Power allocation in an amplify-and-forward cooperative network for outage probability minimization

In cooperative networks, some of the users in neighborhood of the source relay the source information, in order to combat the effects of multipath fading. Recent investigations, on multirelay amplify-and-forward cooperative networks, have shown that a significant performance improvement will be obtained, if the phase information of the channel between relays and destination are feedback to the relays. As, in that case, the relays can send their signals simultaneously but with proper phases, so that these signals are combined coherently at destination. In this paper, we shall assume that the magnitude information of the channels is also feedback to the relays. We will use this information to find an optimum power allocation between the relays and the source. This optimal power allocation will be derived analytically, by minimization of outage probability. Numerical simulation shows that our optimal power allocation significantly improves the outage probability of the system, as compared with equal power allocation.