach.
    Yu Wenjuan, ul Quddus Atta, Vahid Seiamak, Tafazolli Rahim (2018) Opportunistic spectrum access in support of ultra-reliable and low-latency communications,Proceedings of 2018 IEEE Global Communications Conference (GLOBECOM) Institute of Electrical and Electronics Engineers (IEEE)
    This paper addresses the problem of opportunistic
    spectrum access in support of mission-critical ultra-reliable and
    low latency communications (URLLC). Considering the ability
    of supporting short packet transmissions in URLLC scenarios,
    a new capacity metric in finite blocklength regime is introduced
    as the traditional performance metrics such as ergodic capacity
    and outage capacity are no longer applicable. We focus on an
    opportunistic spectrum access system in which the secondary
    user (SU) opportunistically occupies the frequency resources of
    the primary user (PU) and transmits reliable short packets to
    its destination. An achievable rate maximization problem is then
    formulated for the SU in supporting URLLC services, subject to
    a probabilistic received-power constraint at the PU receiver and
    imperfect channel knowledge of the SU-PU link. To tackle this
    problem, an optimal power allocation policy is proposed. Closedform
    expressions are then derived for the maximum achievable
    rate in finite blocklength regime, the approximate transmission
    rate at high signal-to-noise ratios (SNRs) and the optimal average
    power. Numerical results validate the accuracy of the proposed
    closed-form expressions and further reveal the impact of channel
    estimation error, block error probability, finite blocklength and
    received-power constraint.
    Network-enabled sensing and actuation devices are key enablers to connect real-world objects to the cyber world. The Internet of Things (IoT) consists of network-enabled devices and communication technologies that allow connectivity and integration of physical objects (Things) into the digital world (Internet).

    Dealing with the data deluge from heterogeneous IoT resources and services imposes new challenges on indexing, discovery and ranking mechanisms. Novel indexing and discovery methods will enable developing applications that use on-line access and retrieval of ad-hoc IoT data.

    Investigation of the related work leads to the conclusion that there has been significant work on processing and analysing sensor data streams. However, there is still a need for integrating solutions that contemplate the work-flow from connecting IoT resources to make their published data indexable, searchable and discoverable.

    This research proposes a set of novel solutions for indexing, processing and discovery in IoT networks. The work proposes novel distributed in-network and spatial indexing solutions. The proposed solutions scale well and provide up to 92% better response time and higher success rates in response to data search queries compared to a baseline approach.

    A co-operative, adaptive, change detection algorithm has also been developed. It is based on a convex combination of two decoupled Least Mean Square (LMS) windowed filters. The approach provides better performance and less complexity compared to the state-of-the-art solutions. The change detection algorithm can also be applied to distributed networks in an on-line fashion. This co-operative approach allows publish/subscribe based and change based discovery solutions in IoT.

    Continuous transmission of large volumes of data collected by sensor nodes induces a high communication cost
    for each individual node in IoT networks. An Adaptive Method for Data Reduction (AM-DR) has been proposed for reducing the number of data transmissions in IoT networks. In AM-DR, identical predictive models are constructed at both the sensor and the sink nodes to describe data evolution such that sensor nodes require transmitting only their readings that deviate significantly from actual values. This has a significant impact on reducing the data load in IoT data discovery scenarios.

    Finally, a solution for quality and energy-aware resource discovery and accessing IoT resources has been proposed. The solution effectively achieves a communication reduction while retaining a high prediction accuracy (i.e. only a deviation of ±1.0 degree between actual and predicted sensor readings). Furthermore, an energy cost model has been discussed to demonstrate how the proposed approach reduces energy consumption significantly and effectively prolongs the network lifetime.

    Fathy Yasmin, Barnaghi Payam, Tafazolli Rahim (2018) An Online Adaptive Algorithm for Change Detection in Streaming Sensory Data,IEEE Systems Journal pp. 1-12 Institute of Electrical and Electronics Engineers (IEEE)
    There has been a keen interest in detecting abrupt
    sequential changes in streaming data obtained from sensors
    in Wireless Sensor Networks (WSNs) for Internet of Things
    (IoT) applications such as fire/fault detection, activity recognition
    and environmental monitoring. Such applications require (near)
    online detection of instantaneous changes. This paper proposes
    an Online, adaptive Filtering-based Change Detection (OFCD)
    algorithm. Our method is based on a convex combination of
    two decoupled Least Mean Square (LMS) windowed filters with
    differing sizes. Both filters are applied independently on data
    streams obtained from sensor nodes such that their convex combination
    parameter is employed as an indicator of abrupt changes
    in mean values. An extension of our method (OFCD) based
    on a Cooperative scheme between multiple sensors (COFCD) is
    also presented. It provides an enhancement of both convergence
    and steady-state accuracy of the convex weight parameter. Our
    conducted experiments show that our approach can be applied in
    distributed networks in an online fashion. It also provides better
    performance and less complexity compared with the state-of-theart
    on both of single and multiple sensors.
    Mi De, Zhang Lei, Dianati Mehrdad, Muhaidat Sami, Xiao Pei, Tafazolli Rahim (2018) Self-Calibration for Massive MIMO with Channel Reciprocity and Channel Estimation Errors,Proceedings of the IEEE Global Communications Conference, Abu Dhabi, UAE, 9-13 Dec 2018 Institute of Electrical and Electronics Engineers (IEEE)
    In time-division-duplexing (TDD) massive multipleinput
    multiple-output (MIMO) systems, channel reciprocity is
    exploited to overcome the overwhelming pilot training and
    the feedback overhead. However, in practical scenarios, the
    imperfections in channel reciprocity, mainly caused by radiofrequency
    mismatches among the antennas at the base station
    side, can significantly degrade the system performance and might
    become a performance limiting factor. In order to compensate
    for these imperfections, we present and investigate two new
    calibration schemes for TDD-based massive multi-user MIMO
    systems, namely, relative calibration and inverse calibration.
    In particular, the design of the proposed inverse calibration
    takes into account a compound effect of channel reciprocity
    error and channel estimation error. We further derive closedform
    expressions for the ergodic sum rate, assuming maximum
    ratio transmissions with the compound effect of both errors. We
    demonstrate that the inverse calibration scheme outperforms the
    traditional relative calibration scheme. The proposed analytical
    results are also verified by simulated illustrations.
    Chen Hongzhi, Mi De, Fuentes Manuel, Garro Eduardo, Carcel Jose Luis, Mouhouche Belkacem, Xiao Pei, Tafazolli Rahim On the Performance of PDCCH in LTE and 5G New Radio,Proceedings of the IEEE Global Communications Conference, Abu Dhabi, UAE, 9-13 Dec 2018 (GlobeComm 2018)
    5G New Radio (NR) Release 15 has been specified
    in June 2018. It introduces numerous changes and
    potential improvements for physical layer data transmissions,
    although only point-to-point (PTP) communications are considered.
    In order to use physical data channels such as the
    Physical Downlink Shared Channel (PDSCH), it is essential
    to guarantee a successful transmission of control information
    via the Physical Downlink Control Channel (PDCCH).
    Taking into account these two aspects, in this paper, we
    first analyze the PDCCH processing chain in NR PTP as
    well as in the state-of-the-art Long Term Evolution (LTE)
    point-to-multipoint (PTM) solution, i.e., evolved Multimedia
    Broadcast Multicast Service (eMBMS). Then, via link level
    simulations, we compare the performance of the two technologies,
    observing the Bit/Block Error Rate (BER/BLER) for
    various scenarios. The objective is to identify the performance
    gap brought by physical layer changes in NR PDCCH as
    well as provide insightful guidelines on the control channel
    configuration towards NR PTM scenarios.
    The rapid growth in mobile communications due to the exponential demand for wireless access is causing the distribution and maintenance of cellular networks to become more complex, expensive and time consuming. Lately, extensive research and standardisation work has been focused on the novel paradigm of self-organising network (SON). SON is an automated technology that allows the planning, deployment, operation, optimisation and healing of the network to become faster and easier by reducing the human involvement in network operational tasks, while optimising the network coverage, capacity and quality of service. However, these SON autonomous features cannot be achieved with the current drive test coverage assessment approach due to its lack of automaticity which results in huge delays and cost. Minimization of drive test (MDT) has recently been standardized by 3GPP as a key self- organising network (SON) feature. MDT allows coverage to be estimated at the base station using user equipment (UE) measurement reports with the objective to eliminate the need for drive tests. However, most MDT based coverage estimation methods recently proposed in literature assume that UE position is known at the base station with 100% accuracy, an assumption that does not hold in reality. In this work, we develop a novel and accurate analytical model that allows the quantification of error in MDT based autonomous coverage estimation (ACE) as a function of error in UE as well as base station (user deployed cell) positioning. We first consider a circular cell with an omnidirectional antenna and then we use a three-sectored cell and see how the system is going to be affected by the UE and the base station (user deployed cell) geographical location information errors. Our model also allows characterization of error in ACE as function of standard deviation of shadowing in addition to the path-loss.
    Oh Bong-Hwan, Vural Serdar, Wang Ning, Tafazolli Rahim (2018) Priority-based Flow Control for Dynamic and
    Reliable Flow Management in SDN
    ,
    IEEE Transactions on Network and Service Management IEEE
    Software-Defined Networking (SDN) is a promising
    paradigm of computer networks, offering a programmable and
    centralised network architecture. However, although such a
    technology supports the ability to dynamically handle network
    traffic based on real-time and flexible traffic control, SDN-based
    networks can be vulnerable to dynamic change of flow control
    rules, which causes transmission disruption and packet loss in
    SDN hardware switches. This problem can be critical because the
    interruption and packet loss in SDN switches can bring additional
    performance degradation for SDN-controlled traffic flows in the
    data plane. In this paper, we propose a novel robust flow control
    mechanism referred to as Priority-based Flow Control (PFC)
    for dynamic but disruption-free flow management when it is
    necessary to change flow control rules on the fly. PFC minimizes
    the complexity of flow modification process in SDN switches
    by temporarily adapting the priority of flow rules in order to
    substantially reduce the time spent on control-plane processing
    during run-time. Measurement results show that PFC is able
    to successfully prevent transmission disruption and packet loss
    events caused by traffic path changes, thus offering dynamic and
    lossless traffic control for SDN switches.
    The cognitive interference channel extends the classical two-user interference channel to have unidirectional cooperation at the transmitters. In this model, the cognitive transmitter is assumed to have noncausal knowledge of the other transmitter's current message (primary message). This a priori knowledge is used by the cognitive user to accomplish its two main purposes, i.e., to relay the primary message in order to boost the primary user's data rate and to maximise its own data rate by cancelling the interference at its receiver. The cognitive interference channel is well studied in the literature and capacity results are available for the weak and very strong interference regimes, amongst others. A general solution is still elusive. In this thesis we study the capacity region of cognitive structures that are based in their core on the cognitive interference channel but with the aggregate that an additional node is considered, e.g., an additional receiver node, an additional transmitter node or a relay node.
    The cognitive broadcast interference channel consists of the cognitive interference channel with an additional receiver. The cognitive side serves either one or two receivers and the interference goes from the cognitive transmitter to the primary receiver only. In this model we provide a general achievable rate region when the cognitive side serves two receivers. We analyse the discrete memoryless channel and show that the region simplifies to existing results in the literature when certain assumptions are made. An achievable rate region for the Gaussian channel is also provided for the case where the cognitive side sends common information to both receivers. When the cognitive side serves only one receiver, we provide an achievable rate region and an outer bound and show the gap graphically.
    The cognitive interference channel with a relay consists of the cognitive interference channel with an additional relay node. In this model we show that as in the interference channel with a relay, interference forwarding is also beneficial. We describe analytically achievable rate regions and show the benefits of interference forwarding. We also provide an achievable rate region with generalised interference forwarding, i.e., the relay forwards the intended message and the interference simultaneously, and show that allowing the relay to allocate part of its power to forward interference is beneficial when we are in the strong but not in the very strong interference regime.
    The cognitive interference channel with causal unidirectional destination cooperation is formed by transferring the relaying capabilities of the relay node in the previous model to the cognitive receiver and its operation is causal rather than strictly causal. In this model we show that instantaneous amplify and forward is good enough to achieve the capacity region of the Gaussian channel. We derive analytically an inner and outer bounds and show that they coincide for certain values of the antenna gain at the relay in the very strong interference regime. We also analyse the cognitive interference channel with a relay for the case where the relay operates causally. The capacity region is obtained for a special case of very strong interference.
    The cognitive multiple access interference channel consists of the cognitive interference channel with an additional cognitive transmitter. In this model the interference goes from the primary user to the cognitive receiver only. The cognitive users form a MAC channel. We show for this scenario that dirty paper coding achieves the capacity region in the Gaussian case. In the analysis we make use of encoding techniques first utilised for the MAC with state available noncausally at the encoder.
    With the massive deployment of broadband access to the end-users, the continuous improvement of the hardware capabilities of end devices and better video compression techniques, acceptable conditions have been met to unleash over-the-top bandwidth demanding and time-stringent P2P applications, as multiview real-time media distribution. Such applications enable the transmission of multiple views of the same scene, providing consumers with a more immersive visual experience.

