Tomlinson-Harashima Precoding Algorithm Research Articles

Improved Tomlinson-Harashima precoding for the downlink of multi-user MIMO systems

By pre-equalizing the interlayer interference at the transmitter, the Tomlinson-Harashima precoding (THP) algorithm provides a solution for the downlink of multi-user multiple-input multiple-output (MIMO) systems, in which, because of the absence of cooperation among mobiles, receiver-based layer-separation algorithms cannot be implemented. In this paper, a new THP algorithm using the minimum mean-square error (MMSE) criterion is developed for the downlink of multi-user MIMO systems. This algorithm, called the MMSE THP algorithm, provides significant performance improvement compared to the zero-forcing (ZF) THP algorithm discussed in the literature. Moreover, ordering of the rows of the channel matrix is found to be important to the THP system performance, and the way in which this ordering affects the system structure is presented. An ordering lemma that generalizes the conditions, under which the ?best-first? ordering is optimal, is introduced.With this lemma it is proved that the ?best-first? ordering method achieves the optimal order in the minimax noise-variance sense for the ZF THP and the optimal order in the minimax error-variance sense for the MMSE THP. Simulation results show the performance advantage attained by the MMSE THP and the optimal ordering.

A Novel Nonlinear Precoding Algorithm for the Downlink of Multiple Antenna Multi-User Systems

By pre-equalizing inter-layer interference at the transmitter, Tomlinson-Harashima precoding (THP) algorithm provides a solution for the downlink of multiple antenna multi-user systems, in which the decentralized structure of the receivers makes the receiver-processing algorithms impossible. However, for the zero-forcing (ZF) THP algorithm developed in the literature there are significant performance differences between specific mobile stations. In this paper, a novel version of the THP algorithm is proposed. It greatly improves the worst mobile's performance and ensures balanced performance of all the mobiles. For the new THP algorithm, better performance can be obtained by suitably ordering the rows of the channel matrix. We show that the "best-first" ordering method achieves optimal order for BER performance in 2/spl times/2 systems and achieves near optimal order in systems of larger dimensions. Simulation is used to show the advantages of the new THP algorithm and the "best-first" ordering method.