hamnet70-gnuradio-legacy/gr-hamnet70/lib/qam_phase_tracker_impl.cc

/* -*- 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/expj.h>
#include <gnuradio/math.h>
#include "qam_phase_tracker_impl.h"

namespace gr {
	namespace hamnet70 {

		qam_phase_tracker::sptr
		qam_phase_tracker::make(const std::vector<gr_complex> &symbols, float alpha, const std::string &start_tag)
		{
			return gnuradio::get_initial_sptr
				(new qam_phase_tracker_impl(symbols, alpha, start_tag));
		}


		/*
		 * The private constructor
		 */
		qam_phase_tracker_impl::qam_phase_tracker_impl(const std::vector<gr_complex> &symbols, float alpha, const std::string &start_tag)
			: gr::sync_block("qam_phase_tracker",
					gr::io_signature::make(1, 1, sizeof(gr_complex)),
					gr::io_signature::make(1, 1, sizeof(gr_complex))),
				d_alpha(alpha),
				d_startTag(pmt::intern(start_tag)),
				d_avgPhaseOffset(0.0f)
		{
			// use only symbols in the upper right quadrant
			for(auto s : symbols) {
				if(s.real() >= 0 && s.imag() >= 0) {
					d_refSymbols.push_back(s);
					d_refPhase.push_back(gr::fast_atan2f(s));
				}
			}
		}

		/*
		 * Our virtual destructor.
		 */
		qam_phase_tracker_impl::~qam_phase_tracker_impl()
		{
		}

		int
		qam_phase_tracker_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];
			gr_complex *out = (gr_complex *) output_items[0];

			for(int i = 0; i < noutput_items; i++) {
				out[i] = in[i] * gr_expj(-d_avgPhaseOffset);

				std::vector<tag_t> tags;
				get_tags_in_window(tags, 0, i, i+1, d_startTag);

				if(tags.size() > 0) {
					// start tag found on this item -> reset average
					d_avgPhaseOffset = 0;
				}

				// update average phase offset from current symbol

				gr_complex rotated = out[i];

				float re = rotated.real();
				float im = rotated.imag();

				// normalize to positive quadrant
				if(re < 0 && im > 0) {
					rotated *= gr_expj(-M_PI/2);
				} else if(re < 0 && im < 0) {
					rotated *= -1;
				} else if(im < 0) { // && re > 0
					rotated *= gr_expj(M_PI/2);
				} // else already ok

				// find closest reference symbol
				float min_dist = 1e9;
				size_t closest_idx;

				for(size_t r = 0; r < d_refSymbols.size(); r++) {
					float d = std::norm(d_refSymbols[r] - rotated);

					if(d < min_dist) {
						closest_idx = r;
						min_dist = d;
					}
				}

				float phase = gr::fast_atan2f(rotated);
				float delta_phase = phase - d_refPhase[closest_idx];

				if(delta_phase > M_PI/4 || delta_phase < -M_PI/4) {
					continue;
				}

				d_avgPhaseOffset += d_alpha * delta_phase;
			}

			// Tell runtime system how many output items we produced.
			return noutput_items;
		}

	} /* namespace hamnet70 */
} /* namespace gr */