Dr Muhammad Ali Imran
Lecturer in Communications
Qualifications: DIC, MSc, PhD, SMIEEE
Email: m.imran@surrey.ac.uk
Office hours
Wednesday, 1100-1200 hrs
Further information
Biography
I obtained my BSc in Electrical Engineering (Electronics and Communications) from University of Engineering & Technology Lahore in 1999. I worked in Industry as a senior design engineer in a Systems Design company for a duration of two years. Later, I obtained my MSc degree from Imperial College London in Communications and Signal Processing in 2002. I was awarded the Diploma of Imperial College and the PhD degree from Imperial College and University of London in 2007. My research thesis was entitled "Resource Optimisation for Cooperative Broadcasting in WCDMA Networks".
As a post DOC researcher, I worked on formulation of Information Theoretic fundamental capacity limits of wireless cellular networks. This work was funded by Mobile Virtual Center of Excellence UK (a consortium of selected UK Universities and Industry). I have also worked on a European Commission EC funded project ROCKET where I worked on efficient techniques to design and operate a wireless cellular communication system.
In 2009, I joined the faculty of engineering and physical sciences (FEPS) at the University of Surrey as a Lecturer in Communications. I coordinated the University of Surrey team involved in FP7 EC funded project EARTH - looking at Energy Efficient Next Generation of Cellular Networks. The project has won 2012 Best project for the Future of Internet award. I also lead the Theme 9 of India UK Advanced Technology Centre research - Self Organising Multihop Networks. I also supervised a Huawei funded project on a novel air interface technique: LDS-OFDM.
Currently, I am leading an EPSRC funded project - REDUCE that aims to reshape the energy demand of end users using ICT and economic incentives. REDUCE project has deployed a wireless sensor network in CCSR building to monitor and control energy demand of users using persuasive techniques and communication technology. I am a work package leader for IU-ATC phase II funded by EPSRC. I am co-supervising the Huawei funded Green Communications project and Sony funded Machine to Machine communication projects. I am actively participating in EU funded projects LexNet and iJoin.
Research Interests
I have worked under Mobile Virtual Centre of Excellence (MVCE) on a project: Fundamental Capacity Limits of Cellular Networks. The main focus of the work was to investigate information theoretic capacity limits for the cellular networks. This work is done under an Elective Research Programme of the Virtual Centre of Excellence in Mobile & Personal Communications, Mobile VCE, http://www.mobilevce.com. This research has been funded by the following Industrial Companies who are Members of Mobile VCE - BBC, BT, Huawei, Nokia, Nokia Siemens Networks, Nortel, Vodafone. Detailed technical reports on this research are available to staff from these Industrial Members of Mobile VCE.
I have been involved in EC funded ROCKET project where we are looking at efficient techniques of managing interference between the users of a wireless cellular communication system and also efficient methods of allocating the system resources to several users of these systems.
I was also leading the India-UK Advanced Technology Centre's theme 9 on self organising networks from the University of Surrey's end and also coordinated the University of Surrey team involved in FP7 EC funded project EARTH - looking at Energy Efficient Next Generation of Cellular Networks.
I obtained my BSc in Electrical Engineering (Electronics and Communications) from University of Engineering & Technology Lahore in 1999. I worked in Industry as a senior design engineer in a Systems Design company for a duration of two years. Later, I obtained my MSc degree from Imperial College London in Communications and Signal Processing in 2002. I was awarded the Diploma of Imperial College and the PhD degree from Imperial College and University of London in 2007. My research thesis was entitled "Resource Optimisation for Cooperative Broadcasting in WCDMA Networks".
As a post DOC researcher, I worked on formulation of Information Theoretic fundamental capacity limits of wireless cellular networks. This work was funded by Mobile Virtual Center of Excellence UK (a consortium of selected UK Universities and Industry). I have also worked on a European Commission EC funded project ROCKET where I worked on efficient techniques to design and operate a wireless cellular communication system.
In 2009, I joined the faculty of engineering and physical sciences (FEPS) at the University of Surrey as a Lecturer in Communications. I coordinated the University of Surrey team involved in FP7 EC funded project EARTH - looking at Energy Efficient Next Generation of Cellular Networks. The project has won 2012 Best project for the Future of Internet award. I also lead the Theme 9 of India UK Advanced Technology Centre research - Self Organising Multihop Networks. I also supervised a Huawei funded project on a novel air interface technique: LDS-OFDM.
Currently, I am leading an EPSRC funded project - REDUCE that aims to reshape the energy demand of end users using ICT and economic incentives. REDUCE project has deployed a wireless sensor network in CCSR building to monitor and control energy demand of users using persuasive techniques and communication technology. I am a work package leader for IU-ATC phase II funded by EPSRC. I am co-supervising the Huawei funded Green Communications project and Sony funded Machine to Machine communication projects. I am actively participating in EU funded projects LexNet and iJoin.
Research Collaborations
Currently I am collaborating with researchers from all parts of the Europe, Middle East, China, Brazil and the Subcontinent (India and Pakistan).
I am also leading the multidisciplinary research collaborating with researchers in Psychology, Environmental Studies, Economic modelling and Scholarship of Teaching.
Further details can be found on my personal web page.
A full list of publications, conference presentations, and patents can be found here.
Publications
Highlights
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(2011) 'H2-ARQ Relaying: Spectrum and Energy Efficiency Analysis'. IEEE IEEE Journal on Selected Areas in Communications, 29 (8), pp. 1547-1558.Full text is available at: http://epubs.surrey.ac.uk/123391/
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.
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(2010) 'Information Theoretic Capacity of Cellular Multiple Access Channel with Shadow Fading'. IEEE IEEE Transactions on Communications, 58 (5), pp. 1468-1476.Full text is available at: http://epubs.surrey.ac.uk/710815/
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(2009) 'On the Multi-cell Processing Capacity of the Cellular MIMO Uplink Channel in Correlated Rayleigh Fading Environment'. IEEE IEEE Transactions on Wireless Communications, 8 (7), pp. 3704-3715.Full text is available at: http://epubs.surrey.ac.uk/712663/
Abstract
In the context of cellular systems, it has been shown that multicell processing can eliminate inter-cell interference and provide high spectral efficiencies with respect to traditional interference-limited implementations. Moreover, it has been proved that the multiplexing sum-rate capacity gain of multicell processing systems is proportional to the number of Base Station (BS) antennas. These results have been also established for cellular systems, where BSs and User Terminals (UTs) are equipped with multiple antennas. Nevertheless, a common simplifying assumption in the literature is the uncorrelated nature of the Rayleigh fading coefficients within the BS-UT MIMO links. In this direction, this paper investigates the ergodic multicell-processing sum-rate capacity of the Gaussian MIMO Cellular Multiple-Access Channel in a correlated fading environment. More specifically, the multiple antennas of both BSs and UTs are assumed to be correlated according to the Kronecker product model. Furthermore, the current system model considers Rayleigh fading, uniformly distributed User Terminals (UTs) over a planar coverage area and powerlaw path loss. Based on free probabilistic arguments, the empirical eigenvalue distribution of the channel covariance matrix is derived and it is used to calculate both Optimal Joint Decoding and Minimum Mean Square Error (MMSE) Filtering capacity. In addition, numerical results are presented, where the per-cell sum-rate capacity is evaluated while varying the cell density of the system, as well as the level of fading correlation. In this context, it is shown that the capacity performance is greatly compromised by BS-side correlation, whereas UT-side correlation has a negligible effect on the system’s performance. Furthermore, MMSE performance is shown to be greatly suboptimal but more resilient to fading correlation in comparison to optimal decoding.
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(2009) 'Uplink Capacity of a Variable Density Cellular System with Multicell Processing'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE TRANSACTIONS ON COMMUNICATIONS, 57 (7), pp. 2098-2108.Full text is available at: http://epubs.surrey.ac.uk/207032/
Abstract
In this work we investigate the information theoretic capacity of the uplink of a cellular system. Assuming centralised processing for all Base Stations, we consider a power-law path loss model along with variable cell size (variable density of Base Stations) and we formulate an average path-loss approximation. Considering a realistic Rician flat fading environment, the analytical result for the per-cell capacity is derived for a large number of users distributed over each cell. We extend this general approach to model the uplink of sectorized cellular system. To this end, we assume that the user terminals are served by perfectly directional receiver antennas, dividing the cell coverage area into perfectly non-interfering sectors. We show how the capacity is increased (due to degrees of freedom gain) in comparison to the single receiving antenna system and we investigate the asymptotic behaviour when the number of sectors grows large. We further extend the analysis to find the capacity when the multiple antennas used for each Base Station are omnidirectional and uncorrelated (power gain on top of degrees of freedom gain). We validate the numerical solutions with Monte Carlo simulations for random fading realizations and we interpret the results for the real-world systems.
Journal articles
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(2013) 'Non-Intrusive Load Monitoring Approaches for Disaggregated Energy Sensing: A Survey'. MDPI Sensors, 12 (12), pp. 16838-16866.doi: 10.3390/s121216838Full text is available at: http://epubs.surrey.ac.uk/741874/
Abstract
Appliance Load Monitoring (ALM) is essential for energy management solutions, allowing them to obtain appliance-specific energy consumption statistics that can further be used to devise load scheduling strategies for optimal energy utilization. Fine-grained energy monitoring can be achieved by deploying smart power outlets on every device of interest; however it incurs extra hardware cost and installation complexity. Non-Intrusive Load Monitoring (NILM) is an attractive method for energy disaggregation, as it can discern devices from the aggregated data acquired from a single point of measurement. This paper provides a comprehensive overview of NILM system and its associated methods and techniques used for disaggregated energy sensing. We review the state-of-the art load signatures and disaggregation algorithms used for appliance recognition and highlight challenges and future research directions.
