Thomas Kolb
cd9784efb6
- 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.
142 lines
3.9 KiB
C++
142 lines
3.9 KiB
C++
/* -*- c++ -*- */
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/*
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* Copyright 2019 Thomas Kolb.
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*
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* This is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3, or (at your option)
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* any later version.
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*
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* This software is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this software; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street,
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* Boston, MA 02110-1301, USA.
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*/
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include <gnuradio/io_signature.h>
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#include <gnuradio/math.h>
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#include "freq_est_lr_impl.h"
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namespace gr {
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namespace hamnet70 {
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freq_est_lr::sptr
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freq_est_lr::make(const std::vector<gr_complex> &symbols, size_t kappa)
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{
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return gnuradio::get_initial_sptr
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(new freq_est_lr_impl(symbols, kappa));
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}
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/*
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* The private constructor
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*/
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freq_est_lr_impl::freq_est_lr_impl(const std::vector<gr_complex> &symbols, size_t kappa)
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: gr::block("freq_est_lr",
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gr::io_signature::make(1, 1, sizeof(gr_complex)),
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gr::io_signature::make(1, 1, sizeof(float))),
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d_refSymbols(symbols),
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d_kappa(kappa)
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{
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d_recvSymbols.reserve(symbols.size() + 1);
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message_port_register_out(pmt::mp("freq_offset"));
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}
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/*
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* Our virtual destructor.
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*/
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freq_est_lr_impl::~freq_est_lr_impl()
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{
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}
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void
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freq_est_lr_impl::forecast (int noutput_items, gr_vector_int &ninput_items_required)
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{
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ninput_items_required[0] = noutput_items;
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}
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int
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freq_est_lr_impl::general_work (int noutput_items,
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gr_vector_int &ninput_items,
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gr_vector_const_void_star &input_items,
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gr_vector_void_star &output_items)
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{
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const gr_complex *in = (const gr_complex *) input_items[0];
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float *out = (float *) output_items[0];
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std::vector<tag_t> tags;
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get_tags_in_window(tags, 0, 0, ninput_items[0], pmt::intern("corr_est")); // FIXME: make name variable
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size_t tagidx = 0;
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for(size_t i = 0; i < noutput_items; i++) {
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if((tagidx < tags.size()) && (tags[tagidx].offset == nitems_read(0) + i)) {
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d_recvSymbols.clear();
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tagidx++;
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}
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if(d_recvSymbols.size() < d_refSymbols.size()) {
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// buffer symbols of the preamble
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d_recvSymbols.push_back(in[i]);
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} else if(d_recvSymbols.size() == d_refSymbols.size()) {
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// received enough symbols for the preamble => do frequency estimation
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d_recvSymbols.push_back(0); //???
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// remove reference symbols from the received preamble
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std::vector<gr_complex> z;
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z.reserve(d_recvSymbols.size());
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for(size_t k = 0; k < d_recvSymbols.size(); k++) {
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z.push_back( d_recvSymbols[k] * conj(d_refSymbols[k]) );
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}
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// Calculate averaged phase increments for <N> sub-sequences
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size_t N = d_recvSymbols.size()/2;
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std::vector<gr_complex> R_kappa(N);
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for(size_t kappa = 0; kappa < N; kappa++) {
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for(size_t k = 0; k < d_recvSymbols.size() - kappa; k++) {
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R_kappa[kappa] += z[k + kappa] * conj(z[k]);
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}
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R_kappa[kappa] /= z.size() - kappa;
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}
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// Calculate phase estimate (in radians/sample)
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gr_complex sum_R_kappa(0, 0);
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for(size_t kappa = 0; kappa < N; kappa++) {
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sum_R_kappa += R_kappa[kappa];
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}
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float arg = gr::fast_atan2f(sum_R_kappa);
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d_freq_est = arg / (M_PI * (1 + N));
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message_port_pub(pmt::intern("freq_offset"), pmt::from_double(-d_freq_est));
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}
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out[i] = d_freq_est;
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}
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// Do <+signal processing+>
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// Tell runtime system how many input items we consumed on
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// each input stream.
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consume_each (noutput_items);
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// Tell runtime system how many output items we produced.
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return noutput_items;
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}
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} /* namespace hamnet70 */
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} /* namespace gr */
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