STAR-RIS Aided Secure NOMA Integrated Sensing and Communication

Integrated sensing and communication (ISAC) has attracted plenty of attentions as an up-and-coming approach to address the spectrum congestion via sharing the same hardware platform. However, including communication information in the sensing waveform will raise the risk of eavesdropping by the sensing targets as the eavesdroppers. In this paper, we investigate a secure transmission problem in a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) assisted ISAC system, which is segmented into a sensing region and a communication region. The STAR-RIS is deployed to build line-of-sight (LoS) links for sensing the target as well as 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 beampattern gain required by the target. 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 in an iterative manner. Simulation results demonstrate the validity of the proposed scheme and the potential of STAR-RIS to enhance the security of ISAC.