GROUND BASED AUGMENTATION SYSTEM Frequency Planning Criteria Presentation GNSS 3.3 by Christophe DEHAYNAIN Direction G

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GROUND BASED AUGMENTATION SYSTEMFrequency
Planning CriteriaPresentation GNSS 3.3 by
Christophe DEHAYNAIN Direction Générale de
lAviation Civile FRANCE
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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 ?

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GBAS principle

• 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)

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GBAS 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)

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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)

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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

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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

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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

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Determination of minimum Desired/Undesired signal
ratio at which VOR receiver is jammed by GBAS
transmission on co- and adjacent channels
VOR/ILS desired signals
VOR/ILS receiver under test
ILS/VOR indicator
VDB undesired signals
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Computation of minimum geographical distance
between co- and adjacent VOR/GBAS channels
transmitters
Dw
VOR protected volume
GBAS protected volume
Dvor
DGBAS
GBAS
VOR
Dac
Minimum separation
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Computation of minimum geographical distance
between co- and adjacent VOR/GBAS channels
transmitters (2)
Dac, Dw in km Fdoc in microvolts/meter
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What are the current criteria for VOR to GBAS
separation ?
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What are the current criteria for GBAS to GBAS
separation ?
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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)