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(2013) 'Energy efficiency of transmit diversity systems under a realistic power consumption model'. IEEE Communications Letters, 17 (1), pp. 119-122.Full text is available at: http://epubs.surrey.ac.uk/741873/
Abstract
We compare the downlink energy efficiency of spatial diversity multiple transmit antenna schemes. We determine the minimum required transmit power for a given outage probability. Our analysis shows that antenna selection is in general the most energy efficient option as it requires a single radio-frequency chain. We also investigate the limiting distances up to which the antenna selection technique outperforms the transmit beamforming scheme for different numbers of transmit antennas. © 1997-2012 IEEE.
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(2012) 'Semi-Adaptive Beamforming for OFDM based Hybrid Terrestrial-Satellite Mobile System'. IEEE IEEE Transactions on Wireless Communications, 11 (10), pp. 3424-3433.Full text is available at: http://epubs.surrey.ac.uk/735559/
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(2012) 'Energy Efficiency Contours for Broadcast Channels
Using Realistic Power Models'. IEEE Transactions on Wireless Communications, 11 (11), pp. 4017-4025.Full text is available at: http://epubs.surrey.ac.uk/725969/
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.
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(2012) 'On Receiver Design for Low Density Signature OFDM (LDS-OFDM)'. IEEE IEEE Transactions on Communications, 60 (11), pp. 3499-3508.Full text is available at: http://epubs.surrey.ac.uk/726037/
Abstract
Low density signature orthogonal frequency division multiplexing (LDS-OFDM) is an uplink multi-carrier multiple access scheme that uses low density signatures (LDS) for spreading the symbols in the frequency domain. In this paper, we introduce an effective receiver for the LDS-OFDM scheme. We propose a framework to analyze and design this iterative receiver using extrinsic information transfer (EXIT) charts. Furthermore, a turbo multi-user detector/decoder (MUDD) is proposed for the LDS-OFDM receiver. We show how the turbo MUDD is tuned using EXIT charts analysis. By tuning the turbo-style processing, the turbo MUDD can approach the performance of optimum MUDD with a smaller number of inner iterations. Using the suggested design guidelines in this paper, we show that the proposed structure brings about 2.3 dB performance improvement at a bit error rate (BER) equal to 10^{-5} over conventional LDS-OFDM while keeping the complexity affordable. Simulations for different scenarios also show that the LDS-OFDM outperforms similar well-known multiple access techniques such as multi-carrier code division multiple access (MC-CDMA) and group-orthogonal MC-CDMA.
- . (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.
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(2012) 'A Very Tight Approximation of the SISO Energy Efficiency-Spectral Efficiency Trade-Off'. IEEE Communications Letters, Full text is available at: http://epubs.surrey.ac.uk/710806/
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.
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(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.Full text is available at: http://epubs.surrey.ac.uk/710812/
Abstract
Along with spectral efficiency (SE), energy efficiency (EE) is becoming one of the key performance evaluation criteria for communication system. These two criteria, which are conflicting, can be linked through their trade-off. The EE-SE trade-off for the multi-input multi-output (MIMO) Rayleigh fading channel has been accurately approximated in the past but only in the low-SE regime. In this paper, we propose a novel and more generic closed-form approximation of this trade-off which exhibits a greater accuracy for a wider range of SE values and antenna configurations. Our expression has been here utilized for assessing analytically the EE gain of MIMO over single-input single-output (SISO) system for two different types of power consumption models (PCMs): the theoretical PCM, where only the transmit power is considered as consumed power; and a more realistic PCM accounting for the fixed consumed power and amplifier inefficiency. Our analysis unfolds the large mismatch between theoretical and practical MIMO vs. SISO EE gains; the EE gain increases both with the SE and the number of antennas in theory, which indicates that MIMO is a promising EE enabler; whereas it remains small and decreases with the number of transmit antennas when a realistic PCM is considered.
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(2012) 'A Survey of Self Organisation in Future Cellular Networks'. IEEE Communications Surveys & Tutorials, IEEE, 99, pp. 1-26.Full text is available at: http://epubs.surrey.ac.uk/294636/
Abstract
This article surveys the literature over the period of the last decade on the emerging field of self organisation as applied to wireless cellular communication networks. Self organisation has been extensively studied and applied in adhoc networks, wireless sensor networks and autonomic computer networks; however in the context of wireless cellular networks, this is the first attempt to put in perspective the various efforts in form of a tutorial/survey. We provide a comprehensive survey of the existing literature, projects and standards in self organising cellular networks. Additionally, we also aim to present a clear understanding of this active research area, identifying a clear taxonomy and guidelines for design of self organising mechanisms. We compare strength and weakness of existing solutions and highlight the key research areas for further development. This paper serves as a guide and a starting point for anyone willing to delve into research on self organisation in wireless cellular communication networks.
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(2012) 'On the Energy Efficiency-Spectral Efficiency Trade-Off in the Uplink of CoMP System'. IEEE IEEE Transactions on Wireless Communications, 11 (2), pp. 556-561.Full text is available at: http://epubs.surrey.ac.uk/710813/
Abstract
In this paper, we derive a generic closed-form approximation (CFA) of the energy efficiency-spectral efficiency (EE-SE) trade-off for the uplink of coordinated multi-point (CoMP) system and demonstrate its accuracy for both idealistic and realistic power consumption models (PCMs). We utilize our CFA to compare CoMP against conventional non-cooperative system with orthogonal multiple access. In the idealistic PCM, CoMP is more energy efficient than non-cooperative system due to a reduction in power consumption; whereas in the realistic PCM, CoMP can also be more energy efficient but due to an improvement in SE and mainly for cell-edge communication and small cell deployment.
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(2012) 'Iterative turbo beamforming for orthogonal frequency division multiplexing-based hybrid terrestrial-satellite mobile system'. IET IET Communications, 6 (2), pp. 157-164.Full text is available at: http://epubs.surrey.ac.uk/710811/
Abstract
In the context of orthogonal frequency division multiplexing (OFDM)-based systems, pilot-based beamforming (BF) exhibits a high degree of sensitivity to the pilot sub-carriers. Increasing the number of reference pilots significantly improves BF performance as well as system performance. However, this increase comes at the cost of data throughput, which inevitably shrinks due to transmission of additional pilots. Hence an approach where reference signals available to the BF process can be increased without transmitting additional pilots can exhibit superior system performance without compromising throughput. Thus, the authors present a novel three-stage iterative turbo beamforming (ITBF) algorithm for an OFDM-based hybrid terrestrial-satellite mobile system, which utilises both pilots and data to perform interference mitigation. Data sub-carriers are utilised as virtual reference signals in the BF process. Results show that when compared to non-iterative conventional BF, the proposed ITBF exhibits bit error rate gain of up to 2.5 dB with only one iteration.
- . (2012) 'Semi-adaptive beamforming for ofdm based hybrid terestrial-satellite mobile satellite'. IEEE IEEE Trans Wireless Communications, 11 (10), pp. 3424-3433.
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(2012) 'Throughput Analysis for Cognitive Radio Networks with Multiple Primary Users and Imperfect Spectrum Sensing'. IEEE IET Communications, 6 (17), pp. 2787-2795.Full text is available at: http://epubs.surrey.ac.uk/735347/
Abstract
In cognitive radio networks, the licensed frequency bands of the primary users (PUs) are available to the secondary user (SU) provided that they do not cause significant interference to the PUs. In this study, the authors analysed the normalised throughput of the SU with multiple PUs coexisting under any frequency division multiple access communication protocol. The authors consider a cognitive radio transmission where the frame structure consists of sensing and data transmission slots. In order to achieve the maximum normalised throughput of the SU and control the interference level to the legal PUs, the optimal frame length of the SU is found via simulation. In this context, a new analytical formula has been expressed for the achievable normalised throughput of SU with multiple PUs under prefect and imperfect spectrum sensing scenarios. Moreover, the impact of imperfect sensing, variable frame length of SU and the variable PU traffic loads, on the normalised throughput has been critically investigated. It has been shown that the analytical and simulation results are in perfect agreement. The authors analytical results are much useful to determine how to select the frame duration length subject to the parameters of cognitive radio network, such as network traffic load, achievable sensing accuracy and number of coexisting PUs.
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(2011) 'Relay Station Access Link Spectral Efficiency Optimization through SO of Macro BS Tilts'. IEEE IEEE Communications Letters, 15 (12), pp. 1326-1328.Full text is available at: http://epubs.surrey.ac.uk/711386/
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.
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(2011) 'Energy Efficiency Contours for Single-Carrier Downlink Channels'. IEEE COMMUNICATIONS LETTERS, 15 (12), pp. 1307-1309.Full text is available at: http://epubs.surrey.ac.uk/710809/
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(2011) 'H2-ARQ Relaying: Spectrum and Energy Efficiency Analysis'. IEEE IEEE Journal on Selected Areas in Communications, 29 (8), pp. 1547-1558.Full text is available at: http://epubs.surrey.ac.uk/123391/
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.
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(2011) 'Information Theoretic Analysis of LDS Scheme'. IEEE IEEE Communications Letters, 15 (8), pp. 798-800.Full text is available at: http://epubs.surrey.ac.uk/710807/
Abstract
In this paper, the capacity region of Low Density Signature Multiple Access Channel (LDS-MAC) is calculated through information theoretic analysis. LDS Code Division Multiple Access (LDS-CDMA) uses spreading sequences of low density for spreading the data symbols in time domain. This technique benefits from a less complex Multiuser Detector (MUD) compared to conventional CDMA with optimum MUD; while keeping the performance close to the single user scenario for up to 200% loaded conditions. Also evaluated is the effect of different factors on the capacity of LDS MAC.
