--- /dev/null
+/* -*- c++ -*- */
+/*
+ * Copyright 2009 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_FLL_BAND_EDGE_CC_H
+#define INCLUDED_GR_FLL_BAND_EDGE_CC_H
+
+#include <gr_sync_block.h>
+
+class gr_fll_band_edge_cc;
+typedef boost::shared_ptr<gr_fll_band_edge_cc> gr_fll_band_edge_cc_sptr;
+gr_fll_band_edge_cc_sptr gr_make_fll_band_edge_cc (float samps_per_sym, float rolloff,
+ int filter_size, float alpha, float beta);
+
+class gr_fir_ccc;
+class gri_fft_complex;
+
+/*!
+ * \class gr_fll_band_edge_cc
+ * \brief Frequency Lock Loop using band-edge filters
+ *
+ * \ingroup general
+ *
+ * The frequency lock loop derives a band-edge filter that covers the upper and lower bandwidths
+ * of a digitally-modulated signal. The bandwidth range is determined by the excess bandwidth
+ * (e.g., rolloff factor) of the modulated signal. The placement in frequency of the band-edges
+ * is determined by the oversampling ratio (number of samples per symbol) and the excess bandwidth.
+ * The size of the filters should be fairly large so as to average over a number of symbols.
+ *
+ * The FLL works by filtering the upper and lower band edges into x_u(t) and x_l(t), respectively.
+ * These are combined to form cc(t) = x_u(t) + x_l(t) and ss(t) = x_u(t) - x_l(t). Combining
+ * these to form the signal e(t) = Re{cc(t) \\times ss(t)^*} (where ^* is the complex conjugate)
+ * provides an error signal at the DC term that is directly proportional to the carrier frequency.
+ * We then make a second-order loop using the error signal that is the running average of e(t).
+ *
+ * In theory, the band-edge filter is the derivative of the matched filter in frequency,
+ * (H_be(f) = \\frac{H(f)}{df}. In practice, this comes down to a quarter sine wave at the point
+ * of the matched filter's rolloff (if it's a raised-cosine, the derivative of a cosine is a sine).
+ * Extend this sine by another quarter wave to make a half wave around the band-edges is equivalent
+ * in time to the sum of two sinc functions. The baseband filter fot the band edges is therefore
+ * derived from this sum of sincs. The band edge filters are then just the baseband signal
+ * modulated to the correct place in frequency. All of these calculations are done in the
+ * 'design_filter' function.
+ *
+ * Note: We use FIR filters here because the filters have to have a flat phase response over the
+ * entire frequency range to allow their comparisons to be valid.
+ */
+
+class gr_fll_band_edge_cc : public gr_sync_block
+{
+ private:
+ /*!
+ * Build the FLL
+ * \param samps_per_sym (float) Number of samples per symbol of signal
+ * \param rolloff (float) Rolloff factor of signal
+ * \param filter_size (int) Size (in taps) of the filter
+ * \param alpha (float) Loop gain 1
+ * \param beta (float) Loop gain 2
+ */
+ friend gr_fll_band_edge_cc_sptr gr_make_fll_band_edge_cc (float samps_per_sym, float rolloff,
+ int filter_size, float alpha, float beta);
+
+ float d_alpha;
+ float d_beta;
+ float d_max_freq;
+ float d_min_freq;
+
+ gr_fir_ccc* d_filter_upper;
+ gr_fir_ccc* d_filter_lower;
+ bool d_updated;
+ float d_error;
+ float d_freq;
+ float d_phase;
+
+ /*!
+ * Build the FLL
+ * \param samps_per_sym (float) number of samples per symbol
+ * \param rolloff (float) Rolloff (excess bandwidth) of signal filter
+ * \param filter_size (int) number of filter taps to generate
+ * \param alpha (float) Alpha gain in the control loop
+ * \param beta (float) Beta gain in the control loop
+ */
+ gr_fll_band_edge_cc(float samps_per_sym, float rolloff,
+ int filter_size, float alpha, float beta);
+
+public:
+ ~gr_fll_band_edge_cc ();
+
+ /*!
+ * Design the band-edge filter based on the number of samples per symbol,
+ * filter rolloff factor, and the filter size
+ * \param samps_per_sym (float) Number of samples per symbol of signal
+ * \param rolloff (float) Rolloff factor of signal
+ * \param filter_size (int) Size (in taps) of the filter
+ */
+ void design_filter(float samps_per_sym, float rolloff, int filter_size);
+
+ /*!
+ * Set the alpha gainvalue
+ * \param alpha (float) new gain value
+ */
+ void set_alpha(float alpha);
+
+ /*!
+ * Set the beta gain value
+ * \param beta (float) new gain value
+ */
+ void set_beta(float beta) { d_beta = beta; }
+
+ /*!
+ * Print the taps to screen.
+ */
+ void print_taps();
+
+ int work (int noutput_items,
+ gr_vector_const_void_star &input_items,
+ gr_vector_void_star &output_items);
+};
+
+#endif
projects / debian / gnuradio / blobdiff