GNU Radio 3.6.3.1 C++ API
cpm.h
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1 /* -*- c++ -*- */
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20 
21 
22 #ifndef INCLUDED_ANALOG_CPM_H
23 #define INCLUDED_ANALOG_CPM_H
24 
25 #include <analog/api.h>
26 #include <vector>
27 
28 namespace gr {
29  namespace analog {
30 
32  {
33  public:
34  enum cpm_type {
35  LRC,
38  TFM,
40  GENERIC = 999
41  };
42 
43  /*! \brief Return the taps for an interpolating FIR filter (gr_interp_fir_filter_fff).
44  *
45  * These taps represent the phase response \f$g(k)\f$ for use in a CPM modulator,
46  * see also gr_cpmmod_bc.
47  *
48  * \param type The CPM type (Rectangular, Raised Cosine, Spectral Raised Cosine,
49  * Tamed FM or Gaussian).
50  * \param samples_per_sym Samples per symbol.
51  * \param L The length of the phase response in symbols.
52  * \param beta For Spectral Raised Cosine, this is the rolloff factor. For Gaussian
53  * phase responses, this the 3dB-time-bandwidth product. For all other
54  * cases, it is ignored.
55  *
56  * Output: returns a vector of length \a K = \p samples_per_sym x \p L.
57  * This can be used directly in an interpolating FIR filter such as
58  * gr_interp_fir_filter_fff with interpolation factor \p samples_per_sym.
59  *
60  * All phase responses are normalised s.t. \f$ \sum_{k=0}^{K-1} g(k) = 1\f$; this will cause
61  * a maximum phase change of \f$ h \cdot \pi\f$ between two symbols, where \a h is the
62  * modulation index.
63  *
64  * The following phase responses can be generated:
65  * - LREC: Rectangular phase response.
66  * - LRC: Raised cosine phase response, looks like 1 - cos(x).
67  * - LSRC: Spectral raised cosine. This requires a rolloff factor beta.
68  * The phase response is the Fourier transform of raised cosine
69  * function.
70  * - TFM: Tamed frequency modulation. This scheme minimizes phase change for
71  * rapidly varying input symbols.
72  * - GAUSSIAN: A Gaussian phase response. For a modulation index h = 1/2, this
73  * results in GMSK.
74  *
75  * A short description of all these phase responses can be found in [1].
76  *
77  * [1]: Anderson, Aulin and Sundberg; Digital Phase Modulation
78  */
79  static std::vector<float>
80  phase_response(cpm_type type, unsigned samples_per_sym, unsigned L, double beta=0.3);
81  };
82  } // namespace analog
83 } // namespace gr
84 
85 #endif /* INCLUDED_ANALOG_CPM_H */
86