cpm.h

Go to the documentation of this file.

/* -*- c++ -*- */
/*
 * Copyright 2010,2012 Free Software Foundation, Inc.
 *
 * 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_ANALOG_CPM_H
#define INCLUDED_ANALOG_CPM_H

#include <gnuradio/analog/api.h>
#include <vector>

namespace gr {
  namespace analog {

    /*! \brief Return the taps for an interpolating FIR filter
     *   (gr::filter::interp_fir_filter_fff).
     */
    class ANALOG_API cpm
    {
    public:
      enum cpm_type {
        LRC,
        LSRC,
        LREC,
        TFM,
        GAUSSIAN,
        GENERIC = 999
      };

      /*! \brief Return the taps for an interpolating FIR filter
       *   (gr::filter::interp_fir_filter_fff).
       *
       * \details
       * These taps represent the phase response \f$g(k)\f$ for use in a CPM modulator,
       * see also gr_cpmmod_bc.
       *
       * \param type The CPM type (Rectangular, Raised Cosine,
       *             Spectral Raised Cosine, Tamed FM or Gaussian).
       * \param samples_per_sym Samples per symbol.
       * \param L The length of the phase response in symbols.
       * \param beta For Spectral Raised Cosine, this is the rolloff
       *             factor. For Gaussian phase responses, this the
       *             3dB-time-bandwidth product. For all other cases,
       *             it is ignored.
       *
       * Output: returns a vector of length \a K = \p samples_per_sym
       *         x \p L.  This can be used directly in an
       *         interpolating FIR filter such as
       *         gr_interp_fir_filter_fff with interpolation factor \p
       *         samples_per_sym.
       *
       * All phase responses are normalised s.t. \f$ \sum_{k=0}^{K-1}
       * g(k) = 1\f$; this will cause a maximum phase change of \f$ h
       * \cdot \pi\f$ between two symbols, where \a h is the
       * modulation index.
       *
       * The following phase responses can be generated:
       * - LREC: Rectangular phase response.
       * - LRC: Raised cosine phase response, looks like 1 - cos(x).
       * - LSRC: Spectral raised cosine. This requires a rolloff factor beta.
       *         The phase response is the Fourier transform of raised cosine
       *         function.
       * - TFM: Tamed frequency modulation. This scheme minimizes phase change for
       *        rapidly varying input symbols.
       * - GAUSSIAN: A Gaussian phase response. For a modulation index h = 1/2, this
       *             results in GMSK.
       *
       * A short description of all these phase responses can be found in [1].
       *
       * [1]: Anderson, Aulin and Sundberg; Digital Phase Modulation
       */
      static std::vector<float>
        phase_response(cpm_type type, unsigned samples_per_sym,
                       unsigned L, double beta=0.3);
    };
  } // namespace analog
} // namespace gr

#endif /* INCLUDED_ANALOG_CPM_H */