CAR/SAM GNSS/ATN SeminarFrequency planning criteriaPage 1 GROUND BASED AUGMENTATION SYSTEM Frequency Planning Criteria Presentation GNSS 3.3 by Christophe DEHAYNAIN Direction Générale de l’Aviation Civile FRANCE

CAR/SAM GNSS/ATN SeminarFrequency planning criteriaPage 2 GROUND BASED AUGMENTATION SYSTEM Presentation 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 ?

CAR/SAM GNSS/ATN SeminarFrequency planning criteriaPage 3 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 principle

CAR/SAM GNSS/ATN SeminarFrequency planning criteriaPage 4 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 principle

CAR/SAM GNSS/ATN SeminarFrequency planning criteriaPage 5 ICAO GNSSP choice ICAO GNSS Panel validated in June 2000 the VHF D8PSK data Link among five considered options : –VHF Nav MHz D8PSK modulation GFSK modulation –DME UHF band ( MHz) –GPS L1 band ( MHz) –C band ( MHz)

CAR/SAM GNSS/ATN SeminarFrequency planning criteriaPage 6 ICAO GNSSP choice VHF Navigation band ( 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

CAR/SAM GNSS/ATN SeminarFrequency planning criteriaPage 7 Why do we need frequency planning criteria ? GBAS Data Link will use Navigation VHF Band frequencies ( 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

CAR/SAM GNSS/ATN SeminarFrequency planning criteriaPage 8 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

CAR/SAM GNSS/ATN SeminarFrequency planning criteriaPage 9 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

CAR/SAM GNSS/ATN SeminarFrequency planning criteriaPage 10 VOR protected volume GBAS protected volume VOR GBAS Minimum separation D vor D GBAS Dw Dac Computation of minimum geographical distance between co- and adjacent VOR/GBAS channels transmitters

CAR/SAM GNSS/ATN SeminarFrequency planning criteriaPage 11 Computation of minimum geographical distance between co- and adjacent VOR/GBAS channels transmitters (2) Dac, Dw in km Fdoc in microvolts/meter

CAR/SAM GNSS/ATN SeminarFrequency planning criteriaPage 12 What are the current criteria for VOR to GBAS separation ?

CAR/SAM GNSS/ATN SeminarFrequency planning criteriaPage 13 What are the current criteria for GBAS to GBAS separation ?

CAR/SAM GNSS/ATN SeminarFrequency planning criteriaPage 14 What has still to be done ? Compatibility criteria for –ILS Localizer and GBAS in the band MHz have still to be defined (ICAO objectives : ) –VHF AM Communications and GBAS have still to be defined (ICAO objectives : ) –VHF VDL Mode 4 and GBAS have still to be defined (ICAO objectives : ) 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 ( MHz)