Tomlinson-Harashima Precoding for Multiuser MIMO Systems: Sum Rate Analysis with Quantized CSI and User Scheduling

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. We study the sum rate of a greedy user scheduling algorithm combined with the quantized CSI-based TH precoding, termed G-THP-Q. The asymptotic distribution of the output signal to interference plus noise ratio of each selected user and the asymptotic average sum rate as the number of users K grows large are derived. We prove that as K grows large, the G-THP-Q approach can achieve the optimal sum rate scaling of the MIMO broadcast channel. We also prove that, if we ignore the precoding power loss, the average sum rate of G-THP-Q approach converges to the average sum capacity of the MIMO broadcast channel for large K. Our results also provide key insights into the effect of multiuser interference caused by quantized CSI on the multiuser diversity gain.