Energy-Efficient Transmit Probability-Power Control for Covert D2D Communications With Age of Information Constraints

Covert device-to-device (D2D) communication is recently proposed to help D2D pairs hide the existence of transmission from being detected by a warden. However, most of the existing works only focus on guaranteeing the communication covertness, while they ignore the information freshness and energy consumption which are important for the delay-sensitive applications and energy-constrained devices. In this work, we propose an energy-efficient transmit probability-power control scheme for covert D2D communication with the information freshness requirement. Specifically, we first construct a novel status update model in covert D2D communication, and further derive the closed-form average age of information (AoI) to characterize the freshness of status information. Then, from the perspective of warden, we analyze its detection performance and derive the minimum detection error probability to measure the communication covertness. Subsequently, from the perspective of D2D pair, we propose the notion of covert energy efficiency (EE) to characterize the tradeoff between covert rate and power consumption. Guided by this, we jointly optimize the transmit probability and transmit power of status information to maximize the covert EE of the D2D pair subject to the constraints of communication covertness and information freshness. Due to its intractability, we design an iterative algorithm based on the successive convex approximation (SCA) approach. Simulation results verify the correctness of derived expressions and show the effectiveness of our proposed scheme.