Nera Inmarsat-c Service Manual page 145

Unique Word
The 252 symbols from the encoder are affixed with an unique word (uw) to be used for
bit synchronization at the recorder. The uw is 64 bits in length on the MES signaling
channel and 64x2 bits on the NCS/CES TDM channel.
Interleaving and
Permuting Encoder
Interleaving and Permuting Encoder
The figure below shows the interleave matrix, consisting of 64 rows by 162 columns.
Symbol data comes in column by column. Note that columns 0 and 1 are filled with
unique words.
0 1 2 .................................... 161
0
1
Row
1
2
2
3
:
:
:
:
:
:
:
:
62
63 127
63
64
UW 64bits UW 64bits
The first 64 symbols of convolutional encoder output go to column 2, rows 0 to 63.
The next 64 symbols to column 3, rows 0 to 63 and so on.
The interleave block is transmitted on a row by row basis. The symbols in a row are
transmitted in ascending order of column position; that is, the two identical unique
word symbols are transmitted first. However, rows are not transmitted in a sequential
order; they are transmitted according to a permuted sequence. If the rows in the
interleave block are numbered from i = 00 to i = 63 sequentially and the transmitted
order is from j = 0 sequentially through to j = 63; then, i and j are related by
i = (jx39) modulo 64
1 st output j = 0 : i = (0x3S) modulo 64 = 0
2 st output j = 1 : i = (1x3S) modulo 64 = 39
3 st output j = 2 : i = (2x3S) modulo 64 = 14
Modulo 64 is the remainder of division by 64.
Fig. AP1.3.8 UW
Column
65
66
67
128
3 ... 64 ... 128
1 2 65
Fig. AP1.3.9 Interleave Matrix
AP1-24
AP1.3 Channel types and Signal processing
symbol UW
(added)
10177
10177
10177
10239
10240
Bit stream
.................. ...
10177 10240
BPSK modulator
or
interleaver