A relay selection method considering the complete effects of outdated channel state information

In this paper, we propose a relay selection method in an amplify-and-forward (AF) scenario considering complete outdated channel state information (CSI) of all links. Differing from the methods in the literatures considering only outdated CSI over the link from the relay to the destination, another type of outdated CSI, i.e., the outdated CSI over the link from the source to the relay, is also considered in the relay selection. In order to overcome the effect of these outdated CSIs due to feedback delay, we use minimum mean square error (MMSE) estimation to predict the SNRs of the source-to-relay links and the relay-to-destination links at the forwarding instant. Along with the relay selection, an effective power allocation method is proposed to optimize the power allocation between the source and the relays. Moreover, the expression of the system outage probability is derived. The simulation results show that the proposed method, along with the power allocation, improves the outage performance of the system.