Joint Trajectory and Beamforming Optimization for Secure UAV Transmission Aided by IRS

Unmanned aerial vehicle (UAV) communications are susceptible to eavesdropping, and intelligent reflecting surface (IRS) is capable of reconfiguring the propagation environment, thereby facilitating the security for UAV networks. In this paper, we aim to maximize the average secrecy rate for an IRS-assisted UAV network by jointly optimizing the UAV trajectory, the transmit beamforming, and the phase shift of IRS. The complex problem is decomposed into three subproblems and solved via an iterative algorithm. First, the closed-form solution to the active beamforming is derived. Then, the passive beamforming of fractional programming is converted into corresponding parametric sub-problems. Finally, the trajectory problem is reformulated as a convex one by utilizing the successive convex approximation. Simulation results are provided to validate the effectiveness of the proposed scheme.