Weighted Amplify-and-Forward Relay Selection with Outdated Channel State Information

Relay selection (RS) is a promising technique in the cooperative communications, which can achieve full diversity with the best relay when the channel state information (CSI) is perfect. However, the performance of conventional RS degrades greatly, once CSI is outdated. To compensate the performance loss caused by the outdated CSI, we propose the weighted RS scheme, in which a deterministic weight factor is introduced in the selection process. The performance bound of outage probability for the weighted RS is derived and verified, along with the asymptotic expression. Based on the analytical expression, the optimal weight factor in minimizing the outage probability is obtained. Simulation results reveal that when the CSI is outdated, the proposed RS with the optimal weight factor yields the significant performance gain over the conventional RS, especially in high signal-to-noise ratio.