Integrity of GNSS-based Train Positioning: From GNSS to sensor integration

Accurate and safe train position determination is of great importance for railway systems. Additionally, it has become one of the biggest challenges for the Safety-of-Life (SoL) services in railway transport systems using GNSS techniques. The critical performance requirements of these services promote the users to develop safe Train Positioning Systems (TPSs), in which integrity has to be highly concerned to real-timely monitor the quality of the TPS results. This paper presents a solution to the problem of integrity monitoring in GNSS-based train positioning with a global prospect. Different from the RAIM (Receiver Autonomous Integrity Monitoring) approach, a novel hierarchical architecture is proposed to expand the RAIM concept to the TPSAIM (Train Positioning System Autonomous Integrity Monitoring) domain, where integrity monitoring is closely correlated with both GNSS navigation computation at the local level and sensor integration at the global level. Integrity monitoring and fault detection with respect to the integration of GNSS and the Dead Reckoning (DR), which can be simply implemented with odometer and gyroscope, are investigated with different coupling structures. Results from simulations based on the field experiment illustrate characters of the proposed TPSAIM solution, and demonstrate its capabilities in terms of the effectiveness, coverage and flexibility with various TPS structures and operation conditions.