Relay Selection in Amplify-and-Forward Relay Networks with Frequency Selective Fading

We consider relay selection in cooperative relay networks with frequency selective fading, and focus on a system where multiple amplify-and-forward relays share a single channel orthogonal to the source. We propose a relay selection method that achieves the optimal diversity-multiplexing tradeoff (DMT) as proven by outage analysis. This relay selection method, combined with zero-padded transmission and maximum likelihood sequential estimation (MLSE), can achieve full diversity as corroborated by numerical results. Since MLSE may not be affordable in practice due to its high complexity, another relay selection method based on the average decision-point SNR is proposed for linear zero-forcing equalization at the destination, and it asymptotically achieves the optimal DMT.