On 08/05/2019 09:18, Игорь Ч via wsjt-devel wrote:
We should also take in account overlapping spectra as spreading
information between symbols under GFSK will affect decoding of the
overlapped signals mostly if we are using frequency criterion for
candidate ranking and probably due to the inaccurate signal
subtraction, assuming all signals on the band are GFSK modulated.
Hopefully we can evaluate GFSK benefits/losses via simulation of the
signals for overloaded band scenario.
Hi Igor,
Steve and Joe have done much of this work while designing the parameters
for FT4. We have a considerable history of real World FT8 signals using
MFSK modulation on which the GFSK decoder has been tested. We also have
a multi-signal simulator which was used when characterizing the GFSK
decoders. This is how the amount of smoothing applied to make GFSK
signals was chosen, i.e. an amount of smoothing that reduced the number
of successful decodes missed from a data set to an acceptably low level.
There is no inaccurate signal subtraction when using the GFSK decoder to
to subtract GFSK signals, the facsimiles generated for subtraction are
exactly the same as the originally transmitted signals. The only
inaccuracies are in the phase and amplitude and those errors should be
unchanged from that measured by the old MFSK decoder. Perhaps you are
saying that the accuracy of the phase measured from on air GFSK signals
is lower than that measured from otherwise equivalent MFSK signals, if
so I doubt that is significant.
73
Bill
G4WJS.
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