Däubler, L.; Becker, U.; Schnieder, E.:
Availability Analysis of Satellite-Based Train Localisation Systems.
WCRR Tagungsband, S. 224, 9/10 2003. World Congress on Railway Research WCRR 2003/ 28.9.-1.10.2003 Edinburgh.
Safe operation control in guided traffic requires high availability and reliability of train localisation technology. Normally the reliability/availability requirements for train localisation systems can only be met by complex multi-sensory systems comprising on-board and trackside components like odometers, axle counters, balises etc. Satellite-based localisation technology has in recent times been increasingly used in rail traffic applications, and GPS–based systems are already in operation. One of the most promising advantages for guided traffic is the fact that these systems provide absolute location information without requiring trackside equipment. However, satellite-based localisation requires the reception of signals from at least four satellites. But on many tracks, this visibility prerequisite cannot be fulfilled because of shadowing effects from railway embankments, buildings etc. This results in a considerable loss of localisation availability. At the Technical University of Braunschweig a method has therefore been developed within the "SATNAB" project, which allows satellite-based train localisation using the signals from a single or two visible satellites. If we suppose a vehicle is travelling on a known track, its position can be determined by processing the current range between one visible satellite and the vehicle. The range is measured by timing the signal delays between the satellite and the vehicle using a high precision atomic clock that is carried on the vehicle. This method was implemented and successfully tested in various experiments. Our paper gives an overview of the availability properties of satellite-based train localisation systems both in principle and in guided traffic applications. A new localisation method and its test results are also presented.