Improving Positioning Accuracy and Integrity in Rail Safety-Critical Applications Through the Integration of GNSS with a Track Data Base

Yuheng Zheng

Abstract:	Global Navigation Satellite Systems (GNSS) have attracted increasing attention around the world and they have been successfully applied in aviation, vehicle and marine applications. Accordingly, applying GNSS as the primary positioning system in the rail application is a promising research area. GNSS has high accuracy, but it also suffers from line-of-sight (LOS) problems. This is crucial in the railway environment, because trains run through areas where there is low satellite visibility. Additionally, for applications such as signalling, train location systems have high safety-of-life (SOL) requirements and receiver autonomous integrity monitoring (RAIM), which is essential to satisfy SOL requirements, is especially poor in standalone GNSS when satellite visibility is restricted. In the current study, a rigorous mathematical model for the integration of GNSS with a track data base is developed. A key feature of the model is its ability to model errors in both the GNSS observables and the track data base in order to achieve realistic performance statistics for the combined system. Clearly with a track data base railway positioning reduces, in principle, to a one dimensional positioning problem and the system only requires three satellites for RAIM and four satellites for fault detection and exclusion (FDE). It is shown that the integration system improves not only the accuracy and integrity performance but also the availability of RAIM on the ground. So, whilst not being able to completely compensate for the weaknesses of GNSS in the railway environment, the use of a track data base offers significant improvements.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	1456 - 1465
Cite this article:	Zheng, Yuheng, "Improving Positioning Accuracy and Integrity in Rail Safety-Critical Applications Through the Integration of GNSS with a Track Data Base," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 1456-1465.
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