Research On Pilot Contamination In Massive MIMO System

With the rapid development of mobile internet technology,the demand for network throughput,access capacity and high rate communication are increasing day by day.Since the traditional communication technology can not meet the huge demand of the communication in future,massive MIMO(Multi-Input Multi-Output,MIMO)emerges at the historic moment.The technology,as one of the key technologies of 5G communication in future,has attracted extensive interest since it was proposed.Massive MIMO system is equipped with a large number of antennas at the base station,which can serve multiple user terminals simultaneously,owing to the gain brought by those antennas.As the number of the base station antennas is increasing,the system shows many new properties that the traditional MIMO does not have.These properties can greatly improve the spectral efficiency of the MIMO system,alleviate the impact of channel noise,and further increase the practicality of massive MIMO.However,due to the limited frequency of pilot resources in actual cellular,in order to maximize the system capacity,all the cells can multiplex pilot signals among them.In channel estimation phase,the pilot multiplexing leads to the pilot contamination,which limits the advantages of massive MIMO technology.In order to overcome the influence of pilot pollution on the system,in this paper we study the pilot contamination suppression technology in massive MIMO systems,and propose a pilot allocation scheme based on system capacity maximization.On this basis,we further study the user transmit power control technology,and finally combine the pilot allocation scheme and user transmit power control technology to further enhance the system capacity.This article mainly focuses on the above aspects about the pilot pollution problem,the main contents are as follows:1.Based on the introduction of the basic theory of massive MIMO system,this paper discusses the system capacity and emphasizes on the source which causes pilot contamination.The simulation results verifies the influence of pilot contamination on the system,which manifests the necessity of suppressing the pilot contamination.2.On the basis of the theory foundation of traditional pilot suppression scheme,several improved pilot contamination suppression schemes are studied and analyzed.Aiming at the disadvantages of the existing schemes,a low-complexity pilot allocation scheme is proposed by analyzing the system model.The scheme can achieve near optimal system performance with low complexity.In this paper,the pilot allocation scheme is put forward to overcome the shortcomings of the existing schemes.The simulation results show that the proposed scheme can effectively improve the system capacity and reduce the impact of pilot contamination.3.Based on the analysis of the multi-cell multi-user MIMO system,a power control scheme is carried out by employing the basis of pilot allocation.We adjust the power for those users who can improve the quality of communication but still cannot reach the normal communication;For the users who can reach the normal communication,the signal to noise ratio,which needs to be achieved,is guaranteed with the lowest possible power.Finally,the simulation results also verify the power control on the basis of pilot allocation,which can improve the system performance and further reduce the influence of pilot contamination.