Lu, D.; Wu, D.; Schnieder, E.:
Hazard Analysis for GNSS-based Train Localisation Unit with Model Based Approach According to EGNOS SoL and Railway RAMS.
IAIN 2012 - 14th International Association of Institutes of Navigation Congress 2012, Cairo, Egypt, Oktober 2012.
The European Geostationary Navigation Overlay Service (EGNOS) Safety of Life (SoL) requirements are mainly designed for safety related aviation applications. However with the development of Galileo, they will also be applied into railway safety related applications, for example railway train control systems. The EGNOS SoL specifications are described by accuracy, integrity, continuity and availability, meanwhile the railway standard EN50126 specifies system quality as reliability, availability, maintainability and safety (RAMS). To apply Global Navigation Satellite System (GNSS) in safety related applications of railway systems, the gap between GNSS quality specifications and railway system quality requirements should be bridged.
This paper provides a methodology for hazard analysis of the GNSS-based train localisation unit. The methodology is based on formal methods, and implemented on a localisation unit combined by a GNSS receiver and an eddy current sensor (ECS) including the diagnostic test. The hazard list for the localisation unit is generated based on the formal model of the unit. This model can represent the properties and characteristics of the localisation unit properly.
With the formal model, the hazard identification and analysis has been taken, the risk assessment is implemented. A simulation based test is also carried out in the CPN Tools, the simulation data comes from both the EGNOS SoL requirements and evaluation of real GNSS position series in the railway track. Along the railway track, the dynamic of accuracy is evaluated by means of stochastic process. With the risk assessment and simulation the safety integrity level of the localisation unit is allocated according to the safety requirements specification from EN50126.
The hazard analysis and the simulation both generate reasonable results for the risk assessment. After that, the transformation from EGNOS SoL requirements to railway RAMS has been successfully executed. The result of the methodology proves that the EGNOS SoL requirements can be transformed into railway standards properly. Thus the applications of GNSS-based localisation units for safety related applications in railway systems are eligible for safety certification.