High Integrity Two-tiers Augmentation Systems for Train Control Systems

This paper deals with high integrity systems based on a two-tiers Augmentation system architecture. The Augmentation System is based on a regional system and a local system. This work intends to define a Formal mathematical approach to improve the performance in terms of Integrity of a Local Area Augmentation and Integrity Monitoring Network. Such model is due to the stringent requirements in railways application that are described by SIL-4 (Integrity Risk < 10-9 during 1 hour). The Integrity Monitoring is performed on three different levels: Reference Station, Satellite, Constellation. For each of them the fault identification and exclusion algorithms are defined and analyzed. The novelty of this work is the integration of Local Area Augmentation Networks with single regional SBAS Systems in order to develop a 2-tiers High Accuracy and High Integrity Augmentation Systems able to reach the above Integrity requirements. At this aim the false alarm probability has been rigorously defined including 2-tiers Reference Stations fault probabilities. Simulation framework has been developed to assess both satellite and Reference Station faults and evaluate relevant 2-tier Augmentation Systems performances.