Research On Relay Selection In Wireless Cooperative Networks

Relaying is an efficient mechanism for increasing transmission reliability and spectral efficiency in wireless communications. It helps the source node forward data and can generates diversity and effectively combat the deleterious effects of fading. We can improve the network performance by selecting the proper cooperating relays globally, which also helps reduce the waste of energy caused by those relay nodes within poor channel quality. Recently, full-duplex (FD) relaying is regarded as a promising technique to overcome the spectral efficiency loss of half-duplex (HD) relaying. Applying the relay selection concept to FD cooperative systems provides an efficient approach to combine space diversity benefits with FD spectral efficiency. However, the FD relay system suffers from the self-interference (SI) by the signal leakage between the output and input antennas of the relay, because the SI cannot be cancelled ideally in practical systems. And the imperfect channel state information (CSI) will also seriously affect the system performance. And therefore, the study on the impacts of these imperfect factors to the relay selection system attracts considerable attention.In the first place, this paper focuses on the design of amplify-and-forward partial relay selection with feedback delay. When the feedback channel state information (CSI) of the first hop is obtained and partial relay selection scheme is adopted, the end-to-end SNR of the system is presented, and the probability distribution of the each channel is analyzed under outdated CSI. Then this paper derives the closed form of the system outage probability, and a novel relay selection scheme is proposed. The proposed scheme is based on the outdated CSI of the first hop and the channel correlation coefficient, which aims at minimizing the system outage probability. The numerical simulation results show that the proposed strategy has significant performance gain compared with the conventional partial relay selection strategy, and can effetely combat the feedback delay.In the second place, this paper focuses on the study of FD relay selection under residual self-interference. The residual self-interference is modeled as a proportion to the A’th power of the relay’s transmitted power, where λ is often less than one. To control the self-interference, a power allocation (PA) scheme is proposed, aiming at maximizing the system capacity. Based on the approximate close-form expressions of the optimal PA and the end-to-end SINR expression of FD relay system, a modified relay selection schemes is proposed. The optimal PA results show that full power at the FD relay is not necessarily optimal. And within the increase of value of λ, the performance of FD relay system decreases, and is even worse than that of HD relay. So this paper then derives a hybrid relay selection between HD and FD relaying mode. The numerical simulation results show that this hybrid mode can achieve better performance and higher diversity gain.