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the originating aircraft and the destination GES,
n SUs - from 2 to 31 standard length signal units of 96
bits each, and
Flush - a field of 16 bits (all 0s) to flush out the
convolutional encoder.
4.4.5.2.2.1 8.4 kbirs/s C cha~melT. he postamble of the C
channel shall consist of alternating "1"s and "0"s
(commencing with "1") on the I channel and the Q channel.
The length of the 8.4 kbits/s C channel postamble shall be
equivalent lo 104 bits.
4.4.5.2.2.2 All other C channels. The postamble of all
other C channels shall consist of continuous "0"s on the I
channel, and alternating "0" and "1" (commencing with "0")
on the Q channel. The length of the postamble shall be
equivalent to a single interleaver block for channels with
interleaving, and 96 bits for channels without interleaving.
The information field shall be scrambled, coded and
interleaved, in that order.
4.4.4.3.4.1 Scrambling. The Standard in 4.4.2.2.5.1 shall
apply, except that the scrambler shall be re-inilialized at the
beginning of the information field of each burst.
4.4.4.3.4.2 Forward error correction (FEC) coding. The
Standard in 4.4.5.3.3.5.2 shall apply, except that the
convolutional encoder shall be initialized to the all 0s slate at
the beginning of the information field of each burst.
4.4.4.3.4.3 Interleaving. All T channels shall employ
block interleaving. The number of rows in the interleaver shall
be 64 transmission bits, while the number of columns shall
depend on the data rate as shown in Table 4-13. At the
transmitter the output of the convolutional encoder shall be
written into the 64-bit columns, until the specified number of
columns are full. The interlewer row interchange algorithm
shall be in accordance with 4.4.2.2.5.3.
4.4.5.2.3.1 8.4 kbitsh C channel. The C channel shall
operate in burst mode in the to-aircraft direction. In tlus mode,
the C channel shall consist of a series of contiguous frames
followed by a postamble. Each frame shall consist of two
fields: the unique word and the information field as in Figure
4-9 his. Each frame shall be 500 ms long.
4.4.5.2.3.2 All other C channels. All other C channels
shall operate in burst mode in the to-aircraft direction. In this
mode, the C channel burst shall consist of a preamble followed
by a series of contiguous frames followed by a postamble.
Each frame shall consist .of three fields: the unique word, a
dummy field and the information field, as in Figures 4-9 and
4-10. Each frame shall be 500 ms long.
4.4.4.4 Performance. The Standard in 4.4.2.3 shall apply.
4.4.5 C channel
4.4.5.1 Channel rare accuracy. The channel rate error
shall not exceed one part in 2R, where R is the channel rate,
and one part in lo4.
4.4.5.2 ~ N S M I $ $ I O NFO RMATS
4.4.5.2.1 Preamble. The burst preamble for all the C
channel rates, except the 8.4 kbitds channel, shall consist of an
unrnodulated carrier portion followed by a modulated portion.
The length of these shall depend on the channel rate as shown
in Table 4-14 as applicablc to the system capability levels
defined in 4.1.3. The preamble shall be as described in the text
4.4.5.2.4.1 8.4 kbits/s C channel. The C channel shall
operate in continuous mode in the from-aircraft direction. In
this mode, the C channel shall consist of two fields: the unique
word and the information field as in Figure 4-9 bis. Each
frame shall be 500 ms long.
4.4.5.2.4.2 All other C channels. All &her C channels
shall operate in continuous mode in the from-aircraft direction.
Each transmission shall begin with the preamble described in
4.4.5.2.1. In this mode, the C channel frame shall consist of
three tields: the unique word, a dummy field and the
information field as in Figures 4-9 and 4-10. Each frame shall
be 500 ms long.
Note.- In the R and T charznels the informatiorz field
refers to the information bits after forward error correction
coding. With the C channel the infomtion field may or mnay
not include coding depending upon the particular C channel
w e -
Y11IOO
No. 75
Annex 10 - Aeronautical Te2ecomnaunications Volume IIl -
4.4.5.3 FWE FORMAT
4.4.5.3.1.1 8.4 kbitds C channel. The unique word shall
consist of two 52-bit sequences on the I and Q channels of the
A-QPSK signal:
with the lefhnost bit transmitted first.
4.4.5.3.1.2 AU other C channels. The unique word shall
consist of two identical 44-bit sequences on the I and Q
charnels of the AQPSK signal; 0100 0010 1101 1010 1111
0011 0100 1011 1011 0001 0001, with the leftmost bit
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