A suboptimal solution to joint source and relay power allocation of MIMO relay systems

The joint source and relay power allocation (PA) problem of MIMO relay systems is studied in this paper. First, a joint PA cost function is formulated based on the maximization of the capacity. It is then shown that the cost function is only partially convex, i.e., it is convex with respect to only either the power allocation parameters in the source or those in the relay alone, making it very difficult to obtain a truly joint optimal PA solution. Next, a tight lower bound of the capacity is derived and employed to modify the cost function so as to achieve an easy-to-solve convex optimization problem. Finally, a convex solution as a suboptimal PA scheme for the entire relay system is obtained by applying a standard convex optimization method to the modified problem. It is confirmed through computer simulations that the proposed PA scheme outperforms the existing method in terms of the capacity of the MIMO relay system.