| With the advent of the era of intelligent high-speed railways that are safer,more reliable,and more efficient,the railway dedicated mobile communication system has become a crucial system to ensure the safe operation and intelligent operation of high-speed railways.There are three kinds of communication service requirements in the high-speed railway scenario:traffic related services,operation and maintenance related services,and passenger information services to realize the comprehensive perception and ubiquitous interconnection of people,machines and objects between the train and the ground.Different kinds of service requirements bring challenges to the design of dedicated mobile communication system.Mastering the characteristics of radio channel in high-speed mobile scenarios,establishing channel model that can accurately characterize radio channel,and implementing hardware-in-the-loop emulation of radio channel are the premises of physical layer and link layer key technology evaluation,engineering design and network optimization,and equipment high-speed adaptability evaluation for the dedicated mobile communication system.Although numerous researches have been conducted on radio channel measurement and modeling for high-speed railway,there are still following limitations:existing channel measurement methods have certain defficiency in the channel sounding signal design and detection mode selection;lack of Doppler measurement data for railway dedicated frequency,resulting in insufficient understanding of Doppler characteristics of high-speed railway scenario;it is also insufficient for channel measurement,parameter extraction,analysis and modeling in composite scenario composed of multiple single scenarios;the accuracy and consistency of the channel model in the hardware-in-the-loop emulation of high-speed railway dedicated mobile communication systems needs to be improved urgently.In order to solve above problems,this dissertation investigates radio channel measurement,modeling and emulation in high-speed railway scenario.The main contributions are as follows:1)Aiming at the shortcomings of existing composite scenario definition,radio channel measurement methods and platforms of high-speed railway,a definition method of radio propagation composite scenarios that correlates Geographic Information System(GIS)topography information with path loss exponent is proposed.The influence of different detection methods on channel measurement is discussed and a more suitable Root Mean Square(RMS)detection method for channel measurement of narrow-band and broadband mobile communication systems is proposed.A Gauss pulse shaping based channel sounding signal is designed and a narrow pulse radio channel sounding system is developed.The proposed measurement method and platform form the basis of channel measurement of high-speed railway.2)Aiming at the complex and time-varying Doppler characteristics of high-speed mobility scenario,a method of Doppler frequency shift measurement based on phase estimation is proposed,narrow-band channel measurement is conducted and the model of high-speed railway narrow-band Doppler shift is established.Multi-carrier based channel sounding signal is designed,and broadband channel measurement is carried out in the high-speed railway viaduct scenario.Doppler estimation is performed by autocorrelation function algorithm,and power delay profile,Doppler power spectrum and Doppler spread model are given.This research enriches the Doppler model of high-speed railway scenario,and form the basis of research and development of key technologies of Doppler suppression.3)To overcome the shortage of channel measurement and modeling research in high-speed railway composite scenario,the broadband channel measurement is carried out in the composite scenarios composed of tunnel,cutting and viaduct.The delay dispersion characteristics and the extraction and modeling methods of multipath parameters are studied.The path loss exponent,power delay profile and multipath tapped delay line model are established.The deterministic channel model is developed by using 3D ray tracing algorithm.The statistical characteristics of small scale fading and delay-Doppler domain in the composite scenario are obtained,and the identification method of transition regions for different scenarios is proposed,which is helpful to determine the characteristics of fast fading channel and delay dispersion.4)Aiming at the problem of model accuracy and consistency in radio channel emulation of high-speed railway,a basic protocol stack and an improved protocol stack for train-to-ground safe data transmission in packet domain are proposed.The requirement of radio channel emulation for high-speed railway dedicated mobile communication system is formed.The hardware-in-the-loop emulation platform for narrow-band and broadband radio channel of high-speed railway is designed.Based on the field channel measurement,parameters extraction and modeling in chapter 2 to chapter 4,the emulation methods such as path loss and shadow fading,small-scale fading,interference and noise are given.The measurement of quality of service is carried out to verify the accuracy of the emulation method and channel model.In summary,this dissertation investigates the channel measurement,modeling and channel emulation of high-speed railway scenarios,improves the measurement method and platform,extracts the key parameters of Doppler and delay dispersion characteristics in typical scenarios and composite scenario,and enriches the channel model in relevant scenarios.The channel model is applied to the hardware-in-the-loop emulation of high-speed railway dedicated mobile communication system,which compensates the deficiency of model accuracy in channel emulation. |
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