Efficient Power Allocation in Cooperative OFDM System with Channel Variation

Cooperative communication is emerging as an effective approach for realizing efficient wireless networks. Performance of these networks has been shown to be enhanced significantly by dynamic resource allocation, especially in orthogonal frequency division multiplexing (OFDM) systems, where there are more degrees of freedom. On the other hand, dynamic resource allocation imposes signalling and computational overhead on the system. In this paper, a multi-relay OFDM system is considered, where the cooperation gain of distributed antenna array is exploited. First we introduce the optimal power allocation problem and discuss the signaling overhead for implementing the optimal solution. We then propose suboptimal schemes with considerably less overhead and study the conditions under which they perform close to the optimal scheme. Furthermore, we investigate how imperfect implementation of these scheme results in performance degradation. We also analyze how much feedback is needed to implement this scheme with a desirable accuracy.