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GNSS DevelopmentStatus and Future Work
Eric Chatre, EC/ESA Rapporteur Technical WG, GNSS Panel
Agenda Item 6
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Outline
• GNSS Elements
• GNSS Performance Requirements– Definition of parameters
– Relationship betweens parameters
• Integrity Principles
• GNSS Standards
• Future Work
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GNSS Elements
GPS GLONASS
Core Constellations
Augmentations
ABAS
SBAS
GBAS
IOR
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Aircraft-Based Augmentation System (ABAS)
• Stand-alone technique implemented in user equipment/software
• No accuracy improvement, lateral guidance only
• Provides integrity based on consistency check• Needs redundant satellite measurements (5
or more satellites in view with good geometry)• Integrity only• Performance and availability limited to some
phases of flight
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Satellite-Based Augmentation System (SBAS)
• Objectives –Improve accuracy of GPS or GLONASS by
providing corrections for • Satellite errors : clock and ephemeris • Ionospheric errors : model over a geographic area
–Provide integrity information–Lateral and vertical guidance–Improved availability,
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Satellite-Based Augmentation System (SBAS) (cont.)
• Architecture– Network of stations covering a wide area (e.g.
continent)– Transmission of information to users through
geostationary satellites
• Coverage and Service areas– Coverage : Wherever the geostationary
signals are received– Service : Wherever operations have been
approved by States
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SBAS Architecture
Reference Reference StationsStations
Master StationMaster Station
Uplink Uplink StationStation
GEOGEO
GPSGPS
SBASSBASMessageMessage
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Ground-Based Augmentation System (GBAS)
• Objectives –Improve accuracy of GPS or GLONASS
by providing for each satellite a composite correction
• Satellite errors : clock, ephemeris correction valid locally
• Ionospheric errors : local correction• Tropospheric errors : local correction
–Provide integrity information
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Ground-Based Augmentation System (GBAS)(cont.)
• Architecture– Ground Reference Station (typically 1 per
airport) – Transmission of information to users through
a VHF data link (108 to 118 MHz)
• Coverage – Approach area (ILS like coverage)– Terminal area (positioning service)
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GBAS Architecture
GPS and/or GLONASS, GEOs
User
Reference station and VDB
VHF DATA LINK
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Aviation Performance Requirements for GNSS (signal-in-space)
Phase of
Flight
Accuracy
(95%)
Integrity Risk Continuity Risk
Availability
En Route H: 3.7 Km
1x10-7/h 1x10-4/h to 1x10-8/h
0.99 to 0.99999
Terminal H: 0.74 Km
NPA H: 220 m
APV I H: 16 m
V: 20 m
2x10-7/App 8x10-6/ 15sAPV II H: 16 m
V: 8m
Cat I H: 16 m
V: 6 to 4 m
Cat II/III
Surface Ops
Under Development
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Interpretation of parameters
Accuracy : Characterize typical behavior of the system in presence of nominal error components
Integrity : Limit risk of abnormal behaviour of the system due to errors resulting from system failures
-Integrity Risk-Alert Limit-Time to Alert
Continuity : Limit risk of losing the service unexpectedly
Availability : Accuracy + Integrity [+ Continuity]
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Relationship between parameters
Integrity
Accuracy
Continuity
Availability
•Availabilty
-Vertical accuracy/integrity is usually the main driver
-Decreases as accuracy increases
-Decreases as alert limit gets smaller
•GNSS performance is variable :- in time- in space
-New approach to ensure integrity for all users
-Protection Level concept
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Integrity principles
Alert Limit
Computed Position
User Computed Protection Level
Protection Level > Alert Limit Alert
Protection Level < Alert Limit No Alert
Probability 1-1.10-7
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GNSS Standards, Procedures, Guidance Material
• Standards and Recommended Practices (ICAO Annex 10, Vol I)
• GNSS NOTAMS and Phraseology (ICAO Annex 15, PANS-ABC Doc 8400, PANS- ATM Doc 4444)
• Procedure Design Criteria (PANS-OPS, Doc 8168)• Geodetic Reference Datum and Data Base Requirements
(ICAO Annexes 4,11,14 &15, WGS-84 Manual Doc 9674) • Information and guidance on implementation (GNSS Manual)• Industry Standards (RTCA and EUROCAE MOPS/MASPS)
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Industry Standards
• The main actors are :– RTCA in the US, Special Committee 159– EUROCAE in Europe, Working Group 28
• The Documents – Minimum Operational Performance Specifications (MOPS)– Minimum Aviation System Performance Standards (MASPS)
• Existing Standards– ABAS/Basic GNSS receiver : DO-208 / ED-72 / (J)TSO-C129A– SBAS receiver : DO-229 C / TSO-145A/146A– GBAS Cat I receiver : DO-253A– Multi-Mode Receiver including GBAS : ED-88A
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Future Work
• Evolution of currently standardized GNSS elements• GPS modernization with additional civil signal on L5
frequency (1176.45 MHz)• GLONASS modernization (GLONASS K) with additional
civil signal in the 1164-1215 MHz band• Extention of SBAS standards to accomodate new
signals• Extention of GBAS standards to accomodate new
signals and cover Category II/III and surface operations
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Future Work (cont.)
• New GNSS elements• GALILEO system with 3 civil signals and a
dedicated integrity service• Ground-Based Regional Augmentation System
(GRAS)