Using orthogonal designswith feedback in wireless relay networks

Recently, distributed space-time coding over half duplex wireless relay networks has been proposed to achieve higher diversity at the receiver. The use of orthogonal and quasi-orthogonal designs in such relay networks has the advantage of providing maximum diversity at a low decoding complexity. However, similar to their originating space-time codes, these designs are restricted in terms of rate and number of relays. In order to alleviate such restrictions, we propose an extension of group-coherent codes (GCCs) to wireless relay networks. As will be shown, with a very limited amount of feedback from receiver to the relays, it is possible to achieve a distributed code that is applicable for any number of relays without an additional rate loss. In addition, our approach offers the advantages of linear ML decoding complexity, maximum diversity, lower delay, and increased power gain. We further show that it is possible to improve the performance at the price of a higher feedback rate. Finally, the robustness of our scheme against node failures is verified.