Robust Nonlinear Precoding in MU-MIMO using Partial Interfering Beam Feedback

Hybrid linear precoding for mmWave multi-user multiple-input multiple-output (MU-MIMO) has been extensively studied. In this paper, we propose a robust nonlinear Tomlinson-Harashima Precoding (THP) design for MU-MIMO when only partial interfering beam feedback is available at the transmitter. In a partial interfering beam feedback system, each user sends only the information about the top-p interfering beams to the transmitter. First, we propose a THP design based on an approximate effective channel. Then, we propose an iterative method for robust THP design that minimizes the total transmit power under mean square error constraint at each user. This robust method takes into account error in the approximated channel and performs better than THP design directly for the approximated channel. Numerical results show that the proposed non-linear precoding performs better than the linear-precoding in terms of both mean bit error rate (BER) and sum-rate achieved. In addition, the robust method which considers the approximated channel and feedback errors achieves better BER compared to the non-robust hybrid THP method.