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(2011) 'Self-Organized Resource Allocation Using Inter-Cell Interference Coordination(ICIC) in Relay-Asisted Cellular Networks'. Special Issue on Next Generation Wireless Networks and Applications Edition. ICT Academy of Tamil Nadu ICT Journal on Communication Technology, 2 (2), pp. 300-313.Full text is available at: http://epubs.surrey.ac.uk/710816/
Abstract
In a multi-cell scenario, the inter-cell interference (ICI) is detrimental in achieving the intended system performance, in particular for the edge users. There is paucity of work available in literature on ICI coordination (ICIC) for relay-assisted cellular networks (RACN). In this paper, we do a survey on the ICIC schemes in cellular networks and RACN. We then propose a self-organized resource allocation plan for RACN to improve the edge user’s performance by ICIC. We compare the performance of reuse-1, reuse-3, soft frequency reuse (SFR) scheme, proposed plan with and without relays. The performance metrics for comparison are edge user’s spectral efficiency, their signal-to-interference-and-noise ratio (SINR) and system’s area spectral efficiency. We show by the simulation results that our proposed plan performs better than the existing resource allocation schemes in static allocation scenario. Next, we propose to make our resource allocation plan dynamic and self-organized. The distinct features of our proposed plan are: One, it achieves a trade-off between the system’s area spectral efficiency and the edge user’s spectral efficiency performance. Secondly, it introduces a novel concept of interfering neighbor set to achieve ICIC by local interaction between the entities.
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(2011) 'Average Energy Efficiency Contours with Multiple Decoding Policies'. IEEE IEEE Communications Letter, 15 (5), pp. 506-508.Full text is available at: http://epubs.surrey.ac.uk/533675/
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.
- . (2011) 'How much energy is needed to run a wireless network?'. IEEE Wireless Communications, 18 (5), pp. 40-49.
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(2010) 'Information Theoretic Capacity of Cellular Multiple Access Channel with Shadow Fading'. IEEE IEEE Transactions on Communications, 58 (5), pp. 1468-1476.Full text is available at: http://epubs.surrey.ac.uk/710815/
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(2010) 'Collaborative Spectrum Sensing Optimisation Algorithms for Cognitive Radio Networks'. Hindawi Publishing Corporation International Journal of Digital Multimedia Broadcasting, 2010 Article number Article ID 424036 doi: 10.1155/2010/424036Full text is available at: http://epubs.surrey.ac.uk/125629/
Abstract
The main challenge for a cognitive radio is to detect the existence of primary users reliably in order to minimise the interference to licensed communications. Hence, spectrum sensing is a most important requirement of a cognitive radio. However, due to the channel uncertainties, local observations are not reliable and collaboration among users is required. Selection of fusion rule at a common receiver has a direct impact on the overall spectrum sensing performance. In this paper, optimisation of collaborative spectrum sensing in terms of optimum decision fusion is studied for hard and soft decision combining. It is concluded that for optimum fusion, the fusion centre must incorporate signal-to-noise ratio values of cognitive users and the channel conditions. A genetic algorithm-based weighted optimisation strategy is presented for the case of soft decision combining. Numerical results show that the proposed optimised collaborative spectrum sensing schemes give better spectrum sensing performance.
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(2009) 'Uplink Capacity of a Variable Density Cellular System with Multicell Processing'. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE TRANSACTIONS ON COMMUNICATIONS, 57 (7), pp. 2098-2108.Full text is available at: http://epubs.surrey.ac.uk/207032/
Abstract
In this work we investigate the information theoretic capacity of the uplink of a cellular system. Assuming centralised processing for all Base Stations, we consider a power-law path loss model along with variable cell size (variable density of Base Stations) and we formulate an average path-loss approximation. Considering a realistic Rician flat fading environment, the analytical result for the per-cell capacity is derived for a large number of users distributed over each cell. We extend this general approach to model the uplink of sectorized cellular system. To this end, we assume that the user terminals are served by perfectly directional receiver antennas, dividing the cell coverage area into perfectly non-interfering sectors. We show how the capacity is increased (due to degrees of freedom gain) in comparison to the single receiving antenna system and we investigate the asymptotic behaviour when the number of sectors grows large. We further extend the analysis to find the capacity when the multiple antennas used for each Base Station are omnidirectional and uncorrelated (power gain on top of degrees of freedom gain). We validate the numerical solutions with Monte Carlo simulations for random fading realizations and we interpret the results for the real-world systems.
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(2009) 'Information theoretic capacity of Gaussian cellular multiple-access MIMO fading channel'. INST ENGINEERING TECHNOLOGY-IET IET COMMUNICATIONS, 3 (7), pp. 1201-1207.Full text is available at: http://epubs.surrey.ac.uk/710814/
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(2009) 'On the Multi-cell Processing Capacity of the Cellular MIMO Uplink Channel in Correlated Rayleigh Fading Environment'. IEEE IEEE Transactions on Wireless Communications, 8 (7), pp. 3704-3715.Full text is available at: http://epubs.surrey.ac.uk/712663/
Abstract
In the context of cellular systems, it has been shown that multicell processing can eliminate inter-cell interference and provide high spectral efficiencies with respect to traditional interference-limited implementations. Moreover, it has been proved that the multiplexing sum-rate capacity gain of multicell processing systems is proportional to the number of Base Station (BS) antennas. These results have been also established for cellular systems, where BSs and User Terminals (UTs) are equipped with multiple antennas. Nevertheless, a common simplifying assumption in the literature is the uncorrelated nature of the Rayleigh fading coefficients within the BS-UT MIMO links. In this direction, this paper investigates the ergodic multicell-processing sum-rate capacity of the Gaussian MIMO Cellular Multiple-Access Channel in a correlated fading environment. More specifically, the multiple antennas of both BSs and UTs are assumed to be correlated according to the Kronecker product model. Furthermore, the current system model considers Rayleigh fading, uniformly distributed User Terminals (UTs) over a planar coverage area and powerlaw path loss. Based on free probabilistic arguments, the empirical eigenvalue distribution of the channel covariance matrix is derived and it is used to calculate both Optimal Joint Decoding and Minimum Mean Square Error (MMSE) Filtering capacity. In addition, numerical results are presented, where the per-cell sum-rate capacity is evaluated while varying the cell density of the system, as well as the level of fading correlation. In this context, it is shown that the capacity performance is greatly compromised by BS-side correlation, whereas UT-side correlation has a negligible effect on the system’s performance. Furthermore, MMSE performance is shown to be greatly suboptimal but more resilient to fading correlation in comparison to optimal decoding.
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(2008) 'Analysing a Multi-hop UMTS over Multiple Frequency Schemes and an Urban Environment'. ACADEMY PUBLISHER Journal of Networks, 3 Article number 7 , pp. 41-48.Full text is available at: http://epubs.surrey.ac.uk/710808/
Abstract
In this paper we analyse the performance of a relay based UMTS system in an urban environment using multiple hops on multiple frequency bands. Measurement based path loss, fading and shadowing models are used in the Manhattan grid deployment scenario. Both uplink and downlink operations of the cellular system are considered at the same time. Two hop communication links over the uplink and downlink are operated at four non-overlapping spectrum bands in order to minimise interference. This results in several possible frequency schemes. Power solutions are derived analytically for the selected frequency schemes. The system performance is evaluated both by simulation and analysis and improvement by employing relays is shown.
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(2008) 'On the Capacity of Variable Density Cellular Systems under Multicell Decoding'. IEEE IEEE Communications Letters, 12 Article number 7 , pp. 496-498.Full text is available at: http://epubs.surrey.ac.uk/712664/
Abstract
The majority of multicell-decoding cellular models preserve a fundamental assumption which has initially appeared in Wyner’s model, namely the collocation of User Terminals (UTs). Although this assumption produces more tractable mathematical models, it is unrealistic w.r.t. current practical cellular systems. In this paper, we alleviate this assumption by assuming uniformly distributed UTs. The model under investigation is the uplink channel of a planar cellular array in the presence of power-law path loss and flat fading. In this context, we employ a free probability approach to evaluate the effect of UT distribution on the optimal sum-rate capacity of a variable-density cellular system.
- . (2006) 'Message passing algorithm for iterative decoding of channel codes'. HERMIS-mu-pi International Journal of Computer Mathematics and its Applications, 8, pp. 1-20-1-20.
Conference papers
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(2013) 'On the Three-Receiver Multilevel Broadcast Channel with Random Parameters'. 9th International ITG Conference on Systems, Communications and Coding 2013
[ Status: Accepted ] - . (2012) 'Determining the Energy Efficiency of Femtocell Basestations with Multiple Antennas'. Anaheim, California, USA: IEEE Globecom 2012
- . (2012) 'On the Deployment Opportunities for Increasing Energy Efficiency'. LTE-Advanced with Relay Nodes. In 29h Meeting of WWRF, Berlin, Germany,
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(2012) 'Acoustic and Device Feature Fusion for Load Recognition'. IEEE Proceedings of the 6th IEEE International Conference on Intelligent Systems (IEEE IS), Sofia, Bulgaria: in Proceedings of the 6th IEEE International Conference on Intelligent Systems (IEEE IS), pp. 386-392.Full text is available at: http://epubs.surrey.ac.uk/735973/
Abstract
Appliance-specific Load Monitoring (LM) provides a possible solution to the problem of energy conservation which is becoming increasingly challenging, due to growing energy demands within offices and residential spaces. It is essential to perform automatic appliance recognition and monitoring for optimal resource utilization. In this paper, we study the use of non-intrusive LM methods that rely on steady-state appliance signatures for classifying most commonly used office appliances, while demonstrating their limitation in terms of accurately discerning the low-power devices due to overlapping load signatures. We propose a multilayer decision architecture that makes use of audio features derived from device sounds and fuse it with load signatures acquired from energy meter. For the recognition of device sounds, we perform feature set selection by evaluating the combination of time-domain and FFT-based audio features on the state of the art machine learning algorithms. The highest recognition performance however is shown by support vector machines, for the device and audio recognition experiments. Further, we demonstrate that our proposed feature set which is a concatenation of device audio feature and load signature significantly improves the device recognition accuracy in comparison to the use of steady-state load signatures only.
