Joint Precoding Design and Power Control in MIMO Two-Way Relay Network

In order to enhance spatial multiplexing gain of multiple input multiple output (MIMO) two-way relay networks, the transceiver precoding matrixes for all nodes with low complexity were investigated. Using subspace alignment scheme, the bi-directional MIMO channel can be decoupled into several single input single output (SISO) sub-channels. It is accessible for source nodes to use network coding to obtain better spatial multiplexing gain. By calculating and transforming the matrices, an optimal power control method for MIMO two-way relay network was presented. This method can independently optimize each sub-channel power allocation with the fixed precoding matrix. Moreover, a closed-form solution for power allocation among relay nodes and users is derived which considerable decreases the complexity from O(n3) to O(n). Simulation results show that the performance of the proposed approach is close to the iterative gradient descent solution and outperform the traditional pure amplify-and-forward (AF) two-way mode 2.99 bit/(sHz) gains with less computational load in typical scenarios.