Cooperative diversity by relay phase rotations in block fading environments

We consider a wireless network with one source/destination pair and several linear amplify-and-forward relays. All nodes are equipped with one single antenna. To achieve cooperative diversity we propose time-variant and relay specific phase rotations induced at each relay to make the effective channel time-variant. This transformation of spatial diversity into temporal diversity can be exploited by an appropriate outer code. Furthermore we show that the allocation of the amplification gains at the relays has great influence on the diversity performance and we give a low complexity extension to existing gain allocations.