Research On Relay Selection And Full-Duplex Relaying In Cooperative Communication Systems

Relay-assisted wireless communications have currently attracted much attention by cooperation in networks. The cooperative communications result in resource sharing. The cooperative system not only extends the coverage of wireless networks, but also enhances spectral efficiency and transmission reliability. The quality of service(QoS) is improved effectively.Relay selection is a key problem in the field of cooperative communications, especially for mobile devices using battery to supply power. Different from the relay selection algorithm which is based on the instantaneous channel state information(CSI) of two hops, the proposed algorithm which is called threshold comparison algorithm is just based on the instantaneous CSI of the first hop. We analyze the cumulative distribution function(CDF) and probability dense function(PDF) of output signal-noise-rate(SNR) at the optimal relay node and destination node theoretically. The simulation results show that the proposed algorithm can achieve similar performance compared with the former algorithm which is based on the instantaneous CSI of two hops. However, we simply consider the instantaneous CSI between the source node and the relay node, so the relay power consumption as well as the complexity of the algorithm is greatly reduced.To overcome the drawback of spectral efficiency loss in half-duplex relaying, this paper addresses the technology of full-duplex relaying under fading loop interference channel, with optimal relay selection among the relay candidates. Analytically, we derive closed-form expressions for the end-to-end capacity with different power allocation methods. In particular, we evaluate the loop interference threshold value, which is the milestone that the full-duplex mode demonstrates better performance than the half-duplex mode. We also compare the system performance with computer simulation.The interference caused by the relay transmission to reception in full-duplex relaying has a negative effect on transmission quality. We present a means of suppressing the interference for the assumed multiple-input multiple-output (MIMO) relay system over fading channels, in which relay antenna subset selection at both transmitted and received sides are considered jointly. The criterion for selecting the antenna subset is to minimize interference channel capacity. We derive closed-form expression for the end-to-end capacity and furthermore analyze the validity of our proposed method. As a result, simulations demonstrate that our discussed selection scheme mitigates the interference significantly. Therefore, the link quality is efficiently improved in terms of capacity and bit error rate(BER) while the system complexity is reduced.