Joint Trajectory and User Scheduling Optimization for Dual-UAV Enabled Secure Communications

In this article, we address joint optimization of unmanned aerial vehicle (UAV) trajectories and user communication scheduling for a dual-UAV enabled secure communication system, where one UAV moves to serve multiple users on the ground in a time division multiple access (TDMA) mode while the other UAV in the area flies to jam the colluding eavesdroppers on the ground to protect communications of the desired users. Specifically, we maximize the minimum average secrecy rate among the users within each period by jointly optimizing UAV trajectories and user scheduling variables under the maximum UAV speed constraints, the UAV return constraints, and the discrete binary constraints on user scheduling variables. The resulting optimization problem is very challenging due to its highly nonconvex objective function and constraints. We then develop a novel algorithm based on the penalty concave-convex procedure (CCCP) technique to solve it. Based on our simulation results, the proposed joint optimization algorithm achieves significantly better performance than the conventional algorithms.