Professor Rahim Tafazolli

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E-mail:
Phone: 01483 68 9834

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Room: 03 CII 02

Publications

Journal articles

  • Puschmann DP, Barnaghi P , Tafazolli R . (2017) 'Using LDA to Uncover the Underlying Structures and Relations in Smart City Data Streams'. Institute of Electrical and Electronics Engineers (IEEE) IEEE Systems Journal,
    [ Status: Accepted ]

    Abstract

    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%.

  • Zhang L, Ijaz A, Xiao P, Tafazolli R. (2017) 'Multi-service System: An Enabler of Flexible 5G Air-Interface'. IEEE IEEE Communications Magazine,
    [ Status: Accepted ]

    Abstract

    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.

  • Zhang L , Ijaz A, Xiao P , Tafazolli R . (2017) 'Channel Equalization and Interference Analysis for Uplink Narrowband Internet of Things (NB-IoT)'. IEEE IEEE communications Letters, 99
    [ Status: Accepted ]

    Abstract

    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.

  • 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 IEEE Access, 5, pp. pp. 7594-7605.

    Abstract

    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.

  • Hasanpour M, Shariat S, Barnaghi P , Hoseinitabatabaei SA, Vahid S , Tafazolli R . (2017) 'Quantum Load Balancing in Ad Hoc Networks'. Springer Verlag Quantum Information Processing, 16 (148)

    Abstract

    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.

  • Vural S , Wang N , Foster G, Tafazolli R . (2017) 'Success Probability of Multiple-Preamble Based Single-Attempt Random Access to Mobile Networks'. IEEE IEEE Communications Letters, , pp. 1-5.
    [ Status: Accepted ]

    Abstract

    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.

  • Chen G, Xiao P, Kelly J, Li B, Tafazolli R. (2017) 'Full-Duplex Wireless-Powered Relay in Two Way Cooperative Networks'. IEEE IEEE Access, 5, pp. 1548-1558.

    Abstract

    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.

  • Qi Y, Shakir MZ, Imran MA, Qaraqe KA, Quddus AU, 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.
  • Heliot F, Tafazolli R. (2016) 'Optimal Energy-Efficient Joint Resource Allocation for Multi-Hop MIMO-AF Systems'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE TRANSACTIONS ON COMMUNICATIONS, 64 (9), pp. 3655-3668.
  • Ko Y, Quddus AU, Tafazolli R. (2016) 'Multi-Device Selection Scheduling in Non-Identically Distributed Fading Channels'. IET Communications,
    [ Status: Accepted ]

    Abstract

    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.

  • Chen G, Yu G, Xiao P, Tafazolli R. (2016) 'Dual Antenna Selection in Self-Backhauling Multiple Small Cell Networks'. IEEE IEEE Communications Letters, 20 (8), pp. 1611-1614.

    Abstract

    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.

  • Jaber M, Imran MA, Tafazolli R, Tukmanov A. (2016) 'A Distributed SON-based User-Centric Backhaul Provisioning Scheme'. IEEE IEEE Access, , pp. 2314-2330.

    Abstract

    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.

  • 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 IEEE Access, 4, pp. 1925-1939.

    Abstract

    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.

  • Jaber M, Imran MA, Tafazolli R, Tukmanov A. (2016) '5G Backhaul Challenges and Emerging Research Directions: A Survey'. IEEE Access, 4, pp. 1743-1766.
  • 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-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, 15, pp. 1305-1308.
  • 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-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE WIRELESS COMMUNICATIONS LETTERS, 5 (2), pp. 196-199.
  • Ma Y, Yamani A, Yi N, Tafazolli R. (2016) 'Low-Complexity MU-MIMO Nonlinear Precoding Using Degree-2 Sparse Vector Perturbation'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, 34 (3), pp. 497-509.
  • Katsaros K, Dianati M, Tafazolli R, Guo X. (2016) 'End-to-End Delay Bound Analysis for Location-Based Routing in Hybrid Vehicular Networks'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, 65 (9), pp. 7462-7475.
  • Ijaz A, Zhang L, ul Quddus A, Tafazolli R. (2016) 'HARQ in Relay-Assisted Transmission for Machine Type Communications'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE WIRELESS COMMUNICATIONS LETTERS, 5 (2), pp. 172-175.
  • Puschmann D, Barnaghi P, Tafazolli R. (2016) 'Adaptive Clustering for Dynamic IoT Data Streams'. IEEE IEEE Internet of Things,
    [ Status: Accepted ]
  • Vural S, Wang N, Navaratnam P, Tafazolli R. (2016) 'Caching Transient Data in Internet Content Routers'. IEEE/ACM Transactions on Networking,
    [ Status: Accepted ]

    Abstract

    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.

  • 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-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE WIRELESS COMMUNICATIONS LETTERS, 5 (1), pp. 92-95.
  • Onireti O, Imran A, Imran MA, Tafazolli R . (2015) 'Energy Efficient Inter-Frequency Small Cell Discovery in Heterogeneous Networks'. IEEE IEEE Transactions on Vehicular Technology, 65 (9), pp. pp. 7122-7135.

    Abstract

    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.

  • Zhang L, liu W, quddus A, Dianati M, tafazolli R. (2015) 'Adaptive Distributed Beamforming for Relay Networks based on Local Channel State Information'. IEEE IEEE Transactions on Signal and Information Processing over Networks, 1 (2), pp. 117-128.

    Abstract

    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.

  • 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-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE COMMUNICATIONS LETTERS, 19 (10), pp. 1742-1745.
  • 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-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE COMMUNICATIONS SURVEYS AND TUTORIALS, 18 (1), pp. 419-445.
  • Chen H, Maunder RG, Ma Y, Tafazolli R, Hanzo L. (2015) 'Hybrid-ARQ-Aided Short Fountain Codes Designed for Block-Fading Channels'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, 64 (12), pp. 5701-5712.
  • Qi Y, Imran MA, Demo Souza R, Tafazolli R. (2015) 'On the Optimization of Distributed Compression in Multi-Relay Cooperative Networks'. IEEE IEEE Transactions on Vehicular Technology,
    [ Status: Accepted ]

    Abstract

    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.

  • Shariat M, Pateromichelakis E, Quddus A, Tafazolli R. (2014) 'Joint TDD Backhaul and Access Optimization in Dense Small Cell Networks'. IEEE IEEE Transactions on Vehicular Technology, (99)

    Abstract

    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.

  • 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.

    Abstract

    © 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.

  • 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.

    Abstract

    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.

  • Al-Imari M, Xiao P, Imran MA, Tafazolli R. (2014) 'Radio Resource Allocation for Uplink OFDMA Systems with Finite Symbol Alphabet Inputs'. IEEE IEEE Transactions on Vehicular Technology, 63 (4), pp. 1917-1921.

