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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
#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 */
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