GNU Radio 3.6.5.1 C++ API
gr_cpm.h
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20 
21 
22 #ifndef INCLUDED_GR_CPM_H
23 #define INCLUDED_GR_CPM_H
24 
25 #include <gr_core_api.h>
26 #include <vector>
27 
29 {
30  public:
31  enum cpm_type {
32  LRC,
35  TFM,
37  GENERIC = 999
38  };
39 
40  /*! \brief Return the taps for an interpolating FIR filter (gr_interp_fir_filter_fff).
41  *
42  * These taps represent the phase response \f$g(k)\f$ for use in a CPM modulator,
43  * see also gr_cpmmod_bc.
44  *
45  * \param type The CPM type (Rectangular, Raised Cosine, Spectral Raised Cosine,
46  * Tamed FM or Gaussian).
47  * \param samples_per_sym Samples per symbol.
48  * \param L The length of the phase response in symbols.
49  * \param beta For Spectral Raised Cosine, this is the rolloff factor. For Gaussian
50  * phase responses, this the 3dB-time-bandwidth product. For all other
51  * cases, it is ignored.
52  *
53  * Output: returns a vector of length \a K = \p samples_per_sym x \p L.
54  * This can be used directly in an interpolating FIR filter such as
55  * gr_interp_fir_filter_fff with interpolation factor \p samples_per_sym.
56  *
57  * All phase responses are normalised s.t. \f$ \sum_{k=0}^{K-1} g(k) = 1\f$; this will cause
58  * a maximum phase change of \f$ h \cdot \pi\f$ between two symbols, where \a h is the
59  * modulation index.
60  *
61  * The following phase responses can be generated:
62  * - LREC: Rectangular phase response.
63  * - LRC: Raised cosine phase response, looks like 1 - cos(x).
64  * - LSRC: Spectral raised cosine. This requires a rolloff factor beta.
65  * The phase response is the Fourier transform of raised cosine
66  * function.
67  * - TFM: Tamed frequency modulation. This scheme minimizes phase change for
68  * rapidly varying input symbols.
69  * - GAUSSIAN: A Gaussian phase response. For a modulation index h = 1/2, this
70  * results in GMSK.
71  *
72  * A short description of all these phase responses can be found in [1].
73  *
74  * [1]: Anderson, Aulin and Sundberg; Digital Phase Modulation
75  */
76  static std::vector<float>
77  phase_response(cpm_type type, unsigned samples_per_sym, unsigned L, double beta=0.3);
78 };
79 
80 #endif /* INCLUDED_GR_CPM_H */
81