GNU Radio Manual and C++ API Reference 3.7.14.0
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polyphase_filterbank.h
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1/* -*- c++ -*- */
2/*
3 * Copyright 2012 Free Software Foundation, Inc.
4 *
5 * This file is part of GNU Radio
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22
23
24#ifndef INCLUDED_FILTER_POLYPHASE_FILTERBANK_H
25#define INCLUDED_FILTER_POLYPHASE_FILTERBANK_H
26
27#include <gnuradio/fft/fft.h>
28#include <gnuradio/filter/api.h>
31
32namespace gr {
33namespace filter {
34namespace kernel {
35
36/*!
37 * \brief Polyphase filterbank parent class
38 * \ingroup filter_blk
39 * \ingroup pfb_blk
40 *
41 * \details
42 * This block takes in complex inputs and channelizes it to
43 * <EM>M</EM> channels of equal bandwidth. Each of the resulting
44 * channels is decimated to the new rate that is the input
45 * sampling rate <EM>fs</EM> divided by the number of channels,
46 * <EM>M</EM>.
47 *
48 * The PFB channelizer code takes the taps generated above and
49 * builds a set of filters. The set contains <EM>M</EM>
50 * filters and each filter contains ceil(taps.size()/decim)
51 * taps. Each tap from the filter prototype is
52 * sequentially inserted into the next filter. When all of the
53 * input taps are used, the remaining filters in the filterbank
54 * are filled out with 0's to make sure each filter has the same
55 * number of taps.
56 *
57 * Each filter operates using the gr::filter::fir_filter_XXX
58 * class of GNU Radio, which takes the input stream at
59 * <EM>i</EM> and performs the inner product calculation to
60 * <EM>i+(n-1)</EM> where <EM>n</EM> is the number of filter
61 * taps. To efficiently handle this in the GNU Radio structure,
62 * each filter input must come from its own input stream. So the
63 * channelizer must be provided with <EM>M</EM> streams where
64 * the input stream has been deinterleaved. This is most easily
65 * done using the gr::blocks::stream_to_streams block.
66 *
67 * The output is then produced as a vector, where index
68 * <EM>i</EM> in the vector is the next sample from the
69 * <EM>i</EM>th channel. This is most easily handled by sending
70 * the output to a gr::blocks::vector_to_streams block to handle
71 * the conversion and passing <EM>M</EM> streams out.
72 *
73 * The input and output formatting is done using a hier_block2
74 * called pfb_channelizer_ccf. This can take in a single stream
75 * and outputs <EM>M</EM> streams based on the behavior
76 * described above.
77 *
78 * The filter's taps should be based on the input sampling rate.
79 *
80 * For example, using the GNU Radio's firdes utility to building
81 * filters, we build a low-pass filter with a sampling rate of
82 * <EM>fs</EM>, a 3-dB bandwidth of <EM>BW</EM> and a transition
83 * bandwidth of <EM>TB</EM>. We can also specify the out-of-band
84 * attenuation to use, <EM>ATT</EM>, and the filter window
85 * function (a Blackman-harris window in this case). The first
86 * input is the gain of the filter, which we specify here as
87 * unity.
88 *
89 * <B><EM>self._taps = filter.firdes.low_pass_2(1, fs, BW, TB,
90 * attenuation_dB=ATT, window=filter.firdes.WIN_BLACKMAN_hARRIS)</EM></B>
91 *
92 * More on the theory of polyphase filterbanks can be found in
93 * the following book:
94 *
95 * <B><EM>f. harris, "Multirate Signal Processing for
96 * Communication Systems," Upper Saddle River, NJ:
97 * Prentice Hall, Inc. 2004.</EM></B>
98 *
99 */
100
102{
103protected:
104 unsigned int d_nfilts;
105 std::vector<kernel::fir_filter_ccf*> d_fir_filters;
106 std::vector<kernel::fft_filter_ccf*> d_fft_filters;
107 std::vector<std::vector<float> > d_taps;
108 unsigned int d_taps_per_filter;
110
111public:
112 /*!
113 * Build the polyphase filterbank decimator.
114 * \param nfilts (unsigned integer) Specifies the number of
115 * channels <EM>M</EM>
116 * \param taps (vector/list of floats) The prototype filter to
117 * populate the filterbank.
118 * \param fft_forward (bool) use a forward or inverse FFT (default=false).
119 */
120 polyphase_filterbank(unsigned int nfilts,
121 const std::vector<float>& taps,
122 bool fft_forward = false);
123
125
126 /*!
127 * Update the filterbank's filter taps from a prototype
128 * filter.
129 *
130 * \param taps (vector/list of floats) The prototype filter to
131 * populate the filterbank.
132 */
133 virtual void set_taps(const std::vector<float>& taps);
134
135 /*!
136 * Print all of the filterbank taps to screen.
137 */
139
140 /*!
141 * Return a vector<vector<>> of the filterbank taps
142 */
143 std::vector<std::vector<float> > taps() const;
144};
145
146} /* namespace kernel */
147} /* namespace filter */
148} /* namespace gr */
149
150#endif /* INCLUDED_FILTER_POLYPHASE_FILTERBANK_H */
FFT: complex in, complex out.
Definition: fft.h:73
Polyphase filterbank parent class.
Definition: polyphase_filterbank.h:102
std::vector< kernel::fir_filter_ccf * > d_fir_filters
Definition: polyphase_filterbank.h:105
virtual void set_taps(const std::vector< float > &taps)
fft::fft_complex * d_fft
Definition: polyphase_filterbank.h:109
polyphase_filterbank(unsigned int nfilts, const std::vector< float > &taps, bool fft_forward=false)
std::vector< kernel::fft_filter_ccf * > d_fft_filters
Definition: polyphase_filterbank.h:106
unsigned int d_nfilts
Definition: polyphase_filterbank.h:104
std::vector< std::vector< float > > d_taps
Definition: polyphase_filterbank.h:107
std::vector< std::vector< float > > taps() const
unsigned int d_taps_per_filter
Definition: polyphase_filterbank.h:108
#define FILTER_API
Definition: gr-filter/include/gnuradio/filter/api.h:30
static const float taps[NSTEPS+1][NTAPS]
Definition: interpolator_taps.h:9
Include this header to use the message passing features.
Definition: basic_block.h:45