    Abstract

    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.

  • Pilloni V, Navaratnam P, Vural S, Atzori L, Tafazolli R. (2013) 'TAN: a Distributed Algorithm for Dynamic Task Assignment in WSNs'. IEEE Sensor Networks,
    [ Status: Accepted ]
  • Pateromichelakis E, Shariat M, Quddus AU, Dianati M , Tafazolli R . (2013) 'Dynamic Clustering Framework for Multi-Cell Scheduling in Dense Small Cell Networks'. IEEE IEEE Communications Letters, 17 (9), pp. 1802-1805.

    Abstract

    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.

  • Vural S, Navaratnam P, Wang N, Tafazolli R. (2013) 'Asynchronous Clustering of Multihop Wireless Sensor Networks'. ACM Transactions on Sensor Networks,
    [ Status: Submitted ]
  • 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.

    Abstract

    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.

  • He Z, Ma Y, Tafazolli R. (2012) 'A High Accuracy Mobile Positioning Approach in IEEE 802.11a WLANs'. IEICE IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, E95-A (10), pp. 1776-1779.
  • He Z, Ma Y, tafazolli R. (2012) 'Posterior Cramér-Rao Bound for Inertial Sensors Enhanced Mobile Positioning Under The Random Walk Motion Model'. IEEE IEEE Wireless Communications Letters, (99), pp. 1-4.

    Abstract

    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.

  • Vural S, Navaratnam P, Tafazolli R. (2012) 'Transmission Range Assignment for Backbone Connectivity in Clustered Wireless Networks'. IEEE Wireless Communications Letters,
  • He Z, Ma Y, Tafazolli R. (2012) 'Opportunistic Cooperative Positioning in OFDMA Systems'. IEICE IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, Vol.E95-A (9), pp. 1642-1645.
  • Guo T, Quddus AU, Wang N, Tafazolli R. (2012) 'Local Mobility Management for Networked Femtocells Based on X2 Traffic Forwarding'. IEEE IEEE Transactions on Vehicular Technology,
  • Heliot F, Imran MA, Tafazolli R. (2012) 'Energy-efficient Power Allocation for Point-to-point MIMO System over the Rayleigh Fading Channel'. IEEE IEEE Wireless Communications Letters, 1 (4), pp. 304-307.
  • He Z, Ma Y, Tafazolli R. (2012) 'Training Convergence in Range-based Cooperative Positioning with Stochastic Positional Knowledge'. IEICE IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, E95.A (7), pp. 1200-1204.
  • Xiao P, Tafazolli R, Moessner K, Gluhak A. (2012) 'Codebook Based Single-User MIMO System Design with Widely Linear Processing'. IEEE Transactions on Communications,

    Abstract

    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.

  • Heliot F, Imran MA, Tafazolli R. (2012) 'A Very Tight Approximation of the SISO Energy Efficiency-Spectral Efficiency Trade-Off'. IEEE Communications Letters,

    Abstract

    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.

  • 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,
  • Akbari A, Heliot F, Imran MA, Tafazolli R. (2012) 'Energy Efficiency Contours for Broadcast Channels Using Realistic Power Models'. IEEE IEEE Transactions on Wireless Communications, 11 (11), pp. 4017-4025.
  • Heliot F, Imran MA, Tafazolli R. (2012) 'On the Energy Efficiency-Spectral Efficiency Trade-Off over the MIMO Rayleigh Fading Channel'. IEEE IEEE Transactions on Communications, 60 (5), pp. 1345-1356.
  • Cheraghi P, Ma Y, Tafazolli R, Lu Z. (2012) 'Cluster based differential energy detection for spectrum sensing in multi-carrier systems'. IEEE IEEE Transactions on Signal Processing, 60 (12), pp. 6450-6464.
  • Imran MA, Imran A, tafazolli R. (2011) 'Relay Station Access Link Spectral Efficiency Optimization through SO of Macro BS Tilts'. IEEE IEEE Communications Letters, 15 (12), pp. 1326-1328.

    Abstract

    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.

  • Akbari A, Imran MA, Tafazolli R, Dianati M. (2011) 'Energy Efficiency Contours for Single-Carrier Downlink Channels'. IEEE IEEE Communications Letters, 15 (12), pp. 1307-1309.

    Abstract

    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.

  • Wei D, Jin Y, Vural S, Moessner K, Tafazolli R. (2011) 'An Energy-efficient Clustering Solution for Wireless Sensor Networks'. IEEE Transactions on Wireless Communications, United Kingdom: PP (99), pp. 1-11.

    Abstract

    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.

  • Qi Y, Imran MA, Hoshyar R, Tafazolli R. (2011) 'H2-ARQ Relaying: Spectrum and Energy Efficiency Analysis'. IEEE IEEE Journal on Selected Areas in Communications, 29 (8), pp. 1547-1558.

    Abstract

    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.

  • Ma Y, Tafazolli R, Zhang Y, Qian C. (2011) 'Adaptive Modulation for Opportunistic Decode-and-Forward Relaying'. IEEE IEEE Transactions on Wireless Communications, 10 (7), pp. 2017-2022.
  • Akbari A, Imran MA, Hoshyar R, Amich A, Tafazolli R. (2011) 'Average Energy Efficiency Contours with Multiple Decoding Policies'. IEEE IEEE Communications Letter, 15 (5), pp. 506-508.

    Abstract

    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.

  • 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.
  • 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.
  • Heliot F , Hoshyar R, Tafazolli R . (2011) 'An Accurate Closed-Form Approximation of the Distributed MIMO Outage Probability'. IEEE IEEE Transactions on Wireless Communications, 10 (1), pp. pp. 5-11.
    [ Status: Accepted ]

    Abstract

    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.

