1,203 research outputs found

    Performance Analysis, Resource Allocation and Optimization of Cooperative Communication Systems under Generalized Fading Channels

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    The increasing demands for high-speed data transmission, efficient wireless access, high quality of service (QoS) and reliable network coverage with reduced power consumption impose demanding intensive research efforts on the design of novel wireless communication system architectures. A notable development in the area of communication theory is the introduction of cooperative communication systems. These technologies become promising solution for the next-generation wireless transmission systems due to their applicability in size, power, hardware and price constrained devices, such as cellular mobile devices, wireless sensors, ad-hoc networks and military communications, being able to provide, e.g., diversity gain against fading channels without the need for installing multiple antennas in a single terminal. The performance of the cooperative systems can in general be signiïŹcantly increased by allocating the limited power efficiently. In this thesis, we address in detail the performance analysis, resource allocation and optimization of such cooperative communication systems under generalized fading channels. We focus ïŹrst on energy-efficiency (EE) optimization and optimal power allocation (OPA) of regenerative cooperative network with spatial correlation effects under given power constraint and QoS requirement. The thesis also investigates the end-to-end performance and power allocation of a regenerative multi-relay cooperative network over non-homogeneous scattering environment, which is realistic case in practical wireless communication scenarios. Furthermore, the study investigates the end-to-end performance, OPA and energy optimization analysis under total power constraint and performance requirement of full-duplex (FD) relaying transmission scheme over asymmetric generalized fading models with relay self-interference (SI) effects.The study ïŹrst focuses on exact error analysis and EE optimization of regenerative relay systems under spatial correlation effects. It ïŹrst derives novel exact and asymptotic expressions for the symbol-error-rates (SERs) of M -ary quadrature amplitude and M -ary phase-shift keying (M -QAM) and (M -PSK) modulations, respectively, assuming a dual-hop decode-and-forward relay system, spatial correlation, path-loss effects and maximum-ratio-combing (MRC) at the destination. Based on this, EEoptimization and OPA are carried out under certain QoS requirement and transmit power constraints.Furthermore, the second part of the study investigates the end-to-end performance and power allocation of MRC based regenerative multi-relay cooperative system over non-homogeneous scattering environment. Novel exact and asymptotic expressions are derived for the end-to-end average SER for M -QAM and M -PSK modulations.The offered results are employed in performance investigations and power allocation formulations under total transmit power constraints.Finally, the thesis investigates outage performance, OPA and energy optimization analysis under certain system constraints for the FD and half-duplex (HD) relaying systems. Unlike the previous studies that considered the scenario of information transmission over symmetric fading conditions, in this study we considered the scenario of information transmission over the most generalized asymmetric fading environments.The obtained results indicate that depending on the severity of multipath fading, the spatial correlation between the direct and relayed paths and the relay location, the direct transmission is more energy-efficient only for rather short transmission distances and until a certain threshold. Beyond this, the system beneïŹts substantially from the cooperative transmission approach where the cooperation gain increases as the transmission distance increases. Furthermore, the investigations on the power allocation for the multi-relay system over the generalized small-scale fading model show that substantial performance gain can be achieved by the proposed power allocation scheme over the conventional equal power allocation (EPA) scheme when the source-relay and relay-destination paths are highly unbalanced. Extensive studies on the FD relay system also show that OPA provides signiïŹcant performance gain over the EPA scheme when the relay SI level is relatively strong. In addition, it is shown that the FD relaying scheme is more energy-efficient than the reference HD relaying scheme at long transmission distances and for moderate relay SI levels.In general, the investigations in this thesis provide tools, results and useful insights for implementing space-efficient, low-cost and energy-efficient cooperative networks, speciïŹcally, towards the future green communication era where the optimization of the scarce resources is critical

    On the Performance of the Relay-ARQ Networks

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    This paper investigates the performance of relay networks in the presence of hybrid automatic repeat request (ARQ) feedback and adaptive power allocation. The throughput and the outage probability of different hybrid ARQ protocols are studied for independent and spatially-correlated fading channels. The results are obtained for the cases where there is a sum power constraint on the source and the relay or when each of the source and the relay are power-limited individually. With adaptive power allocation, the results demonstrate the efficiency of relay-ARQ techniques in different conditions.Comment: Accepted for publication in IEEE Trans. Veh. Technol. 201

