polyphase_filterbank.h

Go to the documentation of this file.

/* -*- c++ -*- */
/*
 * Copyright 2012 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * GNU Radio is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3, or (at your option)
 * any later version.
 *
 * GNU Radio is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with GNU Radio; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */


#ifndef INCLUDED_FILTER_POLYPHASE_FILTERBANK_H
#define INCLUDED_FILTER_POLYPHASE_FILTERBANK_H

#include <gnuradio/filter/api.h>
#include <gnuradio/filter/fir_filter.h>
#include <gnuradio/filter/fft_filter.h>
#include <gnuradio/fft/fft.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> number
       * of filters and each filter contains ceil(taps.size()/decim)
       * number of 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
       * classs 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=filter.firdes.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;
        fft::fft_complex        *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.
         * \param fft_forward (bool) use a forward or inverse FFT (default=false).
         */
        polyphase_filterbank(unsigned int nfilts,
                             const std::vector<float> &taps,
                             bool fft_forward=false);

        ~polyphase_filterbank();

        /*!
         * 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 */