About FLL and phase tracking error in narrow band domodulation

GNU Radio
1

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 + 2.0d_dampingd_loop_bw + d_loop_bwd_loop_bw);
d_alpha = (4d_dampingd_loop_bw) / denom;
d_beta = (4d_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.

2

On Tue, Jan 08, 2013 at 12:27:29AM -0600, Alex Z. 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-gnuradio/2012-10/msg00019.html

  1. 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?

MB

Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

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