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Re: PSK, Costas Loops, and simplicity (was: RE: AO16/LO19 Uplink w ANY PC!)



>To do it you jointly estimate the data values, clock phase,
>and carrier phase and frequency at the current "sampling
>instant".  This sounds complicated but in reality it isn't
>since you get almost all of the performance out of some
>pretty gross approximations, enough so that it still
>outperforms the Costas loop.

Right, joint estimation is the way to go. Also, if you have known data
imbedded in the stream, e.g., flags or frame synch markers, you can
use that to your advantage more easily in software than in hardware.
As an example, see my software demodulator for the ACE spacecraft's
low rate beacon. This is available in source on my website:

http://people.qualcomm.com/karn/code/acedemod/

I didn't do any Costas loop bit tracking at all; I simply slide a
correlator along the frame looking for the convolutionally encoded
frame sync sequences that delimit each fixed-length frame, and then
interpolate the clock between those sequences.

--Phil
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