Wavecom W61PC V7.5.0 - Manual (Page 182)

172  Transmission Modes WAVECOM Decoder W61PC/LAN Manual V7.5
Baud rate User data
rate (bps) Inter
leaver Modulation (bit
per symbol) FEC coding rate No. of un-
known sym-
bols
(User
Data)
No. of
known 8-
PSK sym-
bols
(Channel
Probe)
2400 4800 variable 8-PSK (3) 1/2, punctured to 3/4 256 31
2400 6400 variable 16-QAM (4) 1/2, punctured to 3/4 256 31
2400 8000 variable 32-QAM (5) 1/2, punctured to 3/4 256 31
2400 9600 variable 64-QAM (6) 1/2, punctured to ¾ 256 31
2400 12800 N/A 64-QAM (6) N/A 256 31
Variable Interleaver
 Ultra short
 Very short
 Short
 Medium
 Long
 Very long
Each transmission of a MIL-188-110B message begins with a synchronization phase (preamble) which in-
cludes 287 8-PSK symbols. In the preamble the modem setting, i.e. user data rate and interleaver size, is
coded. This auto baud feature should be used to configure the modem to decode the data bits. After the
preamble the user data bits are transmitted in blocks of 256 symbols paired with 31-symbol mini-probe
blocks. After 72 user data – mini-probe pairs a 103-symbol mini-preamble is inserted. The number of data
blocks in a transmission is in principle unlimited. A unique bit pattern (in hexadecimal number, 4B65A5B2,
MSB first) is sent to mark the end of message (EOM). The EOM sequence is followed by flush bits, for
flushing the FEC coder and for the complete transmission of the remainder of the interleaver data block
The FEC and the interleaver are used to combat the effects of fading, frequency drift, multi-path effects,
and burst noise etc. in the HF transmission. The mini-probe and regularly re-inserted mini-preamble are
transmitted to help keep the receiver synchronized.
The MIL-188-110B decoder processes all the above settings except 12800 bps. This setting is usually not
to be used for reliable data transmission, because it has neither FEC nor interleaving. Generally MIL-188-
110B transmits the user data in binary mode, i.e. it does not care which type of data is transmitted. This
should be defined by the protocol layer using the MIL-188-110B mode. For this reason the decoder just
Initial Synchronization Preamble – 287 symbols
Data Block – 256 symbols
Mini-probe – 31 symbols
Regularly Re-inserted Mini-Preamble – 103 symbols
... ...