gr_costas_loop_cc.h

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/* -*- c++ -*- */
/*
 * Copyright 2006 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.
 */


#ifndef INCLUDED_GR_COSTAS_LOOP_CC_H
#define INCLUDED_GR_COSTAS_LOOP_CC_H

#include <gr_sync_block.h>
#include <stdexcept>
#include <fstream>


/*! \brief A Costas loop carrier recovery module.
 * \ingroup sync_blk
 *  
 *  The Costas loop locks to the center frequency of a signal and
 *  downconverts it to baseband. The second (order=2) order loop is
 *  used for BPSK where the real part of the output signal is the
 *  baseband BPSK signal and the imaginary part is the error
 *  signal. When order=4, it can be used for quadrature modulations
 *  where both I and Q (real and imaginary) are outputted.
 *
 *  More details can be found online:
 *
 *  J. Feigin, "Practical Costas loop design: Designing a simple and inexpensive
 *  BPSK Costas loop carrier recovery circuit," RF signal processing, pp. 20-36,
 *  2002.
 *
 *  http://rfdesign.com/images/archive/0102Feigin20.pdf
 *  
 * \param alpha the loop gain used for phase adjustment
 * \param beta the loop gain for frequency adjustments
 * \param max_freq the maximum frequency deviation (radians/sample) the loop can handle
 * \param min_freq the minimum frequency deviation (radians/sample) the loop can handle
 * \param order the loop order, either 2 or 4
 */
class gr_costas_loop_cc;
typedef boost::shared_ptr<gr_costas_loop_cc> gr_costas_loop_cc_sptr;


gr_costas_loop_cc_sptr 
gr_make_costas_loop_cc (float alpha, float beta,
                        float max_freq, float min_freq, 
                        int order
                        ) throw (std::invalid_argument);


/*!
 * \brief Carrier tracking PLL for QPSK
 * \ingroup sync_blk
 * input: complex; output: complex
 * <br>The Costas loop can have two output streams:
 *    stream 1 is the baseband I and Q;
 *    stream 2 is the normalized frequency of the loop
 *
 * \p order must be 2 or 4.
 */
class gr_costas_loop_cc : public gr_sync_block
{
  friend gr_costas_loop_cc_sptr gr_make_costas_loop_cc (float alpha, float beta,
                                                        float max_freq, float min_freq, 
                                                        int order
                                                        ) throw (std::invalid_argument);

  float d_alpha, d_beta, d_max_freq, d_min_freq, d_phase, d_freq;
  int d_order;

  gr_costas_loop_cc (float alpha, float beta,
                     float max_freq, float min_freq, 
                     int order
                     ) throw (std::invalid_argument);

  /*! \brief the phase detector circuit for fourth-order loops
   *  \param sample complex sample
   *  \return the phase error
   */
  float phase_detector_4(gr_complex sample) const;    // for QPSK

  /*! \brief the phase detector circuit for second-order loops
   *  \param sample a complex sample
   *  \return the phase error
   */
  float phase_detector_2(gr_complex sample) const;    // for BPSK


  float (gr_costas_loop_cc::*d_phase_detector)(gr_complex sample) const;

public:

  /*! \brief set the first order gain
   *  \param alpha
   */
  void set_alpha(float alpha);

  /*! \brief get the first order gain
   * 
   */
  float alpha() const { return d_alpha; }
  
  /*! \brief set the second order gain
   *  \param beta
   */
  void set_beta(float beta);

  /*! \brief get the second order gain
   * 
   */
  float beta() const { return d_beta; }
  
  int work (int noutput_items,
            gr_vector_const_void_star &input_items,
            gr_vector_void_star &output_items);

  /*! \brief returns the current NCO frequency in radians/sample
   *
   */
  float freq() const { return d_freq; }
};

#endif