Peter Gurník, Oldřich Trégl Satellite based train location

CGSIC European meeting Content  Why want we use GNSS?  Possible hazards of using GNSS  Safety Requirements  GNSS implementation  Conclusion

CGSIC European meeting 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 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 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 Content Why we want to use GNSS?  Possible hazards of using GNSS  Safety Requirements  GNSS implementation  Conclusion

CGSIC European meeting 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 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 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 Content Why we want to use GNSS? Possible hazards of using GNSS  Safety Requirements  GNSS implementation  Conclusion

CGSIC European meeting 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 RAMS  EN Electronic systems for signalling  EN Software for railway control and protection system  EN Safety related communication in open transmission systems

CGSIC European meeting 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 the specified limit for the duration of a transient, potentially hazardous condition.”

CGSIC European meeting 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 precondition for safety”

CGSIC European meeting Safety Requirements GNSS receiver firmware  By the EN is classified as “COTS software”  Requirements for COTS software: “A strategy shall be defined to detect failures of the COTS software and to protect the system from these failures” “The protection 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 Content Why we want to use GNSS? Possible hazards of using GNSS Safety Requirements  GNSS implementation  Conclusion

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

CGSIC European meeting 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 of trains

Thank you Ing. Peter Gurník Ing. Oldřich Trégl