133 lines
3.5 KiB
C++
133 lines
3.5 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 "qam_phase_tracker_impl.h"
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namespace gr {
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namespace hamnet70 {
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qam_phase_tracker::sptr
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qam_phase_tracker::make(const std::vector<gr_complex> &symbols, float alpha, const std::string &start_tag)
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{
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return gnuradio::get_initial_sptr
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(new qam_phase_tracker_impl(symbols, alpha, start_tag));
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}
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/*
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* The private constructor
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*/
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qam_phase_tracker_impl::qam_phase_tracker_impl(const std::vector<gr_complex> &symbols, float alpha, const std::string &start_tag)
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: gr::sync_block("qam_phase_tracker",
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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_alpha(alpha),
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d_startTag(pmt::intern(start_tag)),
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d_avgPhaseOffset(0.0f)
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{
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// use only symbols in the upper right quadrant
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for(auto s : symbols) {
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if(s.real() >= 0 && s.imag() >= 0) {
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d_refSymbols.push_back(s);
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d_refPhase.push_back(gr::fast_atan2f(s));
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}
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}
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}
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/*
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* Our virtual destructor.
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*/
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qam_phase_tracker_impl::~qam_phase_tracker_impl()
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{
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}
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int
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qam_phase_tracker_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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for(int i = 0; i < noutput_items; i++) {
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out[i] = in[i] * gr_expj(-d_avgPhaseOffset);
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std::vector<tag_t> tags;
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get_tags_in_window(tags, 0, i, i+1, d_startTag);
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if(tags.size() > 0) {
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// start tag found on this item -> reset average
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d_avgPhaseOffset = 0;
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}
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// update average phase offset from current symbol
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gr_complex rotated = out[i];
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float re = rotated.real();
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float im = rotated.imag();
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// normalize to positive quadrant
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if(re < 0 && im > 0) {
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rotated *= gr_expj(-M_PI/2);
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} else if(re < 0 && im < 0) {
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rotated *= -1;
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} else if(im < 0) { // && re > 0
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rotated *= gr_expj(M_PI/2);
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} // else already ok
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// find closest reference symbol
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float min_dist = 1e9;
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size_t closest_idx;
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for(size_t r = 0; r < d_refSymbols.size(); r++) {
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float d = std::norm(d_refSymbols[r] - rotated);
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if(d < min_dist) {
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closest_idx = r;
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min_dist = d;
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}
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}
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float phase = gr::fast_atan2f(rotated);
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float delta_phase = phase - d_refPhase[closest_idx];
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if(delta_phase > M_PI/4 || delta_phase < -M_PI/4) {
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continue;
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}
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d_avgPhaseOffset += d_alpha * delta_phase;
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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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