1. MAKING ASSIGNMENTS FOR THE GROUND BASED AUGMENTATION SYSTEM (GBAS) International Civil Aviation Organization Spectrum Seminar Nairobi, Kenya February 17-19, 2004

2. 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

3. 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

4. d Desired Station Undesired Station PuPu PdPd Edge of desired coverage volume Developing Geographical Separation Criteria Testing Determines required P d /P u for proper operation. Separate from the undesired station such that the required P d /P u is satisfied at the edge of the desired coverage volume Resultant distance d is the required geographical separation

5. Channel of undesired VDB in the same time slots Minimum required geographical separation for Tx U = 47 dBm km (NM) Co-channel339 (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

6. Channel of undesired GBAS VOR coverage radius 342 km (185 NM)300 km (162 NM)167 km (90 NM) Co-channel827 km (446 NM)785 km (424 NM)652 km (352 NM) | f Desired - f Undesired | = 25 kHz 805 km (435 NM) 763 km (412 NM) 630 km (340 NM) | f Desired - f Undesired | = 50 kHz 361 km (195 NM) 319 km (172 NM) 185 km (100 NM) | f Desired - f Undesired | = 75 kHz 348 km (188 NM) 306 km (165 NM) 172 km (93 NM) | f Desired - f Undesired | = 100 kHz No restriction No restriction No restriction Example GBAS/VOR Separation Distances