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Note.— If the authorized transmitter power is higher than 150 W, the –105 dBc may not protect reception of emissions in
a s
3.6.3 DATA STRUCTURE
3.6.3.
3. ast timing structure. The time division multiple access (TDMA) timing structure shall be based
on frames and time slots. Each frame shall b re shall be 2 such frames contained in each
1-second UTC epoch. The first of these frames shall start at the beginning of the UTC epoch and the second frame shall start
0.5 seconds after the beginning of the UTC epoch. The frame shall be on multipl t it shall consist of 8
individual time slots (A to H) of 62.5-millisecond duration.
3.6.3.1.2 Bu ime slot shall contain at most 1 burst. To initiate the use of time slot, the GBAS shall
broadcast a burst i frames. ime slot in use, the ground subsystem shall
broadcast a burst i of every 5 consecutive frames.
Note 1.— Bursts messages and may be of var th up to the max m allowed within the slot
as required by 3.6.3.2
Note 2.— During n, the airborne receiver may not receive the first 4 bursts
3.6.3.1.3 Timing b
3.6.3.1.3.1 Each burst shall be contained in a 62.5-millisecond time slot.
3.6.2.6 Emissions in unassign er over a 25 kH
ndwidth, centred on the assigned frequency over any un not exc
lot assigned to another desired transmitter for receivers within 200 metres from the undesired transmitting antenna.
1 TRANSMITTER TIMING
6.3.1.1 Data broadc
e 500 milliseconds in duration. The
time divisi exed such tha
rsts. Each assigned t a
n that time slot in each of 5 consecutive For each t
n at least 1 frame
contain one or more iable leng imu
.
time slot initiatio .
udget for bursts
APP B-77 23/11/06
Annex 10 — Aeronautical Communications Volume I
3.6.3.1.3.2 The beginning of the burst shall occur 95.2 microseconds after the beginning of the time slot with a
ols).
Note.— The transmitter power stabilization period may be used by the aircraft receiver to settle its automatic gain
3.6.3.1.5 Ramp-down. After the final information symbol is transmitted in an assigned time slot, the transmitter output
power level shall decrease to at least 30 dB below the steady-state power within 285.7 microseconds (3 symbols).
3.6.3.2 Burst organization and coding. Each burst shall consist of the data elements shown in Table B-60. Encoding of
e messages shall follow the sequence: application data formatting, training sequence forward error correction (FEC)
generation, application FEC gene ation lin
3.6.3.2.1 Synchronization and a bi sol on d am ty resolution field shall consist of
the 48-bit sequence shown below, with the h ost bit tran t:
010 001 111 1 0 001 1 0 00 11 010 000
Event
Nominal percentage
of steady-state power
tolerance of ±95.2 microseconds.
3.6.3.1.3.3 For GBAS/E equipment, the start of the synchronization and ambiguity resolution portion of the burst,
transmitted with horizontal polarization (HPOL), shall occur within 10 microseconds of the start of the burst transmitted with
vertical polarization (VPOL).
Note.— Table B-59 illustrates the burst timing.
3.6.3.1.4 Ramp-up and transmitter power stabilization. The transmitter shall ramp up to 90 per cent of the steady-state
power level within 190.5 microseconds after the beginning of the burst (2 symbols). The transmitter shall stabilize at the
steady-state power within 476.2 microseconds after the beginning of the burst (5 symb
control.
th
r and bit scramb g.
m guity re ution. The synchr ization an bigui
rig tm smitted firs
101 111 1 100 011 101 0 0 011 0
Table B-59. Burst timing
Nominal event duration
Ramp-up 190.5 μs 0% to 90%
Tran 90% to 100%
S s 100%
Transmission of scrambled data 58 761.9 μs 100%
Ramp-down 285.7 μs (Note 1) 100% to 0%
Notes.—
1. Event duration indicated for transmission of scrambled data is for maximum application data length of 1 776 bits, 2 fill bits and nominal symbo
smitter power stabilization 285.7 μs
ynchronization and ambiguity resolution 1 523.8 μ
l
duration.
2. These timing requirements provide a propagation guard time of 1 259 microseconds, allowing for a one-way propagation range of approximately
370 km (200 NM).
3. Where bursts from a GBAS broadcast antenna can be received at a range more than 370 km (200 NM) greater than the range from another
broadcast antenna using the next adjacent slot, a longer guard time is required to avoid loss of both bursts. To provide a longer guard time, it is
necessary to limit the application data length of the first burst to 1 744 bits. This allows a difference in propagation ranges of up to 692 km
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