Abstract: In order to further enhance the secrecy rate of the unmanned aerial vehicle ( UAV ) communication system, a UAV security communication system base on intelligent reflecting surface(IRS) and cooperative jamming is proposed. By using an IRS to dynamically strengthen the backhaul link and introducing artificial noise through a cooperative UAV to interfere with a illegal eavesdropper, the security of UAV communication system can be improved from the aspect of physical layer security. Considering the trajectory of the source UAV, the trajectory of the jamming UAV, the power control and the phase shift of IRS, a joint optimization problem is proposed with the goal of maximizing the security of the system. An alternate optimization algorithm is proposed, which turns the original problem into four sub-problems, and converts the original non-convex problem into approximately convex sub-problems through successive convex approximation and semidefinite relaxation technique, so that it can be solved directly by convex optimization tools. The simulation results show that the proposed optimization algorithm can converge quickly. Compared with the traditional non-intelligent reflector-assisted communication network, the proposed algorithm can significantly improve the security rate of the system.

Key words: intelligent reflecting surface , physical layer security , unmanned aerial vehicle communication , trajectory optimization