An efficient soft demapper for Tomlinson-Harashima precoded systems

Abstract

Wireless communication systems using Tomlinson-Harashima precoding (THP) suffer from modulo operation error in noisy environments. The error causes fatal performance degradation when soft-input forward error correction is applied because the conventional soft demappers provide unreliable log-likelihood ratio (LLR) values. In this paper, we propose an efficient low complexity soft demapper with reliable LLR values for expanded M-QAM constellations of the THP systems. Computer simulations are given to show the effectiveness of the proposed demapper.