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kame shall end with the 32-bit unique word 11 10 0001 0101
1010 111 0 1 010 01 001 1, with the leftmost bit transmitted
first. With A-QPSK, the unique word shall be the A-BPSK
unique word repeated in each of the in-phase and quadrature
channels.
4.4.2.3 Petfomnce. The over-all physical layer shall be
configured and operated such that the average bit error rate is
1C5 or less after descrarnbling.
4.4.3 R channel
4.4.3.1 Channel rate accuracy. The channel rate error
shall not exceed one part in 2R. where R is the channel rate,
and one part in 104.
4.4.3.2 Burst timing. The beginning of each R channel
burst shall occur within k300 ps of the beginning of an R
channel slot defined by the received P channel superframe. As
shown in Figure 4-5, each P channel superframe shall define
8, 16, 32 and 64 random access slots for R channel data rates
of 0.6, 1.2, 2.4 and 10.5 kbitsts, respectively.
4.4.3.3 BURST FORMAT
4.4.3.3.1 General characteristics. Each R channel burst
shall consist of three fields: the preamble, the unique word and
the information field as shown in Figure 4-6.
4.4.3.3.2 Preamble. The preamble for the R channel shall
consist of an unmodulated carrier portion followed by a
modulated portion. The length of these depend on the data rate
as shown in Table 4-12. The unmodulated portion of the
A-BPSK preamble shall be a signal of constant phase and the
modulated portion shall consist of alternating "0" and "1"
input to a standard A-BPSK modulator. The first bit of the
modulated portion shall be a "0" and shall give a -90 degree
phase change relative to the phase of the unmodulakd signal.
The unmodulated portion of the A-QPSK preamble shall be a
signal of constant phase corresponding to the output of an
ideal A-QPSK modulator with all "0"s at its input. The
modulated portion shall consist of alternating "0" and "1"
(commencing with a "0 in the first bit) on the I channel and
continuous "0"s on the Q channel.
Note.- It is intended that the zinmodulated portion of the
preamble bt used for carrier acquisition and fhe modillated
portion for clock acquisition.
4.4.3.3.3 Unique word. The Standard in 4.4.2.2.6 shall
apply.
3.4.3.3.4 Inf~nnationji eld. The information field of each
R channel burst shall consist of 160 bits and shall contain an
extended signal unit plus 8 flush bits prior to convolutional
encoding, where an extended SU shall have 152 bits and a
Flush field shall be 0000 0000. The information field shall be
scrambled, coded and interleaved, in that order.
4.4.3.3.4.1 Scranzbling. The Standard in 4.4.2.2.5.1 shall
apply, except that the flush bits are not scrambled.
4.4.3.3.4.2 For.vurd error correction (FEC) coding. The
Standard in 4.4.5.3.3.5.2 shall apply, except that the encoder is
re-initialized to the all 0s state at the beginning of the
information field of each burst.
4.4.3.3.4.3 Interleaving. A11 R channels shall employ
block interleaving. The number of rows in the interleaver shall
be 64 transmission bits, while the number of columns shall be
5. Row interchanging in the interleaver shall be performed in
accordance with 4.4.2.2.5.3.
4.4.3.4 Performance. The Standard in 4.4.2.3 shall apply.
4.4.4 T channel
4.4.4.1 Channel rate accuracy The channel rate error
shall not exceed one part in 2R, where R is the channel rate,
and one part in lo4.
4.4.4.2 Timing relative to P channel. The beginning of
each T channel burst shall occur within D 0 0 p of the
beginning of the assigned T channel slot defined by the
received P channcl superframe. As shown in Figure 4-7, each
P channel superframe shall be divided into 16 nominal frames
with 64 T channel slots in each frame. The shortest guard time
between the T channel bursts of two different aircraft is under
coiltrol of the GES and shall be 5 slots.
4.4.4.3 BURST STRUCTURE
4.4.4.3.1 General c/~aracteristics. Each T channel burst
shall consist of three fields: the preamble, the unique word and
the information field as shown in Figure 4-8.
Y11IMI
No. 75
Part I Annex I0 - Aeronautical Telecommunicarions
4.4.4.3.2 Preamble. The Standard in 4.4.3.3.2 shall apply. of 4.4.3.3.2 and in Table 4-14. The 8.4 kbitsls C channel shall
not have a preamble.
4.4.4.3.3 Unique word. The Standard in 4.4.2.2.6 shall
apply.
4.4.4.3.4 Information field. The information field of each
T channel burst shall consist of a burst identifier, n SUs and 16
flush bits prior to convolutional encoding, as follows.
Burst identifier - this field has 48 bits which shall identify
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