  • 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.
  • 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.
  • 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 IEEE Comsoc MMTC E-Letters, 5 (5), pp. 27-31.
  • Yi N, Ma Y, Tafazolli R. (2010) 'Underlay Cognitive Radio with Full or Partial Channel Quality Information'. International Journal of Navigation and Observation, 2010 Article number 105723
  • Dianati M, Tafazolli R, Shen XS, Naik K. (2010) 'Call admission control with opportunistic scheduling scheme'. JOHN WILEY & SONS INC 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-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE COMMUNICATIONS LETTERS, 14 (2), pp. 145-147.
  • Movahhedian M, Ma Y, Tafazolli R. (2010) 'Blind CFO Estimation for Linearly Precoded OFDMA Uplink'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE TRANSACTIONS ON SIGNAL PROCESSING, 58 (9), pp. 4698-4710.
  • Dianati M, Tafazolli R, Shen X, Naik K. (2010) 'Per-user service model for opportunistic scheduling scheme over fading channels'. JOHN WILEY & SONS INC WIRELESS COMMUNICATIONS & MOBILE COMPUTING, 10 (1), pp. 87-100.
  • Hoshyar R, Shariat M, Tafazolli R. (2010) 'Subcarrier and Power Allocation with Multiple Power Constraints in OFDMA Systems'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE COMMUNICATIONS LETTERS, 14 (7), pp. 644-646.
  • Bennis M, Wijting C, Abedi S, Thilakawardana S, Tafazolli R. (2009) 'Performance evaluation of advanced spectrum functionalities for future radio networks'. JOHN WILEY & SONS INC WIRELESS COMMUNICATIONS & MOBILE COMPUTING, 9 (11), pp. 1532-1542.
  • Shariat M, Quddus AU, Ghorashi SA, Tafazolli R. (2009) 'Scheduling as an Important Cross-Layer Operation for Emerging Broadband Wireless Systems'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE COMMUNICATIONS SURVEYS AND TUTORIALS, 11 (2), pp. 74-86.
  • Heliot F, Chu X, Hoshyar R, Tafazolli R. (2009) 'A Tight Closed-Form Approximation of the Log-Normal Fading Channel Capacity'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, 8 (6), pp. 2842-2847.
  • Hanzo L, Tafazolli R. (2009) 'Admission Control Schemes for 802.11-Based Multi-Hop Mobile Ad hoc Networks: A Survey'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE COMMUNICATIONS SURVEYS AND TUTORIALS, 11 (4), pp. 78-108.
  • 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'. SPRINGER WIRELESS PERSONAL COMMUNICATIONS, 48 (1), pp. 175-191.
  • Abaii M, Liu Y, Tafazolli R. (2008) 'An efficient resource allocation strategy for future wireless cellular systems'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, 7 (8), pp. 2940-2949.
  • Ma Y, Yi N, Tafazolli R. (2008) 'Bit and power loading for OFDM-based three-node relaying communications'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE TRANSACTIONS ON SIGNAL PROCESSING, 56 (7), pp. 3236-3247.
  • Thilakawardana D, Moessner K, Tafazolli R. (2008) 'Darwinian approach for dynamic spectrum allocation in next generation systems'. INST ENGINEERING TECHNOLOGY-IET IET COMMUNICATIONS, 2 (6), pp. 827-836.
  • Wang Y, Fan L, He D, Tafazolli R. (2008) 'Performance comparison of scheduling algorithms in network mobility environment'. ELSEVIER SCIENCE BV COMPUTER COMMUNICATIONS, 31 (9), pp. 1727-1738.
  • Hoshyar R, Wathan PP, Tafazolli R. (2008) 'Novel low-density signature for synchronous CDMA systems over AWGN channel'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE TRANSACTIONS ON SIGNAL PROCESSING, 56 (4), pp. 1616-1626.
  • Wathan F, Hoshyar R, Tafazolli R. (2008) 'Dynamic grouped chip-level iterated multiuser detection based on Gaussian forcing technique'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE COMMUNICATIONS LETTERS, 12 (3), pp. 167-169.
  • Wang Y, Fan L, He D, Tafazolli R. (2008) 'Solution to weight-adaptive fair queuing'. INST ENGINEERING TECHNOLOGY-IET ELECTRON LETT, 44 (5), pp. 385-387.
  • Zhang Y, Hoshyar R, Tafazolli R. (2008) 'Timing and frequency offset estimation scheme for the uplink of OFDMA systems'. INST ENGINEERING TECHNOLOGY-IET IET COMMUNICATIONS, 2 (1), pp. 121-130.
  • Navaratnam P, Cruickshank H, Tafazolli R. (2008) 'A link adaptive transport protocol for multimedia streaming applications in multi hop wireless networks'. SPRINGER MOBILE NETWORKS & APPLICATIONS, 13 (3-4), pp. 246-258.
  • Huy DTP, Rodriguez J, Gameiro A, Tafazolli R. (2007) 'Dynamic resource allocation for beyond 3G cellular networks'. SPRINGER WIRELESS PERSONAL COMMUNICATIONS, 43 (4), pp. 1727-1740.
  • Mozaffaripour M, Tafazolli R. (2007) 'Suboptimal search algorithm in conjunction with polynomial-expanded linear multiuser detector for FDD WCDMA mobile uplink'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, 56 (6), pp. 3600-3606.
  • Li Z, Tafazolli R. (2007) 'Location management for packet switched services in 3G partnership project networks'. INST ENGINEERING TECHNOLOGY-IET IET COMMUNICATIONS, 1 (4), pp. 562-569.
  • Widiawan AK, Tafazolli R. (2007) 'High altitude platform station (HAPS): A review of new infrastructure development for future wireless communications'. SPRINGER WIRELESS PERSONAL COMMUNICATIONS, 42 (3), pp. 387-404.
  • Gluhak A, Inoue M, Moessner K, Tafazolli R. (2007) 'Signaling channel for coordinated multicast service delivery in next generation wireless networks'. IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG IEICE TRANSACTIONS ON COMMUNICATIONS, E90B (7), pp. 1780-1790.
  • Ma Y, Tafazolli R. (2007) 'Estimation of carrier frequency offset for multicarrier CDMA uplink'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE TRANSACTIONS ON SIGNAL PROCESSING, 55 (6), pp. 2617-2627.
  • Ma Y, Tafazolli R. (2007) 'Channel estimation for OFDMA uplink: a hybrid of linear and BEM interpolation approach'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE TRANSACTIONS ON SIGNAL PROCESSING, 55 (4), pp. 1568-1573.
  • Dohler M, McLaughlin S, Lee Y, Tafazolli R. (2007) 'Implementable wireless access for B3G networks - Part IV: Resource management issues'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE COMMUNICATIONS MAGAZINE, 45 (3), pp. 106-111.
  • Georgiades M, Akhtar N, Politis C, Tafazolli R. (2007) 'Enhancing mobility management protocols to minimise AAA impact on handoff performance'. ELSEVIER SCIENCE BV COMPUTER COMMUNICATIONS, 30 (3), pp. 608-618.
  • 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.
  • 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.
  • Huang L, Liu Y, Thilakawardana S, Tafazolli R. (2006) 'Network-centric user assignment in the next generation mobile networks'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE COMMUNICATIONS LETTERS, 10 (12), pp. 822-824.
  • 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'. SPRINGER MOBILE NETWORKS & APPLICATIONS, 11 (6), pp. 847-860.
  • 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-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE TRANSACTIONS ON BROADCASTING, 52 (4), pp. 492-504.

    Abstract

    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.

