168 lines
5.3 KiB
C++
168 lines
5.3 KiB
C++
/* -*- c++ -*- */
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/*
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* Copyright 2005,2006 Free Software Foundation, Inc.
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*
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* Tone detect symbol recovery block for GR - Copyright 2012, KA1RBI
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*
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* This file is part of GNU Radio
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*
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* GNU Radio 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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* GNU Radio 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 GNU Radio; 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 <gr_io_signature.h>
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#include <gr_prefs.h>
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#include <gr_math.h>
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#include <gr_expj.h>
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#include <repeater_tdetect_cc.h>
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#include <gri_mmse_fir_interpolator_cc.h>
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#include <stdexcept>
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#include <cstdio>
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#include <string.h>
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#include "cic_filter.h"
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#define VERBOSE_TDETECT 0 // Used for debugging symbol timing loop
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// Public constructor
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repeater_tdetect_cc_sptr
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repeater_make_tdetect_cc (int samples_per_symbol, float step_size, int theta, int cic_length)
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{
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return repeater_tdetect_cc_sptr (new repeater_tdetect_cc (samples_per_symbol, step_size, theta, cic_length));
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}
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repeater_tdetect_cc::repeater_tdetect_cc (int samples_per_symbol, float step_size, int theta, int cic_length)
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: gr_block ("repeater_tdetect_cc",
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gr_make_io_signature (1, 1, sizeof (gr_complex)),
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gr_make_io_signature (1, 1, sizeof (gr_complex))),
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d_samples_per_symbol(samples_per_symbol),
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d_half_sps(samples_per_symbol >> 1),
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d_step_size(step_size),
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d_theta(theta),
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d_cic_length(cic_length),
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d_integrator(), d_comb(cic_length), input_delay(samples_per_symbol),
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d_l2ctr(0),
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d_delta(0),
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d_delta_c(0),
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d_previous_phase_offset(0)
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{
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assert((samples_per_symbol & 1) == 0); // sps must be even
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set_relative_rate (1.0 / (float) samples_per_symbol);
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set_history(samples_per_symbol * 2); // ensure extra input is available
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}
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repeater_tdetect_cc::~repeater_tdetect_cc ()
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{
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}
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void
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repeater_tdetect_cc::forecast(int noutput_items, gr_vector_int &ninput_items_required)
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{
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unsigned ninputs = ninput_items_required.size();
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for (unsigned i=0; i < ninputs; i++)
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ninput_items_required[i] =
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(int) ceil((noutput_items * d_samples_per_symbol));
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}
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/*
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* Tone detect symbol recovery block for GR - Copyright 2012, KA1RBI
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*
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* symbol timing synchronization using tone detection
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*
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* CQPSK signals when AM-demodulated contain a strong tone at 4,800 Hz.
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* This tone is filtered (using a CIC to remove the DC offset at zero Hz).,
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* amplified, and decimated. The resulting error signal is applied to steer
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* the symbol sampling point toward the optimum phase.
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*
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* NOTE: input samples should be normalized (AGC) such that the range of
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* signal magnitudes is in the standard zone (0 through +1.0).
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*
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*
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* Source: Software Radios (Second Ed.) B. Farhang-Boroujeny, Sec. 10.2.3
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*
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*/
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int
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repeater_tdetect_cc::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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gr_complex *out = (gr_complex *) output_items[0];
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int i=0, o=0;
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gr_complex sample;
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while((o < noutput_items) && (i < ninput_items[0])) {
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sample = in[ i++ ];
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sample = input_delay.cycle(sample, d_delta);
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if (++d_l2ctr < d_half_sps)
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continue; // decimate by sps/2
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d_l2ctr = 0;
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int64_t s = (int64_t) (262143.0 * (pow(sample.real(), 2.0) + pow(sample.imag(), 2.0))); /* mag sq */
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s = d_comb.cycle(s, d_cic_length);
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s = d_integrator.cycle(s);
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if (++d_d2ctr & 1)
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continue; // decimate by 2
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float symbol_error = d_step_size * (float)s;
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// now adjust delta_continuous by the amount of the symbol timing error
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d_delta_c += symbol_error;
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while (d_delta_c > d_samples_per_symbol)
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d_delta_c -= d_samples_per_symbol;
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while (d_delta_c < 0)
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d_delta_c += d_samples_per_symbol;
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d_delta = (int) rint(d_delta_c); // quantize to nearest int
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// d_theta sets optimum sampling point phase offset (delay),
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// in one-sample units
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int phase_offset = d_delta + d_theta;
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while (phase_offset > d_samples_per_symbol)
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phase_offset -= d_samples_per_symbol;
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while (phase_offset < 0)
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phase_offset += d_samples_per_symbol;
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// handle frequency mismatch between local clock and extracted clock
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// when mismatch reaches a full cycle we must either insert one "extra"
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// symbol or skip one symbol (depending on algebraic sign of mismatch)
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int dd = phase_offset - d_previous_phase_offset;
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int skip_store = 0;
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if (abs(dd) >= d_half_sps) {
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if (dd < 0 && o < noutput_items-1) {
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sample = input_delay.get(d_previous_phase_offset);
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out[o++] = sample;
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}
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if (dd > 0) {
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skip_store = 1;
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}
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}
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d_previous_phase_offset = phase_offset;
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if (!skip_store) {
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sample = input_delay.get(phase_offset);
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out[o++] = sample;
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}
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}
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consume_each(i);
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return o;
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}
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