Joint Active and Passive Beamforming with Sensing-Assisted Discrete Phase Shifts for Dual-RIS ISAC Systems

TL;DR

This paper proposes a joint active and passive beamforming method for dual-RIS ISAC systems, using sensing-assisted discrete phase shifts to improve performance and user fairness in 6G scenarios.

Contribution

It introduces a novel joint beamforming approach with sensing-assisted discrete phase shifts and dual RISs for enhanced system performance in ISAC.

Findings

Achieves near-ideal continuous phase shift performance

Outperforms existing discrete phase shift algorithms

Significantly improves over single-RIS systems

Abstract

Targeting the requirements of 6G, this paper investigates a semi-passive dual-reconfigurable intelligent surface (RIS)-assisted integrated sensing and communication (ISAC) system, tackling the max-min user signal-to-interference-plus-noise ratio (SINR) problem via joint active and passive beamforming to enhance system performance and ensure user fairness. Addressing this challenge, we first utilize dual RISs for user angle estimation to simplify the solution process of the formulated problem, an efficient alternating optimization algorithm is then developed. Specifically, semi-definite relaxation and the bisection method are employed to solve the transmit beamforming optimization subproblem. For the RIS discrete phase shifts, a sensing-assisted approach is adopted to constrain the optimization search space, with two distinct low-complexity search strategies introduced for different RIS sizes. Numerical simulation results demonstrate that the proposed algorithm achieves performance close to the ideal continuous phase shift benchmark, outperforms conventional discrete phase shift optimization algorithms, and exhibits a significant improvement over single-RIS systems.