    This thesis proposes an architecture to distribute multiview real-time media content using a hybrid DVB-T2, client-server and P2P paradigms, supported by an also novel QoS solution. The approach minimizes packet delay, inter-ISP traffic and traffic at the ISP core network, which are some of the main drawbacks of P2P networks, whilst still meeting stringent QoS demands. The proposed architecture uses DVB-T2 to distribute a self-contained and fully decodable base-layer video signal, assumed to be always available to the end-user, and an IP network to distribute in parallel - with increased delay - additional IP video streams. The result is a decoded video quality that adapts to individual end-user conditions and maximizes viewing experience.

    To achieve its target goal this architecture: defines new services for the ISP?s services network and new roles for the ISP core, edge and border routers; makes use of pure IP multicast transmission at the ISP?s core network, greatly minimizing bandwidth consumption; constructs a geographically contained P2P network that uses P2P application-level multicast trees to assist the distribution of the IP video streams at the ISP access networks, greatly reducing inter-ISP traffic, and; describes a novel QoS control architecture that takes advantage of the Internet resource over-provisioning techniques to meet stringent QoS demands in a scalable manner.

    The proposed architecture has been implemented in both real testbed implementation and ns-2 simulations. Results have shown a highly scalable P2P overlay construction algorithm with very fast computation of application-level multicast trees (in the order of milliseconds) and efficient reaction to peer-churn, with no perceptually annoying impairments noticed. Furthermore, huge bandwidth savings are achieved at the ISP core network, which considerably lower the management and investment costs in infrastructure. The QoS based results have also shown that the proposed approach effectively deploys a fast and scalable resource and admission control mechanism, greatly minimizing QoS related signalling events by using a per-class over-provisioning approach and thus preventing per-flow QoS reservation signalling messages. Moreover, the QoS control architecture is aware of network link resources in real-time and supports for service differentiation and network convergence by guaranteeing that each admitted traffic flow receives the contracted QoS.

    Finally, the proposed Scalable Architecture for Multiview Real-Time Media Distribution for Next Generation Networks, as a component for a large project demonstrator, has been evaluated by an independent panel of experts following ITU recommendations, obtaining an excellent evaluation as computed by Mean Opinion Score.

