Study On Wireless Channel Characteristics And Modeling In High-Speed Railway Environment

In recent years, with the rapid development of high speed railway (HSR), the demands of railway information construction have become more and more urgent. On the one hand, the train’s running status and the security monitoring and controlling information must be transferred to the ground station in real time to ensure a dynamic tracking of the train; on the other hand, the multimedia information involved with the passengers also needs a timely transmission. Moreover, the passenger mobile communication service is claiming a bigger and bigger share in the whole train-ground information transmission. The passenger mobile communication service mainly includes mobile phone, mobile TV, and mobile Internet broadband wireless access. Unfortunately, the existing railway mobile communication system not only cannot meet the needs of current passengers, but also cannot adapt to the development of the future HSR mobile communication system. Therefore, it is very necessary to study the broadband wireless access technology in the HSR environment. Channel modeling and analysis is the foundation of the design and implementation of a communication system, and an accurate channel model is the precondition for the HSR broadband wireless access technology research.The paper firstly introduces the propagation characteristics, the large-scale fading and small-scale fading, of the wireless channel. Also, the specificities of high speed railway channel modeling are summarized and analyzed. Secondly, the paper gives a brief introduction to MIMO (Multiple Input Multiple Output) channel model classification and the typical MIMO channel models. Then the principles of geometric-based channel modeling are given and discussed. Finally, the following two works are done based on the elliptical scattering model:(1) MIMO channel model based on elliptic scattering model:the paper gives a MIMO channel model based on single ellipse and single-bounced rays, the statistical characteristics, such as the space-time cross-correlation function, the temporal autocorrelation function, and the space cross-correlation function, of the model are deduced, simulated and discussed based on the complex impulse response of the channel model;(2) High speed railway MIMO channel model based on elliptic scattering model: the MIMO channel model based on elliptical scattering model is extended to the high speed railway environment by the introduction of time-varying reference frame. And similarly, the temporal autocorrelation function and space cross-correlation function of the model are re-deduced, simulated and analyzed based on the re-calculated complex impulse response. The simulation results indicate the non-stationarity of the HSR MIMO channels.There are mainly two innovations in this paper:(1) the relationship between the angle of departure (AOD) and angle of arrival (AOA) are discussed in the elliptical scattering model based MIMO channel model, and this makes the correlation functions of the model become functions of the angle of arrival, which greatly simplifies the whole model;(2) the introduction of time-varying reference frame in the high speed railway MIMO channel model more accurately characterizes the change of the distance between the moving train and the base station, and thus makes the model more attractive to be used when the train’s moving effects on the time-varying channel model has to be taken into account.