Research On Precoding Technology In Massive MIMO Systems

Massive MIMO(Multiple Input Multiple Output)technology can significantly improve the system's capacity and the reliability of communication process,thus becoming the key technology of 5G(the fifth generation of mobile communications).On the other hand,because the frequency band of traditional electromagnetic wave is unable to meet the requirements of 5G for transmission rate,millimeter wave with abundant unused high-frequency resources,has become an important technology of 5G.Millimeter-wave massive MIMO technology has naturally become a key research direction.In the practical systems,the pure digital precoding technology consumes too much hardware such as RF link,which is difficult to be applied to the millimeter-wave massive MIMO systems with higher number of transmitting antennas.Therefore,this paper mainly studies the hybrid precoding algorithm widely used in the millimeter wave systems,which can effectively reduce the hardware cost.The main contents of this paper are as follows:1)Inspired by the idea of multi-step,some improvements have been made based on the existing OMP(Orthogonal Matching Pursuit)algorithm in the fully-connected millimeter-wave massive MIMO systems.It can be seen from the simulation results that,as compared with the original algorithm,the proposed algorithm effectively reduces the complexity of the algorithm in the case of a small loss of system's achievable rate.2)In this paper,a hybrid precoding scheme based on intelligent search is proposed for the partially-connected millimeter-wave massive MIMO systems.Aiming at the capacity of the system,the proposed scheme transforms the problem of designing the mixed precoding matrix into an optimization problem,and then uses the intelligent search algorithm called SBO(Satin Bowerbird Optimization)to solve this problem.Furthermore,two algorithms called DSBO(satin bowerbird optimization based on dynamic mutation probability)and discrete DSBO are proposed to improve the original SBO algorithm,which increases the system's achievable rate and expands the application range of the algorithm.Simulation results show that,as compared with the hybrid precoding algorithm based on BSA(Bird Swarm Algorithm),the proposed algorithm has higher system's achievable rate and lower bit error rate.3)A mixed precoding scheme based on the maximum equivalent channel gain is proposed for the partially-connected millimeter-wave massive MIMO system.Firstly,an analog precoding matrix is designed based on the maximum equivalent channel gain,and then two improved SIC(Successive Interference Cancellation)algorithms are proposed to obtain the digital precoding matrix.It can be seen from the simulation results that the two proposed algorithms are better than other algorithms in terms of the system's achievable rate.