Thanks for the response. It sounds as if your SW does the
demod-remod-subtract algorithm when second pass decoding is enabled. Very
nicely done to optimize local performance.
Has anything been done to mine the locally created data at a global or
regional level to create a statistical model of the channel? It seems the
WSJT community provides the best data source for this effort that I have
ever even contemplated.
Perhaps the user community would not begrudge a SW package that performed
the best proper local data reduction, and did an "ET phone home" to a
central repository at a reasonable BW at an off-peak time.
The channel description might then enable an even more optimal waveform
design. Or even modes optimized for ionospheric weather conditions.
The data source seems too precious a resource to be ignored.
Thanks for listening. This idea had to have already been considered by
your team. Perhaps any objections raised by cost and scope could be
reduced by a Federal grant?
Regards,
Don Goldston, KE0G
On Feb 19, 2018 7:42 PM, "Steven Franke" <s.j.fra...@icloud.com> wrote:
Don,
> It seems that by assuming a correct decode (and a time-invariant
transmitter) each user could store enough information (already supported by
the SW) to describe the channel statistics. I see hints that you are
trying to provide the capability to describe the transmitter, but what
about the larger question of the channel? Is there a behavior whereby a
large body of users could help describe the channel in a cooperative manner?
The FT8, JT65, and WSPR demodulator/decoders estimate the channel for each
and every decode. Given the decoded message we regenerate the transmitted
waveform and use that as a reference to derive the time-varying, complex,
gain function that describes the channel. We use this to reconstruct a
(nearly) noiseless version of the received signal’s waveform that includes
the channel-induced amplitude fading and phase-variation. The reconstructed
signal is subtracted from the received data, enabling us to uncover weaker
signals that occupy the same frequency slot as the subtracted strong
signal. These weaker signals can often be decoded on a second decoding
pass, after the stronger signals have been subtracted.
Steve K9AN
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