Joint source and relay precoding designs for MIMO two-way relay systems

Abstract—We investigate the source and relay precoding based on the minimum mean-square-error (MSE) criterion for amplify-and-forward (AF) MIMO two-way relay systems. This joint design problem is a highly nonconvex optimization problem. In this work, we present two efficient design algorithms. The first one aims to minimize the total MSE of the two users by alternatively solving three sub-problems and it is iterative in nature. The second design holds a specific precoder structure, which is able to parallelize channels in both the Multiple Access (MAC) and Broadcast (BC) phases of two-way relaying. Based on such structure, the joint precoding design is simply reduced to the joint source and relay power allocation problem. The efficiency of both proposed algorithms is verified via simulation. I