Research On Massive MIMO Beamforming In NLOS

As a key technology of the fifth-generation wireless communication system,Massive MIMO is one of the important technologies that can meet the higher information transmission requirements in the future.In order to effectively improve spectrum utilization,reduce interference between users,and improve the performance of users that expect to receive,beamforming algorithms and user-pairing algorithms based on large-scale antenna technology have received great attention and research.In order to improve the received power of the desired user,most of the existing literatures focus on the beamforming method and the user pairing algorithm in the LOS scenario,and it is necessary to obtain the ideal channel state information on the base station side.However,the actual wireless communication application scenario can neither satisfy the LOS condition,nor can ideal channel information be obtained in many cases,resulting in that the conventional beamforming algorithm cannot achieve the desired performance improvement.To solve this problem,this paper focuses on the research and design of the beamforming algorithm and the user pairing algorithm in the NLOS scene only based on the channel distribution information.For the design of the beamforming algorithm,this paper divides it into single-user scenarios and multi-user scenarios according to the number of users at the receiving end.Firstly,the traditional beamforming algorithms in each scene are described separately,including the beamforming algorithm based on the angle of arrival estimation and the MIMO beamforming algorithm.Then this paper theoretically proves that in the single-user scenario,it can use the spatial correlation matrix to equivalently replace the channel distribution information,so as to obtain a specific optimization problem expression.Based on this,this paper proposes a weighted minimum mean squared error beamforming algorithm to solve the optimization problem with the goal of maximum SNR to obtain the optimal beamforming vector that can maximize the expected user receiving power.The algorithm has a certain performance improvement over the existing algorithm in terms of expected user receiving performance.By building a large-scale MIMO communication system based on MATLAB,the performances of above-mentioned various algorithms are also simulated and verified.For the multi-user massive MIMO beamforming algorithm,this paper first considers the design of the user pairing algorithm,which is divided into LOS scenes and NLOS scenes according to different application scenarios.First,the existing user matching algorithm is still introduced.By analyzing the advantages and disadvantages of the existing algorithms,this paper finds that these algorithms basically need to know the ideal channel state information of all users on the base station side,and each pair needs to traverse all the users that need to be paired and the complexity of the algorithms is relatively high,so after we have demonstrated the relationship between the channel space correlation matrix and the direction of the main path of the channel,this paper proposes a pairing algorithm in the LOS scenario.However,for the NLOS scenario,the attenuation of each path power is very large,and the direction of the main path cannot be determined only through the channel spatial correlation matrix.Therefore,this paper redefines the interference factor from the proportion of the interference energy relative to the signal total energy,and proposes a user pairing algorithm in the NLOS scenario.Afterwards,based on the two pairing algorithms,a multi-user massive MIMO beamforming algorithm is proposed.First,this paper proves that we can use the spatial correlation matrix to equivalently replace the channel distribution information.Then the optimal beamforming weight vector can be obtained by solving the optimization problem with the maximum SINR as the goal.This algorithm has certain performance in sum rate of system compared to the existing algorithm.Then we combined the proposed user-pairing algorithm with the multi-user beamforming algorithm.Compared with the traditional user-pairing algorithm,the system's capacity and throughput performance have been improved.Finally,it is also verified in the system simulation.The massive MIMO beamforming algorithm and the user pairing algorithm proposed in this paper have certain reference significance for reducing the mutual interference between users,improving the expected user receive power and improving the spectrum resource utilization.