Power Allocation Strategy for Soft-Decision-and-Forward Protocol with Alamouti Code Based on ML Decoding

In this paper, the power allocation strategy for the soft-decision-and-forward (SDF) protocol in the cooperative communication network with one source, one relay, and one destination, where each node has two transmit and receive antennas, is determined. For the slow-varying Rayleigh fading channel, the optimal power allocation ratio can be determined so as to minimize the average bit error rate. Due to the difficulty in deriving the optimal value analytically, an alternative strategy of maximizing the product signal-to-noise ratio (SNR) of direct and relay links, which we call the suboptimal power allocation, is considered. Through the numerical analysis, we show that the performance gap between the suboptimal and optimal power allocation strategies is negligible in the high SNR region.