Research On Radio Channel Measurement And Multi-Link Modeling In Rail Traffic Scenarios

As an important part of global intelligent transportation system,rail traffic is widely acknowledged as the fundamental solution for the growth of economy and transportation.To meet the requirements of high safety,availability and comfort in rail traffic opera-tion,wireless communication system plays a significant role in realizing the vision of"Intelligent Travel".There are three kinds of wireless communication service require-ments in rail traffic scenarios:train control and scheduling,operation state monitoring and high-definition backhaul,and passenger information service experience.Different performance indicators generated by diversified service demands bring challenges to the design of rail traffic wireless communication system.Radio channel is the basis of a wireless communication system design.Accurate description of radio channel can provide theoretical support for key technology evalua-tion,system and link simulation,and network planning.Multi-link communication refers to multiple communication links that contain more than two communication nodes in a certain spatial range.Multi-link communication can be divided into multi-site and multi-user communication.Multi-link communication techniques can be used to reduce the frequency of cell switching,improve the efficiency of data transmission and increase the capacity of the channel in the wireless communication system of rail traffic.Therefore,it is necessary to study the radio channel measurement method and modeling theory appli-cable to multi-link communication system in rail traffic scenarios.This dissertation investigates channel measurement method and multi-link channel modeling in rail traffic scenarios to meet aforementioned service requirements.The main works are as follows:1)To measure the wireless channel in rail traffic scenarios,channel measurement method is investigated.The local mean power estimation of radio signal power in various rail traffic scenarios are studied,including the derivation of the upper and lower boundary of the sampling interval and the calculation of the sampling number.Based on multi-tone technique,a channel sounding signal is designed.A channel measurement system that fulfills the demand of parallel multi-antenna channel measurement is implemented on software radio defined platform.System calibration and verification are conducted by a wireless channel emulator.2)To characterize channel fading statistics in rail traffic non line-of-sight(NLOS)s-cenarios,channel measurement and modeling are investigated in a high speed railway NLOS scenario.Based on the multiple scattering radio propagation mechanism,the second-order scattering fading(SOSF)model is established.The "double Rayleigh" dis-tribution is introduced to describe the channel fading characteristics according to multi-path structure of the NLOS scenario.The SOSF model is parameterized and simulated by using the channel measurement data in a cutting environment where the impact of cross-ing bridge is included.Markov state transition probabilities between different fading dis-tributions are calculated,and the accuracy of the SOSF model is verified by measurement data.3)To describe the channel correlation property in rail traffic multi-site communica-tion scenarios,multi-site channel measurement and modeling are investigated in an inter-city railway viaduct scenario.A wideband multi-site channel measurement campaign is designed and conducted by using two base stations.Based on the measurement data from each link,the Large-Scale Parameters(LSPs)of the channel are extracted.Statistical distributions and correlation properties between different links and different LSPs are s-tudied and modeled.Based on the first-order two state Markov chain,multipath birth and death process of intercity railway time-varying channel is described,and tap correlation matrix is introduced based on tapped delay line structure,and a time variant multi-link channel model which can reflect the correlation of two base stations is established.4)To control spatial correlation in rail traffic multi-user communication scenarios,multi-user channel measurement and modeling are studied in an underground railway platform scenario.An extensive measurement campaign of multi-user channels with large antenna arrays is designed and conducted.Based on the measurements,spatial correlation channel parameters are characterized and fitted by an exponential function,and the factors that affect the spatial characteristics of multi-user channels are also discussed.A multi-user channel model for the large antenna array system is established by using the transmit correlation matrix and validated by comparing the measured data and channel simulation results.