pfb_decimator_ccf.h

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/* -*- c++ -*- */
/*
 * Copyright 2009,2012 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 */
 
 
#ifndef INCLUDED_PFB_DECIMATOR_CCF_H
#define INCLUDED_PFB_DECIMATOR_CCF_H
 
#include <gnuradio/filter/api.h>
#include <gnuradio/sync_block.h>
 
namespace gr {
namespace filter {
 
/*!
 * \brief Polyphase filterbank bandpass decimator with gr_complex
 *        input, gr_complex output and float taps
 * \ingroup channelizers_blk
 *
 * \details
 * This block takes in a signal stream and performs integer down-
 * sampling (decimation) with a polyphase filterbank. The first
 * input is the integer specifying how much to decimate by. The
 * second input is a vector (Python list) of floating-point taps
 * of the prototype filter. The third input specifies the channel
 * to extract.  By default, the zeroth channel is used, which is
 * the baseband channel (first Nyquist zone).
 *
 * The <EM>channel</EM> parameter specifies which channel to use
 * since this class is capable of bandpass decimation. Given a
 * complex input stream at a sampling rate of <EM>fs</EM> and a
 * decimation rate of <EM>decim</EM>, the input frequency domain
 * is split into <EM>decim</EM> channels that represent the
 * Nyquist zones. Using the polyphase filterbank, we can select
 * any one of these channels to decimate.
 *
 * The output signal will be the basebanded and decimated signal
 * from that channel. This concept is very similar to the PFB
 * channelizer (see #gr::filter::pfb_channelizer_ccf) where only a single
 * channel is extracted at a time.
 *
 * The filter's taps should be based on the sampling rate before
 * decimation.
 *
 * 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>
 *
 * The PFB decimator code takes the taps generated above and
 * builds a set of filters. The set contains <EM>decim</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.
 *
 * The theory behind this block can be found in Chapter 6 of
 * 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 pfb_decimator_ccf : virtual public sync_block
{
public:
    // gr::filter::pfb_decimator_ccf::sptr
    typedef std::shared_ptr<pfb_decimator_ccf> sptr;
 
    /*!
     * Build the polyphase filterbank decimator.
     * \param decim   (unsigned integer) Specifies the decimation rate to use
     * \param taps    (vector/list of floats) The prototype filter to populate the
     * filterbank. \param channel (unsigned integer) Selects the channel to return
     * [default=0]. \param use_fft_rotator (bool) Rotate channels using FFT method instead
     * of exp(phi). For larger values of \p channel, the FFT method will perform better.
     *                Generally, this value of \p channel is small (~5), but could be
     *                architecture-specific (Default: true).
     * \param use_fft_filters (bool) Use FFT filters (fast convolution) instead of FIR
     * filters. FFT filters perform better for larger numbers of taps but is
     *                architecture-specific (Default: true).
     */
    static sptr make(unsigned int decim,
                     const std::vector<float>& taps,
                     unsigned int channel,
                     bool use_fft_rotator = true,
                     bool use_fft_filters = true);
 
    /*!
     * Resets the filterbank's filter taps with the new prototype filter
     * \param taps    (vector/list of floats) The prototype filter to populate the
     * filterbank.
     */
    virtual void set_taps(const std::vector<float>& taps) = 0;
 
    /*!
     * Return a vector<vector<>> of the filterbank taps
     */
    virtual std::vector<std::vector<float>> taps() const = 0;
 
    /*!
     * Print all of the filterbank taps to screen.
     */
    virtual void print_taps() = 0;
 
    virtual void set_channel(const unsigned int channel) = 0;
};
 
} /* namespace filter */
} /* namespace gr */
 
#endif /* INCLUDED_PFB_DECIMATOR_CCF_H */