/* -*- c++ -*- */

/*

 * Copyright 2010 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_GR_CPM_H

#define INCLUDED_GR_CPM_H

#include <gr_core_api.h>

#include <vector>

class GR_CORE_API gr_cpm

{

 public:

        enum cpm_type {

         LRC,

         LSRC,

         LREC,

         TFM,

         GAUSSIAN,

         GENERIC = 999

        };

    /*! \brief Return the taps for an interpolating FIR filter (gr_interp_fir_filter_fff).

         *

         * 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);

};

#endif /* INCLUDED_GR_CPM_H */