Sum-Rate Maximization Based on Power Constraints for Cooperative AF Relay Networks

In this paper, our objective is maximizing total sum-rate subject to power constraints on total relay transmit power or individual relay powers, for amplify-and-forward single-antenna relay-based wireless communication networks. We derive a closed-form solution for the total power constraint optimization problem and show that the individual relay power constraints optimization problem is a quadratic programming which does not have a closed-form solution. To solve it, we propose a closed-form and low-complex technique which introduces suboptimal solution as an upper bound of system sum-rate. The performance of two new proposed algorithms are evaluated in terms of average achievable sum-rate and energy efficiency in different signal to noise ratios (SNRs). Considering the effect of the number of relays, the effect of channel gains of the source-relay as well as the relay-destination, and also the impact of the level of imperfect CSI are investigated. According to simulation results, higher sum-rate can be achieved in total power constrained scenario for all SNRs but energy efficiency is approximately the same for both of them. In addition, higher sum-rate is achievable by increasing the number of relays and/or improving the quality of uplink and downlink channels as well as decreasing uncertainty of channels.