Research On Constant Modulus Secure Beamforming For Massive MISO Wiretap Channel

With the increasing demand for communication services,the fifth generation of mobile communication systems has been become a hot topic in communication research.In order to achieve higher communication channel capacity,spectrum utilization,energy efficiency and lower hardware device cost,large-scale antenna technology and constant modulus beamforming have been widely researched.In particular,large-scale antenna and beamforming can effectively achieve spatial multiplexing and ensure secure communication from the physical layer.At the same time,communication equipment costs can be reduced by using constant modulus beamformer.Therefore,it is of practical significance to study the beamforming technology under constant modulus constraints in large-scale antenna communication systems.This thesis aims at the Multiple Input Single Output Multiple Antenna Eavesdropper(MISOME)security transmission model to achieve better security transmission performance and optimize the design of transmission constant modulus beamformer.The specific research content is as follows:Firstly,beamforming problem with non-convex constant modulus constraints is researched in the basic point-to-point secure communication system.Two constant modulus beamforming algorithms are proposed in this paper.One is to use Semidefinite Relaxation(SDR)to solve the approximate problem,and then the principal eigenvector projection of the solution to obtain the constant modulus beamformer.In addition,the other method is to use Dinkelbach method to convert objective function of the problem into a series of convexity subproblems,and then iteratively solves them by the non-convex Alternating Direction Method of Multipliers(ADMM).Moreover,the convergence of the algorithm is proved.Simulations show that two algorithms can guarantee secure communication performance,and the latter can achieve better security communication performance and lower computational complexity.Futhermore,non-convex constant modulus constrained beamformer design is considered in secure broadcast communication system.Due to the existence of multiple legitimate users and non-convex constant modulus constraints,the difficulty of the problem is greatly increased.Two algorithms are designed in this eassay.One is to approximate the problem using semi-definite relaxation method and transform it into Semidefinite Programming(SDP)problem.Another is to approximate the objective function using log-sum-exp,and then use Dinkelbach and ADMM algorithm to combine iterative processing.Futhermore,the convergence of the algorithm is illustrated in this thesis.Simulation results show that two algorithms can effectively solve the problem,and the latter obtains better performance.Finally,non-convex constant modulus beamforming problem is considered in multi-eavesdropper broadcast security communication system.For multi-Bob multi-Eve and non-convex constant modulus constraints,two algorithms are presented in this paper.Firstly,the log-sum-exp function is applied to approximate the discontinuous objective function as a continuous derivative function.Afterwards,the first method is to use Projection Gradient(PG)to solve iteratively.The second method is to use fast iterative shrinkage-thresholding algorithm(FISTA)to obtain the constant modulus beamformer.Simulation results show that compared with the SDR-based method,two algorithms can solve the problem more effectively,and the performance and computational complexity of second method are more prominent.