UAV Trajectory, Power, and User-Association Optimization for Covert Communications in ICRNs

Abstract

This paper studies covert communications in an uncrewed aerial vehicle (UAV)-assisted interweave cognitive radio network (ICRN). Specifically, a secondary user (UAV) opportunistically utilizes the idle spectrum resource of a primary user (Warden) to covertly transmit short-packets to ground receivers (GRs), while Warden tries to detect the existence of the UAV covert communications. To ensure fairness of covert communications, this paper maximizes the minimum covert throughput from UAV to GRs, which can be formulated as an optimization problem with the constraints of covertness, UAV trajectory, power and user-association. We further simplify the optimization problem by determining the optimal transmission power of UAV. To solve this optimization problem, we derive the optimal transmission power of UAV and user-association index as analytical expressions of UAV’s positions, respectively. We also define UAV trajectory as a successive hovering-and-flying structure. Based on these results, we employ a successive convex approximation method to obtain the maximum value of the minimum covert throughput. The numerical results are presented to illustrate the impact of system parameters on the minimum covert throughput.