  • Liu Y, Hoshyar R, Yang X, Tafazolli R. (2006) 'Integrated radio resource allocation for multihop cellular networks with fixed relay stations'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, 24 (11), pp. 2137-2146.
  • Ma Y, Yi N, Tafazolli R. (2006) 'Channel estimation for PIRP-OFDM in slowly time-varying channel: First-order or second-order statistics?'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE SIGNAL PROCESSING LETTERS, 13 (3), pp. 129-132.
  • 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.
  • Prammanee S, Moessner K, Tafazolli R. (2006) 'Discovering modalities for adaptive multimodal interfaces'. Interactions, 13 (3), pp. 66-70.
  • Hoshyar R, Wathan FP, Tafazolli R. (2006) 'Novel Low-Density Signature structure for synchronous DS-CDMA systems'. GLOBECOM - IEEE Global Telecommunications Conference,

    Abstract

    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.

Conference papers

  • 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, Toronto, Canada: VTC2017-Fall
    [ Status: Accepted ]

    Abstract

    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.

  • Fathy Y, Barnaghi P, Tafazolli R. (2017) 'Distributed Spatial Indexing for the Internet of Things Data Management'. IEEE Proceedings of IM 2017, Lisbon, Portugal: IFIP/IEEE International Symposium on Integrated Network Management
    [ Status: Accepted ]
  • Qian P, Wang N, Foster G, Tafazolli R. (2017) 'Enabling Context-aware HTTP with Mobile Edge Hint'. IEEE Proceedings of IEEE CCNC 2017, Las Vegas, USA: IEEE CCNC 2017
    [ Status: Accepted ]

    Abstract

    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 DW, Heliot F, Imran MA, Tafazolli R. (2017) 'Spatial Quadrature Modulation for Visible Light Communication in Indoor Environment'. IEEE 2017 IEEE ICC Conference Proceedings, Paris, France: IEEE ICC 2017 Optical Networks and Systems Symposium
    [ Status: Accepted ]
  • Onireti OS, Imran A, Imran M, Tafazolli R. (2016) 'Impact of Positioning Error on Achievable Spectral Efficiency in Database-aided Networks'. Kuala Lumpur, Malaysia: IEEE International Conference on Communications
    [ Status: Accepted ]
  • Nikitopoulos K, Chatzipanagiotis D, Jayawardena C, Tafazolli R. (2016) 'MultiSphere: Massively Parallel Tree Search for Large Sphere Decoders'. IEEE IEEE GLOBECOM 2016 Proceedings, Washington, DC: IEEE GLOBECOM 2016
    [ Status: Accepted ]
  • Akbari I, Onireti O, Imran A, Imran MA, Tafazolli R. (2015) 'Impact of Inaccurate User and Base Station Positioning on Autonomous Coverage Estimation'. IEEE 2015 IEEE 20TH INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELLING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD), Guildford, ENGLAND: IEEE 20th International Workshop on Computer Aided Modelling and Design of Communication Links and Networks (CAMAD), pp. 114-118.
  • 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'. IEEE 2015 IEEE 20TH INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELLING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD), Guildford, ENGLAND: IEEE 20th International Workshop on Computer Aided Modelling and Design of Communication Links and Networks (CAMAD), pp. 237-241.
  • 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), London: IEEE International Conference on Communications, pp. pp. 13-18.
    [ Status: Accepted ]

    Abstract

    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.

  • Onireti OS, Mohamed A, Imran MA, Tafazolli R. (2015) 'Correlation-based Adaptive Pilot Pattern in Control/Data Separation Architecture'. IEEE 2015 IEEE International Conference on Communications (ICC), London: IEEE International Conference on Communications, pp. 2233-2238.

    Abstract

    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.

  • Pateromichelakis E, Shariat M, Quddus A, Tafazolli R. (2015) 'Joint Routing and Scheduling in Dense Small Cell Networks using 60GHz backhaul'. London: IEEE ICC 2015 - Workshop on Cloud-Processing in Heterogeneous Mobile Communication Networks (IWCPM)
    [ Status: Accepted ]
  • Onireti OS, Mohamed A, Qi Y, Imran A, Imran MA, Tafazolli R. (2014) 'Physical Layer Frame in Signalling-Data Separation Architecture: Overhead and Performance Evaluation'. VDE Proceedings of European Wireless 2014; 20th European Wireless Conference, Barcelona, Spain: European Wireless 2014; 20th European Wireless Conference, pp. 820-825.
  • Vural S, Navaratnam P, Wang N, Tafazolli R. (2014) 'Asynchronous Clustering of Multihop Wireless Sensor Networks'. IEEE IEEE International Conference on Communications (ICC), 2014, Sydney, Australia: IEEE ICC, pp. 472-477.
  • Onireti OS, Akbari I, Imran MA, Imran A, Tafazolli R. (2014) 'Effect of Inaccurate Position Estimation on Self-Organising Coverage Estimation in Cellular Networks'. VDE Barcelona, Spain: European Wireless 2014, pp. 176-180.

    Abstract

    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.

  • Imran M, Mohamed A, Tafazolli R. (2014) 'Splitting the data and control functionality: Scalable deployment solution for 5G cellular networks'. IWPC - The International Wireless Industry Consortium Proceedings of International Wireless Industry Consortium (IWPC) Workshop 2014, Oxford, UK: International Wireless Industry Consortium (IWPC) Workshop 2014
  • Pilloni V, Navaratnam P, Vural S, Atzori L, Tafazolli R. (2013) 'Cooperative Task Assignment for Distributed Deployment of Applications in WSNs'. Budapest, Hungary: IEEE International Conference on Communications (ICC 2013)
  • Akbari A, Imran MA, Tafazolli R. (2011) 'Maximising Average Energy efficiency for Two-user AWGN Broadcast Channel'. Warsaw, Poland : IEEE Future Network and Mobile Summit, Warsaw: Future Network & Mobile Summit (FutureNetw), 2011

    Abstract

    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.

  • Yi N, Ma Y, Tafazolli R. (2011) 'Incremental Decode-Forward Relaying over Asymmetric Fading Channels: Outage Probability and Location-Aided Relay Selection'. Nice, France: IEEE SSP'11, pp. 181-184.
  • Imran MA, Tang W, Tafazolli R. (2011) 'Coordination of Energy Efficient Sensing and Transmission in Cognitive Radio Networks'. Liverpool, UK: PGNET Liverpool
  • Heliot F, Imran MA, tafazolli R. (2011) 'On the Energy Efficiency Gain of MIMO Communication under Various Power Consumption Models'. Warsaw, Poland: ICT Future Network & Mobile Summit
  • Yi N, Ma Y, Tafazolli R. (2011) 'Cooperative iterative water-filling for two-user Gaussian frequency-selective interference chanels'. Budapest: IEEE VTC'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.

    Abstract

    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.

