Thanks you all.
I will try to adjust th loop_bw in the fll firstly to see what happened.
And I am not understanding the function advance_loop(error) well:
void
gri_control_loop::advance_loop(float error)
{
d_freq = d_freq + d_beta * error;
d_phase = d_phase + d_freq + d_alpha * error;
}
I am not clear why d_freq and d_phase are updated in this way. Is the
d_freq the frequency offset estimate every step?
According to the
http://www.trondeau.com/blog/2011/8/13/control-loop-gain-values.html , i
have a rough picture on this, but still confused why d_freq is only
dependent on d_beta.
The other question is: Is it possible to turn off the loop when there is no
input signal (only noise) and turn on the loop when signal is detected?
If possible, how to update hte d_freq and d_phase?
On Wed, Mar 6, 2013 at 7:08 AM, Tom Rondeau <t...@trondeau.com> wrote:
> On Wed, Mar 6, 2013 at 6:42 AM, Sreeraj Rajendran
> <srees4sr...@yahoo.co.in> wrote:
> >
> >>>I don't believe this problem can be solved by adjusting the loop
> >>> bandwidth.
> >
> > Acquisition time is roughly inversely proportional to loop_bw and error
> > variance is proportional to loop_bw. So there is always a tradeoff
> between
> > acquisition time and tracking performance. You should try adjusting
> loop_bw
> > (http://www.trondeau.com/blog/2011/8/13/control-loop-gain-values.html).
> >
> >>>Applying faster tracking algorithm may solve this problem, but I think
> it
> >>> takes long time to develop for a new guy.
> >
> > If you have a good understanding of the algorithm, its really easy to
> > prototype the alogorithm in GRC or by using gnuradio python-block coding
> > support. "gr_modtool" is always there to make block coding easier.
> >
> > -Sreeraj
>
>
> Also hand tune to make sure the frequencies of the transmitter and
> receiver are as close as you can get them. The slowest loop in this
> chain is the frequency lock loop, so overcome that by hand and see
> what happens.
>
> Tom
>
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>
--
Alex,
*Dreams can come true – just believe.*
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