--- /dev/null
+/* -*- c++ -*- */
+/*
+ * Copyright 2009,2010 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_GR_PFB_ARB_RESAMPLER_CCF_H
+#define INCLUDED_GR_PFB_ARB_RESAMPLER_CCF_H
+
+#include <gr_block.h>
+
+class gr_pfb_arb_resampler_ccf;
+typedef boost::shared_ptr<gr_pfb_arb_resampler_ccf> gr_pfb_arb_resampler_ccf_sptr;
+gr_pfb_arb_resampler_ccf_sptr gr_make_pfb_arb_resampler_ccf (float rate,
+ const std::vector<float> &taps,
+ unsigned int filter_size=32);
+
+class gr_fir_ccf;
+
+/*!
+ * \class gr_pfb_arb_resampler_ccf
+ *
+ * \brief Polyphase filterbank arbitrary resampler with
+ * gr_complex input, gr_complex output and float taps
+ *
+ * \ingroup filter_blk
+ *
+ * This block takes in a signal stream and performs arbitrary
+ * resampling. The resampling rate can be any real
+ * number <EM>r</EM>. The resampling is done by constructing
+ * <EM>N</EM> filters where <EM>N</EM> is the interpolation rate. We
+ * then calculate <EM>D</EM> where <EM>D = floor(N/r)</EM>.
+ *
+ * Using <EM>N</EM> and <EM>D</EM>, we can perform rational resampling
+ * where <EM>N/D</EM> is a rational number close to the input rate
+ * <EM>r</EM> where we have <EM>N</EM> filters and we cycle through
+ * them as a polyphase filterbank with a stride of <EM>D</EM> so that
+ * <EM>i+1 = (i + D) % N</EM>.
+ *
+ * To get the arbitrary rate, we want to interpolate between two
+ * points. For each value out, we take an output from the current
+ * filter, <EM>i</EM>, and the next filter <EM>i+1</EM> and then
+ * linearly interpolate between the two based on the real resampling
+ * rate we want.
+ *
+ * The linear interpolation only provides us with an approximation to
+ * the real sampling rate specified. The error is a quantization error
+ * between the two filters we used as our interpolation points. To
+ * this end, the number of filters, <EM>N</EM>, used determines the
+ * quantization error; the larger <EM>N</EM>, the smaller the
+ * noise. You can design for a specified noise floor by setting the
+ * filter size (parameters <EM>filter_size</EM>). The size defaults to
+ * 32 filters, which is about as good as most implementations need.
+ *
+ * The trick with designing this filter is in how to specify the taps
+ * of the prototype filter. Like the PFB interpolator, the taps are
+ * specified using the interpolated filter rate. In this case, that
+ * rate is the input sample rate multiplied by the number of filters
+ * in the filterbank, which is also the interpolation rate. All other
+ * values should be relative to this rate.
+ *
+ * For example, for a 32-filter arbitrary resampler and using the
+ * GNU Radio's firdes utility to build the filter, 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 the
+ * interpolation rate (<EM>32</EM>).
+ *
+ * <B><EM>self._taps = gr.firdes.low_pass_2(32, 32*fs, BW, TB,
+ * attenuation_dB=ATT, window=gr.firdes.WIN_BLACKMAN_hARRIS)</EM></B>
+ *
+ * The theory behind this block can be found in Chapter 7.5 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 gr_pfb_arb_resampler_ccf : public gr_block
+{
+ private:
+ /*!
+ * Build the polyphase filterbank arbitray resampler.
+ * \param rate (float) Specifies the resampling rate to use
+ * \param taps (vector/list of floats) The prototype filter to populate the filterbank. The taps
+ * should be generated at the filter_size sampling rate.
+ * \param filter_size (unsigned int) The number of filters in the filter bank. This is directly
+ related to quantization noise introduced during the resampling.
+ Defaults to 32 filters.
+ */
+ friend gr_pfb_arb_resampler_ccf_sptr gr_make_pfb_arb_resampler_ccf (float rate,
+ const std::vector<float> &taps,
+ unsigned int filter_size);
+
+ std::vector<gr_fir_ccf*> d_filters;
+ std::vector<gr_fir_ccf*> d_diff_filters;
+ std::vector< std::vector<float> > d_taps;
+ std::vector< std::vector<float> > d_dtaps;
+ unsigned int d_int_rate; // the number of filters (interpolation rate)
+ unsigned int d_dec_rate; // the stride through the filters (decimation rate)
+ float d_flt_rate; // residual rate for the linear interpolation
+ float d_acc;
+ unsigned int d_last_filter;
+ int d_start_index;
+ unsigned int d_taps_per_filter;
+ bool d_updated;
+
+ /*!
+ * Build the polyphase filterbank arbitray resampler.
+ * \param rate (float) Specifies the resampling rate to use
+ * \param taps (vector/list of floats) The prototype filter to populate the filterbank. The taps
+ * should be generated at the filter_size sampling rate.
+ * \param filter_size (unsigned int) The number of filters in the filter bank. This is directly
+ related to quantization noise introduced during the resampling.
+ Defaults to 32 filters.
+ */
+ gr_pfb_arb_resampler_ccf (float rate,
+ const std::vector<float> &taps,
+ unsigned int filter_size);
+
+ void create_diff_taps(const std::vector<float> &newtaps,
+ std::vector<float> &difftaps);
+
+ /*!
+ * Resets the filterbank's filter taps with the new prototype filter
+ * \param newtaps (vector of floats) The prototype filter to populate the filterbank.
+ * The taps should be generated at the interpolated sampling rate.
+ * \param ourtaps (vector of floats) Reference to our internal member of holding the taps.
+ * \param ourfilter (vector of filters) Reference to our internal filter to set the taps for.
+ */
+ void create_taps (const std::vector<float> &newtaps,
+ std::vector< std::vector<float> > &ourtaps,
+ std::vector<gr_fir_ccf*> &ourfilter);
+
+
+public:
+ ~gr_pfb_arb_resampler_ccf ();
+
+ // FIXME: See about a set_taps function during runtime.
+
+ /*!
+ * Print all of the filterbank taps to screen.
+ */
+ void print_taps();
+
+ int general_work (int noutput_items,
+ gr_vector_int &ninput_items,
+ gr_vector_const_void_star &input_items,
+ gr_vector_void_star &output_items);
+};
+
+#endif
projects / debian / gnuradio / blobdiff