| Railway mobile communication technology is an important means to ensure the safe production of railway transportation.In recent years,with the development of intelligent railways,as a comprehensive product of V2V(Vehicle-to-Vehicle)communication and cooperative communication,T2T(Train-to-Train)communication technology has ushered in new development opportunities.This kind of train self-organization direct communication method that takes the train as the core and minimizes trackside equipment as the goal without the participation of base station.On the one hand,it can be used for train collision protection,on the other hand,it can assist train control systems based on the train-ground wireless communication network.Due to the difference between the surrounding environment of train operation and the traditional cellular network communication scenario,the signal reflection of scatterers distributed in different scenarios and the relative movement state between trains seriously affect the Doppler expansion and multipath delay expansion of the wireless channel between trains,and the requirements for using the corresponding frequency bands in different scenarios are not obvious.In addition,according to the degree of multipath influence,the scene is divided into tunnels and outside tunnels,in which application conditions of mitigating multipath fading technology are not clear.Although the T2 T communication simulation experiment is successfully verified,it still needs to carry out channel analysis and mitigating multipath fading technology research.The main contents of the thesis are as follows:Firstly,based on the theory of radio wave propagation in the Fresnel zone,the geometric relationship between the first Fresnel zone and the tunnel as well as that between the first Fresnel zone and cutting scenarios is analyzed respectively.T2 T communication working frequency band allocation scheme is improved,which realize the multi-band communication requirements.At the same time,the influence of rainfall on the propagation of high-frequency radio waves is specially considered,and the large-scale path loss is calculated,which is the basis for predicting radio wave propagation characteristics and model simulation experiments.Secondly,by analyzing the influence mechanism of factors such as train operation status,radio wave propagation environment and antenna on the T2 T wireless channel is analyzed.according to the relative running speed of the tracking train,the maximum Doppler frequency shift value under line-of-sight conditions is calculated.The ray tracing method is used to simulate multipath waves,a deterministic model of a rectangular double-line tunnel is established,and the model is extended to non-rectangular tunnels.This thesis can more accurately predict the propagation characteristics of radio waves,and obtain the multipath characteristics under a certain number of reflections,and serve for the selection of mitigating multipath fading models parameters.Finally,by using MIMO(Multiple Input Multiple Output)-OFDM(Orthogonal Frequency Division Multiplexing)technology to solve the problem of multipath fading.By analyzing channel space correlation calculation and capacity analysis,the transceiver antenna combination,coding scheme and channel estimation scheme of the transceiver system are selected,and a T2 T communication transmission model based on MIMO-OFDM is established.By analyzing the communication error rate of two trains in the tunnel and outside the tunnel without mobile relay,and the communication error rate of one train in the tunnel with the other train outside the tunnel after joining the mobile relay.After analyzing the communication error rate of two trains in the tunnel and outside the tunnel without mobile relaying,and the communication error rate of one train in the tunnel with the other train outside the tunnel after joining the mobile relaying,we conclude that adding a relay can increase the communication distance and improve the error performance of T2 T communication. |
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