Abstract
The Galileo Safety of Life (SoL) - Level A service has been designed mainly to support aeronautical operations ranging from en-route up to approach with vertical guidance (APV II). This is why the Galileo SoL Service has been specified by means of quality criteria coming from ICAO‘s (International Civil Aviation Organization) Required Navigation Performance (RNP) concept, i.e., in terms of accuracy, integrity, continuity, and availability. However, Galileo SoL – Level A service is also intended for railway signalling which is based on a different safety philosophy. The objective of this paper is to describe links among the Galileo quality criteria and the quality attributes of railway signalling systems (RAMS), according to the CENELEC standards EN 50126, EN 50129 and EN IEC 61508. This paper provides a basic theory and methodology for the employment of the GNSS quality attributes for practical design, validation and verification of railway safety systems based on GNSS. It has been shown that, in spite of the different safety philosophies used in aviation and railway safety systems, the Galileo SoL – Level A service can be described by means of RAMS terminology according to railway standards.
Highlights
Quality of railway signalling systems is described by dependability attributes such as reliability, availability, maintainability and safety (RAMS)
Knowledge of the exact relationship between GNSS quality measures and railway RAMS is important for the design and verification of railway safety related systems
We have shown how to employ GNSS quality criteria according to railway RAMS
Summary
Quality of railway signalling systems is described by dependability attributes such as reliability, availability, maintainability and safety (RAMS). The situation becomes more complicated if a satellite navigation system is considered for railway signalling applications. The existing safety requirements for Signal-In-Space (SIS) of Global Navigation Satellite System (GNSS) were mainly driven by the needs of civil aviation. The aim of this paper is to provide a consistent background on which railway safety applications based on GNSS can be built. The work presented in this paper starts from the reliability of position determination and accuracy guarantee considerations. It is followed by a classification of GNSS failure modes that result from the GNSS quality measures definitions. The emphasis is focused on the significance of GNSS safety, and on the analysis of GNSS availability and its impacts, which is important for the feasibility assessment of future GNSS based railway safety applications
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