Tomlinson-Harashima precoding for multiuser MIMO systems with quantized CSI feedback

This paper considers the implementation of Tomlinson-Harashima (TH) precoding for multiuser MIMO systems based on quantized channel state information (CSI) at the transmitter side. Compared with the results in [1], our scheme applies to more general system setting where the number of users in system K can be not equal to the number of transmit antenna n_T (K ≤ n_T). We also study the achievable average sum rate of the proposed quantized CSI feedback-based TH precoding 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 precoding suffers from imperfect CSI more greatly than linear precoding. Nonlinear TH precoding can achieve much better performance than that of linear zero-forcing precoding for both perfect CSI and quantized CSI cases. In addition, our derived upper bound for TH precoding converges to the true rate loss faster than the upper bound for zero-forcing precoding obtained in [2] as the number of feedback bits increases.