  • 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.

    Abstract

    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.

  • Han C, Dianati M, Tafazolli R, Kernchen R. (2010) 'Throughput Analysis of the IEEE 802.11p Enhanced Distributed Channel Access Function in Vehicular Environment'. Ottowa, Canada: 72nd IEEE Vehicular Technology Conference, pp. 1-5.
  • 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, Instanbul, Turkey: 21st PIMRC 2009, pp. 2354-2359.
  • 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, Instanbul, Turkey: 21st PIMRC 2010, pp. 1332-1336.
  • Auer G, Godor I, Hevizi L, Imran M, Tafazolli R. (2010) 'Enablers for Energy Efficient Wireless Networks'. Ottawa, Canada : IEEE Green Wireless Communications and Networks Workshop � GreeNet, Proc. IEEE VTC Fall 2010, Vehicular Technology Conference Fall (VTC 2010-Fall), 2010 IEEE 72nd, pp. 1-5.

    Abstract

    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.

  • Héliot F, Hoshyar R, Tafazolli R. (2010) 'On the spectral efficiency maximization of Nonregenerative Cooperative MIMO Communication Systems'. Proc. IEEE PIMRC, Istanbul, Turkey: IEEE PIMRC
  • Héliot F, Hoshyar R, Tafazolli R. (2010) 'Power Allocation for the Downlink of Nonregenerative Cooperative Multi-User MIMO Communication system'. Proc. IEEE PIMRC, Istanbul, Turkey: IEEE PIMRC
  • Wei D, Navaratnam P, Gluhak A, Tafazolli R. (2010) 'Energy-efficient Clustering for Wireless Sensor Networks with Unbalanced Traffic Load'. IEEE IEEE Wireless Communications and Networking conference, Sydney: IEEE Wireless Communications & Networking Conference
  • 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, Florence, Italy: ICT Future Network & Mobile Summit
  • Abangar H, Ghader M, Gluhak A, Tafazolli R. (2010) 'Improving the Performance of Web Services in Wireless Sensor Networks'. Florence, Italy: Future Network & Mobile Summit 2010
  • 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, Florence, Italy: ICT Future Network & Mobile Summit
  • 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.
  • Chatzimisios P, Dagiuklas T, Tafazolli R, Verikoukis C. (2010) 'Message from ConWire'10 co-chairs'. Proceedings - International Conference on Computer Communications and Networks, ICCCN,
  • 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.
  • 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.
  • Dianati M, Tafazolli R, Moessner K. (2010) 'Enabling Tussle-Agile Inter-networking Architectures by Underlay Virtualisation'. SPRINGER-VERLAG BERLIN FUTURE INTERNET - FIS 2009, Berlin, GERMANY: 2nd Future Internet Symposium (FIS 2009) 6152, pp. 81-95.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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,
  • 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.
  • 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.
  • 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'. IEEE 2010 IEEE 21st International Symposium on Personal Indoor and Mobile Radio Communications, Istanbul, Turkey: PIMRC 2010, pp. 2471-2476.
  • 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.
  • Qi Y, Hoshyar R, Tafazolli R. (2010) 'A novel hybrid relaying scheme using multilevel coding'. IEEE Vehicular Technology Conference,
  • 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,
  • 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.
  • 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, St. Petersburg, Russia: ICUMT '09
  • Salami GK, Tafazolli R. (2009) 'A framework for UMTS inter-operator spectrum sharing in the UMTS extension band'. IEEE 9th International Symposium on Communications and Information Technology, Icheon, South Korea: 9th ISCIT 2009, pp. 193-198.
  • Yi N, Ma Y, Tafazolli R. (2009) 'Coexistence Strategies and Capacity Theorems of Interference Awareness Cognitive Radio'. IEEE 2009 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATION WORKSHOPS, VOLS 1 AND 2, Dresden, GERMANY: IEEE International Conference on Communications (ICC 2009), pp. 644-648.
  • Heliot F, Hoshyar R, Tafazolli R. (2009) 'A CLOSED-FORM APPROXIMATION OF THE OUTAGE PROBABILITY FOR DISTRIBUTED MIMO SYSTEMS'. IEEE SPAWC: 2009 IEEE 10TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS, Perugia, ITALY: 10th IEEE Workshop on Signal Processing Advances in Wireless Communications, pp. 529-533.
  • Heliot F, Fazel S, Hoshyar R, Tafazolli R. (2009) 'RECEIVE KNOWLEDGE ONLY POWER ALLOCATION FOR NONREGENERATIVE COOPERATIVE MIMO COMMUNICATION'. IEEE SPAWC: 2009 IEEE 10TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS, Perugia, ITALY: 10th IEEE Workshop on Signal Processing Advances in Wireless Communications, pp. 524-528.
  • Ghader M, Tafazolli R. (2009) 'Efficient Employment of Service Location Protocol in Multi-cluster Networks'. Santander, Spain: ICT-MobileSummit 2009
  • Hoshyar R, Heliot F, Tafazolli R. (2009) 'A Novel Multi-layer Cooperative Decode and Forward Scheme'. IEEE 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, Barcelona, SPAIN: 69th IEEE Vehicular Technology Conference, pp. 1248-+.
  • Qi YA, Hoshyar R, Tafazolli R. (2009) 'A New ARQ Protocol for Hybrid DF/CF Relay Scheme'. IEEE 69th IEEE VEHICULAR TECHNOLOGY CONFERENCE, Barcelona, SPAIN: 69th VTC Spring 2009, pp. 1356-1360.
  • Qi YA, Hoshyar R, Tafazolli R. (2009) 'A Novel Quantization Scheme in Compress-and-Forward Relay System'. IEEE IEEE 69th VEHICULAR TECHNOLOGY CONFERENCE, Barcelona, SPAIN: 69th VTC Spring 2009, pp. 1854-1858.
  • 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.
  • 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.
  • Fazel MS, Hoshyar R, Tafazolli R. (2009) 'Flexible Amplify and Forward Relaying Protocol with optimized duplexing'. IEEE 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, Barcelona, SPAIN: 69th IEEE Vehicular Technology Conference, pp. 3176-3180.
  • Mach T, Tafazolli R. (2009) 'Mass Mobility Signaling Congestion Avoidance Mechanism Using Randomized Time Distribution of Cell Reselections'. IEEE 2009 INTERNATIONAL CONFERENCE ON TELECOMMUNICATIONS (ICT), Marrakech, MOROCCO: 16th International Conference on Telecommunications (ICT), pp. 238-242.
  • Salami G, Tafazolli R. (2009) 'On the Performance evaluation of spectrum sharing algorithms between two UMTS operators'. IEEE 2009 INTERNATIONAL CONFERENCE ON TELECOMMUNICATIONS (ICT), Marrakech, MOROCCO: 16th International Conference on Telecommunications (ICT), pp. 260-265.
  • 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.
  • 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,
  • Shariat M, Ul Quddus A, Tafazolli R. (2009) '$publication.get('TITLE')'. IEEE Wireless Communications and Networking Conference, WCNC,
  • Imran A, Tafazolli R. (2009) 'Evaluation and Comparison of Capacities and Costs of Multihop Cellular Networks'. IEEE 2009 INTERNATIONAL CONFERENCE ON TELECOMMUNICATIONS (ICT), Marrakech, MOROCCO: 16th International Conference on Telecommunications (ICT), pp. 160-165.
  • Hamadani E, Mostafavi M, Tafazolli R, Rakocevic V. (2009) 'Analysis of IEEE802.11 DCF Parameters on Achievable Throughput in Ad hoc Networks'. IEEE 2009 IEEE 70TH VEHICULAR TECHNOLOGY CONFERENCE FALL, VOLS 1-4, Anchorage, AK: 70th IEEE Vehicular Technology Conference, pp. 465-470.
  • Liu H, Ma Y, Tafazolli R. (2009) 'Enhanced linear interpolation schemes for chunk-based OFDMA uplink'. IEEE Vehicular Technology Conference,
  • Salami G, Tafazolli R. (2009) 'On the Impact of Varying Bandwidth on the Performance of UMTS Spectrum Sharing Algorithm'. UNIV ZAGREB, FAC ELECT ENGN COMP CONTEL 2009: PROCEEDINGS OF THE 10TH INTERNATIONAL CONFERENCE ON TELECOMMUNICATIONS, Univ Zagreb, Fac Elect Engn & Comp, Zagreb, CROATIA: 10th International Conference on Telecommunications (ConTEL 2009), pp. 319-324.
  • 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.
  • Hoshyar R, Tafazolli R. (2009) 'A Pre-BSC Model for Distributed Turbo Codes'. IEEE 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, Barcelona, SPAIN: 69th IEEE Vehicular Technology Conference, pp. 1936-1940.
  • Hoshyar R, Tafazolli R. (2009) 'Performance evaluation Of HARQ schemes for Cooperative Regenerative Relaying'. IEEE 2009 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-8, Dresden, GERMANY: IEEE International Conference on Communications (ICC 2009), pp. 3355-3360.
  • 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.
  • Qi Y, Hoshyar R, Tafazolli R. (2009) 'Efficient ARQ Protocol for Hybrid Relay Schemes with Limited Feedback'. IEEE 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, Barcelona, SPAIN: 69th IEEE Vehicular Technology Conference, pp. 1849-1853.
  • Qi Y, Hoshyar R, Tafazolli R. (2009) 'On the Performance of HARQ with Hybrid Relaying Schemes'. IEEE 2009 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-8, Dresden, GERMANY: IEEE International Conference on Communications (ICC 2009), pp. 4357-4362.
  • Hoshyar R, Tafazolli R. (2009) 'Optimum Decoding of Full Decode and Forward Scheme over Cooperative Relay Channels'. IEEE 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, Barcelona, SPAIN: 69th IEEE Vehicular Technology Conference, pp. 1054-1058.
  • Psaras I, Dianati M, Tafazolli R. (2009) 'Why Rely on Blind AIMDs? (Work in Progress)'. SPRINGER-VERLAG BERLIN NETWORKING 2009, Aachen, GERMANY: 8th International IFIP TC 6 Network Conference 2009 5550, pp. 404-415.
  • Yarmohammad A, Abaii M, Thilakawardana S, Tafazolli R. (2009) 'Inter-operator Dynamic Spectrum Selection in UMTS'. IEEE 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, Barcelona, SPAIN: 69th IEEE Vehicular Technology Conference, pp. 504-508.
  • Salami G, Thilakawardana S, Tafazolli R. (2009) 'The impact of queuing and call setup delays on UMTS spectrum sharing algorithm'. IEEE WTS: 2009 WIRELESS TELECOMMUNICATIONS SYMPOSIUM, Prague, CZECH REPUBLIC: Wireless Telecommunications Symposium 2009, pp. 402-406.
  • 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.
  • Salami G, Thilakawardana S, Tafazolli R. (2009) 'Dynamic spectrum sharing algorithm between two UMTS operators in the UMTS Extension Band'. IEEE 2009 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATION WORKSHOPS, VOLS 1 AND 2, Dresden, GERMANY: IEEE International Conference on Communications (ICC 2009), pp. 338-343.
  • 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'. ASSOC COMPUTING MACHINERY PE-WASUN09: PROCEEDINGS OF THE SIXTH ACM INTERNATIONAL SYMPOSIUM ON PERFORMANCE EVALUATION OF WIRELESS AD-HOC, SENSOR, AND UBIQUITOUS NETWORKS, Tenerife, SPAIN: 6th ACM International Symposium on Performance Evaluation of Wireless Ad-Hoc, Sensor, and Ubiquitous Networks, pp. 58-62.
  • 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,

