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Re: [Discuss-gnuradio] QAM, carrier tracking and clock recovery


From: Eric Blossom
Subject: Re: [Discuss-gnuradio] QAM, carrier tracking and clock recovery
Date: Thu, 1 Feb 2007 14:16:55 -0800
User-agent: Mutt/1.5.9i

On Thu, Feb 01, 2007 at 11:02:54PM +0100, Martin Dvh wrote:
> > How's it working with the AGC loop?
> The  agc2 seems to work.
> The feedforward agc only works when manually compensating for the noise (1.0 
> + noise as reference)
> This would need an error loopback from the gr_mspk receiver
> 
> I think my main problem now is detecting of which quadrant we are in.

I believe that V.32bis differentially encodes the quadrant rotation to
avoid this problem.

> Or use the right kind of differential coding.
> (I just used the gr.diff_decoder_bb and gr.diff_encoder_bb)
> 
> I have also strugled with the right formulation for the phase_detector error 
> signal.
> (conj or not, pos or neg sign) But I think I got it now.
> 
> I send the complete constellation as list from python to the
> mpsk_receiver as vector.  For some reason I had to reverse this list
> to get it to work.  This could also mean I needed to solve this in a
> different way and it just accidently now sometimes works. (mirror
> the constellation, add pi, something like that)
>
> Greetings,
> Martin




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