Covert Communications in D2D Underlaying Cellular Networks with Power Domain NOMA

A device-to-device (D2D) communication link is vulnerable because it is relatively easy to be compromised by adversaries due to the fact that D2D terminals are power limited nodes. This article proposes a covert communication scheme that allows D2D communication links to transmit covert signals (e.g., privacy sensitive data) to ensure a low probability of detection. We allocate transmit powers of cellular and D2D noncovert signals following a fading D2D channel to add the uncertainty in adversary's background noises. With the help of base station, cooperative power domain nonorthogonal multiple access and successive interference cancellation are used to decode covert signal. Depending on whether a D2D transmitter has the knowledge of adversary's detection threshold, we derive minimum error probability to measure the covertness performance. Furthermore, we evaluate covert throughput, which is defined as a maximum average transmission rate of covert signal, subject to a given covertness performance.