Robust Secure Beamforming Design for Downlink RIS-ISAC Systems Enhanced by RSMA

In this letter, we investigate a reconfigurable intelligent surface (RIS)-aided integrated sensing and communication system enhanced by rate-splitting multiple access. The RIS is deployed to establish a virtual line-of-sight link for target detection, which also act as a potential eavesdropper, and to assist in user communication. To ensure secure communication and detection, we design the communication and radar precoders, allocate a common stream to serve as artificial noise for eavesdroppers at the base station, and adjust the phase shifts of the RIS to maximize the minimum secrecy rate while being subject to constraints on transmit and sensing power. To this end, an efficient alternating optimization algorithm, which leverages semidefinite relaxation, S-procedure, successive convex approximation and rank-one penalty methods, is developed to address this non-convex problem. Simulation results demonstrate that the proposed scheme achieves a superior communication security. And, the results also indicate that, based on user density and radar requirements, the addition or removal of radar sequences can achieve a balance between system complexity and security.