# Presentation: 145846

## Peter Gurník, Oldřich Trégl

- Satellite based train location

## Content

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

- CGSIC European meeting

- 14-15.3.2005

## 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

- 14-15.3.2005

## 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

- 14-15.3.2005

## 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

- 14-15.3.2005

## Content

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

- CGSIC European meeting

- 14-15.3.2005

## 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

- 14-15.3.2005

## 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

- 14-15.3.2005

## 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

- 14-15.3.2005

## Content

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

- CGSIC European meeting

- 14-15.3.2005

## 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 50**126** 	RAMS
- EN 50**129** 	Electronic systems for signalling
- EN 50**128** 	Software for railway control and protection 				system
- EN 50**159-2**	Safety related communication in open 				transmission systems

- CGSIC European meeting

- 14-15.3.2005

## 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

- 14-15.3.2005

## 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

- 14-15.3.2005

## 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 commercial GNSS receiver firmware!

- CGSIC European meeting

- 14-15.3.2005

## Content

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

- CGSIC European meeting

- 14-15.3.2005

## 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

- 14-15.3.2005

## 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

- 14-15.3.2005

## 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

- 14-15.3.2005

## Content

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

- CGSIC European meeting

- 14-15.3.2005

## 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

- CGSIC European meeting

- 14-15.3.2005

## Ing. Peter Gurník 
gurnik.peter@azd.cz

- gurnik.peter@azd.cz

- Ing. Oldřich Trégl
- tregl.oldrich@azd.cz