digital_ofdm_chanest_vcvc.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_CHANEST_VCVC_H
#define INCLUDED_DIGITAL_OFDM_CHANEST_VCVC_H

#include <digital_api.h>
#include <gr_block.h>

class digital_ofdm_chanest_vcvc;

typedef boost::shared_ptr<digital_ofdm_chanest_vcvc> digital_ofdm_chanest_vcvc_sptr;

/*
 * \param sync_symbol1 First synchronisation symbol in the frequency domain. Its length must be
 *                     the FFT length. For Schmidl & Cox synchronisation, every second sub-carrier
 *                     has to be zero.
 * \param sync_symbol2 Second synchronisation symbol in the frequency domain. Must be equal to
 *                     the FFT length, or zero length if only one synchronisation symbol is used.
 *                     Using this symbol is how synchronisation is described in [1]. Leaving this
 *                     empty forces us to interpolate the equalizer taps.
 *                     If you are using an unusual sub-carrier configuration (e.g. because of OFDMA),
 *                     this sync symbol is used to identify the active sub-carriers. If you only
 *                     have one synchronisation symbol, set the active sub-carriers to a non-zero
 *                     value in here, and also set \p force_one_sync_symbol parameter to true.
 * \param n_data_symbols The number of data symbols following each set of synchronisation symbols.
 *                       Must be at least 1.
 * \param eq_noise_red_len If non-zero, noise reduction for the equalizer taps is done according
 *                         to [2]. In this case, it is the channel influence time in number of
 *                         samples. A good value is usually the length of the cyclic prefix.
 * \param max_carr_offset Limit the number of sub-carriers the frequency offset can maximally be.
 *                        Leave this zero to try all possibilities.
 * \param force_one_sync_symbol See \p sync_symbol2.
 */
DIGITAL_API digital_ofdm_chanest_vcvc_sptr
digital_make_ofdm_chanest_vcvc (
                const std::vector<gr_complex> &sync_symbol1,
                const std::vector<gr_complex> &sync_symbol2,
                int n_data_symbols,
                int eq_noise_red_len=0,
                int max_carr_offset=-1,
                bool force_one_sync_symbol=false);

/*!
 * \brief Estimate channel and coarse frequency offset for OFDM from preambles
 * \ingroup ofdm_blk
 * \ingroup syncronizers_blk
 *
 * Input: OFDM symbols (in frequency domain). The first one (or two) symbols are expected
 *        to be synchronisation symbols, which are used to estimate the coarse freq offset
 *        and the initial equalizer taps (these symbols are removed from the stream).
 *        The following \p n_data_symbols are passed through unmodified (the actual equalisation
 *        must be done elsewhere).
 * Output: The data symbols, without the synchronisation symbols.
 *         The first data symbol passed through has two tags:
 *         'ofdm_sync_carr_offset' (integer), the coarse frequency offset as number of carriers,
 *         and 'ofdm_sync_eq_taps' (complex vector).
 *         Any tags attached to the synchronisation symbols are attached to the first data
 *         symbol. All other tags are propagated as expected.
 *
 * Note: The vector on ofdm_sync_eq_taps is already frequency-corrected, whereas the rest is not.
 *
 * This block assumes the frequency offset is even (i.e. an integer multiple of 2).
 *
 * [1] Schmidl, T.M. and Cox, D.C., "Robust frequency and timing synchronization for OFDM",
 *     Communications, IEEE Transactions on, 1997.
 * [2] K.D. Kammeyer, "Nachrichtenuebertragung," Chapter. 16.3.2.
 */
class DIGITAL_API digital_ofdm_chanest_vcvc : public gr_block
{
 private:
  friend DIGITAL_API digital_ofdm_chanest_vcvc_sptr digital_make_ofdm_chanest_vcvc (const std::vector<gr_complex> &sync_symbol1, const std::vector<gr_complex> &sync_symbol2, int n_data_symbols, int eq_noise_red_len, int max_carr_offset, bool force_one_sync_symbol);

  int d_fft_len; //! FFT length
  int d_n_data_syms; //! Number of data symbols following the sync symbol(s)
  int d_n_sync_syms; //! Number of sync symbols (1 or 2)
  //! 0 if no noise reduction is done for the initial channel state estimation. Otherwise, the maximum length of the channel delay in samples.
  int d_eq_noise_red_len;
  //! Is sync_symbol1 if d_n_sync_syms == 1, otherwise sync_symbol2. Used as a reference symbol to estimate the channel.
  std::vector<gr_complex> d_ref_sym;
  //! If d_n_sync_syms == 2 this is used as a differential correlation vector (called 'v' in [1]).
  std::vector<gr_complex> d_corr_v;
  //! If d_n_sync_syms == 1 we use this instead of d_corr_v to estimate the coarse freq. offset
  std::vector<float> d_known_symbol_diffs;
  //! If d_n_sync_syms == 1 we use this instead of d_corr_v to estimate the coarse freq. offset (temp. variable)
  std::vector<float> d_new_symbol_diffs;
  //! The index of the first carrier with data (index 0 is not DC here, but the lowest frequency)
  int d_first_active_carrier;
  //! The index of the last carrier with data
  int d_last_active_carrier;
  //! If true, the channel estimation must be interpolated
  bool d_interpolate;
  //! Maximum carrier offset (negative value!)
  int d_max_neg_carr_offset;
  //! Maximum carrier offset (positive value!)
  int d_max_pos_carr_offset;


  digital_ofdm_chanest_vcvc(const std::vector<gr_complex> &sync_symbol1, const std::vector<gr_complex> &sync_symbol2, int n_data_symbols, int eq_noise_red_len, int max_carr_offset, bool force_one_sync_symbol);

  //! Calculate the coarse frequency offset in number of carriers
  int get_carr_offset(const gr_complex *sync_sym1, const gr_complex *sync_sym2);
  //! Estimate the channel (phase and amplitude offset per carrier)
  void get_chan_taps(const gr_complex *sync_sym1, const gr_complex *sync_sym2, int carr_offset, std::vector<gr_complex> &taps);

 public:
  ~digital_ofdm_chanest_vcvc();

  void forecast (int noutput_items, gr_vector_int &ninput_items_required);
  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 /* INCLUDED_DIGITAL_OFDM_CHANEST_VCVC_H */