/* -*- 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

#define M_TWOPI (2*M_PI)

class gr_cpm

{

 public:

        enum cpm_type {

         LRC,

         LSRC,

         LREC,

         TFM,

         GAUSSIAN,

         GENERIC = 999

        };

        //! Return the taps for an interpolating FIR filter (gr_fir_filter_fff).

        //

        // These taps represent the phase response for use in a CPM modulator.

        //

        // Parameters:

        // \p type: The CPM type (Rectangular, Raised Cosine, Spectral Raised Cosine,

        //          Tamed FM or Gaussian).

        // \p samples_per_sym: Samples per symbol.

        // \p L: The length of the phase response in symbols.

        // \p 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 \p L * \p samples_per_sym. 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 taps are normalised s.t. \sum taps = 1; this causes a maximum phase change

        // of h*pi between two symbols, where 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.

        //

        static std::vector<float>

        phase_response(cpm_type type, unsigned samples_per_sym, unsigned L, double beta=0.3);

};

#endif /* INCLUDED_GR_CPM_H */