Research On Physical Layer Security Of Wireless Communication System Based On Intelligent Reflecting Surface

In recent years,with the continuous development of wireless communication technology,the data communication rate and the system capacity in the network has increased exponentially,people have higher requirements for the security performance of the communication system.However,due to the broadcasting characteristics of wireless channels,wireless communication networks are particularly vulnerable to eavesdropping and simulation attacks from illegal receivers.Physical layer security technology uses inherent characteristics such as channel noise,fading and multipath effects to increase the channel difference between the legitimate receiver and the eavesdropper.Intelligent Reflecting Surface(IRS)is a passive device that can change the wireless communication transmission environment.It adjusts the incident signal by remotely controlling the IRS unit without consuming the power of the transmitter and has become an important research in wireless communication in the past two years.This thesis studies the application of IRS in the physical layer security of wireless communications,the main contents are as follows:(1)Considering the IRS-assisted multiple-input and multiple-output(MIMO)and multiantenna eavesdropper(ME)communication system model,under this model,the transmitter has known channel state information(CSI)of the eavesdropper.For this eavesdropping scenario,under the constraints of the transmitter power and IRS unit phase shift modulus,an optimization problem is established with the goal of maximizing the secrecy rate.Aiming at the non-convex objective function and unrelated constraints,the alternative optimization algorithm is used to transform the optimization problem into two sub-problems.When optimizing the covariance matrix of the sub-problem,using the barrier method to convert the inequality constraint problem into an equality constraint problem,then Newton method and the backtracking line search method are combined to solve the solution of the barrier function KKT condition,and proved that the optimal solution is the optimal solution of the original objective function.When optimizing the IRS phase shift matrix,the implicit objective function of the phase shift matrix is rewritten into the explicit objective function of a single phase shift firstly,and then the phase shift of each reflection unit is optimized one by one,finally the optimal reflection phase shift matrix is iteratively solved.The simulation results show that the proposed algorithm has a significant effect in improving the security performance of the system.In addition,the influence of the IRS only reflecting a single link signal to the legal receiver or the eavesdropper on the system secrecy rate under this model is also studied.(2)For the IRS-assisted multiple-input and multiple-output(MIMO)communication system model,when the CSI of the eavesdropper is unknown at the transmitter,artificial noise(AN)is added to interfere with the signal received by the eavesdropper,thereby improving the security performance of the system.On the premise of meeting the requirements of the legal receiver's quality of service(Qo S),an optimization problem is established with the goal of maximizing AN power.Aiming at the IRS unit modulus constraint,the riemannian manifold optimization algorithm is used to convert the unit constraint problem in Euclidean space into the constraint problem in manifold space.The simulation results show that the proposed algorithm can significantly improve the secrecy rate of the system when the CSI of the eavesdropper is unknown at the transmitter.