    Selinis Ioannis, Katsaros Konstantinos, Allayioti Marion, Vahid Seiamak, Tafazolli Rahim (2018) The Race to 5G Era; LTE and Wi-Fi,IEEE Access 6 pp. 56598-56636 IEEE
    We are on the brink of a new era for the wireless telecommunications, an era that will
    change the way that business is done. The fifth generation (5G) systems will be the first realization in this
    new digital era where various networks will be interconnected forming a unified system. With support
    for higher capacity as well as low-delay and machine-type communication services, the 5G networks
    will significantly improve performance over the current fourth generation (4G) systems and will also
    offer seamless connectivity to numerous devices by integrating different technologies, intelligence, and
    flexibility. In addition to ongoing 5G standardization activities and technologies under consideration in the
    Third Generation Partnership Project (3GPP), the Institute of Electrical and Electronic Engineers (IEEE)
    based technologies operating on unlicensed bands, will also be an integral part of a 5G eco-system. Along
    with the 3GPP-based cellular technology, IEEE standards and technologies are also evolving to keep pace
    with the user demands and new 5G services. In this article, we provide an overview of the evolution of
    the cellular and Wi-Fi standards over the last decade with particular focus on Medium Access Control
    (MAC) and Physical (PHY) layers, and highlight the ongoing activities in both camps driven by the 5G
    requirements and use-cases.
    Chu Zheng, Zhou Fuhui, Xiao Pei, Zhu hengyu, Mi De, Al-Dhahir Naofal, Tafazolli Rahim (2018) Resource Allocation for Secure Wireless Powered Integrated Multicast and Unicast Services with Full Duplex Self-Energy Recycling,IEEE Transactions on Wireless Communications IEEE
    This paper investigates a secure wireless powered
    integrated service system with full duplex self-energy recycling.
    Specifically, an energy-constrained information transmitter (IT),
    powered by a power station (PS) in a wireless fashion, broadcasts
    two types of services to all users: a multicast service intended for
    all users, and a confidential unicast service subscribed to by only
    one user while protecting it from any other unsubscribed users
    and an eavesdropper. Our goal is to jointly design the optimal
    input covariance matrices for the energy beamforming, the multicast
    service, the confidential unicast service, and the artificial
    noises from the PS and the IT, such that the secrecy-multicast
    rate region (SMRR) is maximized subject to the transmit power
    constraints. Due to the non-convexity of the SMRR maximization
    (SMRRM) problem, we employ a semidefinite programmingbased
    two-level approach to solve this problem and find all of
    its Pareto optimal points. In addition, we extend the SMRRM
    problem to the imperfect channel state information case where
    a worst-case SMRRM formulation is investigated. Moreover, we
    exploit the optimized transmission strategies for the confidential
    service and energy transfer by analyzing their own rank-one
    profile. Finally, numerical results are provided to validate our
    proposed schemes.
    Web-based content is a dominant application type in mobile network but accessing such content suffers from poor downloading latency. In modern mobile networks, accelerating web content downloading faces three distinctive challenges. First the web contents enter a rich-media era, with an explosion of the content size and an evolution of content structure which not only requires increased network resources but also incurs noticeable computation latency. Second the unavoidable network uncertainties like RTT variation and random loss aggravate such degraded downloading time, although the network has already offered augmented resources like high bandwidth, low packet loss and latency. Third, the newly standardised protocols like HTTP 2.0 and QUIC are expected to provide an optimised resource utilisation, but existing understanding of such protocols when applying on web content is still superficial. By realising these intertwined technical aspects, we examined three web downloading scenarios, figured out how these aspects qualitatively affect downloading time and then proposed optimisation intelligence accordingly. First, we focused on the fixed single connection number of HTTP 2.0 which cannot be adaptive for various content size and network conditions. By clarifying the numerical relationship between content size, network condition and connection number, we proposed a context-aware mobile edge
    hint framework. In this framework, a mobile edge hint server offline collects the meta-data of popular webpages as well as the network condition and performs online hints of such information upon receiving the user request. Then the user can execute a novel algorithm to select an optimal connection number by understanding the specific network condition and content characteristics
    through the edge hint. Both numerical and test-bed based results validate that this framework
    can bring a noticeable acceleration of webpage downloading. Second, we turned our attention to
    the computation latency which is caused by the unavoidable computation task during webpage
    downloading. We seek for a transport layer approach since pure application layer approaches are
    recognised to have practicality and security limitation. To this end, a non-URL based mobile
    edge computing framework is proposed to serve a novel transport layer IW selection algorithm at
    the client side. This framework is validated to have remarkable performance improvement when
    computation latency occupies less than 50% of total downloading time. Third, we investigated
    QUIC's performance on web content, especially in the presence of network uncertainties. The
    evaluation results carried out on real mobile networks reveal that the different congestion control
    algorithms plugged in QUIC can lead to distinctive shortages under network fluctuations.
    Then we proposed a mQUIC scheme which performs a customised state and congestion window
    synchronisation algorithm based on multiple coordinated connections. We conducted extensive
    evaluations of mQUIC and the results substantiated faster and robust downloading time can be
    achieved by mQUIC when compared to plain QUIC enable contents.
    Araghi Ali, Khalily Mohsen, Ghannad Amirhossein Alizadeh, Xiao Pei, Tafazolli Rahim (2019) Compact Dual Band Antenna for Off-Body-Centric Communications,Proceedings of the 13th European Conference on Antennas and Propagation (EuCAP 2019) European Association on Antennas and Propagation
    A compact size, dual-band wearable antenna for
    off-body communication operating at the both 2.45 and 5.8
    GHz industrial, scientific, and medical (ISM) band is
    presented. The antenna is a printed monopole on an FR4
    substrate with a modified loaded ground plane to make the
    antenna profile compact. Antennas? radiation characteristics
    have been optimized while the proposed antenna placed close
    to the human forearm. The fabricated antenna operating on
    the forearm has been measured to verify the simulation results.
    Li Ang, Ma Yi, Xue Songyan, Tafazolli Rahim, Dodgson Terence E (2019) Unsupervised Deep Learning for Blind Multiuser Frequency Synchronization in OFDMA Uplink,IEEE Communications Society IEEE Communications Society
    In this paper, a novel unsupervised deep learning
    approach is proposed to tackle the multiuser frequency synchronization
    problem inherent in orthogonal frequency-division
    multiple-access (OFDMA) uplink communications. The key idea
    lies in the use of the feed-forward deep neural network (FF-DNN)
    for multiuser interference (MUI) cancellation taking advantage
    of their strong classification capability. Basically, the proposed
    FF-DNN consists of two essential functional layers. One is
    called carrier-frequency-offsets (CFOs) classification layer that
    is responsible for identifying the users? CFO range, and another
    is called MUI-cancellation layer responsible for joint multiuser
    detection (MUD) and frequency synchronization. By such means,
    the proposed FF-DNN approach showcases remarkable MUIcancellation
    performances without the need of multiuser CFO
    estimation. In addition, we also exhibit an interesting phenomenon
    occurred at the CFO-classification stage, where the
    CFO-classification performance get improved exponentially with
    the increase of the number of users. This is called multiuser
    diversity gain in the CFO-classification stage, which is carefully
    studied in this paper.
    Xue Songyan, Ma Yi, Li Ang, Yi Na, Tafazolli Rahim (2019) On Unsupervised Deep Learning Solutions for Coherent MU-SIMO Detection in Fading Channels,IEEE Communications Society IEEE Communications Society
    In this paper, unsupervised deep learning solutions
    for multiuser single-input multiple-output (MU-SIMO) coherent
    detection are extensively investigated. According to the ways
    of utilizing the channel state information at the receiver side
    (CSIR), deep learning solutions are divided into two groups.
    One group is called equalization and learning, which utilizes the
    CSIR for channel equalization and then employ deep learning for
    multiuser detection (MUD). The other is called direct learning,
    which directly feeds the CSIR, together with the received signal,
    into deep neural networks (DNN) to conduct the MUD. It is found
    that the direct learning solutions outperform the equalizationand-
    learning solutions due to their better exploitation of the
    sequence detection gain. On the other hand, the direct learning
    solutions are not scalable to the size of SIMO networks, as
    current DNN architectures cannot efficiently handle many cochannel
    interferences. Motivated by this observation, we propose
    a novel direct learning approach, which can combine the merits
    of feedforward DNN and parallel interference cancellation. It is
    shown that the proposed approach trades off the complexity for
    the learning scalability, and the complexity can be managed due
    to the parallel network architecture.
    Kuzminskiy Alexandr M., Xiao Pei, Tafazolli Rahim (2019) Spectrum Sharing with Decentralized Occupation Control in Rule Regulated Networks,IEEE Transactions on Cognitive Communications and Networking (99) Institute of Electrical and Electronics Engineers (IEEE)
    Decentralized dynamic spectrum allocation (DSA) that exploits adaptive antenna array interference mitigation diversity at the receiver, is studied for interference-limited environments with high level of frequency reuse. The system consists of base stations (BSs) that can optimize uplink frequency allocation to their user equipments (UEs) to minimize impact of interference on the useful signal, assuming no control over resource allocation of other BSs sharing the same bands. To this end?, good neighbor? (GN) rules allow effective trade-off between the equilibrium and transient decentralized DSA behavior if the performance targets are adequate to the interference scenario. In this paper, we 1) extend the GN rules by including a spectrum occupation control that allows adaptive selection of the performance targets; 2) derive estimates of absorbing state statistics that allow formulation of applicability areas for different DSA algorithms; 3) define a semi-analytic absorbing Markov chain model and study convergence probabilities and rates of DSA with occupation control including networks with possible partial breaks of the GN rules. For higher-dimension networks, we develop simplified search GN algorithms with occupation and power control and demonstrate their efficiency by means of simulations.
    Wen Yun, Yoshida Makoto, Zhang Junqing, Chu Zheng, Xiao Pei, Tafazolli Rahim (2019) Machine Learning Based Attack Against Artificial Noise-aided Secure Communication,Proceedings of the 2019 IEEE International Conference on Communications (ICC): Communication and Information Systems Security Symposium (IEEE ICC 2019 - CISS Symposium) Institute of Electrical and Electronics Engineers (IEEE)
    Physical layer security (PLS) technologies have attracted
    much attention in recent years for their potential to
    provide information-theoretically secure communications. Artificial
    Noise (AN)-aided transmission is considered as one of
    the most practicable PLS technologies, as it can realize secure
    transmission independent of the eavesdropper?s channel status.
    In this paper, we reveal that AN transmission has the dependency
    of eavesdropper?s channel condition by introducing our proposed
    attack method based on a supervised-learning algorithm which
    utilizes the modulation scheme, available from known packet
    preamble and/or header information, as supervisory signals of
    training data. Numerical simulation results with the comparison
    to conventional clustering methods show that our proposed
    method improves the success probability of attack from 4.8%
    to at most 95.8% for the QPSK modulation. It implies that
    the transmission to the receiver in the cell-edge with low order
    modulation will be cracked if the eavesdropper?s channel is good
    enough by employing more antennas than the transmitter. This
    work brings new insights into the effectiveness of AN schemes and
    provides useful guidance for the design of robust PLS techniques
    for practical wireless systems.
    Hao Wanming, Chu Zheng, Zhou Fuhui, Xiao Pei, Leung Victor C. M., Tafazolli Rahim (2019) Hybrid Precoding Design for SWIPT Joint Multicast-Unicast mmWave System with Subarray Structure,IEEE ICC Conference Proceedings
    In this paper, we investigate the hybrid precoding
    design for joint multicast-unicast millimeter wave (mmWave) system, where the simultaneous wireless information and power transform is considered at receivers. The subarray-based sparse radio frequency chain structure is considered at base station (BS).
    Then, we formulate a joint hybrid analog/digital precoding and power splitting ratio optimization problem to maximize the energy efficiency of the system, while the maximum transmit power at BS and minimum harvested energy at receivers are considered. Due to the difficulty in solving the formulated problem, we first design the codebook-based analog precoding approach and then, we only need to jointly optimize the digital precoding and power splitting ratio. Next, we equivalently transform the fractional objective function of the optimization problem into a subtractive form one and propose a two-loop iterative algorithm to solve it. For the outer loop, the classic Bi-section iterative algorithm is applied.
    For the inner loop, we transform the formulated problem into a convex one by successive convex approximation techniques, which is solved by a proposed iterative algorithm. Finally, simulation results are provided to show the performance of the proposed algorithm.
    Hao Wanming, Zhou Fuhui, Chu Zheng, Xiao Pei, Tafazolli Rahim, Al Dhahir Naofal (2019) Beam Alignment for MIMO-NOMA Millimeter Wave Communication Systems,IEEE International Conference on Communications (ICC) Conference Proceedings
    Abstract?Millimeter wave (mmWave) communication is a
    promising technology in future wireless networks because of its wide bandwidths that can achieve high data rates. However, high beam directionality at the transceiver is needed due to the large path loss at mmWave. Therefore, in this paper, we investigate the beam alignment and power allocation problem in a nonorthogonal multiple access (NOMA) mmWave system. Diýerent from the traditional beam alignment problem, we consider the NOMA scheme during the beam alignment phase when two users
    are at the same or close angle direction from the base station. Next, we formulate an optimization problem of joint beamwidth selection and power allocation to maximize the sum rate, where the quality of service (QoS) of the users and total power constraints are imposed. Since it is diýcult to directly solve the formulated
    problem, we start by fixing the beamwidth. Next, we transform the power allocation optimization problem into a convex one, and a closed-form solution is derived. In addition, a one-dimensional search algorithm is used to find the optimal beamwidth. Finally, simulation results are conducted to compare the performance of the proposed NOMA-based beam alignment and power allocation scheme with that of the conventional OMA scheme.
    In visible light communication systems, the intensity modulation/direct
    detection channel inherently restricts the transmitted signal to be unipolar
    (nonnegative only) and incoherent. Those restrictions limit the types of
    transceivers that can be used in visible light communication systems; indeed,
    the intensity modulation/direct detection transceivers can be readily
    utilized, whereas classic radio frequency methods (e.g., schemes such as
    pulse amplitude modulation, quadrature amplitude modulation and orthogonal
    frequency division multiplexing) require adjustments that reduce their
    conventional efficiency. A continuous effort has been made to adapt radio
    frequency transceiver techniques to visible light communication; however, up
    to date, the proposed solutions came at the expense of the energy efficiency
    of the systems. In turn, it severely affects the bit error rate performance
    of the system. In light of this, the topic of this thesis is to design energy
    efficient transmission schemes to expand the set of legacy radio frequency
    modulation methods that can be efficiently used in visible light communication
    systems. Thus, the first contribution of this dissertation is a unipolar
    transmission technique that allows conveying bipolar symbols through the
    intensity modulation/direct detection channel without severely consuming
    the amount of transmit power. The second contribution is proposing a
    new technique to simultaneously transmit the two parts of two-dimensional
    signals over the intensity modulation/direct detection channel. The schemes
    are proposed with the objective of minimizing the transmitted power and
    reducing the direct current component of two-dimensional transmit signals
    by relying on multi-waveform transmission techniques, and, in turn,
    providing a high-energy efficient transmission scheme for two-dimensional
    signals. The third contribution is a low complex multi-input multi-output
    system capable of transmitting unipolar two-dimensional signals. Finally,
    the error rate expressions of our proposed transceivers in this work are
    derived, and the performance gains of the proposed schemes are evaluated
    through Monte-Carlo simulations. The findings show that our schemes
    could enhance the energy efficiency of the existing transmission techniques
    in visible light communication systems.
    Alizadeh Ghannad Amir, Khalily Mohsen, Xiao Pei, Tafazolli Rahim, Kishk Ahmed A. (2019) Enhanced Matching and Vialess Decoupling of Nearby Patch Antennas for MIMO System,IEEE Antennas and Wireless Propagation Letters pp. 1-1 Institute of Electrical and Electronics Engineers (IEEE)
    Simultaneous improvement of matching and isolation for a modified two-element microstrip patch antenna array is proposed. Two simple patch antennas in a linear array structure are designed, whereas, the impedance matching and isolation are improved without using any conventional matching networks. The presented low profile multifunctional via-less structure comprises of only two narrow T-shaped stubs connected to feed lines, a narrow rectangular stub between them, and a narrow rectangular slot on the ground plane. This design provides a simple, compact structure with low mutual coupling, low cost and no adverse effects on the radiation and resonance. To validate the design, a compact very-closely-spaced antenna array prototype is fabricated at 5.5 GHz which is suitable for multiple-input-multiple-output (MIMO) systems. The measured and simulated results are in good agreement with a 16 dB, and 40 dB of improvements in the matching and isolation, respectively.
    Ghorbani Mehdi, Khalily Mohsen, Xiao Pei, Tafazolli Rahim (2019) A Wideband High Flat Gain Waveguide-Fed Aperture Antenna Using Superstrate and Shield,IEEE Xplore Digital Library IEEE
    In this paper, a high flat gain waveguide-fed aperture antenna has been proposed. For this purpose, two layers of FR4 dielectric as superstrates have been located in front of the aperture to enhance the bandwidth and the gain of the antenna. Moreover, a conductive shield, which is connected to the edges of the ground plane and surrounding aperture and superstrates, applied to the proposed structure to improve its radiation characteristics. The proposed antenna has been simulated with HFSS and optimized with parametric study and the following results have been obtained. The maximum gain of 13.0 dBi and 0.5-dBi gain bandwidth of 25.9 % (8.96 ? 11.63 GHz) has been achieved. The 3-dBi gain bandwidth of the proposed antenna is 40.7% (8.07-12.20 GHz), which has a suitable reflection coefficient (d-10dBi) in whole bandwidth. This antenna comprises a compact size of (1.5»×1.5»), easy structure and low-cost fabrication.
    Ghorbani Mehdi, Khalily Mohsen, Ghorbaninejad Habib, Xiao Pei, Tafazolli Rahim (2019) Bandwidth Enhancement and Radiation Characteristics Improvement of Triangular Dielectric Resonator Antenna,Proceedings of The 2019 International Symposium on Networks, Computers and Communications (ISNCC'19) Institute of Electrical and Electronics Engineers (IEEE)
    In this paper, an ultra-wideband, Dielectric
    Resonator Antenna (DRA) has been proposed. The proposed
    antenna is based on isosceles triangular DRA (TDRA), which is
    fed from the base side using a 50© probe. For bandwidth
    enhancement and radiation characteristics improvement, a
    partially cylindrical-shape hole is etched from its base side
    which approached probe feed to the center of TDRA. The
    dielectric resonator (DR) is located over an extended conducting
    ground plane. This technique has significantly enhanced
    antennas bandwidth from 48.8% to 80% (5.29-12.35 GHz),
    while the biggest problem was radiation characteristics. The
    basis antenna possesses negative gain in a wide range of
    bandwidth from 7.5 GHz to 10.5 GHz down to -13.8 dBi. Using
    this technique improve antenna gain over 1.6 dBi for whole
    bandwidth, while peak gain is 7.2 dBi.
    Hao Wanming, Sun Gangcan, Chu Zheng, Xiao Pei, Zhu Zhengyu, Yang Shouyi, Tafazolli Rahim (2019) Beamforming Design in SWIPT-Based Joint Multicast-Unicast mmWave Massive MIMO with Lens-Antenna Array,IEEE Wireless Communications Letters pp. 1-1 Institute of Electrical and Electronics Engineers (IEEE)
    In this letter, we study the beamforming design in a lens-antenna array-based joint multicast-unicast millimeter wave massive MIMO system, where the simultaneous wireless information and power transfer at users is considered. First, we develop a beam selection scheme based on the structure of the lens-antenna array and then, the zero forcing precoding is adopted to cancel the inter-unicast interference among users. Next, we formulate a sum rate maximization problem by jointly optimizing the unicast power, multicast beamforming and power splitting ratio. Meanwhile, the maximum transmit power constraint for the base station and the minimum harvested energy for each user are imposed. By employing the successive convex approximation technique, we transform the original optimization problem into a convex one, and propose an iterative algorithm to solve it. Finally, simulation results are conducted to verify the effectiveness of the proposed schemes.
    Wang Jinfei, Ma Yi, Xue Songyan, Yi Na, Tafazolli Rahim, Dodgson Terence E. (2019) Parallel Decoding for Non-recursive Convolutional Codes and Its Enhancement Through Artificial Neural Networks,Proceedings of the 20th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2019) Institute of Electrical and Electronics Engineers (IEEE)
    This paper presents a parallel computing approach
    that is employed to reconstruct original information bits from
    a non-recursive convolutional codeword in noise, with the goal
    of reducing the decoding latency without compromising the
    performance. This goal is achieved by means of cutting a
    received codeword into a number of sub-codewords (SCWs)
    and feeding them into a two-stage decoder. At the first stage,
    SCWs are decoded in parallel using the Viterbi algorithm or
    equivalently the brute force algorithm. Major challenge arises
    when determining the initial state of the trellis diagram for each
    SCW, which is uncertain except for the first one; and such results
    in multiple decoding outcomes for every SCW. To eliminate or
    more precisely exploit the uncertainty, an Euclidean-distance
    minimization algorithm is employed to merge neighboring SCWs;
    and this is called the merging stage, which can also run in
    parallel. Our work reveals that the proposed two-stage decoder
    is optimal and has its latency growing logarithmically, instead
    of linearly as for the Viterbi algorithm, with respect to the
    codeword length. Moreover, it is shown that the decoding latency
    can be further reduced by employing artificial neural networks
    for the SCW decoding. Computer simulations are conducted
    for two typical convolutional codes, and the results confirm our
    theoretical analysis.
    Khalily Mohsen, Brown Tim W. C., Tafazolli Rahim (2019) Machine Learning Based Approach for Diffraction Loss Variation Prediction by the Human Body,IEEE Antennas and Wireless Propagation Letters Institute of Electrical and Electronics Engineers (IEEE)
    This paper presents a machine learning (ML) based
    model to predict the diffraction loss around the human body.
    Practically, it is not reasonable to measure the diffraction loss
    changes for all possible body rotation angles, builds and line
    of sight (LoS) elevation angles. A diffraction loss variation
    prediction model based on a non-parametric learning technique
    called Gaussian process (GP) is introduced. Analysed results state
    that 86% correlation and normalised mean square error (NMSE)
    of 0.3 on the test data is achieved using only 40% of measured
    data. This allows a 60% reduction in required measurements in
    order to achieve a well-fitted ML loss prediction model. It also
    confirms the model generalizability for non-measured rotation
    angles.
    Grau Maxime, Foh Chuan Heng, ul Quddus Atta, Tafazolli Rahim (2019) Preamble Barring: A Novel Random Access Scheme for Machine Type Communications with Unpredictable Traffic Bursts,Proceedings of the 2019 IEEE 90th Vehicular Technology Conference (VTC2019-Fall) Institute of Electrical and Electronics Engineers (IEEE)
    In this paper, we present a novel random access
    method for future mobile cellular networks that support machine
    type communications. Traditionally, such networks establish
    connections with the devices using a random access procedure,
    however massive machine type communication poses several
    challenges to the design of random access for current systems.
    State-of-the-art random access techniques rely on predicting
    the traffic load to adjust the number of users allowed to
    attempt the random access preamble phase, however this delays
    network access and is highly dependent on the accuracy of
    traffic prediction and fast signalling. We change this paradigm by
    using the preamble phase to estimate traffic and then adapt the
    network resources to the estimated load. We introduce Preamble
    Barring that uses a probabilistic resource separation to allow
    load estimation in a wide range of load conditions and combine
    it with multiple random access responses. This results in a
    load adaptive method that can deliver near-optimal performance
    under any load condition without the need for traffic prediction
    or signalling, making it a promising solution to avoid network
    congestion and achieve fast uplink access for massive MTC.
    Hassanpour Asheghabadi Masoud (2019) Pattern profiling of users' behaviour.,

