Rahim Tafazolli

Rahim Tafazolli


Head of the Institute for Communication Systems (ICS)

Biography

Biography

Rahim Tafazolli has been the Professor of Mobile and Satellite Communications at the University of Surrey since April 2000, Director of Institute of Communication Systems (ICS, formerly known as CCSR) since January 2010 and the Director of the 5G Innovation Centre since 2012.

He has over 25 years of experience in digital communications research and teaching. He has authored and co-authored more than 500 research publications and is regularly invited to deliver keynote talks and distinguished lectures to international conferences and workshops. He has also edited two books: “Technologies for the Wireless Future”, Vol.1 ( 2004) and Vol.2 (2006) both published by Wiley's. And he is co-inventor on more than 30 granted patents, all in the field of digital communications.

Professor Tafazolli was the leader of study on “grand challenges in IoT” (Internet of Things) in the UK, 2011-2012, for RCUK (Research Council UK) and the UK TSB (Technology Strategy Board).

He is regularly invited by governments to advise on 5G technologies and was advisor to the Mayor of London with regard to the London Infrastructure Investment 2050 Plan during May and June 2014.

He was also the lead speaker at the Connectivity session of the UK Government's D5 Summit (UK, New Zealand, South Korea, Estonia & Israel) London, 9-10 Dec 2014.

He is a member of:

  • The UK Smart Cities Forum (since November 2013)
  • The IET Communications Policy Panel
  • The UK BIS (Business, Innovation and Skills) Advisory Working Group to the National Measurement Office for NPL Programmes (since March 2012)
  • The Innovate UK ICT Industry Advisory Board (since September 2014).

Professor Tafazolli has given many interviews to international media (tv, radio and press articles).

In 2011, he was appointed as Fellow of the Wireless World Research Forum (WWRF) in recognition of his personal contributions to the wireless world as well as heading one of Europe's leading research groups.

Professor Tafazolli was awarded the 28th KIA Laureate Award- 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 IROST (Iranian Research Organisation of Science and Technology) scientific committee.)

Media Contacts

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Email:

mediarelations@surrey.ac.uk

Phone: +44 (0)1483 684380 / 688914 / 684378
Out-of-hours: +44 (0)7773 479911
Senate House, University of Surrey
Guildford, Surrey GU2 7XH

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
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
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
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
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
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
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
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
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
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
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 JJ, 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
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
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
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
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
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
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
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
Hamid A, Hoshyar R, Tafazolli R (2006) Band Based Dynamic Link Adaptation for MC-CDMA Radio Interface 2006 IEEE 64TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-6 pp. 791-795
Mirzadeh S, Tafazolli R (2005) Secure Service Discovery for Personal Networks
Forum WWR (2006) Technologies for the wireless future
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
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
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
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
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
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
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
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
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
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
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
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
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
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.
Ducoing JCDL, Yi N, Ma Y, Tafazolli R (2015) Using Real Constellations in Fully- and Over-Loaded Large MU-MIMO Systems With Simple Detection IEEE WIRELESS COMMUNICATIONS LETTERS 5 (1) pp. 92-95
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
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
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
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
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
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
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
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
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)
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
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-+
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
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
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
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
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
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
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
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
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
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
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
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
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.
Héliot F, Hoshyar R, Tafazolli R (2010) Low-Complexity Power Allocation Schemes for the Downlink of Nonregenerative Cooperative Multi-User MIMO Communication System Proc. ICT Future Network & Mobile Summit
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
Héliot F, Hoshyar R, Tafazolli R (2010) On the spectral efficiency maximization of Nonregenerative Cooperative MIMO Communication Systems Proc. IEEE PIMRC
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
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.
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 IWCMC 2010 - 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
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 Y, 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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
Hoshyar R, Tafazolli R (2009) A Pre-BSC Model for Distributed Turbo Codes 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5 pp. 1936-1940
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
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
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
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
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
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
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
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
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
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
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
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
Imran MA, Tang W, Tafazolli R (2011) Coordination of Energy Efficient Sensing and Transmission in Cognitive Radio 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
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
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
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
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
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
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
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
Hanzo L, Tafazolli R (2008) Mobile Ad Hoc Networks: Challenges and Solutions for Providing Quality of Service Assurances
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
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
Héliot F, Hoshyar R, Tafazolli R (2010) Power Allocation for the Downlink of Nonregenerative Cooperative Multi-User MIMO Communication system Proc. IEEE PIMRC
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
Yi N, Ma Y, Tafazolli R (2010) Underlay Cognitive Radio with Full or Partial Channel Quality Information International Journal of Navigation and Observation 2010
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
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
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
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
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
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
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
Akbari A, Imran MA, Tafazolli R (2011) Maximising Average Energy efficiency for Two-user AWGN Broadcast Channel Future Network and Mobile Summit
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
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
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
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
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
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
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
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
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
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
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
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 O, Imran A, Imran MA, Tafazolli R (2015) Energy Efficient Inter-Frequency Small Cell Discovery in Heterogeneous Networks IEEE Transactions on Vehicular Technology 65 (9) pp. 7122-7135
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
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.
Mi D (2017) Massive MIMO with imperfect channel state information and practical limitations.
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
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)
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

