GNU Radio Manual and C++ API Reference 3.7.14.0
The Free & Open Software Radio Ecosystem
pfb_decimator_ccf.h
Go to the documentation of this file.
1/* -*- c++ -*- */
2/*
3 * Copyright 2009,2012 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
23
24#ifndef INCLUDED_PFB_DECIMATOR_CCF_H
25#define INCLUDED_PFB_DECIMATOR_CCF_H
26
27#include <gnuradio/filter/api.h>
28#include <gnuradio/sync_block.h>
29
30namespace gr {
31namespace filter {
32
33/*!
34 * \brief Polyphase filterbank bandpass decimator with gr_complex
35 * input, gr_complex output and float taps
36 * \ingroup channelizers_blk
37 *
38 * \details
39 * This block takes in a signal stream and performs integer down-
40 * sampling (decimation) with a polyphase filterbank. The first
41 * input is the integer specifying how much to decimate by. The
42 * second input is a vector (Python list) of floating-point taps
43 * of the prototype filter. The third input specifies the channel
44 * to extract. By default, the zeroth channel is used, which is
45 * the baseband channel (first Nyquist zone).
46 *
47 * The <EM>channel</EM> parameter specifies which channel to use
48 * since this class is capable of bandpass decimation. Given a
49 * complex input stream at a sampling rate of <EM>fs</EM> and a
50 * decimation rate of <EM>decim</EM>, the input frequency domain
51 * is split into <EM>decim</EM> channels that represent the
52 * Nyquist zones. Using the polyphase filterbank, we can select
53 * any one of these channels to decimate.
54 *
55 * The output signal will be the basebanded and decimated signal
56 * from that channel. This concept is very similar to the PFB
57 * channelizer (see #gr::filter::pfb_channelizer_ccf) where only a single
58 * channel is extracted at a time.
59 *
60 * The filter's taps should be based on the sampling rate before
61 * decimation.
62 *
63 * For example, using the GNU Radio's firdes utility to building
64 * filters, we build a low-pass filter with a sampling rate of
65 * <EM>fs</EM>, a 3-dB bandwidth of <EM>BW</EM> and a transition
66 * bandwidth of <EM>TB</EM>. We can also specify the out-of-band
67 * attenuation to use, <EM>ATT</EM>, and the filter window
68 * function (a Blackman-harris window in this case). The first
69 * input is the gain of the filter, which we specify here as
70 * unity.
71 *
72 * <B><EM>self._taps = filter.firdes.low_pass_2(1, fs, BW, TB,
73 * attenuation_dB=ATT, window=filter.firdes.WIN_BLACKMAN_hARRIS)</EM></B>
74 *
75 * The PFB decimator code takes the taps generated above and
76 * builds a set of filters. The set contains <EM>decim</EM>
77 * filters and each filter contains ceil(taps.size()/decim)
78 * taps. Each tap from the filter prototype is
79 * sequentially inserted into the next filter. When all of the
80 * input taps are used, the remaining filters in the filterbank
81 * are filled out with 0's to make sure each filter has the same
82 * number of taps.
83 *
84 * The theory behind this block can be found in Chapter 6 of
85 * the following book:
86 *
87 * <B><EM>f. harris, "Multirate Signal Processing for Communication
88 * Systems," Upper Saddle River, NJ: Prentice Hall, Inc. 2004.</EM></B>
89 */
90
92{
93public:
94 // gr::filter::pfb_decimator_ccf::sptr
95 typedef boost::shared_ptr<pfb_decimator_ccf> sptr;
96
97 /*!
98 * Build the polyphase filterbank decimator.
99 * \param decim (unsigned integer) Specifies the decimation rate to use
100 * \param taps (vector/list of floats) The prototype filter to populate the
101 * filterbank. \param channel (unsigned integer) Selects the channel to return
102 * [default=0]. \param use_fft_rotator (bool) Rotate channels using FFT method instead
103 * of exp(phi). For larger values of \p channel, the FFT method will perform better.
104 * Generally, this value of \p channel is small (~5), but could be
105 * architecture-specific (Default: true).
106 * \param use_fft_filters (bool) Use FFT filters (fast convolution) instead of FIR
107 * filters. FFT filters perform better for larger numbers of taps but is
108 * architecture-specific (Default: true).
109 */
110 static sptr make(unsigned int decim,
111 const std::vector<float>& taps,
112 unsigned int channel,
113 bool use_fft_rotator = true,
114 bool use_fft_filters = true);
115
116 /*!
117 * Resets the filterbank's filter taps with the new prototype filter
118 * \param taps (vector/list of floats) The prototype filter to populate the
119 * filterbank.
120 */
121 virtual void set_taps(const std::vector<float>& taps) = 0;
122
123 /*!
124 * Return a vector<vector<>> of the filterbank taps
125 */
126 virtual std::vector<std::vector<float> > taps() const = 0;
127
128 /*!
129 * Print all of the filterbank taps to screen.
130 */
131 virtual void print_taps() = 0;
132
133 virtual void set_channel(const unsigned int channel) = 0;
134};
135
136} /* namespace filter */
137} /* namespace gr */
138
139#endif /* INCLUDED_PFB_DECIMATOR_CCF_H */
Polyphase filterbank bandpass decimator with gr_complex input, gr_complex output and float taps.
Definition: pfb_decimator_ccf.h:92
virtual std::vector< std::vector< float > > taps() const =0
virtual void set_channel(const unsigned int channel)=0
virtual void set_taps(const std::vector< float > &taps)=0
static sptr make(unsigned int decim, const std::vector< float > &taps, unsigned int channel, bool use_fft_rotator=true, bool use_fft_filters=true)
boost::shared_ptr< pfb_decimator_ccf > sptr
Definition: pfb_decimator_ccf.h:95
synchronous 1:1 input to output with history
Definition: sync_block.h:38
#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