The Research Of Pilot Contamination In Massive MIMO System

With the rapid development of the next generation communication technology,the Massive MIMO technology which is the key technology of 5G attracts increasingly attention owing to its large system capacity and high energy efficiency.The capacity of the system will not increase with the increase of the number of base stations.Because of the finite of coherence time,different cell reuse the same pilot sequence leading to pilot contamination.When the number of base station antennas is large,pilot contamination will be the main factor which limites the Massive MIMO system.In this paper,the problem of pilot contamination in Massive MIMO system is studied.The main work is as follows:The first,the reason for the formation of pilot contamination is analyzed,which is caused by the inter-cell interference.Based on the derivation of the theoretical formula,the effect of pilot on the system performance is analyzed.Moreover,based on the simulation of channel estimation of the large scale MIMO uplink and downlink linear precoding algorithm,the advantages and disadvantages of the different channel estimation and precoding algorithms are analyzed.The second,the pilot scheduling scheme in large scale MIMO systems is analyzed,and a dynamic pilot scheduling scheme is introduced in this paper.By sorting the inter cell interference between the user channel quality and the pilot sequence,the pilot with small inter cell interference is allocated to the users with poor channel quality.The optimization of uplink SINR minimum can be achieved by the method mentioned above.Based on the simulation results of the proposed scheme,it is proved that the results of the proposed scheme can approximate the optimal solution.The performance of the system is significantly improved compared with the pilot random allocation system.Hence,it is very necessary to study the pilot allocation scheme.The third,in the study of the influence of pilot contamination on the downlink of Massive MIMO system,a partial pilot reuse scheme is introduced.This scheme can reduce the pilot contamination of the users at the adjacent cell.Aiming at the shortcomings of this scheme,there is no shortcomings of pilot contamination for the users in central area.An improved partial pilot reuse scheme is proposed.The improved scheme uses the dynamic pilot allocation scheme for the users in the central area of the cell.The simulation results show that the improved scheme can improve the downlink reachability and the rate of the two schemes with the maximum downlink reachability and the rate as the criterion.The improvement program is basically feasible.