    Energy Efficient Massive MIMO and Beamforming for 5G Communications

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    Massive multiple-input multiple-output (MIMO) has been a key technique in the next generation of wireless communications for its potential to achieve higher capacity and data rates. However, the exponential growth of data traffic has led to a significant increase in the power consumption and system complexity. Therefore, we propose and study wireless technologies to improve the trade-off between system performance and power consumption of wireless communications. This Thesis firstly proposes a strategy with partial channel state information (CSI) acquisition to reduce the power consumption and hardware complexity of massive MIMO base stations. In this context, the employment of partial CSI is proposed in correlated communication channels with user mobility. By exploiting both the spatial correlation and temporal correlation of the channel, our analytical results demonstrate significant gains in the energy efficiency of the massive MIMO base station. Moreover, relay-aided communications have experienced raising interest; especially, two-way relaying systems can improve spectral efficiency with short required operating time. Therefore, this Thesis focuses on an uncorrelated massive MIMO two-way relaying system and studies power scaling laws to investigate how the transmit powers can be scaled to improve the energy efficiency up to several times the energy efficiency without power scaling while approximately maintaining the system performance. In a similar line, large antenna arrays deployed at the space-constrained relay would give rise to the spatial correlation. For this reason, this Thesis presents an incomplete CSI scheme to evaluate the trade-off between the spatial correlation and system performance. In addition, the advantages of linear processing methods and the effects of channel aging are investigated to further improve the relay-aided system performance. Similarly, large antenna arrays are required in millimeter-wave communications to achieve narrow beams with higher power gain. This poses the problem that locating the best beam direction requires high power and complexity consumption. Therefore, this Thesis presents several low-complexity beam alignment methods with respect to the state-of-the-art to evaluate the trade-off between complexity and system performance. Overall, extensive analytical and numerical results show an improved performance and validate the effectiveness of the proposed techniques

    Partner selection in indoor-to-outdoor cooperative networks: an experimental study

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    In this paper, we develop a partner selection protocol for enhancing the network lifetime in cooperative wireless networks. The case-study is the cooperative relayed transmission from fixed indoor nodes to a common outdoor access point. A stochastic bivariate model for the spatial distribution of the fading parameters that govern the link performance, namely the Rician K-factor and the path-loss, is proposed and validated by means of real channel measurements. The partner selection protocol is based on the real-time estimation of a function of these fading parameters, i.e., the coding gain. To reduce the complexity of the link quality assessment, a Bayesian approach is proposed that uses the site-specific bivariate model as a-priori information for the coding gain estimation. This link quality estimator allows network lifetime gains almost as if all K-factor values were known. Furthermore, it suits IEEE 802.15.4 compliant networks as it efficiently exploits the information acquired from the receiver signal strength indicator. Extensive numerical results highlight the trade-off between complexity, robustness to model mismatches and network lifetime performance. We show for instance that infrequent updates of the site-specific model through K-factor estimation over a subset of links are sufficient to at least double the network lifetime with respect to existing algorithms based on path loss information only.Comment: This work has been submitted to IEEE Journal on Selected Areas in Communications in August 201

    Contributions to the Performance Analysis of Intervehicular Communications Systems and Schemes

