Performance Evaluation and Improvement of Wireless Amplify-and-Forward Cooperative-Based Systems under Nodes Mobility and Imperfect CSI Estimation Impacts

Cooperative communication techniques have been introduced in wireless networks to achieve spacial diversity-gain via the readiness of multiple users (via relays) to assist a source forwarding its data to a final destination. Cooperative communication techniques have shown their capability in improving system reliability and extending coverage area, and hence, it is believable that they will act as a promising technology for the coming fifth-generation (5G). Nevertheless, most existing work reported in literature on performance studies of wireless cooperative-based systems are based on the assumptions that the multipath fading channels among systems cooperating nodes are quasi-static (i.e., fading channels coefficients are constant over a number of consecutive signaling periods) and channel-state-information (CSI) estimation processes at systems receivers are perfect. Nowadays, however, there is an increased number of users riding high-speed public transportation vehicles and demanding wireless data services through their own terminals. As a result of such high mobility wireless terminals, the assumption of time-selective (i.e., non quasi-static) fading is more realistic. This time-selective fading environment would severely deteriorate the performance of existing wireless cooperative systems that have been already designed based on the assumption of quasi-static fading (low users speeds). Further, due to impairments associated with practical receiver tracking-loops implementation issues, it is more general to assume that CSI estimations at systems receiving sides are imperfect. The scope of this dissertation is to provide comprehensive performance evaluation study for several emerging models of wireless amplify-and-forward (AF) cooperative-based communication systems that operate under the effects of the more general scenarios of high nodes mobility (time-selective fading) and imperfect channel estimations. This performance evaluation study is conducted by deriving closed-form expressions for different performance metrics; including error probability, outage probability and channel capacity. Monte Carlo simulations are also provided to complement and validate the analytical analyses. All of the obtained results in this dissertation are novel and general for mobile as well as non-moving nodes and for imperfect as well as perfect CSI estimations. Moreover, in this dissertation we develop innovative and applicable solutions and receiver designs that are capable of mitigating the detrimental impacts of the high nodes mobility on the performance of the cooperative system models under study

Performance analysis of cooperative communication systems with imperfect channel estimation

This paper investigates the effects of channel estimation errors on the symbol-error-rate (SER) performance of a cooperative communication system operating in an amplify-and- forward (AF) mode. A pilot symbol assisted modulation scheme with linear minimum mean square estimation (LMMSE) is used for the channel estimation. An accurate and easy-to-evaluate SER expression is presented for uncoded cooperative communication systems with quadrature amplitude modulation (QAM) and phase-shift keying (PSK) constellations. Numerical simulations are conducted to verify the correctness of the proposed analytical formulation. It is shown that the performance loss caused by channel estimation errors increases mainly with the normalized maximum Doppler frequency