Research On Key Technology Of Virtual Balise Based On GNSS

Balise is the main positioning device both in European Train Control System and Chinese Train Control System. In order to improve train positioning accuracy, massively developed balises will increase system construction and maintenance cost. Train control system is a safety-critical system, due to external factors such as the environment, the safety of the train operation can not be guaranteed caused by the failure of the balise for high-speed train. It has realistic significance to improve train position accuracy and the safety of the train operation.With the development of Global Navigation Satellite System (GNSS),the research about the train position with GNSS technology has been begun in some countries. For achieving interoperability with ETCS, the location subsystem must translate the positioning information given by the GNSS based locator unit to ETCS message specification. For this purpose the concept of virtual balise has been proposed by the UIC. A virtual balise is a software element that emulates the functionality of a single balise or a balise group via convenient processing of navigation data. The virtual balise sub-system is a modular structure. It has three modules: locator unit module, safety qualifier module, the virtual balise capture and messaging module. On the basis of analyzing VB system architecture and functional requirement, the virtual balise system framework is designed. This thesis includes the following two aspects.First, the virtual balise coding is realized. The virtual balise shall output a virtual balise telegram as specified in ETCS class 1 messages specification. Therefore, this thesis uses Eurobalise coding strategy to realize virtual balise coding. First of all, 830 user bits is got through user data table, then, virtual balise message coding is realized by using coding strategy.Second, this thesis presents a virtual balise capture radius setting method, and designs the virtual balise capture algorithms. Detailed mathematical algorithms are deduced in this thesis. A simulation has been carried out to verify the algorithms. The thesis analyses the relationship among the locator fix rate, the train speed, the capture ratio and the capture precision. Finally, the conclusion that defining the capture zone of a VB as a function of the static speed profile of the line can meet the requirement of the train is given. Also, an experiment has been carried out to verify the correctness of the conclusion of the simulation.