CORDIS

Applications GNSS in Railways are become more and more frequent. The moving GNSS application 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 the use of GNSS in standardised applications, such as the European Railway Traffic Management System (ERTMS), where performance of GNSS receivers must be harmonised to achieve standardised, guaranteed performance and thus interoperability between on-board units of different suppliers. The addition of GNSS could significantly increase the market appeal of ERTMS, as it will provide economical and operational benefits especially for secondary and low density lines.
The application of GNSS in ERTMS can be compared with the application of GNSS in the aviation domain, where accuracy, availability and especially safety are also the key requirements. Considering the background and expertise acquired in the provision of GNSS safety of life services in civil aviation, STARS project reuses a similar approach. Additional challenges in railway applications are however significant, the environment which makes reception of GNSS signals more difficult. Examples are the shading of satellites by building or mountains, multi-path effects due to signal reflections on buildings and electromagnetic interference from railway vehicles themselves as well as from nearby transmitters and other interferers.
The main objective of the STARS project is to fill the gap between ERTMS needs for safety critical applications and GNSS services, through a characterisation of the railway environment and of GNSS performances assessment in that environment. Possibilities and benefits of using EGNOS will also be investigated and documented.

The project is constituted of 3 successive phases: the elaboration of reference data and characterisation of the railway environment through a measurement campaign, the assessment of the GNSS performances achievable in this environment as well as the possible evolutions of European GNSS services and ERTMS/ETCS functions and the analyses of the economic benefits and possible implementation roadmap.

For the Phase 1: Measurement campaign, in the second period the project has
• Installed the measurement equipment on trains in the three countries and obtained the necessary approvals
• Performed a lot of measurements and significant amounts of high quality GNSS raw data collected.
• Produce Ground Truth data for the test trips, to be used as reference for performance analysis.
• Pre-Processed the collected data as well as Ground Truth to uniform formats in a semi- automated data processing.
• Storage of collected data in standardized file naming and in a harmonized structure to the jointly used cloud storage for analysis.
For the Phase 2: EGNSS Performances assessment, safety requirements and impacts on existing systems, the project has:
• Produced the guidelines for data pre-process and sorting, to allow an efficient analysis of large volumes of data.
• Analysed the recorded data using a variety of techniques.
• Qualified and quantified the environmental influences on GNSS has been qualified and quantified.
• GNSS performance degradation has been correlated to the presence of environmental influences, which can be used to predict GNSS performance
• Analysed local effects which significantly degrade performance, covering urban and mountainous environments and forests.
• shown that current receiver algorithms need to be improved to cope with the railway environment, as the true error is not always bound by the protection level algorithm.
• Analysed the performance of EGNOS in the railway environment and shown that using EGNOS from geostationary satellites is not practical.
• Produced a proposal for the evolution of EGNOS for railway applications which overcomes the limitations identified.
For the Phase 3: Economic Benefits and roadmap, the project has:
• Developed a model to analyse cost – benefit for individual applications, which can be applied for individual analysis with customer and application specific cost and benefit figures.
• Performed a cost benefit analysis showing that a positive Benefit/Cost ratio can be achieved in local and regional lines, but is challenging in mainline applications.
• The sensitivity analysis has shown that the cost of the additional on-board module and the saved balises dominate over the cost of maintaining balises, meaning CAPEX dominate over OPEX.

As summary, the STARS project has shown that there is potential in applying GNSS for safety critical applications in the railway environment. Due to significant impact of local effects on performance resulting from the challenging environment a solution with sensor fusion, and possibly map matching will however be required. Critical will be the generation of initial position fixes at start-up, as local effects are more significant in stations and the impact is more significant at standstill. EGNOS will have to distributed to trains via radio, as the reception from geostationary satellite is severely limited by the environment, with large areas of complete unavailability.
It has been shown that the concept of a MOPS similar to the one in aviation is not suitable for the railway environment, as:
• GNSS is not a continuously working system in the railway environment, but only works intermittently.
• Current algorithms for the calculation of the protection level generated wrong results.
• Local effects cannot be embraced by a simple MOPS, unless worst case values are used across entire lines, which degrades the achievable performance dramatically.

The cost – benefit needs to be analysed, using detailed figu

The project is providing the following advances in technology compared to the current state of the art in railway signalling:

· The application of GNSS services will reduce the need for Eurobalises for train position determination, with potential economic benefit of decreasing the installation / operational costs as well as increasing the availability of the system.
· The project is introducing GNSS in safety critical applications to the more challenging railway environment, especially in regard to GNSS signal reception;
· The project will provide the necessary inputs to demonstrate the suitability of using GNSS in safety critical application in the railway environment and will make GNSS performance predictable for all types of foreseen applications;
· The project is following the working approach based on the open specifications and apply where possible the already existing standards from rail as well aviation sector;