    Owing to growth in the popularity of mobile phones, solutions for more efficient mobile network resource management have been increasingly demanded by network operators. Predicting the future state of the network and allocating the network resources based on the predicted state has been proposed as an effective method for efficient management of the network resources by the research community. One of the major factors that changes the future state of network is changes in the behavior of users. As the result, to forecast the future state of network, a major task is to predict the future behaviors of users. This task is accomplished by User Behavior Prediction Models (UBPrMs). In order to maintain the quality of the service, such methods are expected to provide sufficiently accurate prediction. However, the existing methods often are not able to meet this performance requirement.

    The accuracy of a predictive model is affected by two distinct sources of error, namely Modeling Error (ME) and Sampling Error (SaE). As the result, one ought to consider both sources of error while improving the performance of a model. To do this, this thesis aims to study and alleviate the impact of the mentioned sources of error on the performance of a UBPrM.

    To treat the ME, we propose a novel group-level user behaviors prediction framework as a more accurate alternative for population-level user behaviors prediction models and a more computationally efficient alternative for individual-level user behaviors prediction. The novel framework is called Event Profiling Method (EPM). To diminish the impact of ME, the proposed event-based method takes advantage of similarities amongst users' behavior and the existing underlying patterns that repetitively occur in the network.

    To evaluate the proposed framework, EPM method needs to be implemented in real-world scenarios. Video popularity prediction is considered as a suitable use case for EPM. For this purpose, this thesis utilizes the ideas of EPM framework to propose a novel approach for enhancing the video popularity prediction models. Using the proposed approach, we enhance three popularity prediction techniques that outperform the accuracy of the prior state-of-the-art solutions. The major components of the proposed approach are three novel mechanisms for "user grouping", "content classification" and "dominant-follower users identification". The user grouping method is an unsupervised clustering approach that divides the users into an adequate number of user groups with similar interests. The content classification approach identifies the classes of videos with similar early popularity trends. The dominant-follower identification technique divides the users in each group into two distinct subgroups based on their reaction time to the released videos. To predict the popularity of the newly-released videos, our proposed popularity prediction model trains its parameters in each user group and its associated video popularity classes and user subgroups. Evaluations are performed through a 5-fold cross validation and on a dataset containing one month video request records of 26,706 number of BBC iPlayer users. Our analysis shows that the accuracy of the proposed solution outperforms the state-of-the-art including S-H, ML, MRBF models on average by 59%, 27% and 21%, respectively.

    Afterwards, this thesis proposes a novel combination technique for multi-dimensional user profiles that is able to treat the SaE. In doing so, the proposed technique considers the samples of other users' behavior (or in general, other items) as a biased approximation of each user (or an item). The method utilizes two conditions on the magnitude and sign of the estimated bias between two users to decide on combining their profiles or not. The proposed technique is evaluated against synthesized and real-world datasets. Our results show that the proposed method provides better estimations of the st