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    RÉSUMÉ Le but des systĂšmes de communication intervĂ©hicule (Inter-Vehicle Communication – IVC) est d'amĂ©liorer la sĂ©curitĂ© de conduite en utilisant des capteurs et des techniques de communication sans fil pour ĂȘtre en mesure de communiquer mutuellement sans aucune intervention extĂ©rieure. Avec l'utilisation de ces systĂšmes, les communications vĂ©hicule Ă  vĂ©hicule (V2V) peuvent ĂȘtre plus efficaces dans la prĂ©vention des accidents et la dĂ©congestion de la circulation que si chaque vĂ©hicule travaillait individuellement. Une des solutions proposĂ©es pour les systĂšmes IVC est l’utilisation des systĂšmes de communication coopĂ©rative, qui en principe, augmentent l'efficacitĂ© spectrale et Ă©nergĂ©tique, la couverture du rĂ©seau, et rĂ©duit la probabilitĂ© de dĂ©faillance. La diversitĂ© d'antenne (entrĂ©es multiples sorties multiples « Multiple-Input Multiple-Output » ou MIMO) peut Ă©galement ĂȘtre une alternative pour les systĂšmes IVC pour amĂ©liorer la capacitĂ© du canal et la diversitĂ© (fiabilitĂ©), mais en Ă©change d’une complexitĂ© accrue. Toutefois, l'application de telles solutions est difficile, car les communications sans fil entre les vĂ©hicules sont soumises Ă  d’importants effets d'Ă©vanouissements des canaux appelĂ©s (canaux sujets aux Ă©vanouissements de n*Rayleigh, « n*Rayleigh fading channels»), ce qui conduit Ă  la dĂ©gradation des performances. Par consĂ©quent, dans cette thĂšse, nous proposons une analyse de la performance globale des systĂšmes de transmission coopĂ©ratifs et MIMO sur des canaux sujets aux Ă©vanouissements de n*Rayleigh. Cette analyse permettra d’aider les chercheurs pour la conception et la mise en Ɠuvre de systĂšmes de communication V2V avec une complexitĂ© moindre. En particulier, nous Ă©tudions d'abord la performance de la sĂ©lection du relais de coopĂ©ration avec les systĂšmes IVC, on suppose que la transmission via « Amplify-and-Forward» (AF) ou bien «Decode-and-Forward» (DF) est assurĂ©e par N relais pour transfĂ©rer le message de la source Ă  la destination. La performance du systĂšme est analysĂ©e en termes de probabilitĂ© de dĂ©faillance, la probabilitĂ© d'erreur de symbole, et la capacitĂ© moyenne du canal. Les rĂ©sultats numĂ©riques dĂ©montrent que la sĂ©lection de relais rĂ©alise une diversitĂ© de l'ordre de (d≈mN/n) pour les deux types de relais, oĂč m est un paramĂštre Ă©vanouissement de Rayleigh en cascade. Nous Ă©tudions ensuite la performance des systĂšmes IVC Ă  sauts multiples avec et sans relais rĂ©gĂ©nĂ©ratifs. Dans cette Ă©tude, nous dĂ©rivons des expressions approximatives pour la probabilitĂ© de dĂ©faillance et le niveau d’évanouissement lorsque la diversitĂ© en rĂ©ception basĂ©e sur le ratio maximum de combinaison (MRC) est employĂ©e. En outre, nous analysons la rĂ©partition de puissance pour le systĂšme sous-jacent afin de minimiser la probabilitĂ© globale de dĂ©faillance. Nous montrons que la performance des systĂšmes rĂ©gĂ©nĂ©ratifs est meilleure que celle des systĂšmes non rĂ©gĂ©nĂ©ratifs lorsque l’ordre de cascade n est faible, tandis qu’ils ont des performances similaires lorsque n est Ă©levĂ©. Ensuite, nous considĂ©rons le problĂšme de la dĂ©tection de puissance des signaux inconnus aux n* canaux de Rayleigh. Dans ce travail, de nouvelles expressions approximatives sont dĂ©rivĂ©es de la probabilitĂ© de dĂ©tection moyenne avec et sans diversitĂ© en rĂ©ception MRC. En outre, la performance du systĂšme est analysĂ©e lorsque la dĂ©tection de spectre coopĂ©rative (CSS) est considĂ©rĂ©e sous diverses contraintes de canaux (par exemple, les canaux de communication parfaits et imparfaits). Les rĂ©sultats numĂ©riques ont montrĂ© que la fiabilitĂ© de dĂ©tection diminue Ă  mesure que l'ordre n augmente et s’amĂ©liore sensiblement lorsque CSS emploie le schĂ©ma MRC. Il est dĂ©montrĂ© que CSS avec le schĂ©ma MRC maintient la probabilitĂ© de fausse alarme minimale dans les canaux d’information imparfaite plutĂŽt que d'augmenter le nombre d'utilisateurs en coopĂ©ration. Enfin, nous prĂ©sentons une nouvelle approche pour l'analyse des performances des systĂšmes IVC sur n*canaux de Rayleigh, en utilisant n_T antennes d'Ă©mission et n_R antennes de rĂ©ception pour lutter contre l'effet d’évanouissement. Dans ce contexte, nous Ă©valuons la performance des systĂšmes MIMO-V2V basĂ©s sur la sĂ©lection des antennes d'Ă©mission avec un ratio maximum de combinaison (TAS/MRC) et la sĂ©lection combinant (TAS/SC). Dans cette Ă©tude, nous dĂ©rivons des expressions analytiques plus prĂ©cises pour la probabilitĂ© de dĂ©faillance, la probabilitĂ© d'erreur de symbole, et l’évanouissement sur n*canaux Rayleigh. Il est montrĂ© que les deux rĂ©gimes ont le mĂȘme ordre de diversitĂ© maximale Ă©quivalent Ă  (d≈mn_T n_R /n) . En outre, TAS / MRC offre un gain de performance mieux que TAS/ SC lorsque le nombre d'antennes de rĂ©ception est plus que celle des antennes d’émission, mais l’amĂ©lioration de la performance est limitĂ©e lorsque n augmente.