Loading...
Searching...
No Matches
polyphase_filterbank.h
Go to the documentation of this file.
/* -*- c++ -*- */
/*
* Copyright 2012 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* SPDX-License-Identifier: GPL-3.0-or-later
*
*/
#ifndef INCLUDED_FILTER_POLYPHASE_FILTERBANK_H
#define INCLUDED_FILTER_POLYPHASE_FILTERBANK_H
#include <gnuradio/fft/fft.h>
#include <gnuradio/filter/api.h>
#include <gnuradio/filter/fft_filter.h>
#include <gnuradio/filter/fir_filter.h>
namespace gr {
namespace filter {
namespace kernel {
/*!
* \brief Polyphase filterbank parent class
* \ingroup filter_blk
* \ingroup pfb_blk
*
* \details
* This block takes in complex inputs and channelizes it to
* <EM>M</EM> channels of equal bandwidth. Each of the resulting
* channels is decimated to the new rate that is the input
* sampling rate <EM>fs</EM> divided by the number of channels,
* <EM>M</EM>.
*
* The PFB channelizer code takes the taps generated above and
* builds a set of filters. The set contains <EM>M</EM>
* filters and each filter contains ceil(taps.size()/decim)
* taps. Each tap from the filter prototype is
* sequentially inserted into the next filter. When all of the
* input taps are used, the remaining filters in the filterbank
* are filled out with 0's to make sure each filter has the same
* number of taps.
*
* Each filter operates using the gr::filter::fir_filter_XXX
* class of GNU Radio, which takes the input stream at
* <EM>i</EM> and performs the inner product calculation to
* <EM>i+(n-1)</EM> where <EM>n</EM> is the number of filter
* taps. To efficiently handle this in the GNU Radio structure,
* each filter input must come from its own input stream. So the
* channelizer must be provided with <EM>M</EM> streams where
* the input stream has been deinterleaved. This is most easily
* done using the gr::blocks::stream_to_streams block.
*
* The output is then produced as a vector, where index
* <EM>i</EM> in the vector is the next sample from the
* <EM>i</EM>th channel. This is most easily handled by sending
* the output to a gr::blocks::vector_to_streams block to handle
* the conversion and passing <EM>M</EM> streams out.
*
* The input and output formatting is done using a hier_block2
* called pfb_channelizer_ccf. This can take in a single stream
* and outputs <EM>M</EM> streams based on the behavior
* described above.
*
* The filter's taps should be based on the input sampling rate.
*
* For example, using the GNU Radio's firdes utility to building
* filters, we build a low-pass filter with a sampling rate of
* <EM>fs</EM>, a 3-dB bandwidth of <EM>BW</EM> and a transition
* bandwidth of <EM>TB</EM>. We can also specify the out-of-band
* attenuation to use, <EM>ATT</EM>, and the filter window
* function (a Blackman-harris window in this case). The first
* input is the gain of the filter, which we specify here as
* unity.
*
* <B><EM>self._taps = filter.firdes.low_pass_2(1, fs, BW, TB,
* attenuation_dB=ATT, window=fft.window.WIN_BLACKMAN_hARRIS)</EM></B>
*
* More on the theory of polyphase filterbanks can be found in
* the following book:
*
* <B><EM>f. harris, "Multirate Signal Processing for
* Communication Systems," Upper Saddle River, NJ:
* Prentice Hall, Inc. 2004.</EM></B>
*
*/
class FILTER_API polyphase_filterbank
{
protected:
unsigned int d_nfilts;
std::vector<kernel::fir_filter_ccf> d_fir_filters;
std::vector<kernel::fft_filter_ccf> d_fft_filters;
std::vector<std::vector<float>> d_taps;
unsigned int d_taps_per_filter;
// The FFT to handle the output de-spinning of the channels.
fft::fft_complex_rev d_fft;
public:
/*!
* Build the polyphase filterbank decimator.
* \param nfilts (unsigned integer) Specifies the number of
* channels <EM>M</EM>
* \param taps (vector/list of floats) The prototype filter to
* populate the filterbank.
*/
polyphase_filterbank(unsigned int nfilts, const std::vector<float>& taps);
virtual ~polyphase_filterbank() = default;
/*!
* Update the filterbank's filter taps from a prototype
* filter.
*
* \param taps (vector/list of floats) The prototype filter to
* populate the filterbank.
*/
virtual void set_taps(const std::vector<float>& taps);
/*!
* Print all of the filterbank taps to screen.
*/
void print_taps();
/*!
* Return a vector<vector<>> of the filterbank taps
*/
std::vector<std::vector<float>> taps() const;
};
} /* namespace kernel */
} /* namespace filter */
} /* namespace gr */
#endif /* INCLUDED_FILTER_POLYPHASE_FILTERBANK_H */
gr::fft::fft
Definition fft.h:70
gr::filter::kernel::polyphase_filterbank
Polyphase filterbank parent class.
Definition polyphase_filterbank.h:90
gr::filter::kernel::polyphase_filterbank::~polyphase_filterbank
virtual ~polyphase_filterbank()=default
gr::filter::kernel::polyphase_filterbank::set_taps
virtual void set_taps(const std::vector< float > &taps)
gr::filter::kernel::polyphase_filterbank::d_fft
fft::fft_complex_rev d_fft
Definition polyphase_filterbank.h:99
gr::filter::kernel::polyphase_filterbank::d_fir_filters
std::vector< kernel::fir_filter_ccf > d_fir_filters
Definition polyphase_filterbank.h:93
gr::filter::kernel::polyphase_filterbank::d_nfilts
unsigned int d_nfilts
Definition polyphase_filterbank.h:92
gr::filter::kernel::polyphase_filterbank::print_taps
void print_taps()
gr::filter::kernel::polyphase_filterbank::polyphase_filterbank
polyphase_filterbank(unsigned int nfilts, const std::vector< float > &taps)
gr::filter::kernel::polyphase_filterbank::d_taps
std::vector< std::vector< float > > d_taps
Definition polyphase_filterbank.h:95
gr::filter::kernel::polyphase_filterbank::taps
std::vector< std::vector< float > > taps() const
gr::filter::kernel::polyphase_filterbank::d_taps_per_filter
unsigned int d_taps_per_filter
Definition polyphase_filterbank.h:96
gr::filter::kernel::polyphase_filterbank::d_fft_filters
std::vector< kernel::fft_filter_ccf > d_fft_filters
Definition polyphase_filterbank.h:94
std::vector
STL class.
Definition vector_docstub.h:11
fft.h
fft_filter.h
fir_filter.h
api.h
FILTER_API
#define FILTER_API
Definition gr-filter/include/gnuradio/filter/api.h:18
taps
static constexpr float taps[NSTEPS+1][NTAPS]
Definition interpolator_taps.h:9
gr
GNU Radio logging wrapper.
Definition basic_block.h:29