Secure Communication Method Based on Intelligent Reflection Surface Assisted UAV Relay System

To improve the security of wireless transmission system and solve the problem that wireless channel is easily blocked by obstacles, a secure communication method based on an Intelligent Reflecting Surface (IRS) assisted Unmanned Air Vehicle (UAV) relay system is proposed. In the proposed method, the minimum-secrecy are maximized by jointly optimizing the position of UAV, beamforming at base station and phase shifts of IRS. To solve this complicated non-convex optimization problem, the original problem is divided into UAV position optimization sub-problem, beamforming and IRS's phase shifts optimization sub-problem. The first order Taylor expansion method is applied to handle the non-convex terms of the optimization problems. Then, an alternate optimization algorithm is proposed to solve the problem. The simulation results shows that the proposed algorithm can improve the minimum-secrecy rate, and its convergence is well.