Power Allocation Scheme for Channel Capacity Maximization in Multi-relay Amplify-and-forward Cooperative System

摘要

This paper considers the power allocation problem for multi-relay amplify-and-forward cooperative system. Under the condition of the total power constraint, the power allocation scheme to maximize the channel capacity is proposed. We get a non-closed-form solution of this scheme by constructing a Lagrange function and making use of KKT conditions, and its numerical solution also was obtained based on binary search algorithm. Theoretical analysis and simulations show that the proposed scheme greatly can improve the system performance than the traditional equal power allocation scheme in Rayleigh channel, and that the system with multi-relay has more capacity than the system with only a direct link. We also discuss how the system's total power, the number or the position of relay and the power allocation ratio affect the system's channel capacity. Numerical results show that there always exits the optimal number and position of relays, and power allocation ratio to maximize the channel capacity for a certain communication scheme. But when the relay's number reaches to a certain constant, adding relays will only result in the configuration complexity without bringing more gain for the system.