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Diffstat (limited to 'gr-digital/include/digital_fll_band_edge_cc.h')
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diff --git a/gr-digital/include/digital_fll_band_edge_cc.h b/gr-digital/include/digital_fll_band_edge_cc.h new file mode 100644 index 000000000..576dfab87 --- /dev/null +++ b/gr-digital/include/digital_fll_band_edge_cc.h @@ -0,0 +1,213 @@ +/* -*- c++ -*- */ +/* + * Copyright 2009,2011 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_DIGITAL_FLL_BAND_EDGE_CC_H +#define INCLUDED_DIGITAL_FLL_BAND_EDGE_CC_H + +#include <gr_sync_block.h> +#include <gri_control_loop.h> + +class digital_fll_band_edge_cc; +typedef boost::shared_ptr<digital_fll_band_edge_cc> digital_fll_band_edge_cc_sptr; +digital_fll_band_edge_cc_sptr digital_make_fll_band_edge_cc (float samps_per_sym, + float rolloff, + int filter_size, + float bandwidth); + +/*! + * \class digital_fll_band_edge_cc + * \brief Frequency Lock Loop using band-edge filters + * + * \ingroup general + * \ingroup digital + * + * 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 practice, the above equation can be simplified by just comparing + * the absolute value squared of the output of both filters: + * abs(x_l(t))^2 - abs(x_u(t))^2 = norm(x_l(t)) - norm(x_u(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. + * + * It is very important that the band edge filters be the derivatives + * of the pulse shaping filter, and that they be linear + * phase. Otherwise, the variance of the error will be very large. + * + */ + +class digital_fll_band_edge_cc : public gr_sync_block, public gri_control_loop +{ + 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 bandwidth (float) Loop bandwidth + */ + friend digital_fll_band_edge_cc_sptr digital_make_fll_band_edge_cc (float samps_per_sym, + float rolloff, + int filter_size, + float bandwidth); + + float d_sps; + float d_rolloff; + int d_filter_size; + + std::vector<gr_complex> d_taps_lower; + std::vector<gr_complex> d_taps_upper; + bool d_updated; + + /*! + * 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 bandwidth (float) Loop bandwidth + */ + digital_fll_band_edge_cc(float samps_per_sym, float rolloff, + int filter_size, float bandwidth); + + /*! + * 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); + +public: + ~digital_fll_band_edge_cc (); + + /******************************************************************* + SET FUNCTIONS + *******************************************************************/ + + /*! + * \brief Set the number of samples per symbol + * + * Set's the number of samples per symbol the system should + * use. This value is uesd to calculate the filter taps and will + * force a recalculation. + * + * \param sps (float) new samples per symbol + * + */ + void set_samples_per_symbol(float sps); + + /*! + * \brief Set the rolloff factor of the shaping filter + * + * This sets the rolloff factor that is used in the pulse shaping + * filter and is used to calculate the filter taps. Changing this + * will force a recalculation of the filter taps. + * + * This should be the same value that is used in the transmitter's + * pulse shaping filter. It must be between 0 and 1 and is usually + * between 0.2 and 0.5 (where 0.22 and 0.35 are commonly used + * values). + * + * \param rolloff (float) new shaping filter rolloff factor [0,1] + * + */ + void set_rolloff(float rolloff); + + /*! + * \brief Set the number of taps in the filter + * + * This sets the number of taps in the band-edge filters. Setting + * this will force a recalculation of the filter taps. + * + * This should be about the same number of taps used in the + * transmitter's shaping filter and also not very large. A large + * number of taps will result in a large delay between input and + * frequency estimation, and so will not be as accurate. Between 30 + * and 70 taps is usual. + * + * \param filter_size (float) number of taps in the filters + * + */ + void set_filter_size(int filter_size); + + /******************************************************************* + GET FUNCTIONS + *******************************************************************/ + + /*! + * \brief Returns the number of sampler per symbol used for the filter + */ + float get_samples_per_symbol() const; + + /*! + * \brief Returns the rolloff factor used for the filter + */ + float get_rolloff() const; + + /*! + * \brief Returns the number of taps of the filter + */ + int get_filter_size() const; + + /*! + * 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 |