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/* -*- 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>
class 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 */
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