Tomlinson-Harashima Precoding with Adaptive Modulation for Fixed Relay Networks

In this paper, a relaying strategy that uses multiple input multiple output (MIMO) fixed relays with linear processing for multiuser transmission in cellular networks is proposed. This approach applies to the two hop relaying scenario for coverage enhancement, where the base station transmits data to multiple users through one fixed relay (multiuser transmission). The fixed relay processes the received signal by applying a linear transformation and forwards the processed signal to multiple users. We propose an implementable multiuser precoding strategy that combines Tomlinson-Harashima precoding at the base station and linear signal processing at the relay with adaptive stream selection and QAM modulation. We propose a reduced complexity algorithm to select a subset of users to avoid an exhaustive search over all user permutations. Simulations illustrate the sum rate using Tomlinson-Harashima precoding without coding