peter gurník, oldřich trégl satellite based train location
TRANSCRIPT
Peter Gurník, Oldřich Trégl
Satellite based train location
CGSIC European meeting 214-15.3.2005
Content
Why want we use GNSS?Why want we use GNSS? Possible hazards of using GNSS Safety Requirements GNSS implementation Conclusion
CGSIC European meeting 314-15.3.2005
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 414-15.3.2005
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 514-15.3.2005
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 614-15.3.2005
Content
Why we want to use GNSS?
Possible hazards of using GNSSPossible hazards of using GNSS Safety Requirements GNSS implementation Conclusion
CGSIC European meeting 714-15.3.2005
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 814-15.3.2005
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 914-15.3.2005
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 1014-15.3.2005
Content
Why we want to use GNSS? Possible hazards of using GNSS
Safety RequirementsSafety Requirements GNSS implementation Conclusion
CGSIC European meeting 1114-15.3.2005
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 1214-15.3.2005
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 1314-15.3.2005
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 1414-15.3.2005
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”
It’s very hard to accept information's from It’s very hard to accept information's from commercial GNSS receiver firmware!commercial GNSS receiver firmware!
CGSIC European meeting 1514-15.3.2005
Content
Why we want to use GNSS? Possible hazards of using GNSS Safety Requirements
GNSS implementationGNSS implementation Conclusion
CGSIC European meeting 1614-15.3.2005
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 1714-15.3.2005
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 1814-15.3.2005
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 1914-15.3.2005
Content
Why we want to use GNSS? Possible hazards of using GNSS Safety Requirements GNSS implementation
ConclusionConclusion
CGSIC European meeting 2014-15.3.2005
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
