GNU Radio v3.6.2-149-ga6d285d9 C++ API
cpm.h
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00001 /* -*- c++ -*- */
00002 /*
00003  * Copyright 2010,2012 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_ANALOG_CPM_H
00023 #define INCLUDED_ANALOG_CPM_H
00024 
00025 #include <analog/api.h>
00026 #include <vector>
00027 
00028 namespace gr {
00029   namespace analog {
00030 
00031     class ANALOG_API cpm
00032     {
00033     public:
00034       enum cpm_type {
00035         LRC,
00036         LSRC,
00037         LREC,
00038         TFM,
00039         GAUSSIAN,
00040         GENERIC = 999
00041       };
00042       
00043       /*! \brief Return the taps for an interpolating FIR filter (gr_interp_fir_filter_fff).
00044        *
00045        * These taps represent the phase response \f$g(k)\f$ for use in a CPM modulator,
00046        * see also gr_cpmmod_bc.
00047        *
00048        * \param type The CPM type (Rectangular, Raised Cosine, Spectral Raised Cosine,
00049        *             Tamed FM or Gaussian).
00050        * \param samples_per_sym Samples per symbol.
00051        * \param L The length of the phase response in symbols.
00052        * \param beta For Spectral Raised Cosine, this is the rolloff factor. For Gaussian
00053        *             phase responses, this the 3dB-time-bandwidth product. For all other
00054        *             cases, it is ignored.
00055        *
00056        * Output: returns a vector of length \a K = \p samples_per_sym x \p L.
00057        *         This can be used directly in an interpolating FIR filter such as
00058        *         gr_interp_fir_filter_fff with interpolation factor \p samples_per_sym.
00059        *
00060        * All phase responses are normalised s.t. \f$ \sum_{k=0}^{K-1} g(k) = 1\f$; this will cause
00061        * a maximum phase change of \f$ h \cdot \pi\f$ between two symbols, where \a h is the
00062        * modulation index.
00063        *
00064        * The following phase responses can be generated:
00065        * - LREC: Rectangular phase response.
00066        * - LRC: Raised cosine phase response, looks like 1 - cos(x).
00067        * - LSRC: Spectral raised cosine. This requires a rolloff factor beta.
00068        *         The phase response is the Fourier transform of raised cosine
00069        *         function.
00070        * - TFM: Tamed frequency modulation. This scheme minimizes phase change for
00071        *        rapidly varying input symbols.
00072        * - GAUSSIAN: A Gaussian phase response. For a modulation index h = 1/2, this
00073        *             results in GMSK.
00074        *
00075        * A short description of all these phase responses can be found in [1].
00076        *
00077        * [1]: Anderson, Aulin and Sundberg; Digital Phase Modulation
00078        */
00079       static std::vector<float>
00080         phase_response(cpm_type type, unsigned samples_per_sym, unsigned L, double beta=0.3);
00081     };
00082   } // namespace analog
00083 } // namespace gr
00084 
00085 #endif /* INCLUDED_ANALOG_CPM_H */
00086