    Chu Zheng, Yu Wenjuan, Xiao Pei, Zhou Fuhui, Al-Dhahir Naofal, ul Quddus Atta, Tafazolli Rahim (2019) Opportunistic Spectrum Sharing for D2D-Based URLLC,IEEE Transactions on Vehicular Technology pp. 1-1 Institute of Electrical and Electronics Engineers (IEEE)
    A device-to-device (D2D) ultra reliable low latency communications (URLLC) network is investigated in this paper. Specifically, a D2D transmitter opportunistically accesses the radio resource provided by a cellular network and directly transmits short packets to its destination. A novel performance metric is adopted for finite block-length code. We quantify the maximum achievable rate for the D2D network, subject to a probabilistic interference power constraint based on imperfect channel state information (CSI). First, we perform a convexity analysis which reveals that the finite block-length rate for the D2D pair in short-packet transmission is not always concave. To address this issue, we propose two effective resource allocation schemes using the successive convex approximation (SCA)-based iterative algorithm. To gain more insights, we exploit the mono- tonicity of the average finite block-length rate. By capitalizing on this property, an optimal power control policy is proposed, followed by closed-form expressions and approximations for the optimal average power and the maximum achievable average rate in the finite block-length regime. Numerical results are provided to confirm the effectiveness of the proposed resource allocation schemes and validate the accuracy of the derived theoretical results.
    Selinis Ioannis, Katsaros Konstantinos, Vahid Seiamak, Tafazolli Rahim (2018) Control OBSS/PD Sensitivity Threshold for IEEE 802.11ax BSS Color,Proceedings of the 2018 IEEE 29th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC 2018) pp. 1-7 Institute of Electrical and Electronics Engineers (IEEE)
    IEEE 802.11ax Spatial Reuse (SR) is a new category in the IEEE 802.11 family, aiming at improving the spectrum efficiency and the network performance in dense deployments. The main and perhaps the only SR technique in that amendment is the Basic Service Set (BSS) Color. It aims at increasing the number of concurrent transmissions in a specific area, based on a newly defined Overlapping BSS/Preamble-Detection (OBSS/PD) threshold and the Received Signal Strength Indication (RSSI) from Overlapping BSSs (OBSSs). In this paper, we propose a Control OBSS/PD Sensitivity Threshold (COST) algorithm for adjusting OBSS/PD threshold based on the interference level and RSSI from the associated recipient(s). In contrast to the Dynamic Sensitivity Control (DSC) algorithm that was proposed for setting OBSS/PD, COST is fully aware of any changes in OBSSs and can be applied to any IEEE 802.11ax node. Simulation results in various scenarios, show a clear performance improvement of up to 57% gain in throughput over a conservative fixed OBSS/PD for the legacy BSS Color and DSC.
    Selinis Ioannis, Katsaros Konstantinos, Vahid Seiamak, Tafazolli Rahim (2017) Exploiting the Capture Effect on DSC and BSS Color in Dense IEEE 802.11ax Deployments,Proceedings of the 2017 Workshop on ns-3, Porto, Portugal, June 2017 (WNS3 2017) pp. 47-54 Association for Computing Machinery (ACM)
    Future wireless local area networks (WLANs) are expected to serve thousands of users in diverse environments. To address the new challenges that WLANs will face, and to overcome the limitations that previous IEEE standards introduced, a new IEEE 802.11 amendment is under development. IEEE 802.11ax aims to enhance spectrum efficiency in a dense deployment; hence system throughput improves. Dynamic Sensitivity Control (DSC) and BSS Color are the main schemes under consideration in IEEE 802.11ax for improving spectrum efficiency In this paper, we evaluate DSC and BSS Color schemes when physical layer capture (PLC) is modelled. PLC refers to the case that a receiver successfully decodes the stronger frame when collision occurs. It is shown, that PLC could potentially lead to fairness issues and higher throughput in specific cases. We study PLC in a small and large scale scenario, and show that PLC could also improve fairness in specific scenarios.
    Selinis Ioannis, Katsaros Konstantinos, Vahid Seiamak, Tafazolli Rahim (2019) Eliminating the Use of IEEE 802.11 Acknowledgements; A Network Coding Approach,Proceedings of the 2019 IEEE Wireless Communications and Networking Conference (WCNC 2019) Institute of Electrical and Electronics Engineers (IEEE)
    Selinis Ioannis, Katsaros Konstantinos, Vahid Seiamak, Tafazolli Rahim (2019) Damysus: A Practical IEEE 802.11ax BSS Color Aware Rate Control Algorithm,International Journal of Wireless Information Networks pp. 1-23 Springer Verlag
    Institute of Electrical and Electronics Engineers (IEEE) 802.11ax Spatial Reuse (SR) is a new feature in the IEEE 802.11 family, aiming at improving the spectrum efficiency and the network performance in dense deployments. The main and perhaps the only SR technique in that amendment is the Basic Service Set (BSS) Color. It aims at increasing the number of concurrent transmissions in a specific area, based on a newly defined Overlapping BSS/Preamble-Detection threshold. In this paper, we overview the latest developments introduced in the IEEE 802.11ax for the SR and propose a rate control algorithm developed to exploit the BSS Color scheme. Our proposed algorithm, Damysus is specifically designed to function in dense environments where other off-the-shelf algorithms show poor performance. Simulation results in various dense scenarios, show a clear performance improvement of up to 113% gain in throughput over the well known MinstrelHT algorithm.
    Selinis Ioannis, Filo Marcin, Vahid Seiamak, Rodriguez Jonathan, Tafazolli Rahim (2017) Evaluation of the DSC algorithm and the BSS color scheme in dense cellular-like IEEE 802.11ax deployments,Proceedings of the 2016 IEEE 27th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC 2016) pp. 1641-1647 Institute of Electrical and Electronics Engineers (IEEE)
    Coping with the extreme growth of the number of users is one of the main challenges for the future IEEE 802.11 networks. The high interference level, along with the conventional standardized carrier sensing approaches, will degrade the network performance. To tackle these challenges, the Dynamic Sensitivity Control (DSC) and the BSS Color scheme are considered in IEEE 802.11ax and IEEE 802.11ah, respectively. The main purpose of these schemes is to enhance the network throughput and improve the spectrum efficiency in dense networks. In this paper, we evaluate the DSC and the BSS Color scheme along with the PARTIAL-AID (PAID) feature introduced in IEEE 802.11ac, in terms of throughput and fairness. We also, exploit the performance when the aforementioned techniques are combined. The simulations show a significant gain in total throughput when these techniques are applied.
    Mulvey David, Foh Chuan Heng, Imran Muhammad Ali, Tafazolli Rahim (2019) Cell Fault Management Using Machine Learning Techniques,IEEE Access 7 pp. 124514-124539 Institute of Electrical and Electronics Engineers (IEEE)
    This paper surveys the literature relating to the application of machine learning to fault management in cellular networks from an operational perspective. We summarise the main issues as 5G networks evolve, and their implications for fault management. We describe the relevant machine learning techniques through to deep learning, and survey the progress which has been made in their application, based on the building blocks of a typical fault management system. We review recent work to develop the abilities of deep learning systems to explain and justify their recommendations to network operators. We discuss forthcoming changes in network architecture which are likely to impact fault management and offer a vision of how fault management systems can exploit deep learning in the future. We identify a series of research topics for further study in order to achieve this.
    Chen G, Liang D, Ghoraishi M, Xiao Pei, Tafazolli Rahim (2015) Optimum User Selection for Hybrid-Duplex Device-to-Device in Cellular Networks,2015 International Symposium on Wireless Communication Systems (ISWCS) Proceedings pp. 16-20
    This paper studies the optimum user selection scheme in a hybrid-duplex device-to-device (D2D) cellular networks. We derive an analytical integral-form expression of the cumulative distribution function (CDF) for the received signal-to-noise-plus-interference-ratio (SINK) at the D2D node, based on which the closed-form of the outage probability is obtained. Analysis shows that the proposed user selection scheme achieves the best SINK at the D2D node with interference to base station being limited by a pre-defined level. Hybrid duplex D2D can be switched between half and full duplex according to different residual self-interference to enhance the throughput of D2D pair. Simulation results are presented to validate the analysis.
    Razavi R, Xiao Pei, Tafazolli Rahim (2015) Information Theoretic Analysis of OFDM/OQAM with Utilized Intrinsic Interference,IEEE Signal Processing Letters 22 (5) pp. 618-622 Institute of Electrical and Electronics Engineers
    In this paper, the capacity of OFDM/OQAM with isotropic orthogonal transfer algorithm (IOTA) pulse shaping is evaluated through information theoretic analysis. In the conventional OFDM systems the insertion of a cyclic prefix (CP) decreases the system?s spectral efficiency. As an alternative to OFDM, filter bank based multicarrier systems adopt proper pulse shaping with good time and frequency localisation properties to avoid interference and maintain orthogonality in real field among sub-carriers without the use of CP. We evaluate the spectral
    efficiency of OFDM/OQAM systems with IOTA pulse shaping in comparison with conventional OFDM/QAM systems, and our analytical model is further extended in order to gain insights into the effect of utilizing the intrinsic interference on the performance of our system. Furthermore, the spectral efficiency of OFDM/OQAM systems is analyzed when the effect of inter-symbol and inter-carrier interference is considered.
    Cao Aijun, Gao Y, Xiao Pei, Tafazolli Rahim (2015) Performance Analysis of an Ultra Dense Network with and without Cell Cooperation,2015 12th International Symposium on Wireless Communication Systems (ISWCS) Procedings pp. 51-55 IEEE
    This paper presents an analysis on performance of an ultra dense network (UDN) with and without cell cooperation from the perspective of network information theory. We propose a UDN performance metric called Total Average Geometry Throughput which is independent from the user distribution or scheduler etc. This performance metric is analyzed in detail for UDN with and without cooperation. The numerical results from the analysis show that under the studied system model, the total average geometry throughput reaches its maximum when the inter-cell distance is around 6 ~ 8 meters, both without and with cell cooperation. Cell cooperation can significantly reduce inter-cell interference but not remove it completely. With cell cooperation and an optimum number of the cooperating cells the maximum performance gain can be achieved. Furthermore, the results also imply that there is an optimum aggregate transmission power if considering the energy cost per bit.
    Cao Aijun, Xiao Pei, Tafazolli Rahim (2014) Frequency Offset Estimation Based on PRACH Preambles in LTE,The Eleventh International Symposium on Wireless Communication Systems, ISWCS'2014 Proceedings pp. 27-32 IEEE
    This paper presents a novel method to estimate the frequency offset between a mobile phone and the infrastructure when the mobile phone initially attaches to the LTE network. The proposed scheme is based on PRACH (Physical Random Access Channel) preambles and can significantly reduce the complexity of preamble detection at the eNodeB side.
    Hassanpour Asheghabadi Masoud, Hoseinitabatabaei Seyed, Barnaghi Payam, Tafazolli Rahim (2020) Improving the Accuracy of the Video Popularity Prediction Models through User Grouping and Video Popularity Classification,ACM Transactions on the Web 14 (1) 4 Association for Computing Machinery (ACM)
    This paper proposes a novel approach for enhancing the video popularity prediction models. Using the
    proposed approach, we enhance three popularity prediction techniques that outperform the accuracy of the
    prior state-of-the-art solutions. The major components of the proposed approach are two novel mechanisms for
    "user grouping" and "content classification". The user grouping method is an unsupervised clustering approach
    that divides the users into an adequate number of user groups with similar interests. The content classification
    approach identifies the classes of videos with similar popularity growth trends. To predict the popularity of
    the newly-released videos, our proposed popularity prediction model trains its parameters in each user group
    and its associated video popularity classes. Evaluations are performed through a 5-fold cross validation and
    on a dataset containing one month video request records of 26,706 number of BBC iPlayer users. Using the
    proposed grouping technique, user groups of similar interest and up to 2 video popularity classes for each
    user group were detected. Our analysis shows that the accuracy of the proposed solution outperforms the
    state-of-the-art including SH, ML, MRBF models on average by 45%, 33% and 24%, respectively. Finally, we
    discuss how various systems in the network and service management domain such as cache deployment,
    advertising and video broadcasting technologies benefit from our findings to illustrate the implications.
    The concept of Ultra Dense Networks (UDNs) is often seen as a key enabler of the next generation mobile networks. In contrast to the traditional cellular networks, it is foreseen that the UDNs will be in many cases installed without traditional RF planning and proper site selection. One of the main characteristics (and at the same time challenge) of the UDNs is therefore excessive inter-cell interference. Additionally, small cells as one of the main components on UDNs are foreseen to operate in licensed as well as license-exempt frequency bands, and therefore inter-system and inter-tier interference become major concerns.

    Widely used and well established systems such as LTE, or WiFi are often proposed by the industry and academia to be reused in the context of UDNs. However, as these systems were not designed to deal with problems caused by the UDN deployment, a significant effort is currently being undertaken to adapt them and enable their operation in dense and ultra-dense environments. Despite this tremendous effort, due to the need for backward compatibility, the proposed updates and patches usually provide sub-optimal gains and often lead to significant signaling overheads.

    In this thesis we highlight some of the main challenges and requirements related to UDNs and then provide an extensive review of state-of-art UDN performance analysis and approaches to medium access control (MAC) design for UDNs. Then we investigate performance limits of regular and irregural UDNs. More specifically, we examine the impact of the relative antenna height between BS and UE antennas on the performance of UDNs. Based on our study, we found that regular networks share many of the same performance behaviour as irregular network. In partivular, we showed that by decreasing the relative antenna heights across the network we can counter the decay of per cell average achievable rate. We explicitly derived the relationship between BS density and relative antenna height and confirmed that both regular and irregular networks share this property. Despite the pessimistic conclusion related to the per cell performance found in the literature, in this work we also show that area spectral efficiency does not necessarily decay to zero as BS density approaches infinity. In terms of the benefit of proper BS site selection, we compare the average per cell rate of regular networks and that of the irregular networks, and we find that proper BS deployment may improve network performance to some extent. Finally, based on the lessons learned, we present and discuss a novel MAC protocol designed for 5G UDN deployments. In contrast to other candidates considered by the industry for UDN deployment, the proposed MAC provides a number of built-in features which improve its efficiency in dense and ultra dense deployments. The multi-channel operation along with the dynamic channel selection constitutes the core of the proposed MAC, limiting performance degradation resulting from high level of inter-cell interference and simplifying network planning. The proposed MAC design is further evaluated through simulations for outdoor deployments in non-coexistence and coexistence scenarios. Our results reveal that the proposed MAC is capable of operating effectively in highly dense deployment scenarios when tuned appropriately. In case of the coexistence capabilities of the investigated design, we show that coexistence with LBT-based systems such as WiFi is also possible, but requires additional tuning to maintain fair channel access for all systems. Lastly,we show that the proposed MAC design outperforms WiFi and LTE (which are commonly considered for UDN deployment) in all considered scenarios. More specifically, our results indicate that area spectral efficiency for the proposed MAC is approximately 500% higher compared to WiFi (IEEE 802.11ac), and 40% higher compared to LTE (excl. CA and MIMO), with improved performance for cell-edge users.

