Wavecom W61PC V7.5.0 - Manual (Page 49)

WAVECOM Decoder W61PC/LAN Manual V7.5 First start  39
lowing phase comparator calculates the phase difference between the signal from the integrator and the
delayed signal.
A variant of DPSK is used almost exclusively when phase modulation is employed on short wave data
links.
DBPSK
Similar to DPSK, but has two phase shifts at ± 180 degrees.
DQPSK
Similar to DPSK, but has four phase shifts at ± 90 and ± 180 degrees.
DTMF
This demodulator handles multi-frequency signals. Filters are switched in on the various frequencies of the
signal and the amplitude is then calculated for each frequency. Next the amplitudes are evaluated. Two
simultaneous tones are demodulated. The SNR is the same as for the mark-space demodulator.
DXPSK
Adaptive DPSK demodulator for PACTOR-II. This demodulator will automatically adapt itself to DBPSK,
DQPSK, D8PSK or D16PSK.
D8PSK
Similar to DPSK, but has eight phase shifts at ±45, ±90, ±135 and ± 180 degrees.
D16PSK
Similar to DPSK, but has sixteen phase shifts at ±22.5, ±45, ±67.5, ±90, ±112.5, ±135, ±157.5 and
±180 degrees.
FFSK and GFSK
Depending on the mode, the FFSK (Fast Frequency Shift Keying) and GFSK (Gaussian Frequency Shift
Keying) demodulator is automatically selected. Basically this demodulator utilizes the I/Q principle (Hil-
bert). However, filters are adjusted to accommodate the special demands of these modes.
MFSK
This demodulator handles multi-frequency signals. Filters are switched in on the various frequencies of the
signal and the amplitude is then calculated for each frequency. Next the amplitudes are evaluated. De-
pending on the number of tones used, the filters are configured as phase linear FIR filters or as IIR filters.
The SNR is the same as for the mark-space demodulator. Simultaneous multi-tone decoding (e.g. DTMF)
is not possible with this demodulator.
MS (Mark-Space)
The mark-space demodulator processes the two keying frequencies of a FSK signal. These are fed to two
phase linear FIR filters and the amplitude is then calculated. The mark-space demodulator exhibits an ex-
tremely good noise distance and should be used for all FSK modes utilizing a speed of less than 300 Baud.
OQPSK
Carrier recovery is mandatory to demodulate OQPSK. As OQPSK has phase shifts at ±90 degrees, the sig-
nal must be squared two times to produce a carrier at four times the original frequency. A PLL recovers
the carrier in frequency and phase with ambiguities at ±90 and ±180 degrees. A complex mixer down
converts the signal to base band and the resulting signal is the data signal. In contrast to QPSK, OQPSK
has only phase steps of ±90 degrees in one step. First the in-phase part is switched, then after half a
symbol duration the quadrature part is switched. The advantage of this process is a smaller amplitude var-
iation.
OQPSK is used almost exclusively for satellite data links.
QPSK
Carrier recovery is mandatory to demodulate QPSK. As QPSK has phase shifts at ±90 and ±180 degrees,
the signal must be squared two times to produce a carrier at four times the original frequency. A PLL re-
covers the carrier in frequency and phase with ambiguities at ±90 and ±180 degrees. A complex mixer
down converts the signal to base band, and the resulting signal is the data signal.
QPSK is almost exclusively used for satellite data links.