| BeiDou Navigation Satellite System (BDS), as a navigation system of our country’s independent research and development, has been paid more and more attention and application. The train positioning technology based on BDS has also a continuous development for its low cost, convenient maintenance, less trackside equipment and so on. In the train positioning system which regards the satellite navigation system as the main way, the system should have the ability to send alerts to users when unavailable in addition to providing the necessary positioning service, which is called the integrity monitoring function. Receiver Autonomous Integrity Monitoring (RAIM) is widely used as an integrity monitoring method because it needs no external equipment and has a quick response.This thesis researches the integrity of BDS based on the application need in train positioning system, discusses the RAIM prediction and satellite fault detection methods, and develops a set of RAIM system for the railway, so as to ensure the reliability of the positioning system. The main contents are as follows:(1) The pseudo-range positioning principle and relative concepts of BDS is elaborated, and the method process is designed with the Receiver Independent Exchange (RINEX) format data, and the relevant standards are discussed to provide foundation for the research in RAIM.(2) On one hand, there exists a problem of RAIM coverage holes, because the number of satellites in view is insufficient or the geometric structure of the navigation satellites is unsatisfactory. So the Horizontal Protection Level (HPL) method is adopted and designed. Considering the heading angle, a method called Along Track Protection Level (ATPL) is defined, and the availability of the whole railway line is predicted so that the result is more practical; On the other hand, in the train operating process, there can be all kinds of interferences outside that may lead to errors of pseudo-range measurement of satellites that are the soft faults. Sometimes the satellite itself can fail to cause the hard faults in BDS (a low probability), which lead to serious deviations of the positioning results of the train. So distance residual vector obtained from the measurement error is examined with the chi-square test method to detect and exclude the satellite faults.(3) A set of RAIM system software applied to the train positioning system is developed with C# and a detailed deployment of its each function module is made. Apart from the above, the RAIM methods are simulated and validated in Matlab with the laboratory data and field data.Through the study of the above, the results show that:the methods discussed can effectively predict the availability of RAIM, the satellite faults can be detected and excluded accurately, and the developed software system designed is able to realize the function of RAIM prediction and RAIM analysis, which provides reference for the research on the integrity of BDS for train positioning. |
