RIS-Assisted ISAC: Precoding and Phase-Shift Optimization for Mono-Static Target Detection

TL;DR

This paper explores RIS-assisted integrated sensing and communication, proposing joint optimization of phase-shifts and precoding for improved mono-static target detection amid complex clutter and multiple echo paths.

Contribution

It introduces a comprehensive analysis of three target echo paths, derives a GLRT detector, and proposes a novel joint optimization approach for RIS phase-shifts and precoding.

Findings

Joint design significantly improves detection probability.

Clutter-aware detection enhances performance in strong clutter.

Multiple echo paths are effectively modeled and utilized.

Abstract

The reconfigurable intelligent surface (RIS) technology emerges as a highly useful component of the rapidly evolving integrated sensing and communications paradigm, primarily owing to its remarkable signal-to-noise ratio enhancement capabilities. In this paper, our focus is on mono-static target detection while considering the communication requirement of a user equipment. Both sensing and communication benefit from the presence of an RIS, which makes the channels richer and stronger. Diverging from prior research, we comprehensively examine three target echo paths: the direct (static) channel path, the path via the RIS, and a combination of these, each characterized by distinct radar cross sections (RCSs). We take both the line-of-sight (LOS) and the non-line-of-sight (NLOS) paths into account under a clutter for which the distribution is not known, but the low-rank subspace it resides. We derive the generalized likelihood ratio test (GLRT) detector and introduce a novel approach for jointly optimizing the configuration of RIS phase-shifts and precoding. Our simulation results underscore the paramount importance of this combined design in terms of enhancing detection probability. Moreover, it becomes evident that the derived clutter-aware target detection significantly enhances detection performance, especially when the clutter is strong.