Wavecom W61PC V7.5.0 - Manual (Page 234)

224  Transmission Modes WAVECOM Decoder W61PC/LAN Manual V7.5
Using the Frame Format field the decoder can be set to one of the signal configurations. When the Confi-
dence value is greater than 95 (i.e. 95% correct) in a stable state, the Frame Format is correct.
STANAG-4415
The NATO robust, non-hopping, serial (single-tone) mode with tone excision – also known as STANAG-
4415 – transmits user data at 75 bps over severely degraded HF channels with large Doppler and multi-
path spreads.
Parameter Value
Frequency range HF
Operation modes Broadcast/Simplex FEC
Modulation 8-PSK
Center frequency 1800 Hz
Symbol rate 2400.0 Bd
Receiver settings DATA, CW, LSB or USB
Input format(s) AF, IF
Additional Info 16 Bit redundancy
The on-air waveform specified in this mode is identical to the 75 bps waveform of the MIL-188-110A serial
mode. The modulation uses 8-ary phase shift keying (PSK) on a single carrier frequency (1800 Hz). Serial,
binary information (raw data), accepted at the line-side input, is converted into a single 8-ary PSK-
modulated output carrier at a symbol rate of 2400 Bd.
Each data transmission consists of four distinct phases: The synchronization preamble phase, the data
phase, the End-Of-Message (EOM) phase and the coder-interleaver flush phase.
The preamble phase lasts for 0.6 seconds for zero or short interleaver settings and 4.8 seconds when the
interleaver size is set to long. This is followed by the data phase, which consists of an unlimited number of
interleaver blocks. The raw user data, accepted at 75 bps, is first FEC (Forward Error Correction) encoded.
Then the bit-stream is passed through an interleaver with a size of 10*9 = 90 bits size for the short inter-
leaver or 20*36 = 720 bits for the long interleaver. A zero interleaver setting is usually not selected, be-
cause through interleaving the effect of short term fading and burst noise can be mitigated.
The coding rate of FEC is 1/2, i.e. after encoding the data rate is 150 bps. Each two bits are then mapped
to a 32-bit Walsh sequence, thus yielding the 75*32 = 2400 Bd symbol rate.
At the end of transmission, a certain bit pattern (in hexadecimal notation, 4B65A5B2, MSB first) is sent to
mark the end of message (EOM). The EOM sequence is followed by the flush bits, which are for the FEC
coder flushing and for the complete transmission of the remainder of the interleaver matrix data block.
Therefore both the EOM sequence and the flush bits are treated as normal user data bits and passed to
the last interleaver block.
 Preamble (0.6 s or 4.8 s)
 Interleaver 1
 Interleaver 2
 ... ...
 Interleaver N (including EOM & flush bits)
Besides the FEC and interleaver used in this mode, a special component – the tone excision module – is
used to pre-process the waveform, so that a more stringent decoding performance can be reached than is
the case for the MIL-188-110A mode, even for a severely degraded HF radio link. The tone excision mod-
ule mainly adaptively eliminates interfering tones, which may occur during the transmission.
As in the MIL-199-110A mode, the raw user data transmitted by the NATO Robust mode is just binary.
Therefore the NATO Robust decoder displays the user data in BINARY, HEX, ASCII SYNC and two
ASCII ASYNC formats selected from Options | Message Type.... The decoder stops the display after
the EOM bit pattern is received and goes to the SYNC status for preamble hunting.