MMSE-THP with QoS Requirements for the Downlink of Multiuser MIMO Systems

Tomlinson-Harashima precoding (THP) is a popular nonlinear interference mitigation technique employed at the transmitter side which can provide better performance in comparison with linear precoding technique with a slight increase in complexity. It can be considered as a dual to the successive interference cancellation (SIC). In this paper, we focus on a new THP scheme for the downlink of multiuser multiple-input multiple-output (MIMO) systems with decentralized receivers. In contrast to previous approaches, the proposed algorithm allows the provision of transmitting different types of information simultaneously subjected to different Quality of Service (QoS) requirements of each active user. This algorithm is based on minimum mean square error (MMSE) criterion and the closed-form solution of the processing matrices is found by applying Cholesky factorization with symmetric permutation. For this THP algorithm, by suitably ordering the rows of channel matrix we can obtain better performance. Moreover, it significantly improves the bit error rate (BER) performance as well as the achievable rate as compared with zero-forcing (ZF) THP available in the literature, which can be shown from simulation results.