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Applications of Global Navigation Satellite System (GNSS) in Railways are becoming more and more frequent. So far, the focus has been on non-safety related applications, such as passenger information systems and freight logistics,
which are typically also not standardised.

When moving GNSS applications into the domain of safety, such as for train control systems, a much better understanding of GNSS behaviour is needed. This is especially true for standardised applications, such as within the European
Railway Traffic Management System (ERTMS), where the performance and behaviour of GNSS receivers and other components of a GNSS solution will have to be harmonised to achieve standardised, guaranteed performance and thus
interoperability between on-board units of different suppliers, similar to GNSS based landings in aviation.

Many research projects have already investigated the use of GNSS in safety critical railway applications, such as GALOROI, GRAIL, NGTC, ERSAT to just name a few. These projects had varying goals, from building a simple demonstrator
to defining possible architectures. None of them has however attempted to qualify the railway environment regarding impacts on the GNSS performance. For that reason, the STARS project (Satellite Technology for Advanced
Railway Signalling) was proposed to GSA, the European GNSS Agency. The STARS consortium included the major European signalling manufacturers, space industry and research centres. This paper describes the project objectives,
the setup and the results of that project.