    Dawoud Diana, Heliot Fabien, Imran Muhammad, Tafazolli Rahim (2020) A Novel Unipolar Transmission Scheme for Visible Light Communication,IEEE Transactions on Communications pp. 1-1 Institute of Electrical and Electronics Engineers
    This paper proposes a novel unipolar transceiver for visible light communication (VLC) by using
    orthogonal waveforms. The main advantage of our proposed scheme over most of the existing unipolar
    schemes in the literature is that the polarity of the real-valued orthogonal frequency division multiplexing
    (OFDM) sample determines the pulse shape of the continuous-time signal and thus, the unipolar
    conversion is performed directly in the analog instead of the digital domain. Therefore, our proposed
    scheme does not require any direct current (DC) biasing or clipping as it is the case with existing schemes
    in the literature. The bit error rate (BER) performance of our proposed scheme is analytically derived
    and its accuracy is verified by using Matlab simulations. Simulation results also substantiate the potential
    performance gains of our proposed scheme against the state-of-the-art OFDM-based systems in VLC; it
    indicates that the absence of DC shift and clipping in our scheme supports more reliable communication
    and outperforms the asymmetrically clipped optical-OFDM (ACO-OFDM), DC optical-OFDM (DCOOFDM)
    and unipolar-OFDM (U-OFDM) schemes. For instance, our scheme outperforms ACO-OFDM
    by at least 3 dB (in terms of signal to noise ratio) at a target BER of 10
    Arayeshnia Amir, Araghi Ali, Khalily Mohsen, Xiao Pei, Tafazolli Rahim (2020) Trapped Microstrip-Ridge Gap Waveguide for Standalone Millimeter Wave Structures,EUCAP 2020
    This paper presents a novel design of trapped microstrip-ridge gap waveguide by using partially filled air gaps in a conventional microstrip-ridge gap waveguide. The proposed method offers an applicable solution to obviate frustrating assembly processes for standalone high-frequency circuits employing the low temperature co-fired ceramics technology which supports buried cavities. To show the practicality of the proposed approach, propagation characteristics of both trapped microstrip and microstrip-ridge gap waveguide are compared first. Then, a right-angle bend is introduced, followed by designing a power divider. These components are used to feed a linear 4-element array antenna. The bandwidth of the proposed array is 13 GHz from 64~76 GHz and provides the realized gain of over 10 dBi and the total efficiency of about 80% throughout the operational band. The antenna is an appropriate candidate for upper bands of WiGig (63.72~70.2) and FCC-approved 70 GHz band (71~76 GHz) applications.
    Araghi Ali, Khalily Mohsen, Xiao Pei, Tafazolli Rahim (2020) Study on the Location of mmWave Antenna for the
    Autonomous Car?s Detection and Ranging Sensors
    ,
    EUCAP 2020
    The effect of vehicle?s proximity on the radiation
    pattern when the RADAR?s antenna is mounted on the body of autonomous cars is analysed. Two directional radiation patterns with different specifications are placed at different locations of a realistic car body model. The simulation is performed based on
    ray-tracing method at 77 GHz, the standard frequency for self-driving applications. It is shown that to obtain a robust RADAR sensor, the antenna radiation pattern is better to have relatively higher gain and lower side-lobe-level (SLL), than narrower halfpower-
    beamwidth (HPBW) and higher front-to-back (F/B) ratio.
    Both academia and industry can benefit from this study.
    Araghi Ali, Khalily Mohsen, Xiao Pei, Tafazolli Rahim (2020) Holographic-Based mmW-Wideband Bidirectional
    Frequency Scanning Leaky Wave Antenna
    ,
    EUCAP 2020
    Utilizing the holography theory, a bidirectional
    wideband leaky wave antenna in the millimetre wave (mmW)
    band is presented. The antenna includes a printed pattern of continuous metallic strips on an Alumina 99:5% sheet, and a surface wave launcher (SWL) to produce the initial reference waves on the substrate. To achieve a bidirectional radiation pattern, the fundamental TE mode is excited by applying a Vivaldi antenna (as the SWL). The proposed holographic-based leaky wave antenna (HLWA) is fabricated and tested and the measured results are aligned with the simulated ones. The antenna has 22:6% fractional bandwidth with respect to the central frequency of 30 GHz. The interference pattern is designed to generate a 15 deg backward tilted bidirectional radiation
    pattern with respect to the normal of the hologram sheet. The frequency scanning property of the designed HLWA is also investigated.
    Payami Sohail, Khalily Mohsen, Taheri Sohail, Nikitopoulos Konstantinos, Tafazolli Rahim (2020) Channel Measurement and Analysis for Polarimetric
    Wideband Outdoor Scenarios at 26 GHz:
    Directional vs Omni-Directional
    ,
    EUCAP 2020
    This paper presents the measurement results and
    analysis for outdoor wireless propagation channels at 26 GHz
    over 2 GHz bandwidth for two receiver antenna polarization
    modes. The angular and wideband properties of directional
    and virtually omni-directional channels, such as angular spread,
    root-mean-square delay spread and coherence bandwidth, are
    analyzed. The results indicate that the reflections can have a significant
    contribution in some realistic scenarios and increase the
    angular and delay spreads, and reduce the coherence bandwidth
    of the channel. The analysis in this paper also show that using
    a directional transmission can result in an almost frequencyflat
    fading channel over the measured 2 GHz bandwidth; which
    consequently has a major impact on the choice of system design
    choices such as beamforming and transmission numerology.
    Hoseinitabatabei Seyed Amir, Mohamed Abdelrahim, Hassanpour Masoud, Tafazolli Rahim (2020) The Power of Mobility Prediction in Reducing Idle-State Signalling in Cellular Systems: A Revisit to 4G Mobility Management,IEEE Transactions on Wireless Communications Institute of Electrical and Electronics Engineers
    Conventional mobility management schemes tend to hit the core network with increased signaling
    load when the cell size is shrinking and the user mobility speed increases. To mitigate this problem
    research community has proposed various intelligent mobility management schemes that take advantage
    of the predictability of the users mobility pattern. However, most of the proposed solutions are only
    focused on signaling of the active-state (i.e., handover signaling) and proposals on improvement of
    the idle-state signaling has been limited and were not well received from the industrial practitioners.
    This paper first surveys the major shortcomings of the existing proposals for the idle mode mobility
    management and then proposes a new architecture, namely predictive mobility management (PrMM) to
    mitigate the identified challenges. An analytical framework is developed and a closed form solution for
    the expected signaling overhead of the PrMM is presented. The results of numerical evaluations confirm
    that, depending on user mobility and network configuration, the PrMM efficiency can surpass the long
    term evolution (LTE) 4G signaling scheme by over 90%. Analysis of the results shows that the best
    performance is achieved at highly dense paging areas and lower cell crossing rates.
    Xue Songyan, Li Ang, Wang Jinfei, Yi Na, Ma Yi, Tafazolli Rahim, Dodgson Terrence (2019) To Learn or Not to Learn: Deep Learning Assisted Wireless Modem Design,ZTE Communications ZTE
    Deep learning is driving a radical paradigm shift in wireless communications, all the way from the application layer down to the physical layer. Despite this, there is an ongoing debate as to what additional values artificial intelligence (or machine learning) could bring to us,
    particularly on the physical layer design; and what penalties there may have? These questions motivate a fundamental rethinking of the wireless modem design in the artificial intelligence era. Through several physical-layer case studies, we argue for a significant role that machine learning could play, for instance in parallel error-control coding and decoding, channel equalization, interference cancellation,
    as well as multiuser and multiantenna detection. In addition, we will also discuss the fundamental bottlenecks of machine learning as
    well as their potential solutions in this paper.
    Georgis Georgios, Filo Marcin, Thanos Alexios, Husmann Christopher, De Luna Ducoing Juan Carlos, Tafazolli Rahim, Nikitopoulos Konstantinos (2019) SWORD: Towards a Soft and Open Radio Design
    for Rapid Development, Profiling,
    Validation and Testing
    ,
    IEEE Access Institute of Electrical and Electronics Engineers
    The vision, as we move to future wireless communication systems, embraces diverse qualities
    targeting significant enhancements from the spectrum, to user experience. Newly-defined air-interface
    features, such as large number of base station antennas and computationally complex physical layer
    approaches come with a non-trivial development effort, especially when scalability and flexibility need to
    be factored in. In addition, testing those features without commercial, off-the-shelf equipment has a high
    deployment, operational and maintenance cost. On one hand, industry-hardened solutions are inaccessible
    to the research community due to restrictive legal and financial licensing. On the other hand, researchgrade
    real-time solutions are either lacking versatility, modularity and a complete protocol stack, or, for
    those that are full-stack and modular, only the most elementary transmission modes are on offer (e.g., very
    low number of base station antennas). Aiming to address these shortcomings towards an ideal research
    platform, this paper presents SWORD, a SoftWare Open Radio Design that is flexible, open for research,
    low-cost, scalable and software-driven, able to support advanced large and massive Multiple-Input Multiple-
    Output (MIMO) approaches. Starting with just a single-input single-output air-interface and commercial
    off-the-shelf equipment, we create a software-intensive baseband platform that, together with an acceleration/
    profiling framework, can serve as a research-grade base station for exploring advancements towards
    future wireless systems and beyond.
    Mohamed Abdelrahim, Quddus Atta, Xiao Pei, Hunt Bernard, Tafazolli Rahim (2020) 5G and LTE-TDD Synchronized Coexistence with
    Blind Retransmission and Mini-Slot Uplink
    ,
    91st IEEE Vehicular Technology Conference VTC2020-Spring
    The fifth-generation (5G) new radio (NR) cellular
    system promises a significant increase in capacity with reduced latency. However, the 5G NR system will be deployed along with legacy cellular systems such as the long-term evolution (LTE). Scarcity of spectrum resources in low frequency bands motivates adjacent-/co-carrier deployments. This approach comes with a
    wide range of practical benefits and it improves spectrum utilization by re-using the LTE bands. However, such deployments restrict the 5G NR flexibility in terms of frame allocations to avoid the most critical mutual adjacent-channel interference. This
    in turns prevents achieving the promised 5G NR latency figures. In this we paper, we tackle this issue by proposing to use the minislot uplink feature of 5G NR to perform uplink acknowledgement and feedback to reduce the frame latency with selective blind
    retransmission to overcome the effect of interference. Extensive
    system-level simulations under realistic scenarios show that the
    proposed solution can reduce the peak frame latency for feedback
    and acknowledgment up to 33% and for retransmission by up to
    25% at a marginal cost of an up to 3% reduction in throughput.
    In this paper, single-input multiple-output (SIMO)
    system when employing massive binary array-receiver has been investigated while constructive noise has been observed in the single user system to detect the higher-order QAM modulated signals. To fully understand the interesting phenomenon, mathematical
    model has been established and analyzed in this paper.
    Theorems of the signal detectability are studied to understand the best operating signal-to-noise ratio (SNR) range based on the error behaviours of the single user SIMO system. Within the observation and analysis, a novel new multiuser SIMO with binary array-receiver structure has been proposed and can be considered as a solution to deal with the high complexity problem
    that the traditional model has when using maximum likelihood (ML) detection. The key idea of this approach is to set up the multiuser multiple-input multiple-output (MIMO) model into a frequency division multiple access (FDMA) scenario and regard each user as single user SIMO to achieve the goal of decreasing
    the exponentially increased complexity of ML detection method to the number of users. It is shown by numerical results that each user in this system can achieve a promising error behaviour in
    the specific best operating SNR range.
    Xue Songyan, Ma Yi, Tafazolli Rahim (2020) An Orthogonal-SGD based Learning Approach for MIMO
    Detection under Multiple Channel Models
    ,
    IEEE ICC'20 Workshop - 5GLTEIC
    In this paper, an orthogonal stochastic gradient
    descent (O-SGD) based learning approach is proposed to
    tackle the wireless channel over-training problem inherent in artificial neural network (ANN)-assisted MIMO signal detection. Our basic idea lies in the discovery and exploitation of the training-sample orthogonality between the current training epoch and past training epochs. Unlike the conventional SGD that updates the neural network simply based upon current training samples, O-SGD discovers the correlation
    between current training samples and historical training
    data, and then updates the neural network with those
    uncorrelated components. The network updating occurs
    only in those identified null subspaces. By such means, the neural network can understand and memorize uncorrelated components between different wireless channels, and thus is more robust to wireless channel variations. This hypothesis is confirmed through our extensive computer simulations as well as performance comparison with the conventional SGD
    approach.
    Wang Jinfei, Ma Yi, Yi Na, Tafazolli Rahim (2020) On URLLC Downlink Transmission Modes for MEC Task Offloading,IEEE Vehicular Technology Conference 2020
    Multi-access edge computing for mobile computingtask
    offloading is driving the extreme utilization of available degrees of freedom (DoF) for ultra-reliable low-latency downlink communications. The fundamental aim of this work is to find latency-constrained transmission protocols that can achieve a very-low outage probability (e.g. 0:001%). Our investigation is mainly based upon the Polyanskiy-Poor-Verd´u formula on the finite-length coded channel capacity, which is extended from the
    quasi-static fading channel to the frequency selective channel. Moreover, the use of a suitable duplexing mode is also critical to the downlink reliability. Specifically, time-division duplexing
    (TDD) outperforms frequency-division duplexing (FDD) in terms of the frequency diversity-gain. On the other hand, FDD takes the advantage of having more temporal DoF in the downlink, which can be exchanged into the spatial diversity-gain through the use of space-time coding. Numerical study is carried out to compare the reliability between FDD and TDD under various latency constraints.
    Mohamed Abdelrahim, Ruan Hang, Abdelwahab Mohamed, Dorneanu Bogdan, Xiao Pei, Arellano-Garcia Harvey, Gao Yang, Tafazolli Rahim An Inter-disciplinary Modelling Approach in
    Industrial 5G/6G and Machine Learning Era
    ,
    IEEE International Conference on Communications (ICC) IEEE
