UAV and RIS aided Covert ISAC system Design Based on Cramer-Rao Bound Optimization

This paper investigates a covert integrated sensing and communication (CISAC) framework enabled by unmanned aerial vehicles (UAVs) and reconfigurable intelligent surfaces (RIS), addressing the critical challenge of information leakage in open ISAC architectures. Focusing on a UAV-mounted base station (UAV-BS) scenario, we propose a joint optimization scheme to minimize the Cramér-Rao bound (CRB) of eavesdropper target estimation while ensuring covert communication for covert users. The system leverages a dualfunctional signal transmitted by the UAV-BS, assisted by an RIS with phase-shift optimization, to simultaneously support multiuser communication and radar sensing. To tackle the nonconvexity of the problem, we adopt an alternating optimization approach, decoupling beamforming design, RIS configuration, and UAV trajectory optimization. A semi-definite relaxation (SDR) technique and the S-procedure are employed to handle rank-one constraints and secrecy requirements, respectively. Simulation results demonstrate that the proposed scheme achieves a significant reduction in CRB compared to radar-only systems, with up to 35% improvement in sensing accuracy under moderate communication SINR constraints.