GNU Radio 3.5.1 C++ API
gr_cpm.h
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00001 /* -*- c++ -*- */
00002 /*
00003  * Copyright 2010 Free Software Foundation, Inc.
00004  *
00005  * GNU Radio is free software; you can redistribute it and/or modify
00006  * it under the terms of the GNU General Public License as published by
00007  * the Free Software Foundation; either version 3, or (at your option)
00008  * any later version.
00009  *
00010  * GNU Radio is distributed in the hope that it will be useful,
00011  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00012  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00013  * GNU General Public License for more details.
00014  *
00015  * You should have received a copy of the GNU General Public License
00016  * along with GNU Radio; see the file COPYING.  If not, write to
00017  * the Free Software Foundation, Inc., 51 Franklin Street,
00018  * Boston, MA 02110-1301, USA.
00019  */
00020 
00021 
00022 #ifndef INCLUDED_GR_CPM_H
00023 #define INCLUDED_GR_CPM_H
00024 
00025 #include <gr_core_api.h>
00026 #include <vector>
00027 
00028 class GR_CORE_API gr_cpm
00029 {
00030  public:
00031         enum cpm_type {
00032          LRC,
00033          LSRC,
00034          LREC,
00035          TFM,
00036          GAUSSIAN,
00037          GENERIC = 999
00038         };
00039 
00040     /*! \brief Return the taps for an interpolating FIR filter (gr_interp_fir_filter_fff).
00041          *
00042          * These taps represent the phase response \f$g(k)\f$ for use in a CPM modulator,
00043          * see also gr_cpmmod_bc.
00044          *
00045          * \param type The CPM type (Rectangular, Raised Cosine, Spectral Raised Cosine,
00046          *             Tamed FM or Gaussian).
00047          * \param samples_per_sym Samples per symbol.
00048          * \param L The length of the phase response in symbols.
00049          * \param beta For Spectral Raised Cosine, this is the rolloff factor. For Gaussian
00050          *             phase responses, this the 3dB-time-bandwidth product. For all other
00051          *             cases, it is ignored.
00052          *
00053          * Output: returns a vector of length \a K = \p samples_per_sym x \p L.
00054          *         This can be used directly in an interpolating FIR filter such as
00055          *         gr_interp_fir_filter_fff with interpolation factor \p samples_per_sym.
00056          *
00057          * All phase responses are normalised s.t. \f$ \sum_{k=0}^{K-1} g(k) = 1\f$; this will cause
00058          * a maximum phase change of \f$ h \cdot \pi\f$ between two symbols, where \a h is the
00059          * modulation index.
00060          *
00061          * The following phase responses can be generated:
00062          * - LREC: Rectangular phase response.
00063          * - LRC: Raised cosine phase response, looks like 1 - cos(x).
00064          * - LSRC: Spectral raised cosine. This requires a rolloff factor beta.
00065          *         The phase response is the Fourier transform of raised cosine
00066          *         function.
00067          * - TFM: Tamed frequency modulation. This scheme minimizes phase change for
00068          *        rapidly varying input symbols.
00069          * - GAUSSIAN: A Gaussian phase response. For a modulation index h = 1/2, this
00070          *             results in GMSK.
00071          *
00072          * A short description of all these phase responses can be found in [1].
00073          *
00074          * [1]: Anderson, Aulin and Sundberg; Digital Phase Modulation
00075      */
00076         static std::vector<float>
00077         phase_response(cpm_type type, unsigned samples_per_sym, unsigned L, double beta=0.3);
00078 };
00079 
00080 #endif /* INCLUDED_GR_CPM_H */
00081