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4.4.1 General - 4 bits which repeat the previous 4 bits.
4.4.1.1 Aixraft system-timing reference point. The 4.4.2.2.4 Dummyjeld. For channel rates above 2.4 kbitsls
reference timing point for signals generated and received by this field be:
the AES shall be at the antenna.
4.4.1.2 Channel rates. The channel rates as applicable to
the system capability levels defined in 4.1.3 shall be as shown
16 bits for 4.8 kbitsls
178 bits for 10.5 kbitsls
in able 4-9. - The dummy field shall consist of the sequence 0001 repeated
until the required number of bits is obtained.
4.4.1.3 Signal units (SUs). All information to be
transmitted over the P, R, T and sub-band C channels shall be Note.- The dummy field is included to make each frame
in the 'Ormat Of units* For the and Nb-band 0.5 seconds long There is no dummy fild required for data
channel each signal unit shall consist of 96 bits. For the R
channel each signal unit shall consist of 152 bits. The signal rates of 2.4 kbits/s and below.
unit formats shall be as specified in Appendix 2. 4.4.2.2.5 Infomtion field. The information field shall
4.4. 1.3.1 Cyclic ched (cR,-)T. ~~ last two contain multiple signal units which are scrambled, coded and
bytes of each SU shall a C Ro~f t he sum Any received interleaved, in that order. The number of bits in the
SU which fails the CRC shall be discarded. information field shall be as indicated in Table 4-10.
4.4.1.3.2 Signal qualily estimtion. The AES shall make
information such as P channel degradatiodloss and C channel
bit error rate available to the AES management functions and
GES management functions as appropriate.
4.4.2 P channel
4.4.2.1 Channel rate accuracy. The channel rate error
shall not exceed one part in lo6.
4.4.2.2 FRAMEFO RMAT
4.4.2.2.1 General characteristics. All P channel frames
shall be either 500 ms, or a multiple of 500 ms to provide
simple derivation of an 8-second superframe which shall be
used for R channel and T channel slot allocation. Each P
channel frame shall consist of five fields identified as: format
identifier, superframe boundary marker, dummy field (for data
rates greater than 2.4 kbitsls), information field and unique
word, as shown in Figure 4-l* for channel rates of 2.4 kbitsls
and less, and in Figure 4-2 for channel rates greater than
2.4 kbits/s.
Note.- The number of bits in the information jeld is
dependent on the data rate and the number of interleaver
blocks in the jeld.
4.4.2.2.5.1 Scrambling. A scrambler with a 15-stage
generator register shall be used for data scrambling before
FEC coding. The polynomial for the generator register of the
scrambler and the descrambler shall be 1 + X + x". The
scrambler and descrambler shall be clocked at the infomation
rate with the first scrambled bit output before the first shift. In
the absence of programming commands, the shift register shall
be initialized to 1101 0010 1011 001 (leftmost bit in shift
register stage 1) at the beginning of the information field of
each frame. The scrambler and descrambler functions shall be
as illuswaled in Figure 4-3. The scrambler shall be
re-initialized at the beginning of the information field of each
frame.
Note.- The concept of a scrambler is explained in CCZR
Report 384-3, Annex 111, Section 3, Method 1.
4.4.2.2.5.2 Forward error currection (FEC). The Standard
in 4.4.5.3.3.5.2 shall apply.
Note.- There are no flush bits on tho P channel.
4.4.2.2.2 Format identifier: This field shall consist of the
4 bits: 0001. Other values for this field are reserved for future
use. * All figures are located at the end of this chapter.
211 1/00
No. 75
Annex 10 - Aeronautical Teleconamunicalions Volume 611
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 numher of
columns shall depnd on the Wmsmission rate as shown in
Table 4-11. At the transmitter, the output of che convolutional
encoder shall be written into the 64-bit columns until the
prescribed number of columns are full. The rows shall then be
pernluted using the algorithm Row, = (Rowi * 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 Rowj = (Row, * 19)
modulo 64. The soft decision data shall then be read column
by column into the 'FEC decoder.
4.4.2.2.6 U~tique word. With A-BPSK each P channel
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