Covert Beamforming Design for Cooperative NOMA-Assisted Integrated Sensing and Communication Systems

In this paper, we consider covert communication in a cooperative non-orthogonal multiple access (NOMA)-assisted integrated sensing and communication (ISAC) system, where the ISAC relay can communicate with the covert user under the cover of probing waveforms and public communication waveforms without detection by the warden. For the proposed scheme, a closed-form expression for the minimum average detection error probability of warden is derived, where the detection threshold can be dynamically adjusted by the warden. Besides, we jointly design the covert transmission beamforming, target beamforming, and public transmission beamforming for maximizing the covert rate, subject to satisfying the successive interference cancellation decoding order, the quality of service requirement constraint at the public user, the sensing constraint, the covert constraint, and the total transimt power constraint. The sub-optimal solutions can be derived by employing semidefinite relaxation and the Charnes-Cooper transformation, which are provided to solve the proposed non-convex covert rate maximization problem. Simulation results demostrate that the covert rate of the proposed scheme can be effectively enhanced, compared to the ISAC systems assisted by orthogonal multiple access.