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/* -*- c++ -*- */
/*
* Copyright 2006 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* GNU Radio is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3, or (at your option)
* any later version.
*
* GNU Radio is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GNU Radio; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <atsc_fpll.h>
#include <gr_io_signature.h>
#include <atsc_consts.h>
#include <algorithm>
#include "fpll_btloop_coupling.h"
#include <gr_math.h>
atsc_fpll_sptr
atsc_make_fpll()
{
return atsc_fpll_sptr(new atsc_fpll());
}
/*
* I strongly suggest that you not mess with these...
*
* They are strongly coupled into the symbol timing code and
* their value also sets the level of the symbols going
* into the equalizer and viterbi decoder.
*/
static const float FPLL_AGC_REFERENCE = 2.5 * FPLL_BTLOOP_COUPLING_CONST;
static const float FPLL_AGC_RATE = 0.25e-6;
atsc_fpll::atsc_fpll()
: gr_sync_block("atsc_fpll",
gr_make_io_signature(1, 1, sizeof(float)),
gr_make_io_signature(1, 1, sizeof(float))),
initial_phase(0)
{
initial_freq = 5.75e6 - 3e6 + 0.31e6 + 5e3; // a_initial_freq;
agc.set_rate (FPLL_AGC_RATE);
agc.set_reference (FPLL_AGC_REFERENCE);
initialize();
}
void
atsc_fpll::initialize ()
{
float Fs = 19.2e6;
float alpha = 1 - exp(-1.0 / Fs / 5e-6);
afci.set_taps (alpha);
afcq.set_taps (alpha);
printf("Setting initial_freq: %f\n",initial_freq);
nco.set_freq (initial_freq / Fs * 2 * M_PI);
nco.set_phase (initial_phase);
}
int
atsc_fpll::work (int noutput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items)
{
const float *in = (const float *) input_items[0];
float *out = (float *) output_items[0];
for (int k = 0; k < noutput_items; k++){
float a_cos, a_sin;
float input = agc.scale (in[k]);
nco.step (); // increment phase
nco.sincos (&a_sin, &a_cos); // compute cos and sin
float I = input * a_sin;
float Q = input * a_cos;
out[k] = I;
float filtered_I = afci.filter (I);
float filtered_Q = afcq.filter (Q);
// phase detector
// float x = atan2 (filtered_Q, filtered_I);
float x = gr_fast_atan2f(filtered_Q, filtered_I);
// avoid slamming filter with big transitions
static const float limit = M_PI / 2;
if (x > limit)
x = limit;
else if (x < -limit)
x = -limit;
// static const float alpha = 0.037; // Max value
// static const float alpha = 0.005; // takes about 5k samples to pull in, stddev = 323
// static const float alpha = 0.002; // takes about 15k samples to pull in, stddev = 69
// or about 120k samples on noisy data,
static const float alpha = 0.001;
static const float beta = alpha * alpha / 4;
nco.adjust_phase (alpha * x);
nco.adjust_freq (beta * x);
}
return noutput_items;
}
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