    Abstract

    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.

  • 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.

    Abstract

    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.

  • 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,

    Abstract

    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.

  • Yi N, Ma Y, Tafazolli R . (2008) 'Doubly differential communication assisted with cooperative relay'. IEEE 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, Marina Bay, SINGAPORE: 67th IEEE Vehicular Technology Conference 1 - 7, pp. 644-647.

    Abstract

    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.

  • Mirzadeh S, Tafazolli R, Armknecht F, Pallares JJ, Afifi H. (2008) 'CPFP: An efficient key management scheme for large scale personal networks'. IEEE 2008 3RD INTERNATIONAL SYMPOSIUM ON WIRELESS PERVASIVE COMPUTING, VOLS 1-2, Santorini, GREECE: 3rd International Symposium on Wireless Pervasive Computing, pp. 743-747.
  • Zhang Y, Ma Y, Tafazolli R. (2008) 'Improved Coded Cooperation Schemes for Wireless Communications'. IEEE 2008 6th International Symposium on Modeling and Optimization in Mobile, Ad Hoc and Wireless Networks and Workshops, Vols 1 and 2, Berlin, GERMANY: 6th International Symposium on Modeling and Optimization in Mobile, Ad-Hoc, and Wireless Networks, pp. 507-512.
  • Wang M, Georgiades M, Tafazolli R. (2008) 'Signalling cost evaluation of mobility management schemes for different core network architectural arrangements in 3GPP LTE/SAE'. IEEE 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7, Marina Bay, SINGAPORE: 67th IEEE Vehicular Technology Conference, pp. 2253-2258.
  • 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,

    Abstract

    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.

  • 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,
  • 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,
  • 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.

    Abstract

    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.

