Covert Communications in D2D Underlaying Cellular Networks with Multiple Wardens

Covert communication prevents an observant adversary from knowing the existence of the transmission, while providing stronger security protection for device-to-device (D2D) communication. In this paper, we propose a covert communication scheme for D2D underlaying cellular networks in the presence of multiple wardens, where random transmit power is exploited by the cellular user to add the uncertainty on wardens' background noises. Moreover, we analyze two cases that wardens fully know or partially know the channel state information. Specifically, we first derive the detection error probabilities and further derive the closed-form expression of the expected minimum detection error probability over wireless fading channels to characterize the covertness of the D2D link. Furthermore, we optimize the information transmit power and the maximum transmit power of the cellular user to achieve the maximum effective D2D covert rate subject to a covertness requirement. Our analysis shows that increasing the number of wardens leads to significant performance degradation of D2D communication covertness.