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Part I Annex 10 - Aeronautical Telecommunications
Note.- The concept of a scrambler is explained in CCIR
Report 384-3, Annex III, Section 3, Method 1.
4.4.2.2.5.2 Forward error correction (FEC). The
information field shall use rate '/z forward error correction
coding. The FEC coding shall be implemented with a
constraint length 7 rate $5 convolutional encoder. The
generator polynomials for this code shall be:
The output sequence of the encoded symb~lssh all be GI, G2
as shown in Figure 4-3. The convolutional encoder shall not
be initialized between frames.
Note.- There are nojlush bits on the P channel.
4.4.2.2.5.3 Interleaving. All P channels shall employ
block interleaving. The column depth (number of rows) of the
interleaver shall be 64 transmission bits. while the number of
columns shal.1 depend on the transmission rate as shown in
Table 4- 11. At the transmitter, the output of the convolutional
encoder shall be written into the 64-bit columns until the
prescribed number of columns are full. The rows shall then be
permuted using the algorithm Row, = (Row, * 27) modulo 64.
The content of the interleaver shall then be transmitted row by
row as shown in Figure 4-4. At the receiver, the soft decision
data from the demodulator shall be written into the interleaver
row by row, and when it is full the interleaver rows shall be
permuted using the converse algorithm Row, = (Row, * 19)
modulo 64. The soft decision data shall then-be read column
by column into the FEC decoder.
4.4.2.2.6 Unique word. With A-BPSK each P channel
frame Shall end with the 32-bit unique word 1110 0001 0101
1010 11 10 1000 1001 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 Performance. The over-all physical layer shall be
configured and operated such that the average bit error rate is
10.~ or less after descrambling.
4.4.3. I 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.
4.4.3.2 Burst timing. The beginning of each R channel
burst shall occur within k300ps 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 kbitsls. respectively.
4.4.3.3 BURST FORMAT
4.4.3.3.1 General characteristics. Each R channel burst
shaIl consist of thee 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 "I"
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 unmodulated signal.
The unrnodulated 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) onthe I channel and
continuous "0s on the Q channel.
Note.-- It is intended that the unmodulated portion of the
preamble be used for carrier acquisition and the modulated
portion for clock acquisition..
4.4.3.3.3 Unique word. The Standard in 4.3.2.2.6 shall
apply.
4.4.3.3.4 Infonnution$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 Scrambling. 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 Fonvard error correction (FEC) coding. The
Standard in 4.4.2.2.5.2 shall apply, except that the encoder is
re-initialized to the all 0s state at the beginning of the
information frame of each burst.
4.4.3.3.4.3 Inrerleaving. All R channels shall employ
block interleaving. The number of rows in the interleaver shall
　
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