  • Liu H, Ma Y, Tafazolli R. (2008) 'Optimum pilot placement for chunk-based OFDMA uplink: Time direction scenario'. IEEE 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7, Marina Bay, SINGAPORE: 67th IEEE Vehicular Technology Conference, pp. 2547-2551.
  • 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,
  • Hoshyar R, Tafazolli R. (2008) 'Soft decode and forward of MQAM modulations for cooperative relay channels'. IEEE 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7, Marina Bay, SINGAPORE: 67th IEEE Vehicular Technology Conference, pp. 639-643.
  • Touheed H, Quddus AU, Tafazolli R. (2008) 'An improved link adaptation scheme for High Speed Downlink Packet Access'. IEEE 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7, Marina Bay, SINGAPORE: 67th IEEE Vehicular Technology Conference, pp. 2051-2055.
  • Qi Y, Hoshyar R, Tafazolli R. (2008) 'Soft multilevel Slepian-Wolf decoding in systems using Turbo joint decoding and decompressing'. IEEE 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7, Marina Bay, SINGAPORE: 67th IEEE Vehicular Technology Conference, pp. 1514-1518.
  • 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,

    Abstract

    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.

  • Touheed H, Quddus AU, Tafazolli R. (2008) 'Predictive CQI reporting for HSDPA'. IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC,
  • 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,
  • 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,
  • Dianati M, Tafazolli R. (2008) 'Opportunistic scheduling over wireless fading channels without explicit feedback'. IEEE 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7, Marina Bay, SINGAPORE: 67th IEEE Vehicular Technology Conference, pp. 1871-1875.
  • Hoshyar R, Tafazolli R. (2008) 'Achievable full decode and forward rates for cooperative MIMO BICM systems'. IEEE IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, Cannes, France: 19th PIMRC 2008
  • Qi Y, Hoshyar R, Tafazolli R. (2008) 'Performance evaluation of soft decode-and-forward in fading relay channels'. IEEE 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7, Marina Bay, SINGAPORE: 67th IEEE Vehicular Technology Conference, pp. 1286-1290.
  • Hamid A, Hoshyar R, Tafazolli R. (2008) 'Joint rate and power adaptation for MC-CDMA over tempo-spectral domain'. IEEE WCNC 2008: IEEE WIRELESS COMMUNICATIONS & NETWORKING CONFERENCE, VOLS 1-7, Las Vegas, NV: IEEE Wireless Communications and Networking Conference, pp. 969-973.
  • Yi N, Ma Y, Tafazolli R. (2008) 'Rate-adaptive bit and power loading for OFDM based DF relaying'. IEEE 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7, Marina Bay, SINGAPORE: 67th IEEE Vehicular Technology Conference, pp. 1340-1344.
  • Jung J, Abaii M, Tafazolli R. (2008) 'Load Matrix optimization in mobile cellular networks'. IEEE 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7, Marina Bay, SINGAPORE: 67th IEEE Vehicular Technology Conference, pp. 2016-2020.
  • Wathan FP, Hoshyar R, Tafazolli R. (2008) 'PERFORMANCE ANALYSIS OF GROUPED CHIP-LEVEL ITERATED MULTIUSER DETECTION FOR OVERLOADED CDMA SYSTEMS'. IEEE 2008 IEEE 9TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS, VOLS 1 AND 2, Recife, BRAZIL: 9th IEEE Workshop on Signal Processing Advances in Wireless Communications, pp. 131-135.
  • Zhang Y, Ma Y, Tafazolli R. (2008) 'Modulation-adaptive cooperation schemes for wireless networks'. IEEE 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7, Marina Bay, SINGAPORE: 67th IEEE Vehicular Technology Conference, pp. 1320-1324.
  • Quddus AU, Yang X, Tafazolli R. (2008) 'Link-level analysis of downlink handover regions in UMTS'. IEEE 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7, Marina Bay, SINGAPORE: 67th IEEE Vehicular Technology Conference, pp. 2527-2531.
  • Hanzo L, Mostafavi SM, Tafazolli R. (2008) 'Connectivity-related properties of mobile nodes obeying the random walk and random waypoint mobility models'. IEEE 2008 IEEE 67TH VEHICULAR TECHNOLOGY CONFERENCE-SPRING, VOLS 1-7, Marina Bay, SINGAPORE: 67th IEEE Vehicular Technology Conference, pp. 133-137.
  • 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,
  • Ghader M, Tafazolli R. (2007) 'Enhanced Service Location Protocol in Personal Network'. Jaipur, India: WPMC’07
  • Thilakawardana S, Acar G, Hale B, Tafazolli R. (2007) 'Impact of status retry timer values on MFTP performance over bgan satellite multicast'. IEEE 2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9, Athens, GREECE: 18th IEEE International Symposium on Personal, Indoor and Mobile Radio Communication, pp. 4089-4094.
  • Wathan FP, Hoshyar R, Tafazolli R. (2007) 'Iterated SISO MUD for synchronous uncoded CDMA systems over AWGN channel: Performance evaluation in overloaded condition'. IEEE 2007 INTERNATIONAL SYMPOSIUM ON COMMUNICATIONS AND INFORMATION TECHNOLOGIES, VOLS 1-3, Sydney, AUSTRALIA: International Symposium on Communication and Information Technology, pp. 397-402.
  • Hanzo L, Tafazolli R. (2007) 'Throughput assurances through admission control for multi-hop MANETs'. IEEE 2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9, Athens, GREECE: 18th IEEE International Symposium on Personal, Indoor and Mobile Radio Communication, pp. 1945-1949.
  • Schott W, Gluhak A, Presser M, Hunkeler U, Tafazolli R. (2007) 'e-SENSE protocol stack architecture for wireless sensor networks'. IEEE 2007 PROCEEDINGS OF THE 16TH IST MOBILE AND WIRELESS COMMUNICATIONS, VOLS 1-3, Budapest, HUNGARY: 16th IST Mobile and Wireless Communications, pp. 464-468.
  • Liu H, Ma Y, Tafazolli R. (2007) 'Sub-optimum pilot placement for chunk-based OFDMA uplink: Consecutive chunks scenario'. IEEE 2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9, Athens, GREECE: 18th IEEE International Symposium on Personal, Indoor and Mobile Radio Communication, pp. 1925-1929.
  • Hanzo L, Tafazolli R. (2007) 'Quality of Service routing and admission control for mobile ad-hoc networks with a contention-based MAC layer'. IEEE 2006 IEEE International Conference on Mobile Adhoc and Sensor Systems, Vols 1 and 2, Vancouver, CANADA: IEEE International Conference on Mobile Adhoc and Sensor Systems, pp. 451-454.
  • Liu H, Ma Y, Tafazolli R. (2007) 'Optimum pilot placement for chunk-based OFDMA uplink: Single chunk scenario'. IEEE 2007 IEEE 66TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, Baltimore, MD: 66th IEEE Vehicular Technology Conference, pp. 2194-2198.
  • 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,

    Abstract

    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.

