GROUND BASED AUGMENTATION SYSTEM System Overview Christophe DEHAYNAIN Direction Gnrale de lAviation

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GROUND BASED AUGMENTATION SYSTEMSystem
OverviewChristophe DEHAYNAIN Direction Générale
de lAviation Civile FRANCE
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GROUND BASED AUGMENTATION SYSTEMPresentation
Overview

• Why do we need an augmentation to GNSS ?
• Local Area Differential GNSS Principle
• GBAS Ground Segment
• GBAS Airborne Segment
• Conclusions

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GBAS ConceptSystem Overview

• ICAO Name GBAS for Ground Based Augmentation
  System
• Operational Coverage
• minimum same as ILS
• recommended Omni directional (radius 23 NM) up
  to FL 100 and down to 12 ft
• Data-Link Frequency range 108 - 118 MHz (25 kHz
  spacing)
• Operational objective
• minimum Category 1 approach
• optional 2 D navigation (Positioning Service)
• Localisation Airport

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GBAS OverviewDo not mistake GBAS for

• DGPS, LADGPS initial US generic names for GBAS
  concept
• SCAT1 or Special Category 1 US RTCA standard
  defining a non-interoperable system for private
  use
• LAAS Local Area Augmentation System present
  US name for GBAS

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WHY GNSS NEEDS AN AUGMENTATION ?
GPS Only
Civil Aviation
ACCURACY (95)
H. 13 m
V. 23 m
V 4.0 m
H 16.0 m
AVAILABILITY
99.75
99 (RAIM)
3,5.10-7/ approach Time to alarm 6 s
INTEGRITY
?
10-4 / approach (10-5 / 15 s)
CONTINUITY OF SERVICE
?
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LOCAL AREA DIFFERENTIAL PRINCIPLEI - Basic
Principle

• Measurements made by two receivers are affected
  by the same errors as long as these two receivers
  are not too far from each other

RX2
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LOCAL AREA DIFFERENTIAL PRINCIPLEII -
Differential Correction Calculation
Actual SV Position
Broadcast SV Position
Measured Pseudoranges
Calculated Range
Corrections Calculation
Differential Message Broadcast
Known Reference Location

• The first receiver in a reference station can
  calculate these errors knowing its exact location
  (corrections calculated by the GBAS ground
  station)
• The second receiver (the user) will use these
  corrections to correct its own measurements and
  increase the accuracy of these measurements

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GBAS ground segmentI - Basic architecture of a
reference station
Differential Message Broadcast Antenna
GPS/GLONASS Antennas
Receiving Unit (up to 4 Reference Receivers)
Data Broadcast Unit
Data processing for broadcast
Raw Data PR, ephem.,time
Data Processing Unit

• Differential Corrections Calculation
• Integrity Monitoring Functions
• GBAS Messages Elaboration

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GBAS ground segmentII - VHF Data Broadcast (VDB)

• GBAS VDB characteristics
• VHF NAV band (108 - 118 MHz), channel spacing 25
  kHz
• D8PSK (Differential 8 States Phase Shift Keying)
  modulation
• 2 Hz update rate (Pseudorange Corrections)
• 8 slots Time Division Multiple Access technique
  (16 per second)
• Horizontal Polarisation or Elliptical
  Polarisation (Recommendation)
• 50W ground transmitter power (Typically power for
  HPOL)
• Omni-directional antenna
• Coverage 23 NM radius

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GBAS ground segmentIII - VDB message content

• The current SARPS require the transmission of
  three message types
• Differential Code Corrections and integrity Data
• Reference Point and GBAS Data
• Final Approach Path description

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GBAS ground segmentIV - GBAS Ground System
Classification

• The global performances of Ground System are
  linked to
• the Number of installed GNSS receivers (2 to 4)
• The quality of the GNSS signal reception
• A Ground Accuracy Designator (GAD) will qualified
  the ground segment

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GBAS User segmentI-Basic operations

• GBAS will be basically used as an ILS (ILS
  Look-alike concept)
• RNAV 2D operations may be developed if the Ground
  System support the Positioning Service

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GBAS User segmentII-Airborne Equipment

• Multi-mode Receivers (MMR) and their associated
  GPS and VHF antennas will be used for GBAS
  approaches
• No hardware update is foreseen (Software only)

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Conclusions

• The GBAS system as standardised in ICAO Annex 10
  is able to serve Cat-I operations. Advanced
  operations such as Cat-II/III or A-SMGCS are
  under consideration by ICAO GNSS Panel
• GBAS ground stations
• are being built,
• are considered in several implementation
  programmes in the World
• GBAS airborne equipment
• are being developed within Multi-Mode Receiver
• are considered in several aircraft manufacturer
  programmes
• Standards Status
• ICAO Standards (SARPS) are available
• Other Standards (Doc 4444, Doc 8071, PANS OPS)
  are being finalised
• Industry Standards (MOPS) are being developed and
  will be soon available