> 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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