Joint Beamforming Design for Secure Transmission in STAR-RIS Aided ISAC

In this paper, we investigate a secure transmission problem in a simultaneously transmitting and reflecting re-configurable intelligent surface (STAR-RIS) assisted integrated sensing and communication (ISAC) system. The STAR-RIS is exploited to establish line-of-sight links for sensing the target and transmitting the confidential signal to users via non-orthogonal multiple access. Specifically, the sum secrecy rate is maximized by jointly optimizing the transmit beamforming, artificial jamming and STAR-RIS's passive transmission and reflection beamformings, while ensuring the minimum beam-pattern gain required by the target is met. To deal with the non-convex problem, we divide it into two subproblems and leverage successive convex approximation to transform them into convex ones. Then, an alternating optimization algorithm is proposed to solve the problem iteratively. Simulation results demonstrate the effectiveness of the proposed scheme and the potential of STAR-RIS to enhance the security of ISAC.