Quantized CSI Based Tomlinson-Harashima Precoding in Multiuser MIMO Systems

This paper considers the implementation of Tomlinson-Harashima (TH) pre-coding for multiuser MIMO systems based on quantized channel state information (CSI) at the transmitter side. Compared with the results in, our scheme applies to more general system setting where the number of users in the system can be less than or equal to the number of transmit antennas. We also study the achievable average sum rate of the proposed quantized CSI-based TH pre-coding scheme. The expression of an upper bound on the mean loss in sum rate due to CSI quantization is derived. We also present some numerical results. Both the analytical and numerical results show that nonlinear pre-coding suffers from imperfect CSI more greatly than linear pre-coding. Nonlinear TH pre-coding can achieve much better performance than that of linear zero-forcing pre-coding for both perfect CSI and quantized CSI cases. In addition, our derived upper bound on the mean rate loss for TH pre-coding converges to the true rate loss faster than that of zero-forcing pre-coding obtained in as the number of feedback bits becomes large. Both the analytical and numerical results show that nonlinear pre-coding suffers from imperfect CSI more than linear precoding does obtained as the number of feedback bits increases.