MAKING ASSIGNMENTS FOR THE GROUND BASED

AUGMENTATION SYSTEM (GBAS)

International Civil Aviation OrganizationSpectrum Seminar

Nairobi, KenyaFebruary 17-19, 2004

GBAS Basics

• Carrier frequency: 108.025 to 117.950 MHz. • Channel spacing: 25 kHz.• Each frequency includes 8 assignable timeslots

– Nominally 2 slots used per GBAS

– Therefore multiple GBAS can share same frequency

• Broadcast range ~ 20 nm, omnidirectional– One GBAS station may serve multiple close-proximity

airports if coverage can be maintained

• More detail in Annex 10, Volume 1, 3.7.3.5

Channel Assignment Criteria

• GBAS/ILS and GBAS/VHF Comm criteria under development– Until completed, only use band 112.050-117.900 MHz

• GBAS/VOR and GBAS/GBAS criteria specified in Annex 10, Volume 1, Attachment D, 7.2.1

d

Desired Station

Undesired Station

PuPd

Edge of desired coverage volume

Developing Geographical Separation Criteria

• Testing Determines required Pd/Pu for proper operation.

• Separate from the undesired station such that the required Pd/Pu is satisfied at the edge of the desired coverage volume

Resultant distance d is the required geographical separation

 

Channel of undesired VDB in the same time

slots 

Minimum required geographical separation for TxU = 47 dBm

km (NM)

Co-channel 339 (183)

1st adjacent channel (±25 kHz)

78 (42)

2nd adjacent channel (±50 kHz)

44 (24)

3rd adjacent channel (±75 kHz)

44 (24)

4th adjacent channel (±100 kHz)

No restriction

 

Note. No geographic transmitter restrictions are expected between co-frequency, adjacent time slots provided the undesired VDB transmitting antenna is located at least 200 m from areas where the desired signal is at minimum field strength. 

Typical GBAS/GBAS Separation Criteria

Channel of undesired GBAS

VOR coverage radius

342 km (185 NM) 300 km (162 NM) 167 km (90 NM)

Co-channel 827 km (446 NM) 785 km (424 NM) 652 km (352 NM)

| fDesired -

fUndesired |

= 25 kHz

 805 km (435 NM)

 763 km (412 NM)

 630 km (340 NM)

| fDesired -

fUndesired |

= 50 kHz

 361 km (195 NM)

 319 km (172 NM)

 185 km (100 NM)

 

| fDesired -

fUndesired |

= 75 kHz

 348 km (188 NM)

 306 km (165 NM)

 172 km (93 NM)

 

| fDesired -

fUndesired |

= 100 kHz

 No restriction

 No restriction

 No restriction

Example GBAS/VOR Separation Distances