Forum: GNU Radio About FLL and phase tracking error in narrow band domodulation

Hello,

I am reading the code for frequency correction in the demodulation chain
for the narrow band like PSK, GMSK, etc.

In the gnuradio/gr-digital/python/generic_mod_demod.py, two blocks 
contains
the code related to the frequency offset correction.

1. digital.fll_band_edge_cc
  I am not familiar with the algorithm employed in this frequency loop
locking block. Is there any direct reference for this block, such as 
paper
or documentation?

2. digital.constellation_receiver_cb
 It has a member function to update the phase and frequecy of the 
incoming
samples, digital_constellation_receiver_cb::phase_error_tracking()
Is there any reference for me to understand it more easily. Especially,
this member function calls
void
gri_control_loop::advance_loop(float error)
{
  d_freq = d_freq + d_beta * error;
  d_phase = d_phase + d_freq + d_alpha * error;
}

where the d_beta  and d_alpha is updated in
void
gri_control_loop::update_gains()
{
  float denom = (1.0 + 2.0*d_damping*d_loop_bw + d_loop_bw*d_loop_bw);
  d_alpha = (4*d_damping*d_loop_bw) / denom;
  d_beta = (4*d_loop_bw*d_loop_bw) / denom;
}

I did not find any explanation for these two part of codes.
Appreciate any helps.

Thanks

--

Alex,
*Dreams can come true  just believe.*

On Tue, Jan 08, 2013 at 12:27:29AM -0600, Alex Zhang wrote:
> In the gnuradio/gr-digital/python/generic_mod_demod.py, two blocks contains the
> code related to the frequency offset correction.
>
> 1. digital.fll_band_edge_cc
>
>   I am not familiar with the algorithm employed in this frequency loop locking
> block. Is there any direct reference for this block, such as paper or
> documentation?

https://lists.gnu.org/archive/html/discuss-gnuradi...

> 2. digital.constellation_receiver_cb
>
>  It has a member function to update the phase and frequecy of the incoming
> samples, digital_constellation_receiver_cb::phase_error_tracking()
>
> Is there any reference for me to understand it more easily. Especially, this
> member function calls 

Perhaps this helps?
http://www.trondeau.com/blog/2011/8/13/control-loo...

MB
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