/
freqest_impl.cc
92 lines (79 loc) · 3.08 KB
/
freqest_impl.cc
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/* -*- c++ -*- */
/*
* Copyright 2013 <+YOU OR YOUR COMPANY+>.
*
* This 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.
*
* This software 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 this software; 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 <gnuradio/io_signature.h>
#include "freqest_impl.h"
namespace gr {
namespace ais {
freqest::sptr
freqest::make(float sample_rate, int data_rate, int fftlen)
{
return gnuradio::get_initial_sptr
(new freqest_impl(sample_rate, data_rate, fftlen));
}
/*
* The private constructor
*/
freqest_impl::freqest_impl(float sample_rate, int data_rate, int fftlen)
: gr::sync_block("freqest",
gr::io_signature::make(1, 1, sizeof(gr_complex) * fftlen),
gr::io_signature::make(1, 1, sizeof(float)))
{
d_offset = fftlen * (float(data_rate) / float(sample_rate));
d_binsize = float(sample_rate) / float(fftlen);
}
/*
* Our virtual destructor.
*/
freqest_impl::~freqest_impl()
{
}
int
freqest_impl::work (int noutput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items)
{
const gr_complex *in = (const gr_complex *) input_items[0];
float *out = (float *) output_items[0];
unsigned int fftlen = input_signature()->sizeof_stream_item(0) / sizeof(gr_complex);
float maxenergy = 0;
unsigned int maxpos = 0;
float currentenergy;
//you are responsible for organizing the vector
for (int i = 0; i < noutput_items; i++) {
//for each requested output item
maxenergy = 0;
for(unsigned int j = 0; j < fftlen - d_offset; j++) {
//over the entire fft up until the right side of the "window" butts up against the end
currentenergy = std::abs(in[i*fftlen+j]) + std::abs(in[i*fftlen+j+d_offset]); //sum of the two bins at -datarate/2 and +datarate/2
if(currentenergy > maxenergy) {
maxenergy = currentenergy;
maxpos = j + d_offset/2; //add the offset to find the center position
}
}
//now maxpos contains the center bin, and we must translate that to a frequency offset
out[i] = (float(maxpos) - fftlen/2) * d_binsize/2; //subtract fftlen/2 to center the complex FFT around 0
}
return noutput_items;
}
} /* namespace ais */
} /* namespace gr */