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(2012) 'Hybrid Transmission Schemes for Grouped Users in Cellular Systems'. IEEE Limassol, Cyprus: 8th International Wireless Communications and Mobile Computing Conference (IWCMC), pp. 561-566.Full text is available at: http://epubs.surrey.ac.uk/725975/
Abstract
Hybrid systems, where more than one transmission scheme are used within the same cluster, can be used as a way to improve spectral efficiency for the system as a whole and, more importantly, for the cell-edge users. In this paper, we will propose frequency reuse method by grouping the users into two groups, critical and non-critical users. Each user group is served with a transmission scheme, where the most vulnerable users are served by transmission scheme that avoid, make use of, and orthogo-nalise the interference. These schemes include the cooperative maximal ratio transmission and the non-cooperative orthogonal and non-orthogonal schemes. Radio resource allocation is studied and a solution is given for maximal ratio transmission and interference alignment. Simulation results are given, and showing the performance of each scheme when all users are considered critical and one scheme is used. Moreover, results showing the performance of our proposed frequency reuse scheme where different percentage of users considered critical.
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(2012) 'Fairness Evaluation in Cooperative Hybrid Cellular Systems'. IEEE Limassol, Cyprus: 8th International Wireless Communications and Mobile Computing Conference (IWCMC), pp. 389-394.Full text is available at: http://epubs.surrey.ac.uk/725978/
Abstract
Many method has been applied previously to improve the fairness of a wireless communication system. In this paper, we propose using hybrid schemes, where more than one transmission scheme are used in one system, to achieve this objective. These schemes consist of cooperative transmission schemes, maximal ratio transmission and interference alignment, and non-cooperative schemes, orthogonal and non-orthogonal schemes used alongside and in combinations in the same system to improve the fairness. We provide different weight calculation methods to vary the output of the fairness problem. We show the solution of the radio resource allocation problem for the transmission schemes used. Finally, simulation results is provided to show fairness achieved, in terms of Jain's fairness index, by applying the hybrid schemes proposed and the different weight calculation methods at different inter-site distances.
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(2012) 'Performance Evaluation of Low Density Spreading Multiple Access'. Limassol, Cyprus: 8th International Wireless Communications and Mobile Computing Conference (IWCMC), pp. 383-388.Full text is available at: http://epubs.surrey.ac.uk/726033/
Abstract
In this paper, we evaluate the performance of Multicarrier-Low Density Spreading Multiple Access (MC-LDSMA) as a multiple access technique for mobile communication systems. The MC-LDSMA technique is compared with current multiple access techniques, OFDMA and SC-FDMA. The performance is evaluated in terms of cubic metric, block error rate, spectral efficiency and fairness. The aim is to investigate the expected gains of using MC-LDSMA in the uplink for next generation cellular systems. The simulation results of the link and system-level performance evaluation show that MC-LDSMA has significant performance improvements over SC-FDMA and OFDMA. It is shown that using MC-LDSMA can considerably reduce the required transmission power and increase the spectral efficiency and fairness among the users.
- . (2012) 'Iterative Slepian-Wolf Decoding and FEC Decoding for Compress-and-forward Systems'. IEEE VTC Fall 2012, Quebec City, Canada: IEEE VTC Fall 2012
- . (2012) 'Energy-Efficiency based Resource Allocation for the Orthogonal Multi-user Channel'. IEEE VTC Fall 2012, Quebec City, Canada.: IEEE VTC Fall 2012
- . (2012) 'On the Energy Efficiency of Hybrid Relaying Schemes in the Two-way Relay Channel'. IEEE VTC Fall 2012, Quebec City, Canada: IEEE VTC Fall 2012
- . (2012) 'Energy Efficiency Analysis and Optimal Power Allocation in Virtual-MIMO Systems'. Quebec City, Canada: IEEE VTC Fall 2012
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(2012) 'Energy Efficiency and Optimal Power Allocation in Virtual-MIMO Systems'. Quebec City, Canada: 2012 IEEE 76th Vehicular Technology Conference: VTC2012-Fall, pp. 1-6.Full text is available at: http://epubs.surrey.ac.uk/726221/
Abstract
This paper investigates energy efficiency (EE) performance of a virtual multiple-input multiple-output (MIMO) wireless system using the receiver-side cooperation with the compress-and-forward protocol. We derive a linear approximation of EE as a function of spectral efficiency (SE) in the low SE operation regime. In addition, we obtain a closed-form lower bound for EE which is valid for both low and high SE regions. This lower bound can be used for optimizing the power allocation between the transmitter and the relay in order to minimize the overall energy per bit consumption in the system. Both analytical and simulation results demonstrate that the virtual MIMO system using the receiver-side cooperation outperforms the multiple-input single-output (MISO) case in terms of energy efficiency. Finally we show that, with the optimal power allocation, the virtual-MIMO system achieves an EE performance close to that of an ideal MIMO system.
- . (2012) 'On the Energy Efficiency-Spectral Efficiency Trade-Off of the 2BS-DMIMO System'. IEEE VTC Fall 2012, Quebec City, Canada: IEEE VTC Fall 2012
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(2012) 'A Tight Closed-Form Approximation of the SISO Energy Efficiency-Spectral Efficiency Trade-Off'. Berlin, Germany: ICT Future & Mobile SummitFull text is available at: http://epubs.surrey.ac.uk/726078/
Abstract
Due to the rise of the energy efficiency (EE) as a system performance evaluation criterion, the EE-spectral efficiency (SE) trade-off is becoming a key tool for getting insight on how to efficiently design future communication system. As far as the single-input single-output (SISO) Rayleigh fading channel is concerned, the EE-SE trade-off has been accurately approximated in the past but only at low-SE. In this paper, we propose a novel and more generic closed-form approximation (CFA) of this EE-SE trade-off which is very accurate for any SE values. We compare our CFA with two existing CFAs and show the great accuracy of the former for a wider range of SE in comparison with the latter. As an application, we use our CFA to study the variation of EE-SE trade-off when a realistic power model is assumed and to compare the energy consumption of SISO against a 2x2 multi-input multi-output (MIMO) system over the Rayleigh fading channel.
- . (2012) 'On Performance Optimization in Self-Organizing Network using Enhanced Simulated Annealing with Similarity Measure'. MIT, USA,: International Symposium on Information Theory,
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(2012) 'Energy-efficiency based resource allocation for the scalar broadcast channel'. IEEE Wireless Communications and Networking Conference, WCNC, , pp. 193-197.Full text is available at: http://epubs.surrey.ac.uk/726076/
Abstract
Until recently, link adaptation and resource allocation for communication system relied extensively on the spectral efficiency as an optimization criterion. With the emergence of the energy efficiency (EE) as a key system design criterion, resource allocation based on EE is becoming of great interest. In this paper, we propose an optimal EE-based resource allocation method for the scalar broadcast channel (BC-S). We introduce our EE framework, which includes an EE metric as well as a realistic power consumption model for the base station, and utilize this framework for formulating our EE-based optimization problem subject to a power as well as fairness constraints. We then prove the convexity of this problem and compare our EE-based resource allocation method against two other methods, i.e. one based on sum-rate and one based on fairness optimization. Results indicate that our method provides large EE improvement in comparison with the two other methods by significantly reducing the total consumed power. Moreover, they show that near-optimal EE and average fairness can be simultaneously achieved over the BC-S channel. © 2012 IEEE.
- . (2012) 'Controlling Self-Healing Cellular networks using Fuzzy Logic'. IEEE Paris, France: IEEE Wireless Communications and Networking Conference (WCNC), pp. 3080-3084.
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(2012) 'Low Density Spreading for next generation multicarrier cellular systems'. IEEE Baghdad, Iraq: International Conference on Future Communication Networks (ICFCN), pp. 52-57.Full text is available at: http://epubs.surrey.ac.uk/726034/
Abstract
Multicarrier-Low Density Spreading Multiple Access (MC-LDSMA) is a promising technique for high data rate mobile communications. In this paper, the suitability of using MC-LDSMA in the uplink for next generation cellular systems is investigated. The performance of MC-LDSMA is evaluated and compared with current multiple access techniques, OFDMA and SC-FDMA. Specifically, Peak to Average Power Ratio (PAPR), Bit Error Rate (BER), spectral efficiency and fairness are considered as performance metrics. The link and system-level simulation results show that MC-LDSMA has significant performance improvements over SC-FDMA and OFDMA. It is shown that using MC-LDSMA can significantly improve the system performance in terms of required transmission power, spectral efficiency and fairness among the users.
- . (2012) 'Low-complexity energy-efficient coordinated resource allocation in cellular systems'. Kumasi, Ghana: IEEE ICAST
- . (2012) 'Energy efficiency contours for amplify-and-forward and decode-and-forward cooperative protocols'. Proceedings of the 2012 8th International Symposium on Communication Systems, Networks and Digital Signal Processing, CSNDSP 2012,
- . (2012) 'Energy efficiency of amplify-and-forward, repetition coding and parallel coding in short range communications'. 2012 35th International Conference on Telecommunications and Signal Processing, TSP 2012 - Proceedings, , pp. 212-216.
- . (2012) 'Distributed Load Balancing through Self Organisation of cell size in cellular systems'. IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, , pp. 1114-1119.
- . (2012) 'Flexible power modeling of LTE base stations'. IEEE Wireless Communications and Networking Conference, WCNC, , pp. 2858-2862.
