Tomlinson-Harashima Precoding with Imperfect Channel Side Information

In this paper, Tomlinson-Harashima precoding (THP) is studied for a scenario where the transmission system employs multiple transmit antenna and multiple users with single antenna at the receiver so that the cooperation among them is impossible (downlink scenario). Based on minimum mean square error (MMSE) criterion, a new robust solution is derived, which provides significant improvement with respect to conventional optimization method in imperfect channel side information (CSI) scenario. Spatial power loading is found to be important to the THP performance. We develop this loading for robust optimization of MMSE THP in minimum average symbol error rate (SER) sense. Simulation results are used to show the performance advantage attained by the robust optimization and the power loading in imperfect CSI scenario.