Research On Channel Estimation And Precoding In Massive MIMO Systems

With the rapid growth of wireless mobile on devices and services,telecom operators are faced with greater growth in higher data rates,greater network capacity,higher spectral efficiency,higher energy efficiency,and higher mobility required for new wireless applications demand.4G network has been close to the theoretical limit of the data rate,it is difficult to meet the above challenges,the future fifth generation(5G)network technology came into being.Massive-MIMO technology has become one of the 5G key technologies that academics and industry has pay close attention to it.In the multi-cell environment using frequency reuse,the error of the upstream channel state information(CSI)due to pilot contamination will affect the performance of the precoder,which significantly limits the overall rate of the Massive-MIMO system.In addition,intra-cell interference caused by pilot contamination and intra-cell interference will not disappear as the number of antennas grows.Therefore,pilot contamination is a fundamental challenge for Massive-MIMO systems.This paper mainly studies the channel estimation and precoding technology.Firstly,5G communication system is introduced,that is,5G features,key technologies and challenges are introduced,and channel estimation,precoding and pilot contamination of Massive-MIMO technology are reviewed.Secondly,in the case of MIMO OFDM transmission scheme,an improved channel estimation pilot pattern is proposed by inserting zero pilot symbols in the training sequence.The study of the scheme shows that the pilot pattern is not only beneficial to reduce the influence of pilot contamination,but also to realize the pilot multiplexing.Finally,we simulate a MF precoding under Massive-MIMO.The channel matrix of the uplink channel is obtained by performing LS channel estimation on the uplink communication link including a plurality of interfering cells(i.e.,containing pilot contamination);and the downlink is linearly precoded using a known channel matrix.The downside bit error rate(BER)analysis was evaluated here.The analysis and simulation results show that when the ratio of the downlink transmit antenna to the receive antenna is more than 10,a simple linear pre-coding at the base station(BS)can meet certain error performance.