Study On Mitigating Technology Of Pilot Contamination For Massive MIMO In TDD Systems

Massive MIMO is the key technology of 5G.The antenna array gain can be support a large number of data flow,exponentially improve system capacity and transmission rate in the same time-frequency resource.It has become a hot spot in the field of communication research today.In massive MIMO TDD system,because uplink and downlink have reciprocity,as soon as the base station gain uplink precoding matrix and downlink can utilize transposed precoding matrix for transmission.Base station is convenient,and can make full use of the antenna gain of massive MIMO,improve the system spectral efficiency and energy efficiency.However,because the pilot sequence is limited,When the base station carries on the pilot estimation to the target user,it will be interfered by the user of the adjacent cell,pilot contamination problems occur and the problem will not decrease with the increase of the base station antenna,severely limits the performance of massive MIMO multiple antennas.Therefore,from the concept of massive MIMO TDD system and transmission mode,the paper analyzes the causes of multi-cell district pilot pollution,then studies the pilot contamination problem by using different pilot frequencies.Finally,the improved scheme and scheduling process are proposed,and the pilot pollution is analyzed and verified.The main work is as follows:Firstly,the paper introduces the research background of the subject,the Massive MIMO system of pilot frequency contamination of research status are classified and summarized,gives the research significance and the research content.From the MIMO channel model,channel capacity and correlation between antennas,the paper is analyzed and the basic model and transmission principle of massive MIMO are introduced.This paper analyzes and discusses the commonly used linear precoding for channel detection,and analyzes the performance of the simulation.Then,the transmission mode and the pilot frame structure of TDD system are introduced,and the pilot contamination problem in massive MIMO TDD system is introduced.The cause of pilot contamination and the effect of contamination on the performance of massive MIMO system are analyzed in detail,and the simulation results are verified.Results show that in multi-cell system with pilot contamination,the achievable sum rates of the system will not increase with the increase of the number of antennas,only depend on the cross gain value of the cell,the greater the value of cross gain,the more serious the pilot contamination.Based on the analysis of pilot contamination,a multi-cell pilot multiplexing scheme is proposed and the energy efficiency of the system is analyzed by using different pilot frequencies.The simulation results show that the high frequency factor can improve the energy efficiency of the system,and then improve the rate of the system,reduce pilot pollution,but the precondition is to sacrifice more pilot resources.Finally,the paper puts forward an improved system model and pilot scheduling scheme based on pilot power control.Through the definition of community users,this paper carried out pilot scheduling on vulnerable pilot interference of edge users,so as to avoid users who use the same pilot at the same time.Finally,the energy efficiency,spectrum efficiency and achievable sum rate of the system of the improved scheme are simulated and analyzed according to the multi-cell linear precoding method.The simulation results show that compared with the pilot system,the improved scheme can achieve the effect of reducing the pilot contamination.