D2D Covert Communications With Safety Area

In this article, we investigate device-to-device (D2D) relay enabled covert communications. Safety zone is employed to isolate the eavesdroppers from the transmitters and receivers. Different from majority of the existing studies considering fixed relays, dynamic relay selection is first considered for covert communications in this article. Additionally, we formulate dynamic relay selection and power allocation into an infinite-horizon time-average renewal-reward problem subject to the time average constraint on a collection of penalty processes. Furthermore, a novel Lyapunov optimization concepts based drift-plus-penalty algorithm is proposed to solve the problem. The numerical results demonstrate that the validity of the proposed dynamic relay selection by comparing its performance with its benchmarks.