Performance of power allocation schemes in an amplify-and-forward single-relay system with diversity at destination

Abstract

Different strategies can be followed to achieve efficient power allocation in wireless systems. While optimising the average received SNR would directly result in an optimised average BER and outage probability in a direct wireless communication link, it is not clear whether we can achieve an optimised average BER and/or outage probability in a relaying system by optimising the average received SNR. In this paper, the problem of power allocation in a single-relay amplify-and-forward wireless system with maximal ratio combining MRC at the destination terminal is investigated via optimising three different objective functions: average SNR, average BER and outage probability. The average SNR, average BER and outage probability expressions are first derived as a function of source and relay transmit powers and variance of the channel gains. Based on these expressions, closed-form expressions are derived for optimum transmit power allocation between source and relay. It is observed that the BER-based and outage-based power allocation schemes achieve performance improvement over the SNR-based scheme when the relay is closer to the source; however, all the three schemes perform equally when the relay is close to the destination.