Non-orthogonal precoding matrix design for MU-MIMO downlink channels

In this paper, we propose two non-orthogonal approaches to design linear transmit preceding matrices for the downlink of multi-user multi-input multi-output (MU-MIMO) communication over fading wireless channels. Both are better suited to solve the power control problem of minimizing the power output subject to a fixed set of rate requirements and do not have the strict constraint on the transmit and receive antenna numbers as the block-diagonalization (BD) algorithm does. One is named modified MRC scheme in which an iterative approach is introduced and for each user we compute the optimal preceding matrix to compensate the noise and the interference caused by other users without considering the interference it causes to others. The other one is named modified BD scheme in which for each user we only consider the dominant sub-channels that have relatively large channel gains when using the conventional BD algorithm. Theoretic analysis and simulation results reveal that the modified MRC scheme can achieve a better performance than BD algorithm under lower SNR regime and the modified BD scheme outperforms BD algorithm almost in all cases