Research On Precoding In Massive MIMO System Under High-speed Mobility Scenarios

China's high-speed rail lines and the size of high-speed rail network are currently ranked first in the world,which means that the next generation of wireless communication is facing a more severe test.The Global System for Mobile Communications-Railway system,which is currently used by China Railway,can not meet the demand of high-speed mobile Internet users for high-speed mobile Internet.As the core technology of 5G and future broadband mobile communication,multiple Input Multiple Output(MIMO)can provide diversity gain and multiplexing gain in space by using multi-antenna technology at the transmitter and receiver without adding additional system bandwidth,in order to achieve high-capacity wireless transmission.As a result of the use of multi-antenna technology,it will produce interference inevitably between different data streams,between sub-carriers and different users,which requires more complex detection methods to restore the original data.However,the detection technology is limited by the power consumption and the terminal size in practical systems,and its high cost and high complexity become a big limitation for the application of the detection technology.The use of base station precoding technology,can solve the above problems,while eliminating the interference between multiple users,and simplify the receiver detection.In this paper,the precoding technology under the high-speed mobile scenarios is studied,the main works are as follows:Firstly,the technical principle and implementation of MIMO system precoding are introduced,and the characteristics of high speed mobile channel are analyzed.Hence,a large-scale MIMO beamforming design based on Direction of Arrival(DoA)based on above theories is proposed in high speed scene.In order to obtain a better system capacity and a continuous communication between Base Station(BS)and users,an iterative multi-beams selection scheme is proposed,it aims to design different beams for different Mobile Carriage Terminals(MCT)respectively.The proposal adaptively selects the number of antennas for each beam,and adaptively designs the number of beams according to system capacity.Moreover,our scheme needs no Channel State Information(CSI)that can reduce system implementation complexity and cost.Numerical results indicate that the proposed scheme is suitable for high-speed scenarios,the system performance could be improved more.In the actual high-speed railway communication system,the direction of the train traveling is fixed and the speed is predictable,therefore,the CSI can be obtained at the transmitter,as a result,the CSI could be used to improve system performance.In order to increase the total capacity of the communication system in the high-speed mobile scenarios,we proposed to combine the interference alignment based on CSI with the proposed adaptive beamforming technique.It divides the large-scale MIMO antenna into two groups,and then uses the idea of aligning the interference signals to zero space to eliminate the interference between the antennas and increase the spatial degree of freedom.The simulation results show that the proposed method can further increase the system capacity on the basis of adaptive beamforming technology.