  • Li Z, Akhtar N, Tafazolli R. (2007) 'Seamless IP multimedia service continuity support in inter-worked UMTS and WLAN'. IEEE 2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9, Athens, GREECE: 18th IEEE International Symposium on Personal, Indoor and Mobile Radio Communication, pp. 1478-1482.
  • Zhang Y, Ma Y, Tafazolli R. (2007) 'Tighter bounds of symbol error probability for amplify-and-forward cooperative protocol over rayleigh fading channels'. IEEE 2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9, Athens, GREECE: 18th IEEE International Symposium on Personal, Indoor and Mobile Radio Communication, pp. 1920-1924.
  • Grandblaise D, Moessner K, Vivier G, Tafazolli R. (2006) 'Rental protocol for automated spectrum sharing negotiation between base stations'. FACHVERLAG SCHIELE SCHON FREQUENZ, Karlsruhe, GERMANY: 4th Karlsruhe Workshop on Software Radios 60 (9-10), pp. 162-166.
  • 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'. Mykonos, Greece: 15th IST Mobile and Wireless communications Summit
  • 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.
  • Nourizadeh H, Nourizadeh S, Tafazolli R. (2006) 'Performance evaluation of Cellular Networks with Mobile and Fixed Relay Station'. IEEE 2006 IEEE 64TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-6, Montreal, CANADA: 64th IEEE Vehicular Technology Conference, pp. 2434-2438.
  • Qi Y, Hoshyar R, Tafazolli R. (2006) 'Capacity of Intelligent Quadrifiliar Helix Antenna (IQHA) based MIMO system'. IEEE 2006 IEEE International Workshop on Antenna Technology: Small Antennas and Novel Metamaterials (IWAT), White Plains, NY: 2nd IEEE International Workshop on Antenna Technology, pp. 365-368.
  • Nourizadeh H, Nourizadeh S, Tafazolli R. (2006) 'Impact of the Inter-relay Handoff on the Relaying System Performance'. IEEE 2006 IEEE 64TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-6, Montreal, CANADA: 64th IEEE Vehicular Technology Conference, pp. 2529-2533.
  • Hamid A, Hoshyar R, Tafazolli R. (2006) 'Band Based Dynamic Link Adaptation for MC-CDMA Radio Interface'. IEEE 2006 IEEE 64TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-6, Montreal, CANADA: 64th IEEE Vehicular Technology Conference, pp. 791-795.
  • Presser M, Gluhak A, Babb D, Tafazolli R, Herault L. (2006) 'E-SENSE - Capturing ambient intelligence for mobile communications through wireless sensor networks'. INSTICC-INST SYST TECHNOLOGIES INFORMATION CONTROL & COMMUNICATION WINSYS 2006: Proceedings of the International Conference on Wireless Information Networks and Systems, Setubal Coll Business Adm, Setubal, PORTUGAL: International Conference on Wireless Information Networks and Systems, pp. 341-346.
  • 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.
  • Georgiades M, Akhtar N, Ghader M, Li Z, Gultchev S, Tafazolli R. (2005) 'Surrey's Next Generation Wireless Network Testbed'. Marrakech, Morocco: 7th IEEE International Conference on Mobile and Wireless Communications Networks
  • Mirzadeh S, Tafazolli R. (2005) 'Secure Service Discovery for Personal Networks'. Shiraz, Iran: International Symposium on Telecommunications 2005 (IST2005)
  • Ghader M, Olsen RL, Giro-Genet M, Tafazolli R. (2005) 'Service Management Platform for Personal Networks'. Dresden, Germany: 14th IST Mobile and Wireless communications Summit
  • Tang SY, Thilakawardana S, Tafazolli R, Qian Y. (2005) 'Performance analysis of predictive scalable resource allocation for integrated wireless networks'. IEEE 2005 INTERNATIONAL CONFERENCE ON WIRELESS NETWORKS, COMMUNICATIONS AND MOBILE COMPUTING, VOLS 1 AND 2, Maui, HI: International Conference on Wireless Networks, Communications and Mobile Computing, pp. 745-750.
  • Ma Y, Tafazolli R. (2005) 'Exploiting hidden pilots for carrier frequency offset estimation for generalized MC-CDMA systems'. IEEE 2005 IEEE/SP 13th Workshop on Statistical Signal Processing (SSP), Vols 1 and 2, Bordeaux, FRANCE: 13th IEEE Workshop on Statistical Signal Processing, pp. 1237-1241.
  • Sali A, Widiawan A, Thilakawardana S, Tafazolli R, Evans BG. (2005) 'Cross-layer design approach for multicast scheduling over satellite networks'. IEEE 2nd International Symposium on Wireless Communications Systems 2005 (ISWCS 2005), Univ Siena, Siena, ITALY: 2nd International Symposium on Wireless Communications Systems (ISWCS 2005), pp. 701-705.
  • Ghader M, Tafazolli R. (2004) 'Performance of Service Discovery Protocols in Personal Networks'. Shanghai, China: IST MAGNET Workshop, Visions and Beyond
  • Ghader M, Prasad N, Olsen RL, Mirzadeh S, Tafazolli R. (2004) 'Secure Resource and Service Discovery in Personal Networks Wireless'. Toronto, Canada: World Research Forum Meeting #12
  • Ghader M, Moessner K, Tafazolli R. (2004) 'Service Discovery and Provision Protocols for Wireless Networks'. Lyon, France: 13th IST Mobile & Wireless Communications Summit

Books

  • Forum WWR. (2006) Technologies for the wireless future. John Wiley & Sons

Book chapters

  • Han C, Muhaidat S, Abualhaol I, Dianati M, Tafazolli R. (2013) 'Intrusion Detection in Vehicular Ad-Hoc Networks on Lower Layers'. in (ed.) Security, Privacy, Trust, and Resource Management in Mobile and Wireless Communications IGI Global Article number 8
  • Hanzo L, Tafazolli R. (2008) 'Mobile Ad Hoc Networks: Challenges and Solutions for Providing Quality of Service Assurances'. in Kyriazakos S, Soldatos I, Karetsos G (eds.) 4g Mobile and Wireless Communications Technologies River Publishers

Patents

  • Hoseinitabatabaei SA, barnaghi P, tafazolli R, wang C. Method and apparatus for scalable data discovery in IoT systems.

Theses and dissertations

  • Mi D. (2017) Massive MIMO with imperfect channel state information and practical limitations..
    [ Status: Approved ]

    Abstract

    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 take

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