On Mon, 2015-09-07 at 12:48 +0930, David Rowe wrote: > Thomas, > > See "Suggestion to dynamic bandwidth adaption" thread above. It would > be interesting to add QAM constellations to the cohpsk modem. The > pilots symbols could be used as an amplitude as well as phase reference.
Yes, I saw that thread just as I hit "send". Great minds think alike it seems :] It's a bit unclear from the blog post about Trellis decoding whether you're making use of the modem reporting the likelihood of each bit being either zero or one. This kind of information is used in turbo codes to great effect, perhaps it could be useful here too? Especially with an "improvement channel" if the decoder is able to work out that the signal is too bad to make use of the improvement bits, only the "core bits". Have you considered sending the model parameters in analog form, like a vocoder? Say a pilot tone and several FM or even PM carriers. Maybe that would degrade more gracefully.. The problem with digital is that you typically spend the same amount of power on each bit regardless of how significant they are. This gives an idea for the improvement channel: keep all LSBs in the lower-power improvement carriers, spending more power on the MSBs /Tomas, SA2TMS
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