Research On Methods Of Reducing Pilot Contamination In Massive MIMO Systems

Pilot contamination is related to the multi-cell large-scale Multiple Input Multiple Output(MIMO)system,and has been identified as one of the main challenges of the cellular system supporting Multiple Input Multiple Output.This problem occurs when the same pilot set is reused between adjacent cells to save data transmission bandwidth.Therefore,in line with the principle of reducing contamination,the following studies have been carried out:1.According to the strategy of allocating pilots by user measurement coefficients,when the user measurement coefficients are equal,because the order in which the expected users to be allocated pilots choose to interfere with users is different,the users suffer from different pilot pollution levels,which will lead to differences between users.The difference in channel estimation accuracy.To solve this problem,a pilot allocation strategy based on the user’s angle of arrival and distance is proposed.This strategy first calculates the user measurement coefficients,and determines the target user pilot by comparing the measurement coefficients;among them,when the measurement coefficients are equal,priority is given to reusing the interfering user pilot that is the farthest from the expected user in the adjacent interfering cell.Through theoretical analysis and simulation,the channel estimation accuracy,user reachable rate performance are studied.The simulation results show that the channel estimation accuracy,user reachable rate have been improved compared with the original scheme.2.Aiming at the problem that users in different areas of the cell suffer from different contamination levels,through the analysis of the coloring of the graph and the alternate reuse of partial pilots,the advantages and disadvantages of the two schemes are compared.Chapter 4 proposes a method based on large-scale fading coefficients.Joint user grouping and pilot allocation strategy.This scheme is a compromise scheme.The main idea is to first sort the large-scale fading coefficients of users and the base station(Base Station,BS)in ascending order and classify all cell users into security edge users,hazard edge users,and center users in turn.user.Then,a weighted graph coloring scheme and a partial pilot alternate reuse scheme are used to allocate pilot for security edge users and non-safe edge users,respectively.The simulation results show that the proposed pilot allocation scheme not only reduces the complexity of the algorithm,but also effectively improves the user sum-rate,etc.