Performance Analysis of Covert Communications with Non-Orthogonal Multiple Access (NOMA)

In this work, we explore one covert non-orthogonal multiple access (NOMA) communication system where the strong users act as the covert users and weak users are used as legitimate users to cover covert transmission. On this foundation, we first analyze the detection capability of the warden and deduce its probability of detection error (PDE). Moreover, by addressing the best threshold for detection of the warden Willie, a closed-form expression for its minimum PDE is also given. Furthermore, the performance of covert transmission with NOMA is considered, where the closed-form expressions for the outage probabilities of covert and overt links and the effective covert rate are derived. Besides, a power optimization problem has been designed aiming to maximize the effective covert rate. Lastly, numerical simulation results are given to verify our theoretical analysis and derivation, which also shows that NOMA technology can be effectively used for covert transmission.