Peter Gurnk, Oldrich Trgl

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Peter Gurník, Oldrich Trégl

• Satellite based train location

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Content

• Why want we use GNSS?
• Possible hazards of using GNSS
• Safety Requirements
• GNSS implementation
• Conclusion

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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

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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

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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

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Content

• Why we want to use GNSS?
• Possible hazards of using GNSS
• Safety Requirements
• GNSS implementation
• Conclusion

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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

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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

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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

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Content

• Why we want to use GNSS?
• Possible hazards of using GNSS
• Safety Requirements
• GNSS implementation
• Conclusion

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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

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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.

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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

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Safety Requirements

• GNSS receiver firmware
• By the EN 50128 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
• Its very hard to accept information's from
  commercial GNSS receiver firmware!

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Content

• Why we want to use GNSS?
• Possible hazards of using GNSS
• Safety Requirements
• GNSS implementation
• Conclusion

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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

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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

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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

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Content

• Why we want to use GNSS?
• Possible hazards of using GNSS
• Safety Requirements
• GNSS implementation
• Conclusion

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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

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• Ing. Peter Gurník
• gurnik.peter_at_azd.cz

Ing. Oldrich Trégl tregl.oldrich_at_azd.cz