Wavecom W-SPECTRA (Automatic Monitoring System) V1.1.0 - Manual (Page 189)

WAVECOM Monitoring System W-SPECTRA, W-SPEED Manual V1.1.0 Transmission Modes
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In ASCII ASYNC (7 Data bits and No Stop bit) mode, the bit stream is searched with another ASYNC struc-
ture, i.e., one start-bit (0), 7 data-bits. The 7 data-bits are LSB first. In addition to the EOM pattern, the
display will stop if more than 300 NULL characters are received.
In ASCII SYNC mode, each 8 bits (LSB first) represent one ASCII character. The display will stop if the
EOM pattern is received or if more than 20 NULL characters are received.
A switch Options | Output Demodulated Symbol enables symbol output directly after the demodulator and
before channel decoding (FEC). This feature enables the user to analyse the demodulated symbol when
the above coding scheme deviates from the standard.
Tuning the decoder
The mode decoder can process signal in both SSB settings: USB and LSB. This can be set by toggling the
Polarity field: NOR means USB and INV means LSB signal.
The center frequency of the decoder should be set to 1800 Hz when the receiver is correctly tuned to the
sending station. Small frequency deviations are automatically tracked and compensated during the decod-
ing. The center frequency of the decoder can be adjusted to ± 400 Hz from its normal setting. By using
the bar-graph, any remaining frequency difference can be compensated for by fine-tuning of the receiver
frequency or by adjusting the center frequency of the decoder.
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.
Dedicated Phase Plane
See “ MIL-188-110A ” on page 120.
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.