/* -*- 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 <vector>

#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.
	//
	// 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 */