Enhancing Covert Communication and Sensing for NOMA-ISAC Systems With ARIS-Assisted Cooperative Beamforming

Abstract

Despite the significant advantages in multiple access and spectral efficiency, non-orthogonal multiple access (NOMA)-enabled integrated sensing and communication (ISAC) systems are prone to interception and privacy breaches as a result of broadcast characteristics of wireless channels. In this paper, we put forward an active reconfigurable intelligent surface (ARIS)-assisted cooperative beamforming to concurrently boost both the covert communication and sensing performance for a NOMA-enabled ISAC system. In the proposed scheme, both public NOMA signal and dual-functional artificial noise are superposed to shield covert NOMA transmissions. By intelligently reflecting superposed signals at the ARIS in addition to optimizing the transmit and receive beamforming at the base-station, the detectability of covert NOMA transmissions at the warden is effectively suppressed and the required radar output signal-to-noise ratio is guaranteed. The targeted covert rate maximization problem is highly non-convex comprising complicatedly coupled variables, which is efficiently solved via an alternating optimization framework combining majorization–minimization, fractional programming, and Lagrangian dual transformation. The simulation results show that compared with existing benchmark schemes, the proposed scheme significantly enhances the covert communication and sensing performance. Moreover, under imperfect channel state information, the proposed scheme maintains its performance advantage with strong robustness. The impacts of key system parameters on the covert communication and sensing performance are also revealed.