Power Allocation for Amplify-and-Forward Cooperative Transmission Over Rayleigh-Fading Channels

Cooperative transmission has been used to achieve diversity gain through partner to create multiple independent fading channels. It has attracted lots of research attention in recent years. An important question in cooperative communication is power allocation. Given the same total power, how much should be allocated to self-information transmission and how much to relayinginformation transmission. In this paper, we investigate power allocation problem using amplify-and-forward (AF) protocol considering bit error rate (BER) performance of both users and the work region of two cooperative users. We solve cooperative ratio, which is defined as the ratio of power used for cooperative transmission over the total power. We first consider both users applying the same ratio, and then extend to two-dimensional cooperative ratio problem. Our results show that it is sufficient to allocate both users the same ratio. This value is specified by the user with a weaker channel gain to the destination, i.e., bottleneck link. With appropriate selection of the cooperative ratio, the BER performance of both users can be improved significantly. User fairness is also considered in the analysis.