Outage Limited Cooperative Channels: Protocols and Analysis

We propose novel cooperative protocols for various coherent flat-fading channels composed of half-duplex nodes. We consider relay, cooperative broadcast (CB), multiple-access relay (MAR) and cooperative multiple-access (CMA) channels and devise efficient protocols for them. We also present automatic repeat request (ARQ) variants of these protocols. We evaluate the proposed protocols using the diversitymultiplexing tradeoff (DMT). For the relay channel, we investigate two classes of cooperation protocols, i.e., amplify and forward (AF) and decode and forward (DF). For the first class, we establish an upper bound on the achievable DMT with a single relay. We then propose a AF protocol that achieves this upper bound. The proposed algorithm is then extended to the case of arbitrary number of relays. For the class of DF protocols, we propose a dynamic decode and forward (DDF) protocol that achieves the optimal DMT for a range of multiplexing gains. We further show that, with a single relay, the DDF protocol dominates the class of AF protocols for all multiplexing gains. The superiority of the DDF protocol is shown to be more significant in the CB and MAR channels. The situation is reversed in the CMA scenario, where we propose a novel AF protocol that achieves the optimal tradeoff for all multiplexing gains. This result highlights the fundamental difference between the relay and CMA channels.