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(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), 2011Full text is available at: http://epubs.surrey.ac.uk/533674/
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.
- . (2011) 'Energy-aware adaptive sectorisation in LTE systems'. IEEE 2011 IEEE 22nd International Symposium on Personal, Indoor and Mobile Radio Communications, Toronto, Canada: PIMRC'11, pp. 2402-2406.
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(2011) 'Trade-off between Energy Efficiency and Spectral
Efficiency in the Uplink of a Linear Cellular
System with Uniformly Distributed User Terminals'. IEEE Proc. IEEE PIMRC, Toronto, Canada: IEEE PIMRC, pp. 2407-2407.Full text is available at: http://epubs.surrey.ac.uk/534278/
Abstract
In this paper, we propose a tight closed-form approximation of the Energy Efficiency vs. Spectral Efficiency (EE-SE) trade-off for the uplink of a linear cellular communication system with base station cooperation and uniformly distributed user terminals. We utilize the doubly-regular property of the channel to obtain a closed form approximation using the Marˇcenko Pasture law. We demonstrate the accuracy of our expression by comparing it with Monte-Carlo simulation and the EE-SE trade-off expression based on low-power approximation. Results show the great tightness of our expression with Monte-Carlo simulation.We utilize our closed form expression for assessing the EE performance of cooperation for both theoretical and realistic power models. The theoretical power model includes only the transmit power, whereas the realistic power model incorporates the backhaul and signal processing power in addition to the transmit power. Results indicate that for both power models, increasing the number of antennas leads to an improvement in EE performance, whereas, increasing the number of cooperating BSs results in a loss in EE when considering the realistic power model.
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(2011) 'Energy Efficiency Analysis of In-Building MIMO
AF Communication'. IEEE IEEE International Wireless Communicatins and Mobile Computing (IWCMC-2011), Istanbul, Turkey: IEEE International Wireless Communicatins and Mobile Computing (IWCMC-2011), pp. 912-917.Full text is available at: http://epubs.surrey.ac.uk/7065/
Abstract
Cooperative communication is an effective approach for increasing the spectral efficiency and/or the coverage of cellular networks as well as reducing the cost of network deployment. However, it remains to be seen how energy efficient it is. In this paper, we assess the energy efficiency of the conventional Amplify-and- forward (AF) scheme in an in-building relaying scenario. This scenario simplifies the mutual information formulation of the AF system and allows us to express its channel capacity with a simple and accurate closed-form approximation. In addition, a framework for the energy efficiency analysis of AF system is introduced, which includes a power consumption model and an energy efficiency metric, i.e. the bit-per-joule capacity. This framework along with our closed-form approximation are utilized for assessing both the channel and bit-per-joule capacities of the AF system in an in-building scenario. Our results indicate that transmitting with maximum power is not energy efficient and that AF system is more energy efficient than point-to-point communication at low transmit powers and signal-to-noise ratios.
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(2011) 'Hybrid Spectrum Allocation Scheme in wireless cellular networks'. Istanbul, Turkey : IEEE The 7th International Wireless Communication and Mobile Computing Conference-IWCMC, Istanbul: The 7th International Wireless Communication and Mobile Computing Conference-IWCMC, pp. 2093-2097.Full text is available at: http://epubs.surrey.ac.uk/725971/
Abstract
Mobile services have seen a major upswing driven by the bandwidth hungry applications thus leading to higher data rate requirements on the wireless networks. Spectrum being the most precious resource in the wireless industry is of keen interest. Various spectrum assignment and frequency reuse schemes have been proposed in literature. However in future networks, dynamic schemes that adapt to spatio-temporal variation in the environment are desired. We thus present a hybrid spectrum assignment scheme which adapts its allocation strategies depending on user distribution in the system. Results show that the proposed dynamic spectrum assignment strategy improves spectrum utilization thereby providing a higher data rate for the users.
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(2011) 'Improving Fairness by Cooperative Communications and Selection of Critical Users'. Istanbul, Turkey : IEEE The 7th International Wireless Communication and Mobile Computing Conference-IWCMC, Istanbul: The 7th International Wireless Communication and Mobile Computing Conference-IWCMC, pp. 184-188.Full text is available at: http://epubs.surrey.ac.uk/725976/
Abstract
Cooperative Transmission can be used in a multicell scenario where base stations are connected to a central processing unit. This cooperation can be used to improve the fairness for users with bad channel conditions–critical users. This paper will look into using cooperative transmission alongside the orthogonal OFDM scheme to improve fairness by careful selection of critical users and a resource allocation and resource division between the two schemes. A solution for power and subcarrier allocations is provided together with a solution for the selection of the critical users. Simulation results is provided to show the fairness achieved by the proposed critical users selection method, resource allocation and the resource division method applied under the stated assumptions.
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(2011) 'An accurate closed-form approximation of the energy efficiency-spectral efficiency trade-off over the MIMO Rayleigh fading channel'. IEEE International Conference on Communications, Kyoto, Japan: IEEE ICC'11, pp. 1-6.Full text is available at: http://epubs.surrey.ac.uk/725966/
Abstract
Energy efficiency (EE) is gradually becoming one of the key criteria, along with the spectral efficiency (SE), for evaluating communication system performances. However, minimizing the EE while maximizing the SE are conflicting objectives and, thus, the main criterion for designing efficient communication systems will become the trade-off between SE and EE. The EE-SE trade-off for the multi-input multi-output (MIMO) Rayleigh fading channel has been accurately approximated in the past but only in the low-SE regime. In this paper, we propose a novel and more generic closed-form approximation of this EE-SE trade-off which exhibits a greater accuracy for a wider range of SE values and antenna configurations. Our expression, which can easily be used for evaluating and comparing the EE-SE trade-off of MIMO communication system, has been utilized in this paper for analyzing the impact of using multiple antennas on the EE and the EE gain of MIMO in comparison with single-input single-output (SISO) system. Our results indicate that EE can be improved predominantly through receive diversity in the low-SE regime and that MIMO is far more energy efficient than SISO at high SE over the Rayleigh fading channel.
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(2011) 'Subcarrier and Power Allocation for LDS-OFDM System'. Budapest, Hungary : IEEE IEEE Vehicular technology Conference - VTC Spring 2011, IEEE 73rd Vehicular Technology Conference (VTC Spring), 2011, pp. 1-5.Full text is available at: http://epubs.surrey.ac.uk/726032/
Abstract
Low Density Signature-Orthogonal Frequency Division Multiplexing (LDS-OFDM) has been introduced recently as an efficient multiple access technique. In this paper, we focus on the subcarrier and power allocation scheme for uplink LDS-OFDM system. Since the resource allocation problem is not convex due to the discrete nature of subcarrier allocation, the complexity of finding the optimal solutions is extremely high. We propose a heuristic subcarrier and power allocation algorithm to maximize the weighted sum-rate. The simulation results show that the proposed algorithm can significantly increase the spectral efficiency of the system. Furthermore, it is shown that LDS-OFDM system can achieve an outage probability much less than that for OFDMA system.
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(2011) 'Average Energy Efficiency Contours for Single Carrier AWGN MAC'. IEEE IEEE Vehicular technology Conference - VTC Spring 2011, Budapest, Hungary: 2011 IEEE 73rd Vehicular Technology Conference (VTC Spring), pp. 1-5.Full text is available at: http://epubs.surrey.ac.uk/725968/
Abstract
Energy efficiency has become increasingly important in wireless communications, with significant environmental and financial benefits. This paper studies the achievable capacity region of a single carrier uplink channel consisting of two transmitters and a single receiver, and uses average energy efficiency contours to find the optimal rate pair based on four different 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. In addition to the transmit power, circuit power is also accounted for, with the maximum transmit power constrained to a fixed value. Simulation results demonstrate the achievability of the optimal energy-efficient rate pair within the capacity region, and provide the trade-off for energy efficiency, fairness and maximum sum-rate.
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(2011) 'On Achievable Rate Region of Multiple Coordinated Multiple Access Channels'. IEEE 73rd IEEE Vehicular technology Conference, Budapest, Hungary: IEEE VTC-springFull text is available at: http://epubs.surrey.ac.uk/725965/
Abstract
Coordination between two or more multiple access channel (MAC) receivers can enlarge the achievable rate region of the whole system. This paper focuses on coordination by sharing the codebooks of the users between the receivers of MACs. We first define the achievable rate region of the time invariant multiple coordinated MAC (MCMAC) and subsequently derive its achievable rate region. We later express the achievable rate region in terms of the dominating points. We base our numerical analysis on the two-user two-receiver Gaussian coordinated MAC and make comparison with the interference channel, full cooperation and the individual MAC performance analysis. It is observed that this approach though suboptimal is less complex in comparison with full cooperation and that the MCMAC rate region is at least equal to the rate region of the uncoordinated approach. Over several channel states, the rate region of MCMAC exceeds that of the uncoordinated approach.
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(2011) 'EXIT Chart Analysis for Turbo LDS-OFDM Receivers'. Istanbul, Turkey : IEEE 7th International Wireless Communication and Mobile Computing Conference-IWCMC, Istanbul: 7th International Wireless Communications and Mobile Computing Conference (IWCMC), pp. 354-358.Full text is available at: http://epubs.surrey.ac.uk/726035/
Abstract
In this paper, the mutual information transfer characteristics of turbo Multiuser Detector (MUD) for a novel air interface scheme, called Low Density Signature Orthogonal Frequency Division Multiplexing (LDS-OFDM) are investigated using Extrinsic Information Transfer (EXIT) charts. LDS-OFDM uses Low Density Signature structure for spreading the data symbols in frequency domain. This technique benefits from frequency diversity besides its ability of supporting parallel data streams more than the number of subcarriers (overloaded condition). The turbo MUD couples the data symbols' detector of LDS scheme with users' FEC (Forward Error Correction) decoders through the message passing principle. The effect of overloading on LDS scheme's performance is evaluated using EXIT chart. The results show that at Eb/N0 as low as 0.3, LDS-OFDM can support loads up to 300%.
