ofdm_equalizer_static.h

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/* -*- 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_DIGITAL_OFDM_EQUALIZER_STATIC_H
#define INCLUDED_DIGITAL_OFDM_EQUALIZER_STATIC_H

#include <gnuradio/digital/api.h>
#include <gnuradio/digital/constellation.h>
#include <gnuradio/digital/ofdm_equalizer_base.h>

namespace gr {
  namespace digital {

    /*!
     * \brief Very simple static equalizer for OFDM.
     * \ingroup ofdm_blk
     * \ingroup equalizers_blk
     *
     * \details
     * This is an extremely simple equalizer. It will only work for
     * high-SNR, very, very slowly changing channels.
     *
     * It simply divides the signal with the currently known channel
     * state. Whenever a pilot symbol comes around, it updates the
     * channel state on that particular carrier by dividing the
     * received symbol with the known pilot symbol.
     */
    class DIGITAL_API ofdm_equalizer_static : public ofdm_equalizer_1d_pilots
    {
     public:
      typedef boost::shared_ptr<ofdm_equalizer_static> sptr;

      ofdm_equalizer_static(
          int fft_len,
          const std::vector<std::vector<int> > &occupied_carriers = std::vector<std::vector<int> >(),
          const std::vector<std::vector<int> > &pilot_carriers = std::vector<std::vector<int> >(),
          const std::vector<std::vector<gr_complex> > &pilot_symbols = std::vector<std::vector<gr_complex> >(),
          int symbols_skipped = 0,
          bool input_is_shifted = true
      );
      ~ofdm_equalizer_static();

      /*! \brief Divide the input signal with the current channel state.
       *
       * Does the following (and nothing else):
       * - Divide every OFDM symbol with the current channel state
       * - If a pilot symbol is found, re-set the channel state by dividing the received
       *   symbol with the known pilot symbol
       */
      void equalize(gr_complex *frame,
                      int n_sym,
                      const std::vector<gr_complex> &initial_taps = std::vector<gr_complex>(),
                      const std::vector<tag_t> &tags = std::vector<tag_t>());

      /*
       * \param fft_len FFT length
       * \param occupied_carriers List of occupied carriers, see ofdm_carrier_allocator
       *                          for a description.
       * \param pilot_carriers Position of pilot symbols, see ofdm_carrier_allocator
       *                          for a description.
       * \param pilot_symbols Value of pilot symbols, see ofdm_carrier_allocator
       *                          for a description.
       * \param symbols_skipped Starting position within occupied_carriers and pilot_carriers.
       *                        If the first symbol of the frame was removed (e.g. to decode the
       *                        header), set this make sure the pilot symbols are correctly
       *                        identified.
       * \param input_is_shifted Set this to false if the input signal is not shifted, i.e.
       *                         the first input items is on the DC carrier.
       *                         Note that a lot of the OFDM receiver blocks operate on shifted
       *                         signals!
       */
      static sptr make(
        int fft_len,
        const std::vector<std::vector<int> > &occupied_carriers = std::vector<std::vector<int> >(),
        const std::vector<std::vector<int> > &pilot_carriers = std::vector<std::vector<int> >(),
        const std::vector<std::vector<gr_complex> > &pilot_symbols = std::vector<std::vector<gr_complex> >(),
        int symbols_skipped = 0,
        bool input_is_shifted = true
      );
    };

  } /* namespace digital */
} /* namespace gr */

#endif /* INCLUDED_DIGITAL_OFDM_EQUALIZER_STATIC_H */