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1
2nd Australian based CGSIC Meeting
Ground based Regional Augmentation System (GRAS)
Keith McPherson, Manager GNSS
2
GRAS Definition
A system providing GNSS augmentation service by which the user receives information directly from ground-based transmitters, allowing continuous reception of the service over a large geographical area (200Nm+). The ground components may be interconnected in a network
A system providing GNSS augmentation service by which the user receives information directly from ground-based transmitters, allowing continuous reception of the service over a large geographical area (200Nm+). The ground components may be interconnected in a network
3
Rationale behind GRAS• Availability of (D)GNSS is paramount for Air Traffic Management(ATM) development
• Impact on both Navigation, Surveillance and Communications
• Availability must be from gate-to-gate
• Minimum of new systems for CNS – cost efficiency
• Value added service to CNS/ATM – improved business cases
• Available for all user groups at reasonable costs
• High latitudes
• National and/or Regional sovereign control of the service delivery is vital
4
Aircraft GNSS integrity feed…
GNSS Receiver
GPS/GLONASS/GALILEO
Navigation datalink Communications datalink
GRAS ADS-B Service
5
Alternative Augmentation - GRAS
Key BenefitsKey Benefits
Enroute navigation over entire continent
Non-Precision ApproachesApproaches with vertical guidance (APV-II)
No single point of failure for whole system
Relatively inexpensive compared to US and European augmentation systems
Expected potential to further reduce current navigation aids
6
GRAS usage• En-route
• APV I/II CAT I
• Surface movement guidance
• ADS-B Surveillance
7
GRAS Concept
GPS Constellation
GRS GMSSatcom orTerrestrial
Links
Satcom orTerrestrial
LinksGVS
L
LL
VHF
Users
GRAS Master Station• processes GRS data• determines GPS
corrections & integrity status
• generates SBAS messages
GRAS Ref. Stn
• collects GPS meas. & data
• formats/sends data to GMS
GRAS VHF Stn•Receives & verifies SBAS messages
•converts to GBAS..format
•broadcasts GRASmessages at VHF
User Equip.•receives GPS
& GRAS data•computes SARPs-based nav solution
GPS Constellation
GRS GMSSatcom orTerrestrial
Links
Satcom orTerrestrial
Links
Satcom orTerrestrial
Links
Satcom orTerrestrial
LinksGVS
L
LL
VHF
Users
GRAS Master Station• processes GRS data• determines GPS
corrections & integrity status
• generates SBAS messages
GRAS Ref. Stn
• collects GPS meas. & data
• formats/sends data to GMS
GRAS VHF Stn•Receives & verifies SBAS messages
•converts to GBAS..format
•broadcasts GRASmessages at VHF
User Equip.•receives GPS
& GRAS data•computes SARPs-based nav solution
8
Technical concept
GRAS Data Link
Automatic GroundStation selection
GBASFormat
VHF Data Links
Terrestrial Data Link
LargeAirport
SmallAirport
9
• Ground Reference Stations– Broome– Carnavon– Perth– Darwin– Alice Springs
GRAS Schematic
• Master Control Stations– Brisbane & Melbourne
Data Lines
(Operational Concept)Not to Scale
VHF Transmitters– Using current VHF voice
transmission sites– Connected by data-line to Master
Control Station
– Ceduna– Thursday I– Mackay– Canberra– Hobart
10
VHF Sites Across Australia
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GRAS Architecture
Ground network
GRAS Broadcast
Interface to other systems, e.g. other GRAS stations or SBAS/EGNOS(external GRAS)
Remote service monitoring etc.
12
GRAS LATERAL ERROR POINT COOK APPROACH RWY 35
RUN 35
-30
-20
-10
0
10
20
30
10
9.6
9
9.3
7
9.0
3
8.6
8
8.3
4 8
7.6
5
7.3
6.9
5
6.5
9
6.2
4
5.8
9
5.5
4
5.1
8
4.8
2
4.4
6
4.0
9
3.7
2
3.3
6 3
2.6
5
2.3
1.9
4
1.6
1.2
6
0.9
3
0.6
0.2
8
NM TO THRESHOLD
ME
TR
ES
LATERAL ERROR
CAT 1 NSE LIMIT
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GRAS VERTICAL ERROR POINT COOK APPROACH RWY 35
RUN 35
-20
-15
-10
-5
0
5
10
15
20
10
9.6
9
9.3
7
9.0
3
8.6
8
8.3
4 8
7.6
5
7.3
6.9
5
6.5
9
6.2
4
5.8
9
5.5
4
5.1
8
4.8
2
4.4
6
4.0
9
3.7
2
3.3
6 3
2.6
5
2.3
1.9
4
1.6
1.2
6
0.9
3
0.6
0.2
8
NM TO THRESHOLD
ME
TR
ES
VERTICAL ERROR
CAT 1 NSE LIMIT
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VHF Cross-over Tests
Melbourne
Cooma
Sydney
HobartTasmania
New South Wales
Albury
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VHF Cross-over Interference (None so far)
Slots A & H Equal Power Level Slots A & B Equal Power Level
Slots A & B Closer to Cooma
16
20 August 2001
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10014074 10015074 10016074 10017074 10018074 10019074 10020074 10021074 10022074 10023074 10024074 10025074
dB
m Melbourne
Cooma
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GRAS
Navigation Surveillance
En-route through APV to Surface navigation
GNSS AUGMENTATION
ATC, aircraft and surface vehicles
18
GRAS in perspectiveSBAS
+ Wide Coverage- ComplexityInstitutional
GBAS+ Local(23Nm)
- Dedicated landingSystem
Expensive
ABAS+ Autonomous- High End A/C
GRAS+ Regional service
Step wise implementationAdded value service
- Line of sight
19
GRAS today
• Sent to ICAO for standardisation (GNSSP) uses GBAS message format with minor changes
• Solid manufacturing support
• RTCA and EUROCAE MOPS and MASPS to be completed
• Service identical to GBAS standard.
• GRAS supports PVT and is compatible to GNSSP PVT
• Need for broader understanding and inclusion in regional programs as an alternative, regional solution
20
ICAO Approval Status GRAS
• Concept presented to ICAO – Air Navigation Commission tasked GNSS Panel to
develop SARPs 1999– Australia (Airservices) selected to lead SARPs
development
• Standards and Recommended Practices (SARPs)– November 2000 - Concept of Operations developed– March 2001 - first draft of SARPs distributed– November 2001 - text mostly accepted by ICAO– October 2002 - final text agreed– 2002-2003 - validation process– April 2003 - approval sought from GNSS Panel
21
ANY QUESTIONS ??
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