- . (2011) 'On the Energy Efficiency Gain of MIMO Communication under Various Power Consumption Models'. Warsaw, Poland: Future Network and Mobile Summit
- . (2011) 'On the Energy Efficiency Gain of MIMO Communication under Various Power Consumption Models'. Warsaw, Poland: ICT Future Network & Mobile Summit
- . (2011) 'Alamouti Transmit Diversity for Energy Efficient Femtocells'. Budapest, Hungary : 73rd IEEE Vehicular technology Conference - VTC Spring 2011, Budapest: VTC Spring 2011
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(2011) 'Energy Aware Transmission in Cellular Uplink with Clustered Base Station Cooperation'. Budapest, Hungary : IEEE IEEE Vehicular technology Conference - VTC Spring 2011, Budapest: VTC2011-SpringFull text is available at: http://epubs.surrey.ac.uk/207037/
Abstract
We provide an analytical formula to evaluate the performance of the uplink of planar cellular networks when joint processing is enabled among limited number of base stations in a generalised fading environment. Focusing on user transmission power allocation techniques to mitigate inter-cluster interference we investigate the system’s spectral-energy efficiency trade-off. The paper addresses the gains in both cell throughput and transmissions energy efficiency due to the combined strategies of base station cooperation and user power management. We assess the effect of the propagation environment and of the key network design parameters of cooperation cluster size and intersite distance on the overall performance providing numerical results for a real-world scenario.
- . (2011) 'Energy Efficiency Analysis of Idealized Coordinated Multi-Point Communication System'. IEEE Vehicular technology Conference, Budapest, Hungary: IEEE VTC-spring
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(2011) 'Closed-form Approximation for the Trade-Off between Energy Efficiency and Spectral Efficiency in the Uplink of Cellular Network'. Vienna, Austria : IEEE European Wireless, Vienna: 11th European Wireless Conference 2011 - Sustainable Wireless Technologies (European Wireless)Full text is available at: http://epubs.surrey.ac.uk/725963/
Abstract
In this paper we propose a tight closed-form approximation of the Energy Efficiency vs. Spectral Efficiency (EE-SE) trade-off for the uplink of a cellular communication system. We model the uplink of the cellular system by considering the Wyner model with Raleigh fading. We first demonstrate the accuracy of our expression by comparing it with Monte-Carlo simulation and the EE-SE trade-off expression based on lowpower approximation. Results show the great tightness of our expression with Monte-Carlo simulation. We utilize our closed-form for assessing the EE performance of base station (BS) cooperation against non-cooperative system for both a theoretical power model and a realistic power model. The theoretical power model includes only the transmit power, whereas the realistic power model incorporates the backhaul and signal processing powers in addition of the transmit power. Results indicate that BS cooperation is more energy efficient than non cooperative system and the former always outperforms the latter in terms of EE-SE trade-off. This is however no more the case with the realistic power model: the EE performance is then highly dependent on the number of cooperating BSs.
- . (2011) 'Closed-form Approximation for the Trade-off between Energy Efficiency and Spectral Efficiency in the Uplink of Cellular Network'. Vienna, Austria: European Wireless Conference
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(2011) 'Performance of Multicell Joint Processing Planar Cellular Uplink in the Presence of Relay Nodes'. IEEE ICT Future Network and Mobile Summit 2010, Florence Italy: ICT Future Network and Mobile Summit 2010Full text is available at: http://epubs.surrey.ac.uk/534280/
Abstract
In this paper we compare the uplink performance of various deployment scenarios in the planar (hexagonal) cellular system where the received signals at multiple cells are jointly processed by a central processor. A mathematical model of the planar cellular system is presented and its performance metric is based on information theoretic sum rate, and group rate share. The system deployment is as follows; the density of the base station is decreased, relay node replaces alternate base stations and in the last scenario, alternate bases stations are removed while the left over base stations are equipped with an additional antenna. It is observed that in reduction in the density of base stations resulted in reduction in the achievable sum rate and makes the group rate unfair. The introduction of additional antenna resulted in an improvement in the rate (compared with the reduction in density scenario) without any improvement in group rate fairness to cell user at the cell edge. The replacement of base stations with relay node and the implementation of orthogonal amplify and forward scheme resulted in a reduction in the achievable sum rate however it produced a significant improvement in group rate fairness. The result suggest that relay deployment in multicell joint processing system does not improve the sum rate of the system rather it improves the rate share for cell edge users making the user rate distribution fairer.
- . (2011) 'Energy Efficiency Analysis of In-Building MIMO AF Communication'. Istanbul, Turkey : The 7th International Wireless Communication and Mobile Computing Conference-IWCMC,
- . (2011) 'Collaborative spectrum sensing based on upper bound on joint PDF of extreme eigenvalues'. European Signal Processing Conference, , pp. 1214-1218.
- . (2011) 'The Energy Efficiency Analysis of HARQ in Hybrid Relaying Systems'. Budapest, Hungary : IEEE Vehicular technology Conference - VTC Spring 2011,
- . (2011) 'Cellular Energy Efficiency Evaluation Framework'. Budapest, Hungary : IEEE Vehicular technology Conference - VTC Spring 2011,
- . (2011) 'Energy and Spectrum Efficient systems with Adaptive Modulation and Spectrum Sharing for Cellular Systems'. Budapest, Hungary : IEEE Vehicular technology Conference - VTC Spring 2011,
- . (2011) 'Eigenvalue Ratio Detection Based On Exact Moments of Smallest and Largest Eigenvalues'. Osaka, Japan : IEEE CrownCom 2011,
- . (2011) 'Eigenvalue ratio detection based on exact moments of smallest and largest eigenvalues'. Proceedings of the 2011 6th International ICST Conference on Cognitive Radio Oriented Wireless Networks and Communications, CROWNCOM 2011, , pp. 46-50.
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(2010) 'A New Performance Characterization Framework for Deployment Architectures of Next Generation Distributed Cellular Networks'. Istanbul, Turkey : IEEE IEEE PIMRC 2010, Istanbul: IEEE 21st International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC), 2010, pp. 2046-2051.Full text is available at: http://epubs.surrey.ac.uk/735971/
Abstract
Performance of next generation OFDM/OFDMA based Distributed Cellular Network (ODCN) where no cooperation based interference management schemes are used, is dependent on four major factors: 1) spectrum reuse factor, 2) number of sectors per site, 3) number of relay station per site and 4) modulation and coding efficiency achievable through link adaptation. The combined effect of these factors on the overall performance of a Deployment Architecture (DA) has not been studied in a holistic manner. In this paper we provide a framework to characterize the performance of various DA's by deriving two novel performance metrics for 1) spectral efficiency and 2) fairness among users. These metrics are designed to include the effect of all four contributing factors. We evaluate these metrics for a wide set of DA's through extensive system level simulations. The results provide a comparison of various DA's for both cellular and relay enhanced cellular systems in terms of spectral efficiency and fairness they offer and also provide an interesting insight into the tradeoff between the two performance metrics. Numerical results show that, in interference limited regime, DA's with highest spectrum efficiency are not necessarily those that resort to full frequency reuse. In fact, frequency reuse of 3 with 6 sectors per site is spectrally more efficient than that with full frequency reuse and 3 sectors. In case of relay station enhanced ODCN a DA with full frequency reuse, six sectors and 3 relays per site is spectrally more efficient and can yield around 170% higher spectrum efficiency compared to counterpart DA without RS.
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(2010) 'A Novel Self Organizing Framework for Adaptive Frequency Reuse & Deployment in Future Cellular Networks'. Istanbul, Turkey : IEEE IEEE PIMRC 2010, Istanbul: IEEE 21st International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC), 2010, pp. 2354-2359.Full text is available at: http://epubs.surrey.ac.uk/735972/
Abstract
Recent research on Frequency Reuse (FR) schemes for OFDM/OFDMA based cellular networks (OCN) suggest that a single fixed FR cannot be optimal to cope with spatiotemporal dynamics of traffic and cellular environments in a spectral and energy efficient way. To address this issue this paper introduces a novel Self Organizing framework for adaptive Frequency Reuse and Deployment (SO-FRD) for future OCN including both cellular (e.g. LTE) and relay enhanced cellular networks (e.g. LTE Advance). In this paper, an optimization problem is first formulated to find optimal frequency reuse factor, number of sectors per site and number of relays per site. The goal is designed as an adaptive utility function which incorporates three major system objectives; 1) spectral efficiency 2) fairness, and 3) energy efficiency. An appropriate metric for each of the three constituent objectives of utility function is then derived. Solution is provided by evaluating these metrics through a combination of analysis and extensive system level simulations for all feasible FRD's. Proposed SO-FRD framework uses this flexible utility function to switch to particular FRD strategy, which is suitable for system's current state according to predefined or self learned performance criterion. The proposed metrics capture the effect of all major optimization parameters like frequency reuse factor, number of sectors and relay per site, and adaptive coding and modulation. Based on the results obtained, interesting insights into the tradeoff among these factors is also provided.
- . (2010) 'Fairness and user rate distribution in joint processing systems'. Cape Town, South Africa: 2010 IEEE International Conference on Communications (ICC)
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(2010) 'Interference Allowance in Clustered Joint Processing and Power Allocation'. Caen, France : IWCMC 2010, The 6th International Wireless Communication and Mobile Computing Conference, Caen, France: IWCMC 2010Full text is available at: http://epubs.surrey.ac.uk/207040/
Abstract
We derive an analytical formula for the sum rate of the uplink of a linear network of cells when clustered joint processing is adopted among the base stations in a generalised fading environment. An inter-cluster interference allowance scheme is considered and various user power allocation profiles are investigated in terms of optimal achievable sum rate to highlight that cell-based power allocation is preferable to cluster-based. The contribution of each base station on the cluster sum rate is investigated and its importance is discussed. Numerical results are produced for a real-world scenario showing how medium density systems are the most viable case for clustered system design by achieving > 80% of the global cooperation capacity.
