8 research outputs found

    Relay technology for performance improvement in WiMAX system

    Get PDF
    [no abstract

    Contributions to the Performance Analysis of Intervehicular Communications Systems and Schemes

    Get PDF
    RÉSUMÉ Le but des systèmes de communication intervéhicule (Inter-Vehicle Communication – IVC) est d'améliorer la sécurité de conduite en utilisant des capteurs et des techniques de communication sans fil pour être en mesure de communiquer mutuellement sans aucune intervention extérieure. Avec l'utilisation de ces systèmes, les communications véhicule à véhicule (V2V) peuvent être plus efficaces dans la prévention des accidents et la décongestion de la circulation que si chaque véhicule travaillait individuellement. Une des solutions proposées pour les systèmes IVC est l’utilisation des systèmes de communication coopérative, qui en principe, augmentent l'efficacité spectrale et énergétique, la couverture du réseau, et réduit la probabilité de défaillance. La diversité d'antenne (entrées multiples sorties multiples « Multiple-Input Multiple-Output » ou MIMO) peut également être une alternative pour les systèmes IVC pour améliorer la capacité du canal et la diversité (fiabilité), mais en échange d’une complexité accrue. Toutefois, l'application de telles solutions est difficile, car les communications sans fil entre les véhicules sont soumises à d’importants effets d'évanouissements des canaux appelés (canaux sujets aux évanouissements de n*Rayleigh, « n*Rayleigh fading channels»), ce qui conduit à la dégradation des performances. Par conséquent, dans cette thèse, nous proposons une analyse de la performance globale des systèmes de transmission coopératifs et MIMO sur des canaux sujets aux évanouissements de n*Rayleigh. Cette analyse permettra d’aider les chercheurs pour la conception et la mise en œuvre de systèmes de communication V2V avec une complexité moindre. En particulier, nous étudions d'abord la performance de la sélection du relais de coopération avec les systèmes IVC, on suppose que la transmission via « Amplify-and-Forward» (AF) ou bien «Decode-and-Forward» (DF) est assurée par N relais pour transférer le message de la source à la destination. La performance du système est analysée en termes de probabilité de défaillance, la probabilité d'erreur de symbole, et la capacité moyenne du canal. Les résultats numériques démontrent que la sélection de relais réalise une diversité de l'ordre de (d≈mN/n) pour les deux types de relais, où m est un paramètre évanouissement de Rayleigh en cascade. Nous étudions ensuite la performance des systèmes IVC à sauts multiples avec et sans relais régénératifs. Dans cette étude, nous dérivons des expressions approximatives pour la probabilité de défaillance et le niveau d’évanouissement lorsque la diversité en réception basée sur le ratio maximum de combinaison (MRC) est employée. En outre, nous analysons la répartition de puissance pour le système sous-jacent afin de minimiser la probabilité globale de défaillance. Nous montrons que la performance des systèmes régénératifs est meilleure que celle des systèmes non régénératifs lorsque l’ordre de cascade n est faible, tandis qu’ils ont des performances similaires lorsque n est élevé. Ensuite, nous considérons le problème de la détection de puissance des signaux inconnus aux n* canaux de Rayleigh. Dans ce travail, de nouvelles expressions approximatives sont dérivées de la probabilité de détection moyenne avec et sans diversité en réception MRC. En outre, la performance du système est analysée lorsque la détection de spectre coopérative (CSS) est considérée sous diverses contraintes de canaux (par exemple, les canaux de communication parfaits et imparfaits). Les résultats numériques ont montré que la fiabilité de détection diminue à mesure que l'ordre n augmente et s’améliore sensiblement lorsque CSS emploie le schéma MRC. Il est démontré que CSS avec le schéma MRC maintient la probabilité de fausse alarme minimale dans les canaux d’information imparfaite plutôt que d'augmenter le nombre d'utilisateurs en coopération. Enfin, nous présentons une nouvelle approche pour l'analyse des performances des systèmes IVC sur n*canaux de Rayleigh, en utilisant n_T antennes d'émission et n_R antennes de réception pour lutter contre l'effet d’évanouissement. Dans ce contexte, nous évaluons la performance des systèmes MIMO-V2V basés sur la sélection des antennes d'émission avec un ratio maximum de combinaison (TAS/MRC) et la sélection combinant (TAS/SC). Dans cette étude, nous dérivons des expressions analytiques plus précises pour la probabilité de défaillance, la probabilité d'erreur de symbole, et l’évanouissement sur n*canaux Rayleigh. Il est montré que les deux régimes ont le même ordre de diversité maximale équivalent à (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 réception est plus que celle des antennes d’émission, mais l’amélioration de la performance est limitée 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

    MIMO communications over relay channels

    Get PDF

    Capacity and performance analysis of advanced multiple antenna communication systems

