Cooperative Strategies and Capacity Theorems for Relay Networks

Coding strategies that exploit terminal cooperation are developed for relay networks. Two basic schemes are studied: the relays multi-hop the source message to the destination, or they transmit compressed channel outputs to the destination. Strategies that mix these schemes are also considered. The multi-hopping is done in a sophisticated way: the transmitters cooperate and each receiver uses several or all of its past channel output blocks to decode. 

For compression, the relays take advantage of the statistical dependence between their channel outputs and the destination's channel output. The strategies are applied to several wireless channels, and it is shown that one can approach capacity if the terminals form two closely spaced clusters. One can further achieve the ergodic capacity with phase fading if the relays are in a region near the source terminal, and if phase information is available only locally. 

The ergodic capacity results generalize to Rayleigh fading, single-bounce fading, certain quasistatic fading problems, cases where partial channel knowledge is available at the transmitters, and cases where local user cooperation is permitted. The results further extend to multi-source networks such as multi-access and broadcast relay channels.