- . (2010) 'Energy Efficiency with Adaptive Modulation and Spectrum Sharing for Cellular Systems'. Liverpool, UK : 11th Annual Postgraduate Symposium on the Convergence of Telecommunications, Networking & Broadcasting,,
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(2010) 'Downlink Sum-rate Performance for Cooperation and Coordination between Three Interfering Sectors'. Liverpool, UK : 11th Annual Postgraduate Symposium on the Convergence of Telecommunications, Networking & Broadcasting, Liverpool UK: 11th Annual Postgraduate Symposium on the Convergence of Telecommunications, Networking & BroadcastingFull text is available at: http://epubs.surrey.ac.uk/534279/
Abstract
In this paper we investigate the performance of various transmission schemes for the downlink cellular system. These schemes are either biased towards interference minimisation or the efficient utilisation of the available resources. A mathematical model for the various schemes is presented and the performance measure is based on the information theoretic sum rate and the user rate share. The identified schemes are: avoid intra-cell and tolerate inter-cell interference, full orthogonality, single cell cooperation, cooperation for critical users only and the full cooperation scheme. Two categories of users are identified in this paper: non critical users which are close to the base station and the critical user which are at the cell boundary. It is observed that the full cooperation provides an upper bound on the achievable sum rate and has a user rate distribution whose fairness can be improved by allocating more power to the critical users. The full orthogonality scheme has the fairest user rate distribution and much lower achievable sum rate compared with the full cooperation. The performance of the cooperation of critical user scheme can approach the upper bound of full cooperation scheme with lower complexity.
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(2010) 'Self organised cellular networks as the future of wireless communications'. Liverpool, UK : 11th Annual Postgraduate Symposium on the Convergence of Telecommunications, Networking & Broadcasting, 11th Annual Postgraduate Symposium on the Convergence of Telecommunications, Networking & BroadcastingFull text is available at: http://epubs.surrey.ac.uk/725970/
Abstract
An introduction into self organizing cellular networks is presented. This topic has generated a lot of research interest over the past few years as operators have identified it as a necessary feature in future wireless communication systems. We review projects which have studied self organization and with knowledge of system model design in computing, we suggest design rules in developing robust and efficient self organizing algorithms. We finally demonstrate a channel assignment example based on the concept of sectorial neighbours where the system autonomously changes its allocation scheme based on external factors in the environment (e.g. geographical location, interfering sectors and demand for resources). Further research directions are also highlighted.
- . (2010) 'Transmit Diversity and Beamforming for Energy Efficient Femtocells'. Singapore : Annual International Conference on Green Information Technology 2010,
- . (2010) 'Optimization of uplink sum-rate for bin based clustered cellular system using a Genetic Algorithm'. Caen, France : IWCMC 2010, The 6th International Wireless Communication and Mobile Computing Conference,
- . (2010) 'Enablers for Energy Efficient Wireless Networks'. Ottawa, Canada : Green Wireless Communications and Networks Workshop � GreeNet, Proc. IEEE VTC Fall 2010,
- . (2010) 'Ground based and onboard based beamforming for hybrid terrestrial-satellite mobile system'. California, USA : 28th AIAA International Communication Satellite Systems Conference (ICSSC 2010),
- . (2010) 'Cell based Fair Resource Allocation in Fixed Clustered Cellular Systems using a Genetic Algorithm'. Istanbul, Turkey : IEEE PIMRC 2010,
- . (2010) 'Multicell LMMSE Filtering Capacity under Correlated Multiple BS Antennas'. Ottawa, Canada : Proc. IEEE VTC Fall 2010,
- . (2010) 'Preamble based Adaptive Beamformer for Hybrid Terrestrial-Satellite Mobile System'. California, USA : 28th AIAA International Communication Satellite Systems Conference (ICSSC 2010),
- . (2010) 'Frequency Planning of Clustered Cellular Network using Particle Swarm Optimization'. York, UK : ISWCS 2010,
- . (2010) 'The EARTH Project: Towards Energy Efficient Wireless Networks'. Florence Italy : ICT Future Network and Mobile Summit 2010,
- . (2010) 'On the energy aware deployment strategy in cellular systems'. Istanbul, Turkey : Wireless Green Workshop, IEEE PIMRC 2010,
- . (2009) 'Green Communications: A global environmental challenge'. Sendai, Japan : 12th WPMC 2009,
- . (2009) 'Improving downlink performance by reusing the subcarriers within the cell'. Santander, Spain : ICT-MobileSummit,
- . (2009) 'Performance of multicell joint processing cellular uplink in the presence of relay nodes'. Santander, Spain : ICT-MobileSummit,
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(2009) 'Adaptive beamforming for OFDM based hybrid mobile satellite system'. Edinburgh, UK : 27th AIAA International Communication Satellite Systems Conference (ICSSC 2009), Edinburgh, UK: 27th IET and AIAA International Communications Satellite Systems Conference (ICSSC 2009)doi: 10.1049/cp.2009.1228Full text is available at: http://epubs.surrey.ac.uk/735974/
Abstract
Global connectivity cannot be guaranteed by terrestrial networks due to the lack of infrastructure in rural areas. Neither can satellite networks assure this due to lack of signal penetration and capacity coverage issues in densely populated areas. To bridge this gap, we propose an orthogonal frequency domain (OFDM) based hybrid architecture where users are provided service by existing mobile networks in urban areas and are served by satellite in the rural areas. In such a system terrestrial and satellite networks can reuse the portion of spectrum dedicated to each of these systems resulting in significant increase in overall capacity, wider coverage and reduced cost. This frequency reuse induces severe cochannel interference (CCI) at the satellite end and our work focuses on its mitigation using OFDM based adaptive beamforming
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(2009) 'Sum Rate of Linear Cellular Systems with Clustered Joint Processing'. IEEE 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, Barcelona, SPAIN: 69th IEEE Vehicular Technology Conference, pp. 2892-2896.Full text is available at: http://epubs.surrey.ac.uk/207041/
- . (2009) 'The multicell processing capacity of the cellular MIMO uplink channel under correlated fading'. IEEE International Conference on Communications,
- . (2009) 'EARTH - Energy Aware Radio and Network Technologies'. IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC,
- . (2009) 'Uplink Capacity with Correlated Lognormal Shadow Fading'. IEEE 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, Barcelona, SPAIN: 69th IEEE Vehicular Technology Conference, pp. 3009-3013.
- . (2009) 'OFDM based Adaptive Beamforming for Hybrid Terrestrial-Satellite Mobile System with Pilot Reallocation'. IEEE 2009 INTERNATIONAL WORKSHOP ON SATELLITE AND SPACE COMMUNICATIONS, CONFERENCE PROCEEDINGS, Univ Siena, Siena, ITALY: International Workshop on Satellite and Space Communications, pp. 201-205.
- . (2009) 'On the Ergodic Capacity of the Wideband MIMO Channel'. IEEE 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, Barcelona, SPAIN: 69th IEEE Vehicular Technology Conference, pp. 754-758.
- . (2009) 'Reduced-complexity multicell decoding systems with multiple antennas at the base station'. Proceedings of the 2009 ACM International Wireless Communications and Mobile Computing Conference, IWCMC 2009, , pp. 849-853.
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(2008) 'Analyzing uplink capacity of partially overlapping channel based WLANs using a hyper-receiver'. IEEE 2008 IEEE INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATION SYSTEMS (ISWCS 2008), Reykjavik, ICELAND: 5th International Symposium on Wireless Communication Systems, pp. 723-727.Full text is available at: http://epubs.surrey.ac.uk/735976/
Abstract
Spectrum allocation within the fixed unlicensed band affects performance of wireless networks. Fundamental limitations of spectral efficiency on capacity of wireless local area networks (WLANs) hence needs to be studied. Recently, it was shown that the performance can be increased when both non-overlapping and partially overlapping channels are used. Unlike previous studies, this is the first known attempt on analysis of information theoretic capacity for partially-overlapping channels, as characterized by IEEE 802.11b-type systems using a hyper-receiver. Using Marenko-Pastur law distribution, capacity is approximated for such systems. We implement this by proposing a novel channel model for our analysis. The results conform to Monte Carlo simulations, with an approximate mean error of less than 5%. Fundamental tradeoffs of channel interference and power gain are discussed. We further explore the effect of access point density and find that systems based on partially overlapping channels perform well in high density deployments. We also compute capacity for a range of channel overlaps and conclude that rates close to capacity are achievable for a channel overlap of 90% and above.
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(2008) 'Framework to Compare the Uplink Capacity of the Cellular Systems with Variable Inter Site Distance'. Cannes, France : IEEE IEEE 19th International Symposium on Personal, Indoor and Mobile Radio Communications 2008, PIMRC’08, Cannes, France: PIMRC’08Full text is available at: http://epubs.surrey.ac.uk/207038/
Abstract
In this paper we derive the information theoretic capacity of the uplink of a cellular system with variable inter site distance and a generalised fading environment. The capacity is shown to be a direct function of the ratio of total received signal power (from within and outside of a cell) to the AWGN noise power, at any BS. This ratio is defined as the Rise over Thermal (RoT). It is shown that the variation in system parameters like the path loss exponent, number of users, transmit power constraint and the inter site distance, changes the region of operation on a capacity-versus-RoT curve. Results are interpreted for practical channel models and it is shown that RoT provides a useful framework to compare various practical systems.
