Research On Characteristics And Modeling Approaches Of Rapidly Time-varying Channels In High-Speed Train Scenarios

The railway is the main artery of the national economy,and it is also a new business card for China s foreign cooperation and an important area for the joint initiative of the"Belt and Road".By the end of 2018,China s railway operating mileage has reached 131,000 km.Among them,the high-speed railway has reached 29,000 km,accounting for more than 23 of the world's total mileage,and the cumulative number of passengers has exceeded 9 billion,which becomes the main channel for China s railway transporta-tion.The railway-dedicated mobile communication system is the key infrastructure of the high-speed railway,and it carries important services related to train driving safety,such as railway dispatching command,train operation control,and fault warning.In order to strengthen the high-speed green and efficient comparative advantages and achieve conve-nient and comfortable high-quality services,new railway mobile communication services are emerging,such as railway multimedia dispatching and commanding communications,train remote video surveillance,railway Internet of Things,and passenger entertainment services.Railway mobile communications has embarked on the evolution of the Glob-al System for Mobile Communications for Railway(GSM-R)to the next generation of the Long Term Evolution for Railway(LTE-R).For the development of smart railways,the 5th Generation Communications for Railway(5G-R)based on 5G communication technology has carried out research on basic theories and key technologies.Consider the issues that the difference of mobile communication systems and the di-versity of radio propagation environments for the high-speed train(HST),this dissertation is future railway services-oriented and key HST communication technologies-oriented,characternzed by high-mobility of HST.It studies the characteristics and modeling ap-proaches of rapidly time-varying channels in high-speed train scenarios,based on the theories such as radio wave propagation,modeling,probability,and stochastic process.The main contributions of the dissertation include:1)To characterize the multi-dimensional dynamic channel characteristics of HST sce-narios,the dissertation proposes a characteristic analysis method for rapidly time-varying channels.Using the wideband channel measurement data in typical HST scenario,it verifies the ray tracing(RT)simulator,and develop a high-performance channel simulation tool.The tool is suitable for the LTE-R mobile communication system to collect accurate and comprehensive channel information from HST scenar-ios,which solves the problem of HST channel data missing in the Doppler domain and the three-dimensional angle domain.Based on the RT simulated data,the dis-sertation proposes a quasi-stationary interval analysis method for HST time-varying channels in different scenarios to obtain the analysis window of reasonable statistical quantization channel characteristic parameters.It reveals the changing mechanism of the multi-dimensional characteristics of HST rapidly time-varying channels,to expound the relationship between the spatial distribution of multipath signals and scatterers,and extract the significant scatterers of different typical HST scenarios.2)To describe the general characteristics of radio propagation in HST scenario for LTE-R communication systems,the dissertation proposes a stochastic channel model for the multi-dimensional time-varying channel in three typical HST scenarios.In such scenarios,by using the measurement-validated RT simulator,the time-space-frequency statistical characteristic parameters of the channel are extracted to fill the tap-delay-line(TDL)model and the spatial correlation matrix,which effectively sim-ulates the multi-dimensional and general characteristics of the wireless channel in different typical HST scenarios.For the small-scale characteristics of taps,when the scatterers within the tap are with the sparse and clustered distribution,the long-delay multipath signals will be fast fading.The Weibull distribution is used to model such fading.The dissertation proposes an efficient 2×2 MIMO channel stochastic model for LTE-R comrmunication systems and establishes an LTE-R link-level simulation for channel implement to evaluate key technology in LTE-R reliable transmission.3)To describe the multipath distribution of the millimeter-wave channel and the fast-changing characteristics of the structure in the 5G-R HST scenarios,the dissertation proposes a dominant multipath modeling method of the millimeter-wave time-varying non-stationary channel in the HST urban scenario.Using HST millimeter-wave chan-nel measurement data,verifying RT simulator,constructing millimeter-wave multi-antenna,static and dynamic channel simulation tools suitable for HST typical envi-ronment and 5G-R mobile communication scenarios,solving data shortage problem in HST millimeter-wave dynamic channel.On measurement-validated RT basis,it reveals the law of dominant multipath variation in millimeter-wave HST urban time-varying channel.The dominant multipath is detected and tracked by the geometric factor that can reflect the position information of the scatterer,and the dynamic delay and Doppler of the channel are derived.The relationship between the Doppler shift and the variable geometry factor is proposed.The dominant multipath dynamic mod-el of the channel based on the mixed probability density distribution is proposed,and the accuracy of the model is verified,through which the mechanism of the dominant multipath in the fast-changing environment is accurately described.4)To obtain the real multi-dimensional and fine-grained channel information of the 5G-R HST scenarios,the dissertation proposes a dynamic modeling method based on the environmental pattern(EP)for the millimeter-wave channel of the HST urban scenario.Using the measurement-validated 5G-R channel simulation tool,it reveal-s the different propagation mechanisms of millimeter waves caused by significant scatterers in HST urban scenario and the distribution law of significant scatterers cor-responding to different propagation mechanisms,thus,establishing the EPR The EP simplifies the geometric modeling of dynamic channels.The geometrical and trans-fer functions of line-of-sight path,reflected multipath and scattered multipath signals are modeled in turn,and the frequency dependence of the channel is considered.A ultra wideband and directional dynamic channel model for HST millimeter-wave mo-bile communication systems is proposed,and its accuracy verification is presented.In addition,using the model,the time-varying characteristics of the channel delay domain and Doppler domain are analyzed.A guiding scheme for the time-frequency domain signal transmission of the 5G-R millimeter wave communication is proposed.