Research On Hybrid Precoding Technology In Millimeter Wave Massive MIMO Systems

With the rapid increase in the demand for wireless communication capacity,it is difficult for the communication system operating in the microwave frequency band to meet the user's high-speed transmission requirements.Therefore,in the past few years,many advanced technologies have been used to improve spectrum efficiency,such as relay cooperation,diversity multiplexing and cognitive radio.However,compared with the explosive system capacity requirements,the gains obtained are too limited.In order to solve the shortage of frequency resources,millimeter waves are considered as potential radio frequency candidates.Due to the gigabit per second data rate,millimeter waves will be deployed in the fifth-generation wireless communication system.In addition,due to the increase in the number of antennas,large-scale multiple-input multiple-output technology can effectively improve the spectrum efficiency and channel capacity of the system,and it has become the key technology of the fifth generation of mobile communications.Therefore,millimeter wave large-scale multiple input multiple output technology has become a key research toptic.In addition,the hybrid precoding technology effectively reduces the hardware cost of the pure digital precoding system,which is more compatible with the millimeter wave large-scale multiple input multiple output system.Therefore,this paper mainly studies the hybrid precoding technology of mm Wave massive MIMO system.Aiming at the problems of high complexity of existing algorithms and low spectrum efficiency of the system,some novel hybrid precoding schemes are studied.The main work of this paper is as follows:(1)In a partially connected single-user millimeter wave large-scale multiple-input multiple-output system,a hybrid precoding scheme based on phase alignment is proposed.The scheme first extracts the conjugate transpose of the channel matrix.The phase method is used to design analog precoding to obtain higher antenna gain.Secondly,the digital precoding matrix is obtained by singular value decomposition.Simulation results show that,as compared with the hybrid precoding algorithm of maximizing equivalent channel gain,the proposed algorithm can effectively reduce the computational complexity at the loss of a small amount of system spectrum efficiency.(2)Under the single-user millimeter wave large-scale multiple-input multiple-output system with partially connected structure,this paper proposes a hybrid precoding scheme based on column-by-column optimization.This scheme finds the near-optimal solution of analog precoding through a column-by-column optimization algorithm.The precoding matrix is obtained by the singular value decomposition method.Simulation results show that,as compared with the hybrid precoding algorithm based on the maximum equivalent channel gain,the proposed algorithm effectively improves the spectrum efficiency of the system at the cost of a slight increase of the complexity.(3)Under the multi-user millimeter wave large-scale multi-input multi-output system with partial connection structure,this paper proposes a two-stage hybrid precoding scheme.The scheme uses a column-by-column optimization algorithm to find the near-optimal solution of analog precoding.The coding design is divided into two parts,one part uses a zero-forcing algorithm to eliminate interference between users,and the other part is used to approximate full digital precoding.Simulation results show that,as compared with the existing hybrid precoding scheme,the proposed scheme effectively improves the spectrum efficiency of the system at the cost of a slight increase of the complexity.