    Recently, the fifth-generation (5G) cellular system
    has been standardised. As opposed to legacy cellular systems geared towards broadband services, the 5G system identifies key use cases for ultra-reliable and low latency communications
    (URLLC) and massive machine-type communications (mMTC).
    These intrinsic 5G capabilities enable promising sensor-based vertical applications and services such as industrial process automation. The latter includes autonomous fault detection and prediction, optimised operations and proactive control.
    Such applications enable equipping industrial plants with a sixth sense (6S) for optimised operations and fault avoidance. In this direction, we introduce an inter-disciplinary approach integrating wireless sensor networks with machine learningenabled
    industrial plants to build a step towards developing
    this 6S technology. We develop a modular-based system that can be adapted to the vertical-specific elements. Without loss of generalisation, exemplary use cases are developed and presented including a fault detection/prediction scheme, and a sensor
    density-based boundary between orthogonal and non-orthogonal transmissions. The proposed schemes and modelling approach are implemented in a real chemical plant for testing purposes, and a high fault detection and prediction accuracy is achieved
    coupled with optimised sensor density analysis.
    Chu Zheng, Hao Wanming, Xiao Pei, Khalily Mohsen, Tafazolli Rahim (2020) Resource Allocations for Symbiotic Radio with Finite Block Length Backscatter Link,IEEE Internet of Things Journal Institute of Electrical and Electronic Engineers
    This paper exploits a generic downlink symbiotic radio (SR) system, where a Base Station (BS) establishes a direct (primary) link with a receiver having an integrated backscatter device (BD). In order to accurately measure the backscatter link, the backscattered signal packets are designed to have ?nite block length. As such, the backscatter link in this SR system employs the ?nite block-length channel codes. According to different types of the backscatter symbol period and transmission rate, we investigate the non-cooperative and cooperative SR (i.e., NSR and CSR) systems, and derive their average achievable rate of the direct and backscatter links, respectively. We formulate two optimization problems, i.e., transmit power minimization and energy ef?ciency maximization. Due to the non-convex property of these formulated optimization problems, the semide?nite programming (SDP) relaxation and the successive convex approximation (SCA) are considered to design the transmit beamforming vector. Moreover, a low-complexity transmit beamforming structure is constructed to reduce the computational complexity of the SDP relaxed solution. Finally, the simulation results are demonstrated to validate the proposed schemes.
    As an alternative to classic point-to-point (PTP) unicast transmission, point-to-multipoint (PTM) broadcast/multicast transmission offers simultaneous transmission of the same content to multiple receivers, using just a fixed amount of radio resources for a given coverage area. Such transmission capability has been kept enhancing in the legacy 4th Generation long-term evolution (4G-LTE), namely evolved multimedia broadcast multicast service (eMBMS). As the current multicast systems in the eMBMS use time division multiplexing (TDM) to separate different transmissions, which, however, can cause inefficient utilization of scarce radio resources, and even becomes an impediment in developing such systems to meet new use cases in the 5th generation (5G). To tackle this problem, we proposed a Rate-Splitting (RS) based precoding design to improve the multicast system performances.
    However, as an emerging precoding technology, various theoretical questions, and practical issues remain to be abundantly investigated. To this end, the overall objective of the proposed research is to first investigate the eMBMS system with both LTE and new radio (NR) specifications and then propose effective approaches i.e., Rate-Splitting to improve the PTM system performance.
    Firstly, we conduct a study of the eMBMS technique from the physical layer perspective, comparing between the two major techniques of the eMBMS i.e. multicast broadcast single frequency network (MBSFN) and single cell point to multipoint (SC-PTM), via link-level simulations. A selection of key performance indicators (KPIs) defined by the ITU-R for the IMT-2020 evaluation has been evaluated on data channel, e.g., physical downlink shared channel (PDSCH). This performance evaluation serves as a benchmark for comparison with a potential 5G broadcast solution. Furthermore, we investigate the error performance, mobility tolerance, and coverage of the control channel, e.g., physical downlink control channel (PDCCH) based on both LTE and NR specifications.
    Secondly, we target at an overloaded downlink multicarrier multigroup multicast system with RS under the assumption of Gaussian input, looking into both the achievable rate and error performance. Two optimization methods are provided, i.e., weight minimum mean square error (WMMSE) and successive convex approximation (SCA), to jointly optimize the precoding matrix and subcarrier allocation. Simulation results reveal that RS provides a substantial user experience improvement compared to the state-of-the-art multicast transmission schemes.
    Thirdly, we investigate the RS under the constraint of finite-alphabet constellations. We formulate an optimization problem that maximizes the weighted sum rate of the RS system and solve the problem with an iterative gradient descent algorithm to find the optimal precoder. The simulation results show that compared to the traditional linear precoding scheme, RS can reach the maximum achievable sum-rate with a less transmit power. Then, based on the obtained RS precoder with corresponding constellation inputs, we look into the error performance, e.g., bit error rate (BER) and symbol error rate (SER) of the proposed RS scheme, with channel coding and iterative soft detection and decoding. On top of the performance improvement in terms of achievable rate, the proposed RS scheme also has a better error performance compared to other considered linear precoding schemes in overloaded scenarios.
    Abediankasgari Mohammad, Khalily Mohsen, Danesh Shadi, Xiao Pei, Tafazolli Rahim (2020) Reconfigurable Dielectric Resonator Antenna Using an Inverted U-shaped Slot,Proceedings of the 2020 IEEE International Symposium on Networks, Computers and Communications (ISNCC'20) Institute of Electrical and Electronics Engineers (IEEE)
    A novel reconfigurable dielectric resonator antenna (DRA) employed a T-Shaped microstrip-fed structure in order to excite the dielectric resonator is presented. By carefully adjusting the location of the inverted U-shaped slot, switches, and length of arms, the proposed antenna can support WLAN wireless system. In addition, the presented DRA can be proper for cognitive radio because of availability switching between wideband and narrowband operation. The proposed reconfigurable DRA consisting of a Roger substrate with relative permittivity 3 and a size of 20 mm × 30 mm × 0.75 mm and a dielectric resonator (DR) with a thickness of 9 mm and the overall size of 18 mm × 18 mm. Moreover, the antenna has been fabricated and tested, which test results have enjoyed a good agreement with the simulated results. As well as this, the measured and simulated results show the reconfigurability that the proposed DRA provides a dual-mode operation and also three different resonance frequencies as a result of switching the place of arms.
    Danesh Shadi, Araghi Ali, Khalily Mohsen, Xiao Pei, Tafazolli Rahim (2020) Millimeter Wave Phased Array Antenna Synthesis Using a Machine Learning Technique for Different 5G Applications,Proceedings of the 2020 IEEE International Symposium on Networks, Computers and Communications (ISNCC'20) Institute of Electrical and Electronics Engineers (IEEE)
    A machine learning (ML) technique has been used
    to synthesis a linear millimetre wave (mmWave) phased array
    antenna by considering the phase-only synthesis approach. For
    the first time, gradient boosting tree (GBT) is applied to estimate
    the phase values of a 16-element array antenna to generate
    different far-field radiation patterns. GBT predicts phases while
    the amplitude values have been equally set to generate different
    beam patterns for various 5G mmWave transmission scenarios
    such as multicast, unicast, broadcast and unmanned aerial vehicle
    (UAV) applications.
    Ning Zili, Wang Ning, Tafazolli Rahim (2020) Deep Reinforcement Learning for NFV-based Service Function Chaining in Multi-Service Networks : Invited Paper,2020 IEEE 21st International Conference on High Performance Switching and Routing (HPSR) pp. 1-6 Institute of Electrical and Electronics Engineers (IEEE)
    With the advent of Network Function Virtualization (NFV) techniques, a subset of the Internet traffic will be treated by a chain of virtual network functions (VNFs) during their journeys while the rest of the background traffic will still be carried based on traditional routing protocols. Under such a multi-service network environment, we consider the co-existence of heterogeneous traffic control mechanisms, including flexible, dynamic service function chaining (SFC) traffic control and static, dummy IP routing for the aforementioned two types of traffic that share common network resources. Depending on the traffic patterns of the background traffic which is statically routed through the traditional IP routing platform, we aim to perform dynamic service function chaining for the foreground traffic requiring VNF treatments, so that both the end-to-end SFC performance and the overall network resource utilization can be optimized. Towards this end, we propose a deep reinforcement learning based scheme to enable intelligent SFC routing decision-making in dynamic network conditions. The proposed scheme is ready to be deployed on both hybrid SDN/IP platforms and future advanced IP environments. Based on the real GEANT network topology and its one-week traffic traces, our experiments show that the proposed scheme is able to significantly improve from the traditional routing paradigm and achieve close-to-optimal performances very fast while satisfying the end-to-end SFC requirements.
    Yang Bowen, Zhang Lei, Onireti Oluwakayode, Xiao Pei, Imran Muhammad Ali, Tafazolli Rahim (2020) Mixed-numerology Signals Transmission and Interference Cancellation for Radio Access Network Slicing,IEEE Transactions on Wireless Communications pp. 1-14 Institute of Electrical and Electronics Engineers (IEEE)
    A clear understanding of mixed-numerology signals multiplexing and isolation in the physical layer is of importance to enable spectrum efficient radio access network (RAN) slicing, where the available access resource is divided into slices to cater to services/users with optimal individual design. In this paper, a RAN slicing framework is proposed and systematically analyzed from a physical layer perspective. According to the baseband and radio frequency (RF) configurations imparities among slices, we categorize four scenarios and elaborate on the numerology relationships of slices configurations. By considering the most generic scenario, system models are established for both uplink and downlink transmissions. Besides, a low out of band emission (OoBE) waveform is implemented in the system for the sake of signal isolation and inter-service/slice-band-interference (ISBI) mitigation. We propose two theorems as the basis of algorithms design in the established system, which generalize the original circular convolution property of discrete Fourier transform (DFT). Moreover, ISBI cancellation algorithms are proposed based on a collaboration detection scheme, where joint slices signal models are implemented. The framework proposed in the paper establishes a foundation to underpin extremely diverse user cases in 5G that implement on a common infrastructure.
    Selinis Ioannis, Wang Ning, Da Bin, Yu Delei, Tafazolli Rahim (2020) On the Internet-scale Streaming of Holographic-type Content with Assured User Quality of Experiences,Proceedings of the 19th International Federation for Information Processing (IFIP) Networking 2020 Conference (NETWORKING 2020) Institute of Electrical and Electronics Engineers (IEEE)
    Holographic-type Communication (HTC) has been
    widely deemed as an emerging type of augmented reality (AR)
    media which offers Internet users deeply immersive experiences.
    In contrast to the traditional video content transmissions, the
    characteristics and network requirements of HTC have been
    much less studied in the literature. Due to the high bandwidth
    requirements and various limitations of today?s HTC platforms,
    large-scale HTC streaming has never been systematically attempted
    and comprehensively evaluated till now. In this paper, we
    introduce a novel HTC based teleportation platform leveraging
    cloud-based remote production functions, also supported with
    newly proposed adaptive frame buffering and end-to-end signalling
    techniques against network uncertainties, which for the
    first time is able to provide assured user experiences at the public
    Internet scale. According to our real-life experiments based on
    strategically deployed cloud sites for remote production functions,
    we have demonstrated the feasibility of supporting user assured
    performances for such applications at the global Internet scale.
    Kuzminskiy Alexandr, Xiao Pei, Tafazolli Rahim (2020) Good Neighbor Alternative to Best Response and
    Machine Learning Based Beamforming and Power Adaptation for MIMO Ad Hoc Networks
    ,
    2020 IEEE 31st Annual International Symposium on Personal, Indoor and Mobile Radio Communications: Track 2: Networking and MAC Institute of Electrical and Electronics Engineers
    Decentralized joint transmit power and beam-
    forming selection for multiple antenna wireless ad hoc net-
    works operating in a multi-user interference environment is
    considered. An important feature of the considered environ-
    ment is that altering the transmit beamforming pattern at
    some node generally creates more signiýcant changes to in-
    terference scenarios for neighboring nodes than variation of
    the transmit power. Based on this premise, a good neighbor
    algorithm is formulated in the way that at the sensing node,
    a new beamformer is selected only if it needs less than the
    given portion of the transmit power required for the current
    beamformer. Otherwise, it keeps the current beamformer
    and achieves the performance target only by means of power
    adaptation. Equilibrium performance and convergence be-
    havior of the proposed algorithm compared to the best re-
    sponse and regret matching solutions is demonstrated by
    means of semi-analytic Markov chain performance analysis
    for small scale and simulations for large scale networks.
    One of the ways to provide greater coverage and capacity for future wireless networks is through network densification. This is also one of the drivers for future IEEE 802.11 deployments, aiming not only to improve throughput per link, but the overall network performance in dense deployments. That said, the IEEE 802.11ax amendment is currently focusing on addressing the challenges and improving the spectrum efficiency in dense deployments with hundreds of Access Points (APs) and Stations (STAs). This
    work strives to shed some light in the area of spectrum efficiency by trying to understand (i) the operation and the impact of the newly introduced Spatial Reuse feature of
    the IEEE 802.11ax amendment and (ii) if it is possible to realise multicast/broadcast transmissions over Wi-Fi while preserving reliability.

