Joint Beamforming Design for RIS-Aided Secure Integrated Sensing and Communication Systems

This letter investigates the physical layer security of reconfigurable intelligent surface (RIS) aided integrated-sensing-and-communication (ISAC) systems, in which the high-power radar signal is used as the interference to disturb the eavesdropper. We formulate a joint beamforming optimization problem of active beamforming of base station and passive beamforming of RIS to minimize the maximum eavesdropping signal-to-interference-plus-noise (SINR). To find its solution, we decompose the original problem into two subproblems and then use the alternating optimization (AO) technique based on the fraction programming (FP) and semi-definite programming (SDP) methods. Simulation results show that the proposed FP-SDP-AO algorithm has good convergence performance and can effectively suppress the SINR of eavesdroppers while maintaining a satisfactory quality of service for legitimate users.

I. Introduction

Integrated Sensing and Communication (ISAC) is considered to be one of the key technologies to beyond-fifth-generation (B5G) and sixth-generation (6G) wireless networks [1]. As Multiple-input multiple-output (MIMO) technologies can provide additional spatial degrees of freedom (DoFs) to achieve better performance, some scholars have introduced them into ISAC systems. Liu et al. propose a beamforming technique for joint MIMO radar communication systems in which a single device acts as a radar and communication base station (BS) by simultaneously communicating with downlink users and detecting radar targets [2]. In addition, the authors of [3], and [4] have also studied the ISAC systems under MIMO deployments, demonstrating the importance of optimizing beamforming.