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GROUND BASED AUGMENTATION SYSTEM Presentation Overview

GROUND BASED AUGMENTATION SYSTEM System Overview Christophe DEHAYNAIN Direction Générale de l’Aviation Civile FRANCE. GROUND BASED AUGMENTATION SYSTEM Presentation Overview. Why do we need an augmentation to GNSS ? Local Area Differential GNSS Principle GBAS Ground Segment

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GROUND BASED AUGMENTATION SYSTEM Presentation Overview

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  1. GROUND BASED AUGMENTATION SYSTEMSystem OverviewChristophe DEHAYNAIN Direction Générale de l’Aviation Civile FRANCE

  2. 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

  3. 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

  4. 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

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

  6. RX1 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

  7. REF USER LOCAL AREA DIFFERENTIAL PRINCIPLEII - Differential Correction Calculation Actual SV Position Broadcast SV Position • 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 Measured Pseudoranges Calculated Range Corrections Calculation Differential Message Broadcast Known Reference Location

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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)

  14. 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

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