Formalized Modeling And Performance Analysis Of Railway Time Synchronization Network

Railway time synchronization network is an important part of railway communication network, including ground time synchronization network and train time synchronization network. In order to ensure the safety of train operation and the accuracy of fault location, the railway time synchronization network can provide unified standard time information for railway. At present, the railway time synchronization network has not been fully established yet, so the study about its performance has an important role for the network design, the time synchronization scheme selection and specification development. In this thesis, taking the railway time synchronization network as the research object, the formalized modeling and performance analysis are operated on the ground time synchronization network and train time synchronization network through the stochastic Petri net(SPN) and its simulation analysis tool(TimeNET software).Because of the railway communication system is featured with the characteristics of large coverage area and long communication line, the ground time synchronization network adopts network time protocol(NTP) for time synchronization. Network communication delay and malfunction’s randomicity have a large influence on timing accuracy of NTP. In this case, the formal modeling method SPN is chosen for its strong description ability to easily describe the randomness of the network time. TimeNET is the application software developed for SPN performance analysis, which can analyze the structural properties of the SPN model. So the method of a combination of SPN and TimeNET are chosen to analyze the ground time synchronization network. Firstly, the communication model of the ground time synchronization network is established by SPN, and the relationship between the performance indicators is calculated. Then, the TimeNET software is used to simulate the performance of the link. Finally, a reliability analysis was carried out on the equipment of the master clock which acts as the network reference timing source. According to the main failure factors which influence normal clock timing, the failover model of all levels is established as well as the reliability of master clock is analyzed. The analysis results showed that the ground time synchronization network performance can reach the actual performance requirements and the reference timing source posses high reliability.At present, there is no fixed time synchronization scheme for train time synchronization network. The requirement analysis was carried out for the time synchronization of the on-board signaling equipment when the train time synchronization network was analyzed. According to the requirements of equipment, communication of equipments and time reference sources, two types of train time synchronization schemes were put forward, which are the time synchronization scheme for cab integrated radio communication equipment(CIR) device information shared to other vehicle equipment, and the synchronization schemes for the on-board equipments using global positioning system(GPS) timing respectively. Proper synchronized success rate was analyzed by using SPN and TimeNET software according to these two schemes. Then the analysis of the two schemes was compared to put forward a reasonable time synchronization scheme. The analysis results showed that each on-board signaling equipment using GPS receiving module to receive time information and checking the time among the devices regularly can have a higher rate of properly synchronized.