Active-RIS-Aided Covert Communications in NOMA Systems With Cooperative Jamming
Xueyu Kang, Hongjiang Lei, Liang Yang, Gaofeng Pan, Theodoros A. Tsiftsis, Hongwu Liu
Abstract
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.