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gri_mmse_fir_interpolator.h
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1 /* -*- c++ -*- */
2 /*
3  * Copyright 2002 Free Software Foundation, Inc.
4  *
5  * This file is part of GNU Radio
6  *
7  * GNU Radio is free software; you can redistribute it and/or modify
8  * it under the terms of the GNU General Public License as published by
9  * the Free Software Foundation; either version 3, or (at your option)
10  * any later version.
11  *
12  * GNU Radio is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15  * GNU General Public License for more details.
16  *
17  * You should have received a copy of the GNU General Public License
18  * along with GNU Radio; see the file COPYING. If not, write to
19  * the Free Software Foundation, Inc., 51 Franklin Street,
20  * Boston, MA 02110-1301, USA.
21  */
22 #ifndef _GRI_MMSE_FIR_INTERPOLATOR_H_
23 #define _GRI_MMSE_FIR_INTERPOLATOR_H_
24 
25 #include <gr_core_api.h>
26 #include <vector>
27 
28 class gr_fir_fff;
29 
30 /*!
31  * \brief Compute intermediate samples between signal samples x(k*Ts)
32  * \ingroup filter_primitive
33  *
34  * This implements a Mininum Mean Squared Error interpolator with 8 taps.
35  * It is suitable for signals where the bandwidth of interest B = 1/(4*Ts)
36  * Where Ts is the time between samples.
37  *
38  * Although mu, the fractional delay, is specified as a float, it is actually
39  * quantized. 0.0 <= mu <= 1.0. That is, mu is quantized in the interpolate
40  * method to 32nd's of a sample.
41  *
42  * For more information, in the GNU Radio source code, see:
43  * \li gnuradio-core/src/gen_interpolator_taps/README
44  * \li gnuradio-core/src/gen_interpolator_taps/praxis.txt
45  */
46 
48 public:
51 
52  unsigned ntaps () const;
53  unsigned nsteps () const;
54 
55  /*!
56  * \brief compute a single interpolated output value.
57  * \p input must have ntaps() valid entries.
58  * input[0] .. input[ntaps() - 1] are referenced to compute the output value.
59  *
60  * \p mu must be in the range [0, 1] and specifies the fractional delay.
61  *
62  * \returns the interpolated input value.
63  */
64  float interpolate (const float input[], float mu) const;
65 
66 protected:
67  std::vector<gr_fir_fff *> filters;
68 };
69 
70 
71 #endif /* _GRI_MMSE_FIR_INTERPOLATOR_H_ */