hamnet70-gnuradio-legacy/gr-hamnet70/lib/freq_est_lr_impl.cc
Thomas Kolb cd9784efb6 Added frequency estimator blocks
- correct_frequency: Correct frequency by averaging the phase drift on
                     the preamble
- freq_est_lr: Luise & Reggiannini frequency estimator
- pid_controller: a PID controller that takes error values at the input
                  and generates steering values at the output

The combination of freq_est_lr and PID controller can be used together
with an NCO (signal source) to create a closed control loop for
frequency offset compensation.
2019-07-23 23:16:48 +02:00

142 lines
3.9 KiB
C++

/* -*- c++ -*- */
/*
* Copyright 2019 Thomas Kolb.
*
* 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 <gnuradio/math.h>
#include "freq_est_lr_impl.h"
namespace gr {
namespace hamnet70 {
freq_est_lr::sptr
freq_est_lr::make(const std::vector<gr_complex> &symbols, size_t kappa)
{
return gnuradio::get_initial_sptr
(new freq_est_lr_impl(symbols, kappa));
}
/*
* The private constructor
*/
freq_est_lr_impl::freq_est_lr_impl(const std::vector<gr_complex> &symbols, size_t kappa)
: gr::block("freq_est_lr",
gr::io_signature::make(1, 1, sizeof(gr_complex)),
gr::io_signature::make(1, 1, sizeof(float))),
d_refSymbols(symbols),
d_kappa(kappa)
{
d_recvSymbols.reserve(symbols.size() + 1);
message_port_register_out(pmt::mp("freq_offset"));
}
/*
* Our virtual destructor.
*/
freq_est_lr_impl::~freq_est_lr_impl()
{
}
void
freq_est_lr_impl::forecast (int noutput_items, gr_vector_int &ninput_items_required)
{
ninput_items_required[0] = noutput_items;
}
int
freq_est_lr_impl::general_work (int noutput_items,
gr_vector_int &ninput_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];
std::vector<tag_t> tags;
get_tags_in_window(tags, 0, 0, ninput_items[0], pmt::intern("corr_est")); // FIXME: make name variable
size_t tagidx = 0;
for(size_t i = 0; i < noutput_items; i++) {
if((tagidx < tags.size()) && (tags[tagidx].offset == nitems_read(0) + i)) {
d_recvSymbols.clear();
tagidx++;
}
if(d_recvSymbols.size() < d_refSymbols.size()) {
// buffer symbols of the preamble
d_recvSymbols.push_back(in[i]);
} else if(d_recvSymbols.size() == d_refSymbols.size()) {
// received enough symbols for the preamble => do frequency estimation
d_recvSymbols.push_back(0); //???
// remove reference symbols from the received preamble
std::vector<gr_complex> z;
z.reserve(d_recvSymbols.size());
for(size_t k = 0; k < d_recvSymbols.size(); k++) {
z.push_back( d_recvSymbols[k] * conj(d_refSymbols[k]) );
}
// Calculate averaged phase increments for <N> sub-sequences
size_t N = d_recvSymbols.size()/2;
std::vector<gr_complex> R_kappa(N);
for(size_t kappa = 0; kappa < N; kappa++) {
for(size_t k = 0; k < d_recvSymbols.size() - kappa; k++) {
R_kappa[kappa] += z[k + kappa] * conj(z[k]);
}
R_kappa[kappa] /= z.size() - kappa;
}
// Calculate phase estimate (in radians/sample)
gr_complex sum_R_kappa(0, 0);
for(size_t kappa = 0; kappa < N; kappa++) {
sum_R_kappa += R_kappa[kappa];
}
float arg = gr::fast_atan2f(sum_R_kappa);
d_freq_est = arg / (M_PI * (1 + N));
message_port_pub(pmt::intern("freq_offset"), pmt::from_double(-d_freq_est));
}
out[i] = d_freq_est;
}
// Do <+signal processing+>
// Tell runtime system how many input items we consumed on
// each input stream.
consume_each (noutput_items);
// Tell runtime system how many output items we produced.
return noutput_items;
}
} /* namespace hamnet70 */
} /* namespace gr */