GNSS Implementation for Improved Train Location and Safety

1. Peter Gurník, Oldřich Trégl Satellite based train location

2. Content • Why want we use GNSS? • Possible hazards of using GNSS • Safety Requirements • GNSS implementation • Conclusion CGSIC European meeting

3. Why want we use GNSS? • Train location is key information for rail transport control • Track circuits – classical concept • Train position in line segment – low accuracy • Trackside wires are needed – not cost effective • Fixed block – low efficiency of using line • ATO is hardly applicable without additional technology CGSIC European meeting

4. Why want we use GNSS? • New concept – passive balise + odometry • Technology supported in ERTMS project - all corridor lines in Europe will be equipped with balises – future interoperability • Passive point device - no trackside wires are needed • High precise positioning – control centre has real-time information • Possibility of using moving blocks – higher density of train transportation CGSIC European meeting

5. Why want we use GNSS? • Balises vs. GNSS positioning • Some countries (Russia, Australia) refused to join in ERTMS project because of high cost • In average 2 balises per km are needed • Implementation of ERTMS in Europe could be faster if cheaper technology would exists • Virtual balise concept – integrating GNSS into ERTMS-ETCS could spare some balises on the track • We need to find a cheap solution for low density lines • Efficiency of control suburban lines is low • Safety could be improved • Poor equipped lines – mostly no track circuits • Information about train position - based on voice communication CGSIC European meeting

6. Content • Why we want to use GNSS? • Possible hazards of using GNSS • Safety Requirements • GNSS implementation • Conclusion CGSIC European meeting

7. Possible hazards of using GNSS • GNSS space segment • Faulty satellite can cause unboundary error of train position • GNSS control segment • TTA is not guaranteed • Examples from past • Faulty navigation message data – SVN 35, 1997 • Satellite clock error – PRN 22, 2001 CGSIC European meeting

8. Possible hazards of using GNSS • Transmission SIS • Low availability: canyons, tunnels, forests • High availability in stations is needed – poor visibility (urban area) • Multipaths – common in canyons and on the bridges upon the lakes / rivers (reflexive surface) • Atmospheric delays • Jamming – weak signal – easy to jam • Authenticity of message have to be proved CGSIC European meeting

9. Possible hazards of using GNSS • Using commercial GNSS receiver • Possible systematic error in HW/SW • Problematic determination of position • Iterative methods • Error could transfer to following fixes • Undetected error can expose for relative long period of time • Stability • Some algorithms are unstable in some cases • Digital filters • Based on statistical methods • Some errors could remain masked CGSIC European meeting

10. Content • Why we want to use GNSS? • Possible hazards of using GNSS • Safety Requirements • GNSS implementation • Conclusion CGSIC European meeting

11. Safety Requirements • Safety integrity • Ability of a safety-related system to achieve its required safety functions under all the stated conditions within a stated operational environment and within a stated period of time • SIL - a number which indicates the required degree of confidence that a system will meet its specified safety functions with respect to systematic failures • Standards • EN 50126 RAMS • EN 50129 Electronic systems for signalling • EN 50128 Software for railway control and protection system • EN 50159-2 Safety related communication in open transmission systems CGSIC European meeting

12. Safety Requirements • Single faults (EN50129) • “It is necessary to ensure that SIL 3 and SIL 4 systems remain safe in the event of any kind of single random hardware fault which is recognized as possible.” • Reactive fault-safety (EN50129) • “Maximum total time taken for detection + negation shall not exceed thespecified limit for the duration of a transient, potentially hazardous condition.” CGSIC European meeting

13. Safety Requirements • common-cause failures (EN50129) • “In systems containing more than one item whose simultaneous malfunction could be hazardous, independence between items is a mandatory preconditionfor safety” CGSIC European meeting

14. Safety Requirements • GNSS receiver firmware • By the EN 50128 is classified as “COTS software” • Requirements for COTS software: • “A strategy shallbe defined to detect failures of the COTSsoftware and to protect the system from these failures” • “Theprotection strategy shall be the subject of validation testing” • “As far as practicable only the simplest functions of the COTS software shall be used” • It’s very hard to accept information's from commercial GNSS receiver firmware! CGSIC European meeting

15. Content • Why we want to use GNSS? • Possible hazards of using GNSS • Safety Requirements • GNSS implementation • Conclusion CGSIC European meeting

16. GNSS implementation • Integrity Monitoring • Main goal is avoid using faulty satellites in position calculation • WAAS/SBAS • Integrity information from WAAS/SBAS will be transferred to train using radio channel – because of poor visibility of GEO in real terrain • LAAS • Local monitor station – stationary receiver with good visibility of satellites • Only positive confirmed satellites can be included to position calculation in mobile unit CGSIC European meeting

17. GNSS implementation • Odometry – why is useful? • To improve availability • In some areas (tunnels, canyons, forests) there are still low number of visible satellites – we cant guarantee the integrity or we are unable to compute position • To improve precision • In some areas an odometry CI is better then CI derived from GNSS data processing CGSIC European meeting

18. GNSS implementation • Accuracy • For resolution of parallel track – high accuracy is needed • High accuracy GNSS positioning method (D-GNSS), or • Using additional location-oriented devices in station • Balises CGSIC European meeting

19. Content • Why we want to use GNSS? • Possible hazards of using GNSS • Safety Requirements • GNSS implementation • Conclusion CGSIC European meeting

20. Conclusion • GNSS could be solution for low density lines • Technology for low-cost positioning is needed • Effort to improve safety • Future integration to ETCS • Concept of virtual balises • Non safety-critical applications • Conflict-avoiding systems • Information system for passengers and management • Real-time tracking oftrains CGSIC European meeting

21. Ing. Peter Gurník gurnik.peter@azd.cz Ing. Oldřich Trégl tregl.oldrich@azd.cz