GNSS Enables a BaliseFree Railway

1
GNSS Enables a Balise-Free Railway

• Demetri James
• Lockheed Martin
• 8 February 2005

2
Introduction

• ERTMS/ETCS uses balises to obtain position fixes
  and to coordinate message exchanges
• Significant effort required to deploy and
  maintain balises on the ground, and balise
  readers on trains
• European commitment to GNSS enables
  implementation of ERTMS/ETCS without balises
• This paper addresses the concept of GNSS and
  virtual balises to implement a balise-free,
  ERTMS/ETCS compliant railway

European Rail Traffic Management System/
European Train Control System
3
The Legacy

• Signalling and train control systems provide safe
  operation of trains on network
• Simple systems may limit performance
• Complex systems increase cost and limit
  interoperability
• Historical reliance on trackside equipment due to
  inherent land-based operation, stringent safety
  requirements, and available technology
• Marine navigation and control had/has higher
  reliance on vehicle-based technology
• Accuracy and integrity available from GNSS
  enables inertially-aided satellite-based
  positioning to transition from trackside to
  trainborne paradigm

4
ERTMS/ETCS Levels
Level 1

• ERTMS/ETCS has 3 levels of operation
• Level 1 is overlay to underlying signalling
  system with movement authorities passed to train
  by balises
• Level 2 is overlay to underlying signalling
  system with movement authorities passed to train
  via GSM-R with balises providing position
  references
• Level 3 is independent radio-based signalling
  system but retains balises for position reference

Level 2
Level 3
5
Virtual Balise Concept

• Rather than install balises at their designed
  locations, store their location and message
  content in a virtual balise database (VBDB)
• Replaces need to install balise and maintain
  accurate knowledge of its location with simply
  maintaining knowledge of its designed location
• Provide the VBDB to the train and respond to the
  balise associated message when the balise is
  traversed as determined by trainborne GNSS
  position information
• Retain location referencing to balises to
  minimise impact on ERTMS specifications
• Concept applicable to Level 2 and 3
  implementations

6
Train Location Determination

• Train location determination is fundamentally
  different with satellite-based positioning
• Unbounded growth in train location error with
  ERTMS/ETCS odometry function

• Radar doppler velocity integrated to compute
  distance travelled from Last Relevant Balise
  Group (LRBG)
• Bounded Train Location error with GNSS-based
  odometry function
• Allows reduction in number of balises

7
Train Integrity and Train Detection

• Accurate on-board Train Location, and on-board
  Train Integrity, enables on-board Train Detection
• Eliminates need for track circuits or axle
  counters
• GNSS data alone cannot meet Train Detection
  requirements
• GNSS occlusions
• Absolute track discrimination
• Along track accuracy requirement
• Points detection
• GNSS performance enhancement possible with
• Gyroscope and accelerometers
• Map matching
• GNSS-based odometry can replace doppler radar
  velocimeter

8
Inertially-Aided Satellite-Based Positioning
Position Accuracy (metres)
GPSDGPSTachometer AccelerometerGyro Track
Database
GPS Only
GPSDGPS
GPSDGPSTachometer
9
Balise Messages

• 32 possible packets in balise messages
• 22 via radio or balise transmission
• 10 are balise only packets
• 6 of 10 for Level 1 only
• 2 of 10 no longer required
• Equivalent means to accommodate 2 of 10 balise
  only packets could be achieved by radio
  transmission
• 132 Danger for Shunting Information
• 137 Stop if in Staff Responsible Mode
• Use of switchable balises must be avoided

10
Train Awakening

• On cold start, ERTMS/ETCS train operates in Staff
  Responsible mode until balise is traversed and
  initial location is confirmed
• GNSS may not be sufficiently accurate/available
  to confirm initial position
• Confirmation by inertially-aided GNSS Location
  Determination System possible once set of points
  has been traversed, or specific track signature
  identified
• Covered station areas can be supplemented with
  GNSS pseudolites

11
Interoperability

• Interoperability issues will arise unless
  ERTMS/ETCS Specifications are supplemented to
  admit satellite-based positioning

Notes 1- Yes, if fixed balises are installed as
required to support Standard ERTMS train, or a
portable Balise-Free ERTMS system is placed on
ERTMS equipped train transiting network area 2-
Yes, if required additional data preloaded or
supplied from RBC
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Specification Supplements
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Benefits

• Reduced lineside infrastructure costs
• No balises or reduced number of balises
• Elimination of lineside train detection
• Elimination of lineside signalling
• Fewer possessions required for upgrades
• Reduced train fitment costs and time
• No undercarriage balise readers or doppler radars
• Facilitates migration plan across network

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Benefits (cont.)

• Reduced power requirement
• No need to illuminate balises
• Higher operating efficiencies
• Network Management
• Moving block operation
• Enhanced functionality
• Trainborne level crossing activation
• Railway worker protection

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Summary

• GNSS presents an opportunity to shift the train
  signalling and control paradigm from trackside to
  trainborne system capability
• Support for position referencing infrastructure
  transferred from railway to GNSS provider
• Significant performance and cost benefits
  available from switching to GNSS-based
  positioning
• Supplements to ERTMS/ETCS required or
  interoperability issues may arise
• Supplements appear to be easily achieved,
  however, detailed, exhaustive analysis necessary
  to validate modifications

16
Lockheed MartinLocation Determination System
17
Lockheed Martin Location Determination System

• Continuously Provides train position in lieu of
  track circuits or balises
• Uses GPS and differential GPS
• Uses gyro and accelerometers
• Uses track database and patented data fusion
  algorithms
• Extensive diversity and self checking for system
  vitality
• Performance Accuracy
• Demonstrated position lt 3 meters
• Velocity lt 0.8 kph
• Autonomous Track Discrimination
• Open Interfaces

Sensor Interface
DGPS
80586 Processor
Communications
18
LDS Rail Testing

• Tests conducted at Transportation Technology
  Center, Inc.
• Tested at speeds of 2 mph to 107 mph
• Along track accuracy tests
• Position lt 3 meters, 99 confidence level
• Velocity lt 0.8 kph, 99 confidence level
• Directional tests
• 100 correctly determined train direction
• 100 correctly determined movement conditions
• 100 correctly determined stopped conditions
• Track discrimination tests
• 100 turn out detection