Key Technologies Of Relay Transmission System

Compared with the existing one-hop communication systems, the dual-hop relay can be deployed to improve the coverage and the reliability of wireless communication. How to analyze and measure the theoretical performance lim-its of relay systems is the fundamental problem in the relay research com-munity. Based on the basic three-node relay model, the performance of two amplify-and-forward (AF) relay protocols is studied in the general dual-hop mixed type fading channel. Then, we extend the three-node relay system to the multiple relay scenario, based on which the performance analysis of partial relay selection (PRS) in transmit-diversity-assisted downlink relay networks is presented. For the relay system in the presence of co-channel interference (CCI), the outage probabilities of the fixed-gain AF relay and the spectrum-sharing decode-and-forward (DF) relay systems are derived, respectively. For the relay system with feedback delay, we analyze the performance of both the multiuser relay network (MRN) and the multiple input and multiple out-put (MIMO) two-way relay (TWR) system. Specifically, the main contribution of this thesis is summarized as follows:The mixed Nakagami-m and Rician fading channel model is proposed to characterize the asymmetric properties of the practical dual-hop relay chan-nels. Using the basic three-node relay system model, the exact and closed-form expressions for the outage probability and symbol error probability (SEP) are derived for two catalogues of AF relay systems in mixed Nakagami-m and Ri-cian fading channels. Then, we extend the simple single-relay system to the transmit-diversity-assisted downlink multiple-relay system and derive the per-formance measures for PRS algorithm in mixed Rayleigh and Rician fading channels. The correctness and the convergence property of all the derived re- sults are confirmed by the theoretical and simulation results.The performance of fixed-gain AF relay is studied in the presence of multi-ple co-channel interference, and the impact of the power distribution of multiple interference on the relay performance is also obtained. Specifically, a general interference model is considered, in which both the relay and the destination node are suffered with multiple unequal-power interference. Motivated by this system model, a new type of end-to-end signal-to-interference-and-noise ratio (SINR) expression is obtained, based on which the closed-form expression of the outage probability for the fixed-gain AF relay is derived in Rayleigh fad-ing channels. We also prove the fact that equal-power interference leads to the worst outage performance.The impact of primary user’s interference on the secondary spectrum-sharing relay system, also termed as cognitive relay network (CRN), is studied. In the CRN, the instantaneous transmit power of the secondary relay system is strictly constrained due to the interference-power level on the primary user. The closed-form and asymptotic expressions of the outage probability are de-rived for the DF relay system, in the presence of primary user’s interference. Furthermore, the impact of various key system parameters on the outage prob-ability performance is discussed in the asymptotic regimes. The theoretical and simulation results reveal that the primary user’s interference degrades the performance of spectrum-sharing relay system, dramatically.The performance of downlink multiuser relay network (MRN) with trans-mit beamforming is studied in the presence of feedback delay in both the beam-forming and user selection process. To guarantee the fairness between different mobile users, we adopt the normalized signal-to-noise ratio (SNR) criterion to select the best user for the transmission. The exact and asymptotic expressions of the key system performance measures, i.e., outage probability and SEP, are derived, from which we show that when the feedback delay exists in either transmit beamforming or user scheduling process, the MRN will not achieve any diversity gain.The impact of feedback delay on the MIMO two-way relay (TWR) net-works is presented. Using the induced order statistics theory, the exact and asymptotic expressions of the overall probability for the antenna selection-assisted MIMO TWR is derived in the presence of feedback delay, which can be used to guide the MIMO TWR system design. The theoretical and simula-tion results show that full diversity order can be achieved for the ideal-feedback scenario, whereas no diversity gain can be obtained if the feedback delay exists in either transmission link.