    Get PDF
    Multiple-input multiple-output (MIMO) antenna systems have been shown to be able to substantially increase date rate and improve reliability without extra spectrum and power resources. The increasing popularity and enormous prospect of MIMO technology calls for a better understanding of the performance of MIMO systems operating over practical environments. Motivated by this, this thesis provides an analytical characterization of the capacity and performance of advanced MIMO antenna systems. First, the ergodic capacity of MIMO Nakagami-m fading channels is investigated. A unified way of deriving ergodic capacity bounds is developed under the majorization theory framework. The key idea is to study the ergodic capacity through the distribution of the diagonal elements of the quadratic channel HHy which is relatively easy to handle, avoiding the need of the eigenvalue distribution of the channel matrix which is extremely difficult to obtain. The proposed method is first applied on the conventional point-to-point MIMO systems under Nakagami-m fading, and later extended to the more general distributed MIMO systems. Second, the ergodic capacity of MIMO multi-keyhole and MIMO amplify-and-forward (AF) dual-hop systems is studied. A set of new statistical properties involving product of random complex Gaussian matrix, i.e., probability density function (p.d.f.) of an unordered eigenvalue, p.d.f. of the maximum eigenvalue, expected determinant and log-determinant, is derived. Based on these, analytical closedform expressions for the ergodic capacity of the systems are obtained and the connection between the product channels and conventional point-to-point MIMO channels is also revealed. Finally, the effect of co-channel interference is investigated. First, the performance of optimum combining (OC) systems operating in Rayleigh-product channels is analyzed based on novel closed-form expression of the cumulative distribution function (c.d.f.) of the maximum eigenvalue of the resultant channel matrix. Then, for MIMO Rician channels and MIMO Rayleigh-product channels, the ergodic capacity at low signal-to-noise ratio (SNR) regime is studied, and the impact of various system parameters, such as transmit and receive antenna number, Rician factor, channel mean matrix and interference-tonoise- ratio, is examined

    Statistical analysis of the capacity of mobile radio channels

    Get PDF
    Doktorgradsavhandling i informasjons- og kommunikasjonsteknologi, Universitetet i Agder, Grimstad, 201

    Performance analysis for cooperative wireless communications

    Get PDF
    Cooperative relaying has been proposed as a promising solution to mitigate and combat the deleterious effects of fading by sending and receiving independent copies of the same signal at different nodes. It has attracted huge attention from both industry and academia. The purpose of this thesis is to provide an analytical performance evaluation of the cooperative wireless systems while taking some realistic conditions into consideration. To achieve this, first, performance analysis of amplify-and-forward (AF) relaying using pilot-aided maximum likelihood estimation is studied in this thesis. Both disintegrated channel estimation (DCE) and cascaded channel estimation (CCE) are considered. Based on this analysis, optimal energy allocation is proposed. Then, performance analysis for AF relaying corrupted by interferers are investigated. Both randomly distributed and fixed interferers are considered. For random interferers, both the number and the locations of the interferers are random while for fixed interferers, both the number and the locations are fixed. Next, multihop relaying and multiple scattering channels over α - μ fading are analyzed. Channels with interferences and without interferences are considered. Exact results in the form of one-dimensional integral are derived. Also, approximate results with simplified structure and closed-form expressions are provided. Finally, a new hard decision fusion rule that combines arbitrary numbers of bits for different samples taken at different nodes is proposed. The best thresholds for the fusion rules using 2 bits, 3 bits and 4 bits are obtained through simulation. The bit error rate (BER) for hard fusion rule with 1 bit is provided. Numerical results are presented to show the accuracy of our analysis and provide insights. First, they show that our optimal energy allocation methods outperform the conventional system without optimal energy allocation, which could be as large as several dB’s in some cases. Second, with the increase of signal-to-interference-plus-noise ratio (SINR) for AF relaying with interference, the outage probability decreases accordingly for both random and fixed interferers. However, with the change of interference-to-noise ratio (INR) but with the SINR fixed, the outage probability for random interferers change correspondingly while the outage probability for fixed interferers remains almost the same. Third, our newly derived approximate expressions are shown to have acceptable performances in approximating outage probability in wireless multihop relaying system and multiple scattering channel considering interferences and without interferences. Last, our new hard decision fusion rule is shown to achieve better performance with higher energy efficiency. Also they show that there is a tradeoff between performance and energy penalty in the hard decision fusion rule

    Advanced Trends in Wireless Communications

    Get PDF
    Physical limitations on wireless communication channels impose huge challenges to reliable communication. Bandwidth limitations, propagation loss, noise and interference make the wireless channel a narrow pipe that does not readily accommodate rapid flow of data. Thus, researches aim to design systems that are suitable to operate in such channels, in order to have high performance quality of service. Also, the mobility of the communication systems requires further investigations to reduce the complexity and the power consumption of the receiver. This book aims to provide highlights of the current research in the field of wireless communications. The subjects discussed are very valuable to communication researchers rather than researchers in the wireless related areas. The book chapters cover a wide range of wireless communication topics

    Cooperative MIMO Relaying with Orthogonal Space-Time Block Codes in Wireless Channels with and without Keyholes

    No full text
    Cooperative multiple-input multiple-output (MIMO) relaying is investigated in the paper. We introduce DFAF selection MIMO relaying, where the relay equipped with multiple antennas can adaptively switch between decode-and-forward (DF) and amplify-and-forward (AF) according to its decoding state of the sourcemessage. We consider two wireless environment scenarios: 1)The scenario with traditional channels are considered firstly. We analyze the outage performance of DF-AF selection MIMO relaying, and a closed-form expression is derived. In addition, the diversity order is obtained based on the expression. For comparison purpose, we also obtain the closed-form outage probability and the diversity order for the AF MIMO relaying and the DF MIMO relaying. 2)We investigate the cooperative MIMO relaying in the presnece of keyholes secondly. We present performance analysis of orthogonal space-time block coded transmission for a cooperative MIMO relaying system with keyholes. For DF MIMO relaying, exact outage probability and symbol error probability (SEP) are obtained. Regarding AF MIMO relaying and DF-AF selection MIMO relaying, the lower and upper bounds are derived. In both traditional and keyhole scenarios, theoretical analysis which has been further verified through Monte-Carlo simulations demonstrate that the DF-AF selection MIMO relaying has better performance than the AF MIMO relaying and the DF MIMO relaying
    corecore