Study of Tomlinson-Harashima Precoders for Rate-Splitting-Based Cell-Free MIMO Networks

TL;DR

This paper investigates non-linear Tomlinson-Harashima precoding combined with rate-splitting and multi-branch techniques in cell-free MIMO networks, demonstrating performance improvements over traditional linear methods under imperfect CSIT conditions.

Contribution

It introduces a novel MB-THP precoding scheme for RS-based CF systems, addressing practical CSIT limitations and enhancing system performance.

Findings

MB-THP outperforms linear precoders in simulations

Rate-splitting effectively mitigates CSIT imperfections

Multi-branch concept improves overall system robustness

Abstract

Cell-free (CF) systems have the potential to fulfill the increasing performance demand of future wireless applications by employing distributed access points (APs) that transmit the information over the same time-frequency resources. Due to the simultaneous transmission, multiuser interference (MUI) degrades the overall performance. To cope with the MUI in the downlink several linear precoding techniques, which rely on perfect channel state information at the transmitter (CSIT), have been studied. However, perfect CSIT is hardly obtained in practical systems. In this context, rate-splitting (RS) has arisen as a potential solution to deal with CSIT imperfections. In contrast to existing works, we explore non-linear precoding techniques along with RS-CF systems. Furthermore, the multi-branch (MB) concept is included to further enhance the overall performance of the system. Simulations show that the proposed MB-THP for RS-based CF systems outperforms the conventional linear precoders.