Robust MMSE Tomlinson-Harashima Precoder for Multiuser MISO Downlink With Imperfect CSI
Non-linear precoding for the downlink of a multiuser MISO (Multiple-Input Single-Output) communication system in the presence of imperfect Channel State Information (CSI) is considered. The base station is equipped with multiple transmit antennas and each user terminal is equipped with a single receive antenna. The CSI at the transmitter is assumed to be perturbed by an estimation error. They propose a robust Minimum Mean Square Error (MMSE) Tomlinson-Harashima Precoder (THP) design, which can be formulated as an optimization problem that can be solved efficiently by the method of Alternating Optimization (AO).