Packet-level Channel Modeling Of High-speed Train-to-ground Communications

In recent years,high-speed railways have experienced rapid development.At the same time,the rise of new science and technology leads mankind into the era of intelligence which has also put forward new requirements for high-speed railways.The intelligent high-speed railway emerges as the times required and has aroused wide concern.The high-reliable transmission of broadband train-to-ground services is the basis for achieving emerging services such as automatic driving,real-time diagnosis of intelligent high-speed railways.However,the problems caused by high-speed mobility,complicated radio wave propagation scenarios,and insufficient spectrum resources have brought great challenges to the intelligent high-speed railway.Comprehensive understanding of the characteristics of channel changing and establishing the both efficient and accurate channel model are the prerequisites for meeting the above challenges.The physical channel models and the statistical analysis channel models are with high calculation complexity which are not able to track the channel dynamic changes quickly and adjust transmission schemes in time.The packet-level channel models have a good compromise between complexity and accuracy.However,related researches about packet-level channel models under high-speed railways are insufficient and they cannot describe accurately the rapid variations of high-speed channels in both time and frequency domain.Therefore,it is particularly important to establish the channel model to describe the characteristics of high-speed train-to-ground channels accurately and efficiently.The main research contents around the above requirements and scene characteristics are as follows:(1)The time-domain packet-level train-to-ground channel model is established based on the high-speed characteristics which comprehensively considers the effects of pathloss,shadowing,multipath fading in this dissertation.On the analysis and feature extraction of channel statistic characteristics,the Markov channel model based on the signal-to-noise ratio(SNR)of the composite fading channel is established.Also according to the variable changing theorem and the basic probability theorems,the mathematical expressions of the steady-state probability(SSP)and the state transition probability(STP)matrix of the Markov channel model are given.The proposed model is able to describe the cross-state transition of the rapidchanging channel under high-speed environment.The verification about the proposed channel model according to the measurement data is given.The research on the packet-level Markov channel model of high-speed time-varying channels is of great significance to reveal the influence of vehicle speed for high-speed channels.(2)According to the trend of high-speed railway communications and services,the frequency-domain packet-level channel model for multipath fading channel is established in this dissertation.For the broadband railway communication system,the statistical characteristics and frequency correlation model of the received signal SNR are established from the frequency domain.The methods for establishing the frequency-domain packet-level channel model are given.We derive the SSP and STP matrix which can calculate the transition probabilities between any Markov states to describe the characteristics of rapid changing of high-speed channel in frequency-domain.The comparisons and analyses between the measurement data and the proposed channel model are given.The research on the frequency-domain packet-level channel model is a powerful tool to reveal the characteristics of frequency-domain channel under high-speed train-to-ground communications.