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.
135 lines
3.6 KiB
C++
135 lines
3.6 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/expj.h>
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#include <gnuradio/math.h>
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#include "correct_frequency_impl.h"
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namespace gr {
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namespace hamnet70 {
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correct_frequency::sptr
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correct_frequency::make(const std::vector<gr_complex> &symbols)
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{
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return gnuradio::get_initial_sptr
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(new correct_frequency_impl(symbols));
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}
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/*
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* The private constructor
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*/
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correct_frequency_impl::correct_frequency_impl(const std::vector<gr_complex> &symbols)
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: gr::sync_block("correct_frequency",
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gr::io_signature::make(1, 1, sizeof(gr_complex)),
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gr::io_signature::make(1, 1, sizeof(gr_complex))),
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d_symbols(symbols),
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d_correctionIncrement(1, 0),
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d_correctionVector(1, 0),
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d_filteredPhaseInc(0.0f),
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d_preIdx(symbols.size()+1) // somewhere out of symbols' index range
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{}
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/*
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* Our virtual destructor.
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*/
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correct_frequency_impl::~correct_frequency_impl()
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{
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}
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int
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correct_frequency_impl::work(int noutput_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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gr_complex *out = (gr_complex *) output_items[0];
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std::vector<tag_t> tags;
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get_tags_in_window(tags, 0, 0, noutput_items, pmt::intern("corr_est")); // FIXME: make name variable
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size_t tagidx = 0;
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for(int 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_preIdx = 0;
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tagidx++;
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}
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if(d_preIdx < d_symbols.size()) {
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gr_complex tmp = conj(d_symbols[d_preIdx]) * (*in);
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float phase = gr::fast_atan2f(tmp);
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if(d_preIdx != 0) {
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float phaseIncrement = phase - d_lastPhase;
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if(phaseIncrement > M_PI) {
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add_item_tag(0, nitems_read(0) + i, pmt::intern("phase_overflow"), pmt::from_double(phaseIncrement));
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phaseIncrement -= 2*M_PI;
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} else if(phaseIncrement < -M_PI) {
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add_item_tag(0, nitems_read(0) + i, pmt::intern("phase_underflow"), pmt::from_double(phaseIncrement));
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phaseIncrement += 2*M_PI;
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}
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/*
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d_filteredPhaseInc = c_phaseInc_alpha * phaseIncrement +
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(1 - c_phaseInc_alpha) * d_filteredPhaseInc;
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*/
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d_filteredPhaseInc += phaseIncrement;
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if(d_preIdx > d_symbols.size()/2) {
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d_correctionIncrement = gr_expj(-d_filteredPhaseInc/d_preIdx);
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}
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} else {
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d_unwrapOffset = 0;
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d_filteredPhaseInc = 0;
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}
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d_lastPhase = phase;
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if(d_preIdx == d_symbols.size()/2) {
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d_correctionVector = gr_complex(1, 0);
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}
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d_preIdx++;
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}
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d_correctionVector *= d_correctionIncrement;
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*out = *in * d_correctionVector;
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in++;
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out++;
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}
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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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