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polyphase_filterbank.h
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/* -*- c++ -*- */
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/*
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* Copyright 2012 Free Software Foundation, Inc.
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*
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* This file is part of GNU Radio
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*
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* GNU Radio is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3, or (at your option)
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* any later version.
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*
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* GNU Radio is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with GNU Radio; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street,
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* Boston, MA 02110-1301, USA.
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*/
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#ifndef INCLUDED_FILTER_POLYPHASE_FILTERBANK_H
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#define INCLUDED_FILTER_POLYPHASE_FILTERBANK_H
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#include <
gnuradio/filter/api.h
>
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#include <
gnuradio/filter/fir_filter.h
>
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#include <
gnuradio/filter/fft_filter.h
>
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#include <
gnuradio/fft/fft.h
>
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namespace
gr {
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namespace
filter {
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namespace
kernel {
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/*!
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* \brief Polyphase filterbank parent class
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* \ingroup filter_blk
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* \ingroup pfb_blk
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*
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* \details
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* This block takes in complex inputs and channelizes it to
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* <EM>M</EM> channels of equal bandwidth. Each of the resulting
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* channels is decimated to the new rate that is the input
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* sampling rate <EM>fs</EM> divided by the number of channels,
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* <EM>M</EM>.
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*
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* The PFB channelizer code takes the taps generated above and
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* builds a set of filters. The set contains <EM>M</EM> number
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* of filters and each filter contains ceil(taps.size()/decim)
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* number of taps. Each tap from the filter prototype is
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* sequentially inserted into the next filter. When all of the
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* input taps are used, the remaining filters in the filterbank
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* are filled out with 0's to make sure each filter has the same
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* number of taps.
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*
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* Each filter operates using the gr::filter::fir_filter_XXX
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* classs of GNU Radio, which takes the input stream at
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* <EM>i</EM> and performs the inner product calculation to
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* <EM>i+(n-1)</EM> where <EM>n</EM> is the number of filter
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* taps. To efficiently handle this in the GNU Radio structure,
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* each filter input must come from its own input stream. So the
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* channelizer must be provided with <EM>M</EM> streams where
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* the input stream has been deinterleaved. This is most easily
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* done using the gr::blocks::stream_to_streams block.
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*
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* The output is then produced as a vector, where index
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* <EM>i</EM> in the vector is the next sample from the
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* <EM>i</EM>th channel. This is most easily handled by sending
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* the output to a gr::blocks::vector_to_streams block to handle
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* the conversion and passing <EM>M</EM> streams out.
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*
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* The input and output formatting is done using a hier_block2
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* called pfb_channelizer_ccf. This can take in a single stream
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* and outputs <EM>M</EM> streams based on the behavior
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* described above.
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*
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* The filter's taps should be based on the input sampling rate.
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*
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* For example, using the GNU Radio's firdes utility to building
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* filters, we build a low-pass filter with a sampling rate of
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* <EM>fs</EM>, a 3-dB bandwidth of <EM>BW</EM> and a transition
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* bandwidth of <EM>TB</EM>. We can also specify the out-of-band
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* attenuation to use, <EM>ATT</EM>, and the filter window
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* function (a Blackman-harris window in this case). The first
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* input is the gain of the filter, which we specify here as
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* unity.
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*
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* <B><EM>self._taps = filter.firdes.low_pass_2(1, fs, BW, TB,
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* attenuation_dB=ATT, window=filter.firdes.WIN_BLACKMAN_hARRIS)</EM></B>
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*
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* More on the theory of polyphase filterbanks can be found in
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* the following book.
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*
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* <B><EM>f. harris, "Multirate Signal Processing for
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* Communication Systems," Upper Saddle River, NJ:
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* Prentice Hall, Inc. 2004.</EM></B>
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*
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*/
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class
FILTER_API
polyphase_filterbank
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{
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protected
:
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unsigned
int
d_nfilts
;
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std::vector<kernel::fir_filter_ccf*>
d_fir_filters
;
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std::vector<kernel::fft_filter_ccf*>
d_fft_filters
;
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std::vector< std::vector<float> >
d_taps
;
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unsigned
int
d_taps_per_filter
;
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fft::fft_complex
*
d_fft
;
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public
:
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/*!
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* Build the polyphase filterbank decimator.
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* \param nfilts (unsigned integer) Specifies the number of
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* channels <EM>M</EM>
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* \param taps (vector/list of floats) The prototype filter to
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* populate the filterbank.
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* \param fft_forward (bool) use a forward or inverse FFT (default=false).
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*/
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polyphase_filterbank
(
unsigned
int
nfilts,
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const
std::vector<float> &
taps
,
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bool
fft_forward=
false
);
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~
polyphase_filterbank
();
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/*!
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* Update the filterbank's filter taps from a prototype
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* filter.
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*
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* \param taps (vector/list of floats) The prototype filter to
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* populate the filterbank.
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*/
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virtual
void
set_taps(
const
std::vector<float> &
taps
);
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/*!
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* Print all of the filterbank taps to screen.
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*/
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void
print_taps();
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/*!
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* Return a vector<vector<>> of the filterbank taps
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*/
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std::vector<std::vector<float> >
taps
()
const
;
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};
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}
/* namespace kernel */
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}
/* namespace filter */
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}
/* namespace gr */
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#endif
/* INCLUDED_FILTER_POLYPHASE_FILTERBANK_H */
gr-filter
include
gnuradio
filter
polyphase_filterbank.h
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