Opportunistic Cooperation via Relay Selection with Minimal Information Exchange

Opportunistic cooperation is a technique where in each transmission the best relay (or k best relays) are chosen to assist. In a multiuser cooperative network, coordinating the cooperating users requires exchange of channel information between various nodes. As the number of nodes increases, this information exchange can get out of hand. In this work, we propose an opportunistic cooperation technique where at most two bits of information per relay are exchanged for each cooperation period (one bit feedback and one bit feedforward). Our method does not need any carrier sensing technique or any information regarding source-relay channels for its operation. We show that this frugal technique is capable of achieving the same diversity-multiplexing tradeoff (DMT) achieved by distributed space-time-coded cooperation protocols (DSTC) in Laneman and Wornell (2003). Also we show how bandwidth allocation between a user and its partner affects the diversity-multiplexing tradeoff.