Intelligent Reflecting Surface Enabled Multi-Target Sensing

TL;DR

This paper explores IRS-assisted multi-target sensing, proposing novel schemes to optimize sensing performance without direct target links, including time division, signature sequence, and hybrid methods for flexible sensing strategies.

Contribution

It introduces three innovative IRS-assisted sensing schemes and joint optimization techniques to enhance multi-target sensing in challenging scenarios without direct paths.

Findings

Proposed three IRS-assisted sensing schemes: TD, SS, and hybrid TD-SS.

Joint optimization of beamforming and IRS phase shifts improves sensing performance.

Hybrid scheme offers flexible trade-offs between beam gain and sensing frequency.

Abstract

Besides improving communication performance, intelligent reflecting surfaces (IRSs) are also promising enablers for achieving larger sensing coverage and enhanced sensing quality. Nevertheless, in the absence of a direct path between the base station (BS) and the targets, multi-target sensing is generally very difficult, since IRSs are incapable of proactively transmitting sensing beams or analyzing target information. Moreover, the echoes of different targets reflected via the IRS-established virtual links share the same directionality at the BS. In this paper, we study a wireless system comprising a multi-antenna BS and an IRS for multi-target sensing, where the beamforming vector and the IRS phase shifts are jointly optimized to improve the sensing performance. To meet the different sensing requirements, such as a minimum received power and a minimum sensing frequency, we propose three novel IRS-assisted sensing schemes: Time division (TD) sensing, signature sequence (SS) sensing, and hybrid TD-SS sensing. First, for TD sensing, the sensing tasks are performed in sequence over time. Subsequently, a novel signature sequence (SS) sensing scheme is proposed to improve sensing efficiency by establishing a relationship between directions and SSs. To strike a flexible balance between the beam pattern gain and sensing efficiency, we also propose a general hybrid TD-SS sensing scheme with target grouping, where targets belonging to the same group are sensed simultaneously via SS sensing, while the targets in different groups are assigned to orthogonal time slots. By controlling the number of groups, the hybrid TD-SS sensing scheme can provide a more flexible balance between beam pattern gain and sensing frequency. Moreover, ...