Joint Waveform and Reflection Design for Sensing-Assisted Secure RIS-Based Backscatter Communication

In this letter, we investigate the sensing-assisted secure transmission for reconfigurable intelligent surface (RIS)-based backscatter systems, where an integrated sensing and communications (ISAC) base station communicates with multiple IoT devices against an aerial eavesdropper (AE). Particularly, based on the previous sensing result, we jointly design the transmit electromagnetic waveform and the RIS phase shift to prevent information leakage and maximize the sum-rate, while satisfying the Cramér-Rao lower bound constraint for AE's angle estimation. To deal with the coupled variables, we propose a fractional programming-based alternating optimization algorithm, where successive convex approximation and manifold optimization techniques are employed to tackle the non-convex constraints. Simulation results demonstrate that the proposed algorithm effectively ensures the sensing accuracy for AE and significantly improves the sum secrecy rate with the assistance of sensing results.