Research On Beamforming Precoding For Massive MIMO In Railway Mobile Communications

With the rapid development of the Internet industry and the popularity of multimedia communication equipment,the demand for data traffic services is exploding rapidly,and the fifth generation mobile communication systems after 2020 will face higher and faster data transmission rate requirements.Therefore,the traditional MIMO technology consisting of several antennas can no longer meet the needs of data services,and will be replaced by massive MIMO(M-MIMO)technology with a large number of antennas.This technology is effective by configuring large-scale antenna arrays on the base station side.The spectrum efficiency and link reliability of the system are improved.Based on the concept of beam-domain space division multiple access,this thesis analyzes and studies the simplified method of beamforming precoding and the adaptive allocation method of beam sets in mobile scenes in large-scale MIMO scenarios.Precoding in high-speed railway scenarios can be achieved by modifying the precoding method in static scenes.Therefore,the problem of precoding and simplification of massive MIMO in static scenes is studied.Zero Forcing(ZF)and Minimum Mean Square Error(MMSE)are two widely used methods of beamforming precoding.However,in massive MIMO systems,when the number of antennas at transmitter and receiver is larger,the calculation of inverse matrix becomes more complex.In this paper,we propose a beam-domain dimension reduction precoding scheme by using beam domain channel matrix to decompose the full-dimensional channel matrix and precoding the low-dimensional matrixes respectively.The computation of beamforming precoding could be decreased by this method.Finally,the feasibility of this scheme is verified by simulation.Based on the above scheme,we continue to study the beam domain precoding scheme in the high-speed train scenario.Since the MS moves faster in the high-speed train scenario,if the beam set to be allocated to the terminal is calculated once before each signal is transmitted,It will waste a lot of computing resources and delay the data transmission.We propose a scheme for adaptive dynamic adjustment of the beam set.First,we reduce the dimension of the channel in the beam domain,simplify the precoding calculation.Then,the beam set is adjusted according to the position information during the MS movement,so that the beam set with the highest gain is allocated to the MS.Finally,the feasibility of this scheme is verified by simulation.