Active-RIS-Aided Covert Communications in NOMA Systems With Cooperative Jamming

In this paper, cooperative jamming is employed to enhance the covert communication performance of active reconfigurable intelligent surface (RIS)-aided non-orthogonal multiple access (NOMA) system. Taking into account the constraints of the active-RIS power budget and covertness requriments, we formulate the covert rate maximization problem by jointly optimizing the transmit power allocation, jamming power allocation, and active-RIS beamforming. To tackle the highly coupled non-concave covert rate maximization problem, the optimal solutions for the decoupled sub-problems of the transmit power allocation, jamming power allocation, and active-RIS beamforming are derived, respectively. Specifically, closed-form expressions for the transmit power and jamming power optimization sub-problems are derived and a penalized Dinkelbach transform approach is proposed to optimize the rank-1 constrained active-RIS beamforming. Finally, the enhanced covert communication performance of our proposed scheme is demonstrated and corroborated by numerical results.