RIS-Enabled Integrated Sensing and Covert Communication with A Finite Blocklength

In this work, we consider an integrated sensing and covert communication (ISACC) system with a finite blocklength aided by a reconfigurable intelligent surface (RIS). Specifically, with the aid of RIS, a transmitter Alice is designed to detect the existence of a target, but she is also probabilistically trying to send information to a receiver Bob covertly (i.e., trying to hide her communication to Bob from a warden Willie). Meanwhile, Willie is to detect whether Alice is sensing the target only or conducting ISACC. We formulate an optimization problem to determine Alice’s optimal power allocation fraction ρ between her sensing and covert information signals and RIS’s optimal beamforming vector v, to maximize the effective throughput from Alice to Bob, subject a covertness constraint, a detection performance constraint, and other inherent constraints. To facilitate solving the optimal design problem, we first derive its feasibility condition, which indicates that a higher transmit power is desired for a shorter blocklength. Then, we identify the optimal ρ for a given v via solving a fixed-point equation under the derived feasibility condition. Then, with the aid of our conducted analysis, we convert the optimization of v into a convex optimization problem. Our results show that the overall ISACC performance increases with the finite blocklength, although the performance per channel use decreases with it. In addition, our examination shows that the achievable covert communication performance generally increases with Alice’s transmit power for both sensing and covert communication.