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(2008) 'INFORMATION THEORETIC CAPACITY OF THE CELLULAR UPLINK - AVERAGE PATH LOSS APPROXIMATION'. 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. 605-609.Full text is available at: http://epubs.surrey.ac.uk/207039/
- . (2008) 'Capacity of the Cellular Uplink using Joint Multi-cell Processing (Hyper-receiver) with OFDM and CDMA'. Newbury, UK : International Research Workshop on LTE-Advanced Technologies,
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(2008) 'Capacity of cellular uplink with multiple tiers of users and path loss'. Proceedings - 4th Advanced International Conference on Telecommunications, AICT 2008, , pp. 287-292.doi: 10.1109/AICT.2008.49Full text is available at: http://epubs.surrey.ac.uk/735977/
Abstract
With the emergence and continuous growth of wireless data services, the value of a wireless network is not only defined by how many users it can support, but also by its ability to deliver higher data rates. Information theoretic capacity of cellular systems with fading is usually estimated using models originally inspired by Wyner's Gaussian Cellular Multiple Access Channel (GCMAC). In this paper we extend this model to study the cellular system with users distributed over the cellular coverage area. Based on the distance from the cell-site receiver, users are grouped as tiers, and received signals from each tier are scaled using a distance dependent attenuation factor. The optimum capacity in fading environment is then found by calculating the path-loss for users in each tier using a specific path-loss law and some interesting insights are derived. The results correspond to a more realistic model which boils down to Wyner's model with fading, with appropriate substitutions of parameter values. The results are verified using Wyner's model with fading and Monte-Carlo simulations. Insights are provided for the real world scenarios. © 2008 IEEE.
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(2008) 'Information Theoretic Uplink Capacity of the Linear Cellular Array'. Athens, Greece : IEEE Proc. Fourth Advanced International Conference on Telecommunications AICT ’08, Athens: Fourth Advanced International Conference on Telecommunications, 2008. AICT '08, pp. 249-254.doi: 10.1109/AICT.2008.35Full text is available at: http://epubs.surrey.ac.uk/735978/
Abstract
In the information-theoretic literature, Wyner's model has been the starting point for studying the capacity limits of cellular systems. This simple cellular model was adopted and extended by researchers in order to incorporate flat fading and path loss. However, the majority of these extensions preserved a fundamental assumption of Wyner's model, namely the collocation of User Terminals (UTs). In this paper, we alleviate this assumption and we evaluate the effect of user distribution on the sum-rate capacity. In this context, we show that the effect of user distribution is only considerable in low cell-density systems and we argue that "collocated" models can be utilized to approximate the "distributed" ones in the high cell-density regime. Subsequently, we provide closed forms for the calculation of the interference factors of "collocated" models given the system parameters. In addition, the asymptotics of the per-cell sum-rate capacity are investigated. Finally, the presented results are interpreted in the context of practical cellular systems using appropriate figures of merit.
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(2008) 'Uplink Coverage-Capacity Estimation Using Analysis and Simulation'. Proc. Fourth Advanced International Conference on Telecommunications AICT ’08, , pp. 151-156.doi: 10.1109/AICT.2008.58
- . (2008) 'Capacity of Variable Density Cellular Systems with Distributed Users'. University of Surrey, Guildford, UK : Second International Workshop on Fundamental Capacity Limits for Wireless Cellular Communication Systems,
- . (2008) 'Optimal information theoretic capacity of the planar cellular uplink channel'. Pernambuco, Brazil : Proc. IEEE 9th Workshop on Signal Processing Advances in Wireless Communications SPAWC 2008, , pp. 196-200.
- . (2008) 'Transmit Power Formulation for Relay-enhanced UMTS using Simulation and Theory'. Cannes, France : IEEE 19th International Symposium on Personal, Indoor and Mobile Radio Communications 2008, PIMRC’08,
- . (2008) 'Uplink Capacity of MIMO Cellular Systems with Multicell Processing'. IEEE 2008 IEEE INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATION SYSTEMS (ISWCS 2008), Reykjavik, ICELAND: 5th International Symposium on Wireless Communication Systems, pp. 333-337.
- . (2008) 'Uplink Capacity of Variable-Density Cellular System with Distributed Users and Fading'. Cannes, France : IEEE 19th International Symposium on Personal, Indoor and Mobile Radio Communications 2008, PIMRC’08,
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(2008) 'The Effect of User Distribution on a Linear Cellular Multiple-Access Channel'. IEEE 2008 THIRD INTERNATIONAL CONFERENCE ON COMMUNICATIONS AND NETWORKING IN CHINA, VOLS 1-3, Hangzhou, PEOPLES R CHINA: 3rd International Conference on Communications and Networking in China, pp. 90-94.Full text is available at: http://epubs.surrey.ac.uk/533673/
- . (2008) 'Spectral efficiency of variable density cellular systems with realistic system models'. IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC,
- . (2007) 'Impact of Orthogonality Factor on UMTS Capacity Simulation'. Proceedings of the 2nd ACM Workshop on Performance Monitoring and Measurement of Heterogenous Wireless and Wired Networks PM2HW2N ’07,
- . (2006) 'Blind Minimum Mean Squared Error (MMSE) Multiuser Detection with Reliable Subspace Estimation (RSE)'. Proc. International Conference on Wireless and Mobile Communications ICWMC ’06,
- . (2005) 'Channel Coding for Cooperative Broadcasting'. Proc. of Hellenic European Research on Computer Mathematics and its Applications (HERCMA) 2005,
- . (2004) 'Graph theoretic multiple access interference reduction for CDMA based radio LAN'. Proc. IEEE International Conference on Communications, 7, pp. 4147-4151.
Book chapters
- . (2012) 'Green Relay Techniques in Cellular Systems'. in Yu FR, Leung V-C, Zhang X (eds.) Green Communications and Networking CRC Press
- . (2012) 'On the Energy Efficiency-Spectral Efficiency Trade-off in Cellular Systems'. in Wu J, Sundeep R, Honggang Z (eds.) Green Communications: Theoretical Fundamentals, Algorithms and Applications CRC Press
- . (2012) 'Green Wireless Access Networks'. in Wu J, Sundeep R, Honggang Z (eds.) Green Communications: Theoretical Fundamentals, Algorithms and Applications CRC Press
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(2012) 'How much energy is needed to run a wireless network'. in Hossain E, Bhargava VK, Fettweis GP (eds.) Green Radio Communication Networks
Cambridge University Press Full text is available at: http://epubs.surrey.ac.uk/735354/
Abstract
Presenting state-of-the-art research on green radio communications and networking technology by leaders in the field, this book is invaluable for researchers and professionals working in wireless communication.
- . (2010) 'Capacity Limits of Base Station Cooperation in Cellular Networks'. in Uysal M (ed.) Cooperative Communications for Improved Wireless Network Transmission: Framework for Virtual Antenna Array Applications
- . (2009) 'Capacity Limits in Cooperative Cellular Systems'. in Zhang Y, Chen H-H, Guizani M (eds.) Cooperative Wireless Communications 1st Edition. Auerbach Publications, Taylor & Francis Group , pp. 25-51.
- . (2008) 'Capacity of Sectorized Cellular Systems: An Information Theoretic Perspective'. in Vishnevsky V, Vinel A, Koucheryavy Y, Staehle D (eds.) Selected Lectures on Multiple Access and Queuing Systems SAINT-PETERSBURG : Russian Academy of Science, St Petersburg, Russia , pp. 130-138.
Reports
- . (2009) Cooperation among Base Stations and Relay Stations for OFDMA Multi-hop Cellular Networks.
- . (2009) Multi-cell Coordination Techniques for OFDMA Multi-hop Cellular Networks.
- . (2009) Multi User Cooperative Transmission techniques for OFDMA Multi-hop Cellular Networks.
- . (2007) Results and analysis for the rate limits for Wireless City model.
- . (2007) Fundamental limits for practical deployments of wireless cellular networks.
- . (2007) Fundamental limits for wireless cellular networks.
- . (2006) Book of assumptions and known results for the fundamental limits of wireless networks.
Teaching
ELEC III (University of Surrey, UK):
2012 Module Coordinator
2nd Year UG course covering Differential Equations, Laplace transforms and applications, Circuit Analysis and Communication Systems for a group of around 80 students
ELEC IV (University of Surrey, UK):
2009/2010/2011/2012/2013
Electronics and Communication Systems: 20 Hours of Lectures for second year undergraduate students. A group of around 70 students.
EE2.COM (University of Surrey, UK):
Spring 2009
Wireless Communications: 12 Hours of Lectures for second year undergraduate students. A group of around 80 students.
EE3.DCM (University of Surrey, UK):
2008 - 2012
Digital Communication and Modulation: 20 Hours of Lectures for final year undergraduate students and MSc students. A group of around 100 students.
Lecture Series (National Univerity of Science & Technology, Pakistan):
Summer 2008
Wireless Channel Modelling and Simulations - 30 Hours of Lectures and Lab sessions
Demonstrations/Teaching Assistance (Imperial College London):
Fall 2002 - 06
Electronics Laboratory
Compilers Laboratory
First Year and Second Year Tutorials
Computer Programming Helpdesk
Departmental Duties
Post Graduate Admissions Tutor (for Subcontinent Region and Greece)
Visiting Tutor to Professional Training Year Placement students
Member of course review panel
Member of subcommittee for Faculty Learning and Teaching Committee
Affiliations
Senior Member IEEE
Associate Fellow Higher Education Academy
Research Supervision
Technical Experience
Service Desk Specialist (part-time)
2003 - 06
Information and Communication Technologies (ICT): IT support at Imperial College London.
Design Engineer
1999 - 2001
And-Or Logic, Inc. Islamabad, Pakistan
