Beamforming in Hybrid RIS assisted Integrated Sensing and Communication Systems

TL;DR

This paper proposes a hybrid RIS design with active and passive elements to enhance integrated sensing and communication systems, optimizing beamformers and RIS coefficients for improved target illumination and communication performance.

Contribution

It introduces a joint design method for hybrid RIS and transmit beamformers using alternating optimization, improving ISAC system performance over passive RIS and no-RIS setups.

Findings

Hybrid RIS significantly improves system performance.

Active elements enhance target illumination power.

Proposed method outperforms passive RIS and no-RIS systems.

Abstract

In this paper, we consider a hybrid reconfigurable intelligent surface (RIS) comprising of active and passive elements to aid an integrated sensing and communication (ISAC) system serving multiple users and targets. Active elements in a hybrid RIS include amplifiers and phase shifters, whereas passive elements include only phase shifters. We jointly design transmit beamformers and RIS coefficients, i.e., amplifier gains and phase shifts, to maximize the worst-case target illumination power while ensuring a desired signal-to-interference-plus-noise ratio for communication links and constraining the RIS noise power due to the active elements. Since this design problem is not convex, we propose a solver based on alternating optimization to design the transmit beamformers and RIS coefficients. Through numerical simulations, we demonstrate that the performance of the proposed hybrid RIS assisted ISAC system is significantly better than that of passive RIS assisted ISAC systems as well as ISAC systems without RIS even when only a small fraction of the hybrid RIS contains active elements.