Level Crossing Rate and Average Fade Duration of the Multihop Rayleigh Fading Channel

We present a novel analytical framework for the evaluation of important second order statistical parameters, as the level crossing rate (LCR) and the average fade duration (AFD) of the amplify-and-forward multihop Rayleigh fading channel. More specifically, motivated by the fact that this channel is a cascaded one, which can be modelled as the product of N fading amplitudes, we derive novel analytical expressions for the average LCR and AFD of the product of N Rayleigh fading envelopes, or of the recently so-called N*Rayleigh channel. Furthermore, we derive simple and efficient closed-form approximations to the aforementioned parameters, using the multivariate Laplace approximation theorem. It is shown that our general results reduce to the specific dual-hop case, previously published. Numerical and computer simulation examples verify the accuracy of the presented mathematical analysis and show the tightness of the proposed approximations

Time and angle of arrival statistics of mobile-tomobile communication channel employing dual annular strip model

Abstract: In this paper, a generalized channel model for mobile-to-mobile communication based on the single bounce geometrybased channel modeling techniques has been proposed and analyzed. The model assumes the scatterers to be present in annular strips around the transmitting and the receiving mobile stations. Time of arrival and angle of arrival statistics, being two important channel parameters, have been derived and verified through computer simulations

On the Second Order Statistics of the Multihop Rayleigh Fading Channel

Second order statistics provides a dynamic representation of a fading channel and plays an important role in the evaluation and design of the wireless communication systems. In this paper, we present a novel analytical framework for the evaluation of important second order statistical parameters, as the level crossing rate (LCR) and the average fade duration (AFD) of the amplify-and-forward multihop Rayleigh fading channel. More specifically, motivated by the fact that this channel is a cascaded one and can be modeled as the product of N fading amplitudes, we derive novel analytical expressions for the average LCR and the AFD of the product of N Rayleigh fading envelopes (or of the recently so-called N*Rayleigh channel). Furthermore, we derive simple and efficient closed-form approximations to the aforementioned parameters, using the multivariate Laplace approximation theorem. It is shown that our general results reduce to the corresponding ones of the specific dual-hop case, previously published. Numerical and computer simulation examples verify the accuracy of the presented mathematical analysis and show the tightness of the proposed approximations

TEKNIK EQUALIZER UNTUK SISTEM ORTHOGONAL FREQUENCY DIVISON MULTIPLEXING (OFDM) PADA KANAL MOBILE

Orthogonal frequency divison multiplexing (OFDM) adalah teknik multicarrier yang memiliki frekuensi orthogonal satu sama lain dengan menggunakan bandwidth yang sempit. Salah satu kelemahan pada sistem OFDM adalah terjadinya fading dan hilangnya orthogonalitas pada subchannel yang diakibatkan oleh pergeseran Doppler. Permasalahan yang timbul akibat pergeseran Doppler adalah terjadinya intercarrier interference (ICI) pada kanal sehingga diperlukan mitigasi ICI untuk meningkatkan kinerja pada sistem. Pada penelitian ini, mitigasi ICI dilakukan menggunakan zero forcing equalizer, MMSE equalizer dan LMS equalizer. LMS equalizer memiliki kinerja yang lebih baik dibandingkan zero forcing equalizer dan MMSE equalizer yaitu pada kanal mobile-to-fix rayleigh fading mampu bertahan pada BER ketika frekuensi Doppler ternormalisasi dengan Eb/No 33dB dan pada kanal mobile-to-mobile rayleigh fading mampu bertahan pada BER ketika frekuensi Doppler ternormalisasi dengan Eb/No 30dB. Kata Kunci : Doppler, Equalizer, Kanal Mobile , Mitigasi ICI, OFD

Mobile Networks

The growth in the use of mobile networks has come mainly with the third generation systems and voice traffic. With the current third generation and the arrival of the 4G, the number of mobile users in the world will exceed the number of landlines users. Audio and video streaming have had a significant increase, parallel to the requirements of bandwidth and quality of service demanded by those applications. Mobile networks require that the applications and protocols that have worked successfully in fixed networks can be used with the same level of quality in mobile scenarios. Until the third generation of mobile networks, the need to ensure reliable handovers was still an important issue. On the eve of a new generation of access networks (4G) and increased connectivity between networks of different characteristics commonly called hybrid (satellite, ad-hoc, sensors, wired, WIMAX, LAN, etc.), it is necessary to transfer mechanisms of mobility to future generations of networks. In order to achieve this, it is essential to carry out a comprehensive evaluation of the performance of current protocols and the diverse topologies to suit the new mobility conditions

