GNSS-based failsafe train positioning system for low-density traffic lines based on one- dimensional positioning algorithm

The paper describes the positioning principles, design, and results of the testing for the prototype train-borne positioning system developed within the framework of the LOCOLOC/LOCOPROL projects. The primary objective of both projects was to develop and demonstrate a complete very low-cost failsafe train positioning system based on GNSS. Existing three-dimensional satellite navigation systems cannot be used as a sole means of navigation because they do not satisfy the integrity level required for safety-critical railway applications. Our new railway-specific positioning algorithms can reach the required level of integrity because the required accuracy for Low-Density Traffic Lines (LDTLs) is quite low (a few hundred meters). These algorithms are based on the previous knowledge of the track, which makes the positioning problem one-dimensional: only along-track position is to be computed. This significantly increases availability and redundancy of GNSS satellites (e.g., even 4 satellites are enough to compute position in a safe manner) and hence the integrity of the solution increases to the level required for safety-critical operation (probability of a failure 10E-12/hour).