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 O, Imran A, Imran MA, Tafazolli R (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
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
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 F, Imran MA, Tafazolli R (2012) Green Relay Techniques in Cellular Systems
Zhang L, Xiao P, Zafar A, Quddus AU, Tafazolli R (2016) FBMC System: An Insight into Doubly Dispersive Channel Impact IEEE Transactions on Vehicular Technology 66 (5) pp. 3942-3956
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 P, Kelly J, Li B, Tafazolli R (2017) Full-Duplex Wireless-Powered Relay in Two Way Cooperative Networks IEEE Access 5 pp. 1548-1558
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
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
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
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)
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

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
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
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.
Chandrasekaran G (2017) Device-level content management in LTE-A based network environments.
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
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
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
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
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.
Sabagh M (2017) Energy-efficient and QoS aware surplus resource allocation in OFDMA systems.
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
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 L, Ijaz A, Xiao P, Quddus AU, Tafazolli R (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
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
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 M (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 L, Ijaz A, Molu M, Tafazolli R (2017) Filtered OFDM Systems, Algorithms and Performance Analysis for 5G and Beyond IEEE Transactions on Communications
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.
Abbas Fathy Abbas Y, Barnaghi P, Tafazolli R (2017) Large-Scale Indexing, Discovery and Ranking for the Internet of Things (IoT) ACM Computing Surveys
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
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
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 M, Xiao P, Khalily M, Cumanan K, Zhang L, Tafazolli R (2017) Low-Complexity and Robust Hybrid Beamforming Design for Multi-Antenna Communication Systems IEEE Transactions on Wireless Communications 17 (3) pp. 1445-1459
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 G, Wang N, hassanpourasheghabadi M, Xu M, Tafazolli R (2017) Mobility as a Service (MaaS): A D2D-based Information Centric Network Architecture for Edge-Controlled Content Distribution IEEE Access 6 pp. 2110-2129
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.
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
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
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
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 A, Imran M, Xiao P, Tafazolli R (2018) Memory-full Context-aware Predictive Mobility Management in Dual Connectivity 5G Networks IEEE Access
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 A, Xiao P, Tafazolli R (2018) Good Neighbor Distributed Beam Scheduling in Coexisting Multi-RAT Networks Proceedings of WCNC 2018
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.
De Luna Ducoing J (2018) Advanced modulation techniques for scaling up multiuser MIMO communications.
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 P, Wang N, Tafazolli R (2018) Achieving Robust Mobile Web Content Delivery Performance Based on Multiple Coordinated QUIC Connections IEEE Access
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
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
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
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 pp. 1-1
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 S, Pervaiz H, Ali Hassan S, Musavian L, Ni Q, Imran M, Ge X, Tafazolli R (2018) Energy-Aware Radio Resource Management in D2D-Enabled Multi-Tier HetNets IEEE Access
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 H, Pervaiz H, Hassan S, Musavian L, Ni Q, Imran M, Tafazolli R (2018) Computationally Intelligent Techniques for Resource Management in mmWave Small Cell Networks IEEE Wireless Communications
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 M, Taheri S, Payami S, Ghoraishi M, Tafazolli R (2018) Indoor Wideband Directional Millimeter Wave Channel Measurements and Analysis at 26 GHz, 32 GHz, and 39 GHz Transactions on Emerging Telecommunications Technologies
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
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 S, Fathy Y, Barnaghi P, Wang C, Tafazolli R (2018) A Novel Indexing Method for Scalable IoT Source Lookup IEEE Internet of Things Journal
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 A, Farooq H, Imran A, Tafazolli R (2018) Analytical Modelling for Mobility Signalling in Ultra-Dense HetNets IEEE Transactions on Vehicular Technology
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
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.