Performance analysis of power allocation and relay assignment in OFDM systems

In this paper, an optimal algorithm is proposed for the joint power allocation and relay assignment problem in OFDM relay networks. The network model consists of single-source single-destination with N half-duplex decode-and-forward (DF) relays. The source node uses orthogonal frequency division multiplexing (OFDM) to transmit information to relays where each serves one subcarrier. Our objective is to find the best subcarrier-relay assignment and power allocation, that maximizes the minimum received signal-to-noise ratio (SNR). This non-convex optimization problem could be solved by exhaustive search with complexity order of O(N!). Suboptimal methods, that solve the relay assignment problem and power allocation separately, have less time complexity in the expense of performance degradation. We propose a simple algorithm to jointly solve the subcarrier-relay assignment and power allocation problem. It is shown that the proposed algorithm finds the optimal solution with complexity order of O(N4).