    Although the IEEE 802.11ax Spatial Reuse feature, namely BSS Color, offers several advantages and good potential for improving spectrum efficiency, it also imposes several
    challenges. Towards filling the aforementioned gaps and address challenges, particular contributions were made in this thesis. First, this work presents a performance evaluation of the BSS Color scheme in various scenarios, where its shortcomings are identified. Second, this work proposes a generic framework to obtain throughput for dense cellular-like (small-cell) deployments, based on a mathematical model. Third, this work introduces COST, a novel Spatial Reuse technique for improving BSS Color performance by exploiting the information provided by this scheme and providing throughput gain of up to 57% while preserving fairness between BSSs. Fourth, this thesis proposes the design of a rate control algorithm that leverages the BSS Color and COST, providing up to 113% throughput gain in dense deployments when compared to the traditional off-the-shelf MinstrelHT. Finally, this thesis elaborates a network coding approach to enable multicast/broadcast transmissions over Wi-Fi, that could enhance throughput performance by 20% when compared with the legacy MAC feedback mechanism. The main goal for this contribution is to provide a means for realising reliable multicast/broadcast communications by reducing the use of the Wi-Fi feedback mechanism.

    The above contributions were evaluated through system-level simulations, emulating real-world deployments. This work showed that advanced techniques, that exploit all available information by monitoring the inter-BSS and intra-BSS frames, are required to support the IEEE 802.11ax Spatial Reuse feature operation and provide throughput gain while preserve fairness among users. Furthermore, it was shown that the network coding should carefully be designed and enabled only when it is required, otherwise throughput loss could be observed due to the transmitted overhead. The scenario and application?s requirements should also be taken into account (e.g. latency).

    Chen Hongzhi, Mi De, Liu Zilong, Xiao Pei, Tafazolli Rahim (2020) Rate-Splitting for Overloaded Multigroup Multicast:
    Error Performance Evaluation
    ,
    IEEE ICC 2020
    In this work, we provide the first attempt to evaluate
    error performance of Rate-Splitting (RS) based transmission
    strategies with constellation-constrained coding/modulation. The consider scenario is an overloaded multigroup multicast, where RS can mitigate the inter-group interference thus achieve a better max-min fair group rate over conventional transmission strategies.
    We bridge the RS-based rate optimization with modulationcoding scheme selection, and implement them in a developed transceiver framework with either linear or non-linear receiver, where the latter equips with a generalized sphere decoder. Simulation results of a coded bit error rate demonstrate that, while the conventional strategies suffer from the error floor in the considered scenario, the RS-based strategy delivers a superior
    performance even with low complexity receiver techniques.
    The proposed analysis, transceiver framework and evaluation
    methodology provide a generic baseline solution to validate the effectiveness of the RS-based system design in practice.
    Index Terms?Rate-splitting, overloaded system, multigroup
    multicast, rank-deficient, generalized sphere decoder, coded bit error rate.
    Serghiou Demos, Khalily Mohsen, Singh Vikrant, Araghi Ali, Tafazolli Rahim (2020) Sub-6 GHz Dual-Band 8×8 MIMO Antenna for 5G Smartphones,IEEE Antennas and Wireless Propagation Letters Institute of Electrical and Electronics Engineers (IEEE)
    In this letter, a dual-band 8x8 MIMO antenna that
    operates in the sub-6 GHz spectrum for future 5G multiple-input
    multiple-output (MIMO) smartphone applications is presented.
    The design consists of a fully grounded plane with closely spaced
    orthogonal pairs of antennas placed symmetrically along the long
    edges and on the corners of the smartphone. The orthogonal
    pairs are connected by a 7.8 mm short neutral line for mutual
    coupling reduction at both bands. Each antenna element consists
    of a folded monopole with dimensions 17.85 x 5mm2 and can
    operate in 3100-3850 MHz for the low band and 4800-6000 MHz
    for the high band ([S11] Â -10dB). The fabricated antenna
    prototype is tested and offers good performance in terms of
    Envelope Correlation Coefficient (ECC), Mean Effective Gain
    (MEG), total efficiency and channel capacity. Finally, the user
    effects on the antenna and the Specific Absorption Rate (SAR)
    are also presented.
    Jarchi Saguar, Khalily Mohsen, Tafazolli Rahim (2020) Effects of Metamaterial Loading on Miniaturization
    of Loop and Open Loop Microstrip Filters
    ,
    5th International Conference on UK-China Emerging Technologies (UCET)
    In this paper, metamaterial loading on loop and
    open loop microstrip filters is investigated where both
    rectangular loop and open loop structures are considered. Spiral resonators are loaded on the four sides of the square loop and result in higher size reduction compared to the conventional split ring resonators with identical structural parameters. It is shown that, for both proposed filters, metamaterial loading provides size reduction, due to possessing lower resonant
    frequency of spiral resonators. The structures are analytically investigated through the transmission matrix method. In the designed rectangular loop filters, there are two nulls on both sides of the pass-band, which provide high out-of-band rejection and is preserved in the corresponding miniaturized metamaterial loaded structures. However open loop resonators provide lower resonant frequencies or more compact size filters. The proposed filter is fabricated and tested and measured results are in good agreement with simulation ones.
    Payami Sohail, Khalily Mohsen, Araghi Ali, Hong Loh Tian, Cheadle David, Nikitopoulos Konstantinos, Tafazolli Rahim (2020) Developing the First mmWave Fully-Connected Hybrid Beamformer
    with a Large Antenna Array
    ,
    IEEE Access Institute of Electrical and Electronics Engineers
    Millimeter wave (mmWave) systems with effective beamforming capability play a key role
    in fulfilling the high data-rate demands of current and future wireless technologies. Hybrid analog-todigital
    beamformers have been identified as a cost-effective and energy-efficient solution towards deploying
    such systems. Most of the existing hybrid beamforming architectures rely on a subconnected phase shifter
    network with a large number of antennas. Such approaches, however, cannot fully exploit the advantages of
    large arrays. On the other hand, the current fully-connected beamformers accommodate only a small number
    of antennas, which substantially limits their beamforming capabilities. In this paper, we present a mmWave
    hybrid beamformer testbed with a fully-connected network of phase shifters and adjustable attenuators and
    a large number of antenna elements. To our knowledge, this is the first platform that connects two RF inputs
    from the baseband to a 16ý 8 antenna array, and it operates at 26 GHz with a 2 GHz bandwidth. It provides
    a wide scanning range of 60ý, and the flexibility to control both the phase and the amplitude of the signals
    between each of the RF chains and antennas. This beamforming platform can be used in both short and
    long-range communications with linear equivalent isotropically radiated power (EIRP) variation between
    10 dBm and 60 dBm. In this paper, we present the design, calibration procedures and evaluations of such a
    complex system as well as discussions on the critical factors to consider for their practical implementation.
    Bridges Matthew, Khalily Mohsen, Abediankasgari Mohammad, Serghiou Demos, Xiao Pei, Tafazolli Rahim (2020) High Isolation 8×8 MIMO Antenna Design for 5G Sub-6 GHz Smartphone Applications,2020 International Conference on UK-China Emerging Technologies (UCET)
    In this paper, an 8×8 Multiple Input Multiple
    Output (MIMO) antenna design for Fifth Generation (5G) sub-
    6GHz smartphone applications is presented. The antenna
    elements are based off a folded quarter wavelength monopole
    that operate at 3.4-3.8GHz. Isolation between antenna elements is provided through physical distancing. The fabricated antenna prototype outer casing is made from Rogers R04003C with dimensions based on future 5G enabled phones. Measured results show an operating bandwidth of 3.32 to 3.925GHz (S11 Specific Absorption Rate (SAR) model has been constructed and presented showing the user?s effects on the antenna?s Sparameter results. Measurements of the amount of power
    absorbed by the head and hand during operation have also been simulated.
    Singh Vikrant, Khalily Mohsen, Amlashi Salman Behboudi, Carey J. David, Tafazolli Rahim (2020) Fully-Transparent Transmission Surface for
    Outdoor-Indoor mmWave Coverage Enhancement
    ,
    5th International Conference on UK-China Emerging Technologies (UCET)
    This paper presents a fully-transparent and novel
    frequency selective surface (FSS) that can be deployed instead of conventional glass to reduce the penetration loss encountered by millimeter wave (mmWave) frequencies in typical outdoorindoor (O2I) communication scenarios. The presented design uses a 0:035 mm thick layer of indium tin oxide (ITO), which is a transparent conducting oxide (TCO) deposited on the surface of the glass, thereby ensuring the transparency of the structure. The paper also presents a novel unit cell that has been used to design the hexagonal lattice of the FSS structure. The dispersion and transmission characteristics of the proposed design are presented and compared with conventional glass. The presented FSS can be used for both 26 GHz and 28 GHz bands of the mmWave spectrum and offers a lower transmission loss as compared to conventional glass without any considerable impact on the aesthetics of the building infrastructure.
    Serghiou Demos, Khalily Mohsen, Johny S., Stanley M., Fatadin I., Brown T.W.C, Ridler N., Tafazolli Rahim (2020) Ultra-Wideband Terahertz Channel Propagation Measurements from 500 to 750 GHz,2020 International Conference on UK-China Emerging Technologies (UCET)
    This paper presents empirically based ultrawideband
    and directional channel measurements, performed in
    the Terahertz (THz) frequency range over 250 GHz bandwidth
    from 500 GHz to 750 GHz. Measurement setup calibration
    technique is presented for free-space measurements taken at
    Line-of-Sight (LoS) between the transmitter (Tx) and receiver(Rx) in an indoor environment. The atmospheric effects on signal propagation in terms of molecular absorption by oxygen and
    water molecules are calculated and normalized. Channel impulse responses (CIRs) are acquired for the LoS scenario for different antenna separation distances. From the CIRs the Power Delay Profile (PDP) is presented where multiple delay taps can be observed caused due to group delay products and reflections from the measurement bench.
    Mao Chun Xu, Khalily Mohsen, Xiao Pei, Zhang Long, Tafazolli Rahim (2020) High-Gain Phased Array Antenna with End-Fire Radiation for 26 GHz Wide-Beam-Scanning Applications,IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    In this paper, a high-gain phased array antenna with wide-angle beam-scanning capability is proposed for fifth- generation (5G) millimeter-wave applications. First, a novel, end-fire, dual-port antenna element with dual functionalities of radiator and power splitter is designed. The element is composed a substrate integrated cavity (SIC) and a dipole based on it. The resonant frequencies of the SIC and dipole can be independently tuned to broaden the impedance bandwidth. Based on this dual-port element, a 4-element subarray can be easily constructed without resorting to a complicated feeding network. The end-fire subarray features broad beam-width of over 180 degrees, high isolation, and low profile, rendering it suitable for wide-angle beam-scanning applications in the H-plane. In addition, the methods of steering the radiation pattern downwards or upwards in the E-plane are investigated. As a proof-of-concept, two phased array antennas each consisting of eight subarrays are designed and fabricated to achieve the broadside and wide-angle beam-scanning radiation. Thanks to the elimination of surface wave, the mutual coupling between the subarrays can be reduced for improving the scanning angle while suppressing the side-lobe level. The experimental predictions are validated by measurement results, showing that the beam of the antenna can be scanned up to 65 degrees with a scanning loss only 3.7 dB and grating lobe less than -15 dB.