The Effects of Railway Track Database Quality on the Performance of Tightly Coupled GNSS/Track Database Train Positioning System

Y. Zheng, P. Cross, M. Quddus

Abstract:	A review of literature suggests that GNSS technology such as GPS has been widely utilised for non-safety critical rail applications such as locating trains for realtime passenger information. Recent studies have also indicated that GNSS has a great potential to support the navigation modules of Safety-of-life (SOL) critical rail services. In order to perform locating tasks effectively and accurately, GPS requires at least four visible satellites at a particular place and time to calculate the position of a train and five visible satellites to monitor integrity in terms of alarm limit, time-to-alarm and integrity risk. However, it is known that GNSS suffers from line-of-sight problems, especially in the low satellite visibility environments such as deep cuttings, forests, urban canyons and tunnels. It is, therefore, difficult to achieve the required accuracy and integrity within such operational environments by using a stand-alone GPS,. This is not acceptable for SOL critical railway applications, suggesting that GPS should be aided with spatial rail network data and/or other sensors such as inertial navigation systems (INS). Since a train travels to a known-destination with a pre-defined route, spatial rail network data on its own have the potential not only to determine the physical location of a train but also to improve the required positioning accuracy, integrity and availability. The primary object of this paper is to test and to assess a tightly coupled GNSS and railway track data system for the railway applications. One of the key features of this system is its ability to take into account uncertainties in both GPS observables and spatial rail network data. Since trains travel in pre-defined fixed routes, 3-D positioning estimate (i.e., estimate of x, y, z coordinates) becomes a 1- D positioning (i.e., estimate of only x, or y or z coordinate) problem, to estimate the position of the train along the track. Spatial railway track database is then used to estimate the other two coordinates. In this way, the accuracy of the railway track database is crucial for the integration system. Unfortunately, the necessary accuracy of railway track database has not been revealed. In this paper, the different accuracies of track database are tested. Based on the result, the necessary accuracy of track database is suggested in this paper.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	2146 - 2155
Cite this article:	Zheng, Y., Cross, P., Quddus, M., "The Effects of Railway Track Database Quality on the Performance of Tightly Coupled GNSS/Track Database Train Positioning System," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 2146-2155.
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