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Re: [Phys-l] WIFI



On 04/08/2012 08:00 PM, Bernard Cleyet wrote:
Do these communications suppress the carrier (unnecessary as a local oscillator is used?)

Yes.

bc knows SSSC requires a crystal controlled exciter (BFO?). Or perhaps a lock-in receiver?

It's a phaselock loop.

It has to be done that way, partly because you could not possibly
have a local oscillator that would be accurate enough open-loop,
and even if you did have an accurate oscillator, it still wouldn't
work, because the receiver can move and/or the pathlength can
change (due to other stuff moving around).

I don't know the details, but here is an "existence proof" i.e.
one way they could do it:

Look at the last 1000 codewords received. Fit to the data to
determine 1001 parameters, namely the codes plus the carrier
frequency.

During the start-up transient, they do all sorts of additional
tricky stuff, to make it easier to recover the carrier (at the
cost of having a temporarily lower data rate).
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