Covert communications assisted by simultaneously transmitting and reflecting
reconfigurable intelligent surface (STAR-RIS) in non-orthogonal multiple access
(NOMA) systems have been explored in this paper. In particular, the access
point (AP) transmitter adopts NOMA to serve a downlink covert user and a public
user. The minimum detection error probability (DEP) at the warden is derived
considering the uncertainty of its background noise, which is used as a
covertness constraint. We aim at maximizing the covert rate of the system by
jointly optimizing APs transmit power and passive beamforming of STAR-RIS,
under the covertness and quality of service (QoS) constraints. An iterative
algorithm is proposed to effectively solve the non-convex optimization problem.
Simulation results show that the proposed scheme significantly outperforms the
conventional RIS-based scheme in ensuring system covert performance.Comment: arXiv admin note: text overlap with arXiv:2305.04930,
arXiv:2305.0399