IRS-Assisted Secure UAV Communication System for Multiuser With Hardware Impairments

Perfect hardware conditions are often difficult to meet in practical networks due to the inevitable hardware impairments (HIs). The secure multiuser communication of an intelligent reflecting surface (IRS)-aided unmanned aerial vehicle (UAV) system with HIs at the transceiver and the IRS is studied in this article. Aiming for maximizing the average sum secrecy rate (ASSR) of the UAV system, we jointly optimize the transmit precoding (TPC) matrices, IRS phase shift matrices, and UAV trajectory. To deal with the nonconvexity, we break down this problem into three subproblems and solve them using an alternating optimization (AO) algorithm. Specifically, the semidefinite programming method is used to solve the TPC and phase shift matrices, while the successive convex approximation method is used to obtain the UAV trajectory. In addition, a low complexity mathod on the basis of the Riemannian Manifold Gradient is proposed to solve the IRS phase shift matrix. Simulation results verify the effectiveness of the algorithm. Our robust algorithm can improve ASSR by 22% compared to that without IRS. Furthermore, the nonrobust design without considering HIs will cause a loss of secrecy performance.