GNSS introduction in the rail sector

GRAIL will introduce GNSS technology in the railway domain for different applications in Europe. Technology developments following different paths has prevented the use of a common approach, which would allow interoperability of the technical solutions at different system levels in similar applications, and the reusability of products for different applications. The project proposes a strategy, consistent with the current deployment process of ERTMS/ETCS in Europe, for a smooth integration of GNSS into control and command applications and particularly in signalling.

During the last few years, several projects funded both by ESA and the EC have been studying and demonstrating the use of GNSS for safety-related applications in railways, especially the ERTMS/ETCS application. In the framework of the GADEROS project a workshop was organised by the GJU to bring together representatives from these projects (GADEROS, INTEGRAIL, RUNE and LOCOLOC/LOCOPROL) with the EC, ESA, ERTMS users group and the GJU. During the review of the findings of those projects, it was detected that although they do not follow the same approach the conclusions reached were similar. These projects have proved the feasibility of introducing GNSS in railways and in particular ETCS by means of theoretical studies and demonstrations:

• Safety analysis on these concepts has already been performed (however, not yet as formal safety cases) and the results are positive;
• Some system prototypes have already been developed by the industry; - Both railway signalling and GNSS industry have provided good co-operation towards a common interest.

Several different functional and technical concepts have been presented by these projects but they can be mainly summarised as follows:

1. GNSS system as odometry: GNSS-based location is used as a substitute or complement of the current odometry sensors (tachometers, INS, Doppler radar, etc.). Thus it can remain internal to the ETCS.
2. GNSS for the fixed balise marker: The GNSS system is used to provide the ETCS onboard system with a message equivalent to that provided to a fixed balise in the track for a position marker.

The technical approach being followed to fulfil the first objective is:

1. Determining the user requirements for this application: functional, performance, RAM and safety requirements.
2. Achieving a full specification for the user terminal (including system, GNSS receiver, interface and test specifications) to be integrated in ETCS equipment.
3. Carrying out a safety analysis of the GNSS odometer module for ETCS, based on the user terminal specifications and taking into account the boundaries imposed by the ETCS system, as the target application.
4. Building a prototype of the user terminal. Two different prototypes will be developed to cover the objectives of the testing activities:
   • One lab prototype will demonstrate, in a simulated environment, the capabilities of Galileo by means of a Galileo simulator.
   • One HW/SW prototype will be integrated in an ETCS onboard system in a train cabin, using an EGNOS signal and other sensors.
5. Testing these prototypes in order to demonstrate the fulfilment of the user requirements. The scope of the tests are:
   • Laboratory tests (integration and functional laboratory tests) will be carried out at the CEDEX premises. It is worth mentioning that a simulated GNSS environment is being developed in the GARDA project and will be adapted for this project.
   • On-site tests will be carried out on a high-speed line in Spain with a train provided by ADIF. The approach for the second project objective will be similar, aimed at advanced applications like Absolute Positioning and Train Awakening, but testing will only be done in simulated environments. The results of this process will be used to draw conclusions about how the enhanced performances or the new odometry system can be used to improve the operation of trains or to reduce the equipment installed in the tracks. Also, comparison between the use of EGNOS and Galileo for this application will be made.

Objectives

This project proposes a strategy, consistent with the current deployment process of ERTMS/ETCS in Europe, to provide a smooth integration of GNSS into control and command applications, particularly in ERTMS/ETCS. The GRAIL project will be based on three main objectives:

1. To specify, develop and test a GNSS prototype system for enhanced odometry, ready to be integrated in ETCS onboard systems;
2. To pave the way for the future introduction of more ambitious approaches at different levels of ERTMS/ETCS architecture;
3. To complete the perspective of safety-related applications with the study and demonstration of non-safety applications and the study of economical and legal issues.