Low-complexity unitary preprocessing scheme for limited feedback multiuser MIMO systems

In this paper, a practical downlink multiuser multiple-input multiple-output (MU-MIMO) scheme with lowrate feedback channel is considered. Firstly, we propose a preferred-beam feedback method, which effectively conveys information of user channel and inter-user interference. Secondly, we propose a new low-complexity method to compute unitary preprocessing matrix based on the feedback method. The proposed method reduces considerably computational complexity by utilizing SVD operation compared to the conventional unitary preprocessing scheme. Finally, for the case that the number of users exceeds the number of transmit antennas, we provide two simple user selection algorithms to exploit multiuser diversity. Numerical results show that the proposed low-complexity unitary preprocessing scheme achieves higher sum-rate than previous linear preprocessing schemes, especially at low SNR or with small number of active users.