GROUND BASED AUGMENTATION SYSTEM Presentation Overview

CAR/SAM GNSS/ATN SeminarFrequency planning criteria Page 1

GROUND BASED AUGMENTATION SYSTEMFrequency Planning Criteria

Presentation GNSS 3.3 by Christophe DEHAYNAIN Direction Générale de l’Aviation Civile FRANCE

GROUND BASED AUGMENTATION SYSTEMFrequency Planning Criteria

Presentation GNSS 3.3 by Christophe DEHAYNAIN Direction Générale de l’Aviation Civile FRANCE


GROUND BASED AUGMENTATION SYSTEMPresentation Overview

GROUND BASED AUGMENTATION SYSTEMPresentation Overview

• GBAS principle• Why do we need frequency planning criteria ?• How the ICAO criteria have been established ? • What are the current criteria ? • What has still to be done ?

• GBAS principle• Why do we need frequency planning criteria ?• How the ICAO criteria have been established ? • What are the current criteria ? • What has still to be done ?


• The Ground Based Augmentation System is composed of 3 segments :– the space segment (GPS, GLONASS, GALILEO

satellites)– the ground segment (GBAS ground station)– the airborne segment (the users equipment)

GBAS principleGBAS principle


• Objective of the Data Link:– interface between the ground and the airborne

segments

• Type of transmitted information:– Pseudo Range Corrections (high rate)– Integrity parameters (,B values) (high rate)– Final Approach Segments description (low rate)

GBAS principleGBAS principle


ICAO GNSSP choice

• ICAO GNSS Panel validated in June 2000 the VHF D8PSK data Link among five considered options :– VHF Nav. 108-117.975 MHz

• D8PSK modulation• GFSK modulation

– DME UHF band (960-1215 MHz)– GPS L1 band (1575.42 MHz)– C band (5030-5150 MHz)


ICAO GNSSP choice

• VHF Navigation band (108-117.975 MHz) • 25 KHz channel spacing• horizontal polarisation (possibility to have

vertical also) • D8PSK modulation• 31.5Kbit/s rate• TDMA (Time Division Multiple access) : 8

slots per 0.5 s frame


Why do we need frequency planning criteria ?

• GBAS Data Link will use Navigation VHF Band frequencies (108 - 118 MHz)

• This frequency band is already used for VOR and ILS localizer assignations

• GBAS, ILS and VOR will coexist during a transition phase

• The three services need to be protected from mutual interference


How the ICAO criteria have been established ?

• Determination of minimum Desired/Undesired signal ratio at which VOR receiver is jammed by GBAS transmission on co- and adjacent channels (and vice- versus)

• Use of the GNSS SARPS to determine the minimum Desired/Undesired signal ratio at which GBAS is jammed by VOR or GBAS transmission on co- and adjacent channels

• Computation of minimum geographical distance between co- and adjacent VOR/GBAS and GBAS/GBAS channels transmitters


VOR/ILS receiver under test

VOR/ILS desired signals

VDB undesired signals

ILS/VOR indicator

Determination of minimum Desired/Undesired signal ratio at which VOR receiver is jammed by

GBAS transmission on co- and adjacent channels


VOR protected volume

GBAS protected volume

VOR GBAS

Minimum separation

Dvor

DGBAS

Dw

Dac

Computation of minimum geographical distance between co- and adjacent VOR/GBAS channels transmitters


Computation of minimum geographical distance between co- and adjacent

VOR/GBAS channels transmitters (2)

D Dac w

ERP D I Log Fdoc

1020 74 8

20

/ ( ) . )

Dac, Dw in kmFdoc in microvolts/meter


What are the current criteria for VOR to GBAS separation ?

FrequencyOffset(KHz)

AssumedD/U toprotect VORreceiver

Minimumseparation for a185 nm VORDoc

0 +26 446 NM

25 0 435 NM

50 -34 195 NM

75 -46 188 NM

100 -65 No restriction


What are the current criteria for GBAS to GBAS separation ?

FrequencyOffset(KHz)

Required D/U toprotect GBAS rcxfrom GBAStransmission

Minimum GBAS/GBASseparation for a +47 dBmGBAS EIRP

0 +26 183 NM

25 -18 42 NM

50 -43 24 NM

75 -46 24 NM

100 -46 No restriction


What has still to be done ?

• Compatibility criteria for – ILS Localizer and GBAS in the band 108 - 112 MHz have still to be

defined (ICAO objectives : 2004-2005)

– VHF AM Communications and GBAS have still to be defined (ICAO objectives : 2004-2005)

– VHF VDL Mode 4 and GBAS have still to be defined (ICAO objectives : 2004-2005)

• Compatibility criteria for elliptical polarised GBAS signals need to be defined (No ICAO plan)

• Before these criteria are defined, GBAS Data-link frequencies have to be assigned in a limited band (112.025 - 116.400 MHz)

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GROUND BASED AUGMENTATION SYSTEM Presentation Overview