gr_clock_recovery_mm_ff.cc

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/* -*- c++ -*- */
/*
 * Copyright 2004 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * GNU Radio 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.
 *
 * GNU Radio 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 GNU Radio; 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 <gr_io_signature.h>
#include <gr_clock_recovery_mm_ff.h>
#include <gri_mmse_fir_interpolator.h>
#include <stdexcept>

#define DEBUG_CR_MM_FF	0		// must be defined as 0 or 1

// Public constructor

gr_clock_recovery_mm_ff_sptr 
gr_make_clock_recovery_mm_ff(float omega, float gain_omega, float mu, float gain_mu,
			     float omega_relative_limit)
{
  return gr_clock_recovery_mm_ff_sptr (new gr_clock_recovery_mm_ff (omega,
								    gain_omega, 
								    mu,
								    gain_mu,
								    omega_relative_limit));
}

gr_clock_recovery_mm_ff::gr_clock_recovery_mm_ff (float omega, float gain_omega, float mu, float gain_mu,
						  float omega_relative_limit)
  : gr_block ("clock_recovery_mm_ff",
	      gr_make_io_signature (1, 1, sizeof (float)),
	      gr_make_io_signature (1, 1, sizeof (float))),
    d_mu (mu), d_gain_omega(gain_omega), d_gain_mu(gain_mu),
    d_last_sample(0), d_interp(new gri_mmse_fir_interpolator()),
    d_logfile(0), d_omega_relative_limit(omega_relative_limit)
{
  if (omega <  1)
    throw std::out_of_range ("clock rate must be > 0");
  if (gain_mu <  0  || gain_omega < 0)
    throw std::out_of_range ("Gains must be non-negative");

  set_omega(omega);			// also sets min and max omega
  set_relative_rate (1.0 / omega);

  if (DEBUG_CR_MM_FF)
    d_logfile = fopen("cr_mm_ff.dat", "wb");
}

gr_clock_recovery_mm_ff::~gr_clock_recovery_mm_ff ()
{
  delete d_interp;

  if (DEBUG_CR_MM_FF && d_logfile){
    fclose(d_logfile);
    d_logfile = 0;
  }
}

void
gr_clock_recovery_mm_ff::forecast(int noutput_items, gr_vector_int &ninput_items_required)
{
  unsigned ninputs = ninput_items_required.size();
  for (unsigned i=0; i < ninputs; i++)
    ninput_items_required[i] =
      (int) ceil((noutput_items * d_omega) + d_interp->ntaps());
}

static inline float
slice(float x)
{
  return x < 0 ? -1.0F : 1.0F;
}

/*
 * This implements the Mueller and Müller (M&M) discrete-time error-tracking synchronizer.
 *
 * See "Digital Communication Receivers: Synchronization, Channel
 * Estimation and Signal Processing" by Heinrich Meyr, Marc Moeneclaey, & Stefan Fechtel.
 * ISBN 0-471-50275-8.
 */
int
gr_clock_recovery_mm_ff::general_work (int noutput_items,
				       gr_vector_int &ninput_items,
				       gr_vector_const_void_star &input_items,
				       gr_vector_void_star &output_items)
{
  const float *in = (const float *) input_items[0];
  float *out = (float *) output_items[0];

  int 	ii = 0;				// input index
  int  	oo = 0;				// output index
  float mm_val;

  while (oo < noutput_items){

    // produce output sample
    out[oo] = d_interp->interpolate (&in[ii], d_mu);
    mm_val = slice(d_last_sample) * out[oo] - slice(out[oo]) * d_last_sample;
    d_last_sample = out[oo];

    d_omega = d_omega + d_gain_omega * mm_val;
    if (d_omega > d_max_omega)
      d_omega = d_max_omega;
    else if (d_omega < d_min_omega)
      d_omega = d_min_omega;

    d_mu = d_mu + d_omega + d_gain_mu * mm_val;

    ii += (int) floor(d_mu);
    d_mu = d_mu - floor(d_mu);
    oo++;

    if (DEBUG_CR_MM_FF && d_logfile){
      fwrite(&d_omega, sizeof(d_omega), 1, d_logfile);
    }
  }

  consume_each (ii);

  return noutput_items;
}