Diversity-multiplexing tradeoffs in cooperative protocols with relay selection

We study the performance in cooperative diversity protocols employing relay selection, utilizing the diversity-multiplexing tradeoff. We note that for the class of orthogonal cooperation protocols studied by Laneman and Wornell, there is no loss in performance if only one (suitably chosen) relay participates in cooperation. This observation also holds in systems which incorporate decision feedback from the destination. We also quantify performance loss due to relay selection in non-orthogonal dynamic-decode-and-forward protocol studied by Azarian, El Gamal and Schniter. Our results present a simple alternative to distributed space-time codes for realizing the potential gains in multiple relay, user cooperation systems, and open new avenues for fruitful interaction between routing and cooperative diversity.