----------Abstract The purpose of intervehicular communication (IVC) systems is to enhance driving safety, in which vehicles use sensors and wireless communication techniques to talk to each other without any roadside intervention. Using these systems, vehicle-to-vehicle (V2V) communications can be more effective in avoiding accidents and traffic congestion than if each vehicle works individually. A potential solution can be implemented in this research area using cooperative communications systems which, in principle, increase spectral and power efficiency, network coverage, and reduce the outage probability. Antenna diversity (i.e., multiple-input multiple output (MIMO) systems) can also be an alternative solution for IVC systems to enhance channel capacity and diversity (reliability) but in exchange of an increased complexity. However, applying such solutions is challenging since wireless communications among vehicles is subject to harsh fading channels called ‘n*Rayleigh fading channels’, which leads to performance degradation. Therefore, in this thesis we provide a comprehensive performance analysis of cooperative transmission and MIMO systems over n*Rayleigh fading channels that help researchers for the design and implementation of V2V communication systems with lower complexity. Specifically, we first investigate the performance of cooperative IVC systems with relay selection over n*Rayleigh fading channels, assuming that both the decode-and-forward and the amplify-and-forward relaying protocols are achieved by N relays to transfer the source message to the destination. System performance is analyzed in terms of outage probability, symbol error probability, and average channel capacity. The numerical results have shown that the best relay selection approach achieves the diversity order of (d≈mN/n) where m is a cascaded Rayleigh fading parameter. Second, we investigate the performance of multihop-IVC systems with regenerative and non-regenerative relays. In this study, we derive approximate closed-form expressions for the outage probability and amount of fading when the maximum ratio combining (MRC) diversity reception is employed. Further, we analyze the power allocation for the underlying scheme in order to minimize the overall outage probability. We show that the performance of regenerative systems is better than that of non-regenerative systems when the cascading order n is low and they have similar performance when n is high. Third, we consider the problem of energy detection of unknown signals over n*Rayleigh fading channels. In this work, novel approximate expressions are derived for the average probability of detection with and without MRC diversity reception. Moreover, the system performance is analyzed when cooperative spectrum sensing (CSS) is considered under various channel constraints (e.g, perfect and imperfect reporting channels). The numerical results show that the detection reliability decreases as the cascading order n increases and substantially improves when CSS employs MRC schemes. It is demonstrated that CSS with MRC scheme keeps the probability of false alarm minimal under imperfect reporting channels rather than increasing the number of cooperative users. Finally, we present a new approach for the performance analysis of IVC systems over n*Rayleigh fading channels, using n_T transmit and n_R receive antennas to combat fading influence. In this context, we evaluate the performance of MIMO-V2V systems based on the transmit antenna selection with maximum ratio combining (TAS/MRC) and selection combining (TAS/SC) schemes. In this study, we derive tight analytical expressions for the outage probability, the symbol error probability, and the amount of fading over n*Rayleigh fading channels. It is shown that both schemes have the same maximum diversity order equivalent to (d≈mn_T n_R /n). In addition, TAS/MRC offers a better performance gain than TAS/SC scheme when the number of receive antennas is more than that of transmit antennas, but the performance improvement is limited as n increases

    Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey

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    This paper provides a comprehensive review of the domain of physical layer security in multiuser wireless networks. The essential premise of physical-layer security is to enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers without relying on higher-layer encryption. This can be achieved primarily in two ways: without the need for a secret key by intelligently designing transmit coding strategies, or by exploiting the wireless communication medium to develop secret keys over public channels. The survey begins with an overview of the foundations dating back to the pioneering work of Shannon and Wyner on information-theoretic security. We then describe the evolution of secure transmission strategies from point-to-point channels to multiple-antenna systems, followed by generalizations to multiuser broadcast, multiple-access, interference, and relay networks. Secret-key generation and establishment protocols based on physical layer mechanisms are subsequently covered. Approaches for secrecy based on channel coding design are then examined, along with a description of inter-disciplinary approaches based on game theory and stochastic geometry. The associated problem of physical-layer message authentication is also introduced briefly. The survey concludes with observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials, 201
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