Contributions to the Performance Analysis of Intervehicular Communications Systems and Schemes

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

Modelling and Analysis of Non-Stationary Mobile Fading Channels Using Brownian Random Trajectory Models

Doktorgradsavhandling i informasjons- og kommunikasjonsteknologi, Universitetet i Agder, Grimstad, 2014The demanding mobility features of communication technologies call for the need to advance channel models (among other needs), in which non-stationary aspects of the channel are carefully taken into consideration. Owing to the mathematical complexity imposed by mobility features of the mobile station (MS), the number of non-stationary channel models proposed in the literature is very limited. The absence of a robust trajectory model for capturing the mobility features of the MS also adds to the depth of this gap. Not only statistically non-stationary channels, but also physically non-stationary channels, such as vehicle-to-vehicle channels in the presence of moving scatterers, have been rarely investigated. In the literature, there exist two fundamental channel modelling approaches, namely deterministic and stochastic approaches. Deterministic approaches, such as measurement-based channel modelling, are known to be accurate, but site-specific and economically expensive. The stochastic approaches, such as geometry-based channel modelling, are known to be economically inexpensive, computationally fair, but not as accurate as the deterministic approach. Among these approaches, the geometry-based stochastic approach is the best to capture the non-stationary aspects of the channel. In this dissertation, we employ the geometry-based stochastic approach for the development of three types of channel models, namely stationary, physically nonstationary, and statistically non-stationary channel models. We geometrically track the plane waves emitted from the transmitter over the local scatterers up to the receiver, which is assumed to be in motion. Under the assumptions that the scatterers are fixed and the observation time is short enough, we develop the stationary channel models. In this regard, we propose a unified disk scattering model (UDSM), which unifies several well-established geometry-based channel models into one robust channel model. We show that the UDSM is highly flexible and outperforms several other geometric models in the sense of matching empirical data. In addition, we provide a new approach to develop stationary channel models based on delay-angle joint distribution functions. Under the assumption that the scatterers are in motion and the observation time is again short enough, we develop a physically non-stationary channel model. In this connection, we model vehicle-to-vehicle (V2V) channels in the presence of moving scatterers. Proper distributions for explaining the speed of relatively fast and relatively slow moving scatterers are provided. The statistical properties of the proposed channel model are also derived and validated by measured channels. It is shown that relatively fast moving scatterers have a major impact on both V2V and fixed-to-fixed (F2F) communication links, as they are significant sources of the Doppler spread. However, relatively slow moving scatterers can be neglected in V2V channels, but not in F2F channels. Under the assumption that the scatterers are fixed and the observation time is not necessarily short anymore, we develop the statistically non-stationary channel models. To this aim, we first introduce a new approach for generating fully spatial random trajectories, which are supposed to capture the mobility features of the MS. By means of this approach, we develop a highly flexible trajectory model based on the primitives of Brownian fields (BFs). We show that the flexibility of the proposed trajectory is threefold: 1) its numerous configurations; 2) its smoothness control mechanism; and 3) its adaptivity to different speed scenarios. The statistical properties of the trajectory model are also derived and validated by data collected from empirical studies. We then introduce a new approach to develop stochastic non-stationary channel models, the randomness of which originates from a random trajectory of the MS, rather than from the scattering area. Based on the new approach, we develop and analyze a non-stationary channel model using the aforementioned Brownian random trajectory model. We show that the channel models developed by this approach are very robust with respect to the number of scatterers, such that highly reported statistical properties can be obtained even if the propagation area is sparsely seeded with scatterers. We also show that the proposed non-stationary channel model superimposes large-scale fading and small-scale fading. Moreover, we show that the proposed model captures the path loss effect. More traditionally, we develop and analyze two non-stationary channel models, the randomness of which originates from the position of scatterers, but not from the trajectory of the MS. Nevertheless, the travelling path of the MS is still determined by a sample function of a Brownian random trajectory. It is shown that the proposed channel models result in a twisted version of the Jakes power spectral density (PSD) that varies in time. Accordingly, it is demonstrated that non-stationarity in time is not in line with the common isotropic propagation assumption on the channel