Covert Communications for Intelligent Reflecting Surface-Enabled D2D Networks

In this paper, we explore covert communications in a device-to-device (D2D) network consisting of an intelligent reflecting surface (IRS), a base station, a cellular user, a D2D pair, and an adversary warden. With the help of the IRS, the D2D pair attempts to perform covert communication, while the warden also tries to detect the very existence of such a transmission. To investigate the covert performance under the scenario, we derive the detection error probability at Warden, the optimal detection threshold for minimizing the probability, and the transmission outage probabilities for D2D and cellular communications, respectively. We further jointly optimize the transmission powers of the cellular user and the D2D transmitter, the reflection phase shifts, and the amplitudes of the IRS reflecting elements to improve covert communication performance. Finally, we provide numerical results to reveal the impact of system parameters on the covert performance and also to exhibit the merits of IRS-enabled D2D networks for achieving covert communications.