Wireless Relay Communication Systems And Their Performance Analysis Over Nakagami And Rayleigh Fading Channels

Wireless relaying technology has been adopted in several communication standards such as IEEE802.11s, IEEE802.16j and3GPP LTE-Advanced, since it has the potential of extending wireless service coverage, improving the system capability of combating interferences. Based on the characteristics of information flows, relaying technologies can be classified as one-way relaying and two-way relaying. In one-way relaying, only a single node transmits its information to another node with the help of one or more relays. In two-way relaying, two or more nodes exchange their information with the help of one or more relays. As is well known, channel fading has significant impacts on the performances of wireless communication systems, therefore, the study of new transmission schemes and performance analysis for various relay systems over fading channels is of high importance. In this thesis, some novel results are obtained for a variety of relay systems over Nakagami/Rayleigh fading channels, in terms of performance evaluation and new transmission schemes.Firstly, some novel results on the average bit error rate (BER) and ergodic capacity of dual-hop relay systems over Nakagami-m fading channels are obtained. Specifically, for independent but not necessarily identically distributed (i.n.i.d.) channels of two hops, an exact closed-form average BER expression for binary phase shift keying (BPSK) which is valid for integer fading parameters is derived while a closed-form lower bound for ergodic capacity is obtained for arbitrary fading parameters. For independent and identically distributed (i.i.d.) channels of two hops, exact closed-form expressions are derived for both the average BER of BPSK and the ergodic capacity, which are valid for arbitrary fading parameters.Secondly, an exact error rate analysis of channel state information (CSI-) assisted amplify-and-forward (AF) cooperative diversity wireless systems over i.n.i.d. Nakagami-m fading channels is conducted. An exact expression for the moment generating function (MGF) of the output signal-to-noise ratio (SNR) is derived. Using the unified MGF-based approach, the exact average symbol error rate (SER) of M-ary phase shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) is determined. The theoretical results are useful for guiding the performance optimization of cooperative diversity systems in Nakagami-m fading.Thirdly, tight lower bounds as well as asymptotic expressions at high signal-to-interference ratio (SIR) for the outage probability and the average SER are obtained by studying the impacts of the outdated channel state information (CSI) on the performances of multiuser cooperative relay systems corrupted by a finite number of co-channel interferers. It is revealed by the relationships among system parameters that the cochannel interference and outdated CSI have significant negative impacts on the multiuser relay system. The obtained analytical results provide theoretical guidance for the design of multiuser cooperative relay systems with co-channel interferers and outdated CSI.Fourthly, an opportunistic transmission scheme based on optimal source scheduling is proposed and studied in a multiuser two-way relay system. An exact closed-form lower bound and an asymptotic expression for the outage probability are obtained. It can be seen from the asymptotic outage probability expression that the full system diversity order can be achieved. The proposed transmission scheme has higher reliability than analog network coding (ANC) and time-division broadcast (TDBC) schemes, especially at low data rates. This provides an optional choice for the uplink/downlink in relay-based cellular systems.Fifthly, a new relay selection scheme based on switch-and-stay combining (SSC) in two-way relay systems with two amplify-and-forward (AF) relays is proposed. The system can operate either in ANC and TDBC protocol. In both cases, exact closed-form lower bounds for the outage probability and the average BER are obtained. Asymptotic analysis for both the outage probability and the average BER at high SNR is also presented. It is found that the SSC can achieve the full diversity order in two-way relay systems for both ANC and TDBC protocols with proper predetermined switching thresholds.Finally, closed-form expressions are derived for the averages of the product of two Gaussian Q-functions over Nakagami-m and Nakagami-q (Hoyt) distributions, respectively, which are valid for arbitrary fading parameters. The derived results are then applied to analyze the exact average SER of general rectangular QAM signals. Closed-form SER expressions are obtained for general rectangular QAM systems with maximal ratio combining (MRC) diversity reception. Moreover, asymptotic SER at high SNR for general rectangular QAM over fading channels is also investigated in terms of coding gain and diversity gain. In particular, it is worthy to point out that the obtained results are also useful for other wireless applications, such as performance analysis of multihop decode-and-forward (DF) relay systems and performance analysis of cooperative DF relay systems with selection combining (SC), etc.