Cramer-Rao Bound Optimization for Active RIS-Empowered ISAC Systems

TL;DR

This paper proposes a novel optimization framework for active RIS-assisted ISAC systems to improve radar and communication performance by jointly designing transmit and reflection beamforming, validated through simulations.

Contribution

It introduces a joint design method for BS precoding and active RIS reflection to optimize CRB in ISAC systems, a novel approach in this context.

Findings

Enhanced DoA estimation accuracy with active RIS

Effective joint beamforming design algorithm

Simulation results confirm performance improvements

Abstract

Integrated sensing and communication (ISAC), which simultaneously performs sensing and communication functions within a shared frequency band and hardware platform, has emerged as a promising technology for future wireless systems. Nevertheless, the weak echo signal received by the low-sensitivity ISAC receiver significantly constrains sensing performance in scenarios involving obstructed targets. Active reconfigurable intelligent surface (RIS) has become a prospective solution by situationally manipulating the wireless propagations and amplifying the signals. In this paper, we investigate active RIS-empowered ISAC systems to enhance radar echo signal quality as well as communication performance. In particular, we focus on the joint design of the base station (BS) transmit precoding and the active RIS reflection beamforming to optimize the parameter estimation performance in terms of Cramer-Rao bound (CRB) subject to the communication users' signal-to-interference-plus-noise ratio (SINR) requirements. An efficient algorithm based on alternating optimization, semidefinite relaxation (SDR), and majorization-minimization (MM) is proposed to solve the formulated challenging non-convex problem. Finally, simulation results validate the effectiveness of the developed algorithm and the potential of employing active RIS in ISAC systems to enhance direct-of-arrival (DoA) estimation performance.