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2nd Australian based CGSIC Meeting

Ground based Regional Augmentation System (GRAS)

Keith McPherson, Manager GNSS

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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

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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

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Aircraft GNSS integrity feed…

GNSS Receiver

GPS/GLONASS/GALILEO

Navigation datalink Communications datalink

GRAS ADS-B Service

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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

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GRAS usage• En-route

• APV I/II CAT I

• Surface movement guidance

• ADS-B Surveillance

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GRAS Concept

GPS Constellation

GRS GMSSatcom orTerrestrial

Links

Satcom orTerrestrial

Links GVS

LL

L

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

Links GVS

LL

L

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

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Technical concept

GRAS Data Link

Automatic GroundStation selection

GBASFormat

VHF Data Links

Terrestrial Data Link

LargeAirport

SmallAirport

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• 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

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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.

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GRAS LATERAL ERROR POINT COOK APPROACH RWY 35

RUN 35

-30

-20

-10

0

10

20

30

10

9.69

9.37

9.03

8.68

8.34 8

7.65 7.3

6.95

6.59

6.24

5.89

5.54

5.18

4.82

4.46

4.09

3.72

3.36 3

2.65 2.3

1.94 1.6

1.26

0.93 0.6

0.28

NM TO THRESHOLD

MET

RES

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

9.69

9.37

9.03

8.68

8.34 8

7.65 7.3

6.95

6.59

6.24

5.89

5.54

5.18

4.82

4.46

4.09

3.72

3.36 3

2.65 2.3

1.94 1.6

1.26

0.93 0.6

0.28

NM TO THRESHOLD

MET

RES

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

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20 August 2001

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

010014074 10015074 10016074 10017074 10018074 10019074 10020074 10021074 10022074 10023074 10024074 10025074

dBm Melbourne

Cooma

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GRAS

Navigation Surveillance

En-route through APV to Surface navigation

GNSS AUGMENTATION

ATC, aircraft and surface vehicles

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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

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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

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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

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ANY QUESTIONS ??

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