Research On Massive Multiuser MIMO Precoding Algorithms

With the increasing of number of users on the mobile side,Massive MIMO(Multiple Input Multiple Output)technology was born out by deploying a large number of antennas at the base station to achieve higher spectral efficiency.Since Massive MIMO system can effectively improve the spectrum utilization and system capacity,it has become a hot topic for scholars in recent years.In addition,the precoding technique can improve the performance of the system by knowing the CSI(Channel State Information),by making a pre-processing on the transmitted signal at the base station to facilitate the signal detection on the receiver.However,in the Massive MU-MIMO(Muti-User MIMO)system with FDD(Frequency Division Duplexing)transmission mode,a large number of users will lead to the difficulty to access CSI.Therefore,how to design the precoding scheme to reduce the feedback overhead becomes a problem to be solved.First,several classic precoding algorithms,including linear precoding and nonlinear precoding are researched deeply.Secondly,under the dual polorized antenna channel model,this paper adopts the scheme which combines porlarized antenna whith BD(Block Diagonalization)dual structured precoding scheme based on spatial correlation.This scheme cascades BD beamforming pre-processing based on long-term CSIT(CSI at Transmitter)and RZF(Regularized Zero Force)precoding based on short-term CSIT.This scheme cascades BD beamforming pre-processing based on long-term CSIT and RZF precoding based on short-term CSIT.The simulation result shows that,in FDD transmission mode,the scheme can still reduce the feedback overhead,still has better sum rate performance than traditional precoding technology,and is not affected by cross-polarization parameters ?.Finally,in order to further reduce the feedback overhead,this paper designs BDS(BD and Subgrouping)dual structured precoding scheme.This scheme takes the dual-polarized antenna into account to precode,based on the BD dual-structure precoding scheme.The simulation result shows that,this scheme can obtain better sum rate performance than the BD dual structure precoding scheme,but it is affected by the cross-polarization parameter ?.Therefore,this paper considered setting a threshold value,and select BD or BDS precoding scheme according to the threshold,so that the better sum rate performance could be obtained.