Iterative Detection for Orthogonal Time Frequency Space Modulation with Unitary Approximate Message Passing

TL;DR

This paper introduces a novel UAMP-based iterative detection method for OTFS modulation that improves performance and reduces complexity, especially in high mobility scenarios with large or fractional Doppler shifts.

Contribution

It develops a UAMP-based detector for OTFS that exploits channel matrix structure and incorporates noise variance estimation, outperforming existing message passing detectors.

Findings

UAMP-based detectors outperform state-of-the-art methods.

The proposed iterative joint detection and decoding significantly improves performance.

The new method offers efficient implementation for high mobility wireless channels.

Abstract

The orthogonal-time-frequency-space (OTFS) modulation has emerged as a promising modulation scheme for high mobility wireless communications. To harvest the time and frequency diversity promised by OTFS, some promising detectors, especially message passing based ones, have been developed by taking advantage of the sparsity of the channel in the delay-Doppler domain. However, when the number of channel paths is relatively large or fractional Doppler {shifts have} to be considered, the complexity of existing detectors is a concern, and the message passing based detectors may suffer from performance loss due to the short loops involved in message passing. In this work, we investigate the design of OTFS detectors based on the approximate message passing (AMP). In particular, {leveraging the unitary AMP (UAMP), we design new detectors that enjoy} the structure of the channel matrix and allow efficient implementation. In addition, the estimation of noise variance is incorporated into the UAMP-based detectors. Thanks to the robustness of UAMP relative to AMP, the UAMP-based detectors deliver superior performance, and outperform state-of-the-art detectors significantly. We also investigate iterative joint detection and decoding in a coded OTFS system, where the OTFS detectors are integrated into a powerful turbo receiver, leading to considerable performance gains.