Wireless Channel Model In High-Speed Mountain Scenes

High-speed railway has the characteristics of strong passenger capacity,high speed,high safety and low rate of delays.In recent years,with the development of high-speed railway,more and more passengers choose high-speed railway as their way of travel.At the same time,users are demanding higher and higher stability and real time of high-speed railway wireless communication system.During the train operation,a reliable and stable communication system not only supports the information service needs of passengers,but also ensures the safe operation of high speed railway.As the basis of high-speed railway wireless communication system,channel model can not only reflect the characteristics of wireless channel in different scenarios along the high-speed railway,but also provide a simple and feasible basis for computer simulation,so that designers can simulate and evaluate the wireless communication system.Nowadays,wireless channel modeling for high-speed railway has become a hot research direction.As a common high-speed rail terrain,mountain scenes are widely distributed in the southwest and northwest of China.New high-speed railways in China,such as Guangzhou-Shenzhen railway and Chengdu-Guiyang passenger dedicated line,pass through vast mountainous areas.The characteristics of channel propagation environment in high-speed railway mountainous scenes are as follows: the propagation of radio wave needs to consider not only the line of sight(LoS)path between base station and train,but also the reflection path caused by trees,buildings along the railway and distant mountains;The location-based characteristics of channel parameters in mountain scenes are also very complex and obvious,which will change with the rapid movement of trains.According to the existing high-speed railway channel model and the particularity of high-speed railway mountainous environment,this thesis chooses and constructs a three-dimensional(3D)channel model based on Geometry Based Stochastic Model(GBSM).The main contents and research results of this thesis include:(1)Firstly,the wireless channel model of high-speed railway is studied.The signal measurement of high-speed railway is difficult.Although the existing ray-tracing model,channel model based on propagation graph and statistical model have high accuracy,they need a lot of measurement data and lack of universality.Therefore,this thesis chooses GBSM to model mountain scenes.Traditional 2D GBSM models assume that the radio waves of base stations only propagate from a single plane to mobile stations,which obviously does not correspond to the undulating mountain scenes.Therefore,this thesis constructs a 3D GBSM model for mountain scenes of high-speed railway: The spherical surface with the mobile station as the center of the sphere is used to simulate the local scatters such as trees and polesnear the train,and the elliptical cylinder with the focus of the base station and mobile station is used to simulate the remote scatters such as mountains.(2)In this thesis,the expression of Channel Impulse Response(CIR)is derived from the geometric positions of base stations,mobile stations and scatters.On this basis,the mathematical expressions of space-time correlation function(STCF),cross correlation function(CCF)and time autocorrelation function(ACF)of 3D channel model are derived.Considering the mobility of high-speed rail,this thesis deduces the time-varying expression of distance function,and further deduces the time-varying expression of K factor from the position change characteristics of K factor in mountain scenes.In order to better complete the simulation and comparison work,Von Mises Fisher(VMF)distribution is used to characterize the distribution of scatters in the theoretical model so as to take into account the influence of azimuth and elevation of scatters on channel statistical characteristics,and the discrete angle values in the simulation model are determined by equal volume method.(3)Finally,through theoretical analysis and simulation experiments,the correctness of the model and deduced formula is verified,and the influence of different factors on the space-time correlation characteristics of the channel are found.The simulation results show that compared with the 2D channel model,the 3D model can more accurately characterize the spatial diversity of radio waves.