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/* -*- c++ -*- */
/*
* Copyright 2004 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.
*/
/*
* config.h is generated by configure. It contains the results
* of probing for features, options etc. It should be the first
* file included in your .cc file.
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <dab_ofdm_coarse_frequency_correct.h>
#include <gr_io_signature.h>
/*
* Create a new instance of dab_ofdm_coarse_frequency_correct and return
* a boost shared_ptr. This is effectively the public constructor.
*/
dab_ofdm_coarse_frequency_correct_sptr
dab_make_ofdm_coarse_frequency_correct (unsigned int fft_length, unsigned int num_carriers)
{
return dab_ofdm_coarse_frequency_correct_sptr (new dab_ofdm_coarse_frequency_correct (fft_length, num_carriers));
}
dab_ofdm_coarse_frequency_correct::dab_ofdm_coarse_frequency_correct (unsigned int fft_length, unsigned int num_carriers) :
gr_sync_block ("ofdm_coarse_frequency_correct",
gr_make_io_signature2 (2, 2, sizeof(gr_complex)*fft_length, sizeof(char)),
gr_make_io_signature2 (2, 2, sizeof(gr_complex)*num_carriers, sizeof(char))),
d_fft_length(fft_length), d_num_carriers(num_carriers), d_freq_offset(0)
{
d_zeros_on_left = (d_fft_length-d_num_carriers)/2;
}
float
dab_ofdm_coarse_frequency_correct::mag_squared(const gr_complex sample) {
const float __x = sample.real();
const float __y = sample.imag();
return __x * __x + __y * __y;
}
void
dab_ofdm_coarse_frequency_correct::correlate_energy(const gr_complex *symbol)
{
unsigned int i, index;
double sum=0, max=0;
/* energy based correlation - note that DAB uses a zero central carrier -
* we always sum up the energy for all carriers except DC; this is however
* only done for the first offset; for the others, the diff is calculated
*/
/* offset 0 */
for (i=0; i<d_num_carriers+1; i++) {
if (i != d_num_carriers/2)
sum+=(double)mag_squared(symbol[i]);
}
max = sum;
index = 0;
/* other offsets */
for (i=1; i<d_fft_length-d_num_carriers; i++) {
/* diff on left side */
sum -= (double)mag_squared(symbol[i-1]);
/* diff for zero carrier */
sum += (double)mag_squared(symbol[i+d_num_carriers/2-1]);
sum -= (double)mag_squared(symbol[i+d_num_carriers/2]);
/* diff on rigth side */
sum += (double)mag_squared(symbol[i+d_num_carriers]);
/* new max found? */
if (sum > max) {
max = sum;
index = i;
}
}
d_freq_offset = index;
fprintf(stderr, "cfs: coarse_frequency_offset: %d\n", d_freq_offset+d_num_carriers/2-d_fft_length/2);
}
int
dab_ofdm_coarse_frequency_correct::work (int noutput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items)
{
unsigned int i;
/* partially adapted from gr_ofdm_frame_acquisition.cc */
const gr_complex *iptr = (const gr_complex *) input_items[0];
const char *frame_start = (const char *) input_items[1];
gr_complex *optr = (gr_complex *) output_items[0];
char *frame_start_out = (char *) output_items[1];
if (frame_start[0]) {
frame_start_out[0] = 1;
correlate_energy(iptr);
} else {
frame_start_out[0] = 0;
}
for (i=0;i<d_num_carriers/2;i++) {
optr[i] = iptr[d_freq_offset+i];
}
for (i=d_num_carriers/2;i<d_num_carriers;i++) {
optr[i] = iptr[d_freq_offset+i+1];
}
return 1;
}
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