Research On Physical Layer Security For Intelligent Reflecting Surfaces-aided UAV Communication

With the development of society,people have higher requirements for mobile communication.Convenient,reliable,and high-speed wireless accessing have become one of the main directions for the modern mobile communication technology.For the high mobility,low cost,and on-demand deployment,Unmanned Aerial Vehicles(UAVs)can provide reliable and cost-effective wireless communication solutions for a variety of practical scenarios through reasonable deployment and control of the UAVs.With the developing of 6G,Intelligent Reflecting Surface(IRS)has emerged as a brand revolutionary technology.By reflecting the incident signals intelligently,the IRS has the capability of reconfiguring the wireless propagation environment.Therefore,the IRS-aided UAV communication system can be expected to improve the quality of the UAV communication systems.As the security problems caused by the broadcasting characteristics of the wireless channels,the IRS-aided UAV secure communication has attracted the researchers’ attention.In contrast to additional energy loss of the UAV that the traditional encryption methods require complex encryption and decryption algorithms,which will bring additional energy loss to UAV.Considering the limited energy of the UAV,exploiting the physical characteristics of the wireless channel to ensure UAV secure communication has become the first choice.Based on this,physical layer security technology is used to improve the security performance of the IRS-aided UAV communication system in this paper.The main research work as follows:(1)IRS-aided cooperative multi-point receiving UAV communication system,where the UAV serves as an aerial base station to communicate with multiple ground users.The IRS can reflect the signal transmitted by the UAV.Considering the fairness of all ground users,a mixed integer non-convex optimization problem with the goal of maximizing the minimum average safe rate of all ground users is established.It is divided into four sub-problems with the block coordinate descent(BCD)technology:IRS passive beamforming optimization,ground user scheduling optimization,UAV transmission power and flight trajectory optimization.The problem of UAV transmission power and the flight trajectory can be tackled by the successive convex approximation(SCA)technology.Finally,an iterative algorithm of four sub-problems is used to efficiently obtain a local optimal solution of the optimization problem.Simulation results show that the proposed algorithm can achieve better secure performance than the benchmark scheme.(2)IRS-aided full-duplex UAV cooperative interference communication system,where the ground users send information signals to the UAV,and the UAV sends interference signals to the eavesdroppers while receiving the information signals.The IRS builds an additional reflection path for both of the information signal sent by a ground user and the interference signal sent by UAV.By jointly optimizing IRS passive beamforming,source transmit power,UAV interference power and flight trajectory,the maximum average secrecy rate of the system achieved.Since the joint optimization is a non-convex optimization problem,it is difficult to solve it directly.Consequently,it is approximated as a convex optimization problem by using BCD and SCA techniques.The simulation results show that the secure performance of the IRS-aided UAV communication system can be significantly improved.