Optimal relay selection for decode-and-forward opportunistic relaying

In this paper, we consider the optimal relay selection policy for decode-and-forward opportunistic relaying systems under the assumption that the channel gain of the source-destination link is good-enough to produce some improvement in the end-to-end performance over the relay channels. The optimal relay selection policy shows that the conventional relay selection policy that appeared in the literature is suboptimal. We derive the exact expression for the end-to-end outage probability over Rayleigh fading channels. In addition, we look into the asymptotic high signal-to-noise ratio (SNR) regime, and characterize the diversity order and coding gain. Our findings reveal that the new optimal relay selection policy outperforms the suboptimal relay selection policy via coding gain while both policies have the same diversity order. We provide simulation results to verify the validity of our theoretical analysis.