ofdm_sync_sc_cfb.h

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/* -*- c++ -*- */
/* 
 * Copyright 2013 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_SYNC_SC_CFB_H
#define INCLUDED_DIGITAL_OFDM_SYNC_SC_CFB_H

#include <gnuradio/digital/api.h>
#include <gnuradio/hier_block2.h>

namespace gr {
  namespace digital {

    /*!
     * \brief Schmidl & Cox synchronisation for OFDM
     * \ingroup ofdm_blk
     * \ingroup synchronizers_blk
     *
     * \details
     * Input: complex samples.
     * Output 0: Fine frequency offset, scaled by the OFDM symbol duration.
     *           This is \f$\hat{\varphi}\f$ in [1]. The normalized frequency
     *           offset is then 2.0*output0/fft_len.
     * Output 1: Beginning of the first OFDM symbol after the first (doubled) OFDM
     *           symbol. The beginning is marked with a 1 (it's 0 everywhere else).
     *
     * The evaluation of the coarse frequency offset is *not* done in this block.
     * Also, the initial equalizer taps are not calculated here.
     *
     * Note that we use a different normalization factor in the timing metric than
     * the authors do in their original work[1]. If the timing metric (8) is
     * \f[
     * M(d) = \frac{|P(d)|^2}{(R(d))^2},
     * \f]
     * we calculate the normalization as
     * \f[
     * R(d) = \frac{1}{2} \sum_{k=0}^{N-1} |r_{k+d}|^2,
     * \f]
     * i.e., we estimate the energy from *both* half-symbols. This avoids spurious detects
     * at the end of a burst, when the energy level suddenly drops.
     *
     * [1] Schmidl, T.M. and Cox, D.C., "Robust frequency and timing synchronization for OFDM",
     *     Communications, IEEE Transactions on, 1997.
     */
    class DIGITAL_API ofdm_sync_sc_cfb : virtual public hier_block2
    {
     public:
      typedef boost::shared_ptr<ofdm_sync_sc_cfb> sptr;

      /*! \param fft_len FFT length
       *  \param cp_len Length of the guard interval (cyclic prefix) in samples
       *  \param use_even_carriers If true, the carriers in the sync preamble are occupied such
       *                     that the even carriers are used (0, 2, 4, ...). If you use all
       *                     carriers, that would include the DC carrier, so be careful.
       *  \param threshold detection threshold. Default is 0.9.
       */
      static sptr make(int fft_len, int cp_len, bool use_even_carriers=false,
                       float threshold=0.9);

      virtual void set_threshold(float threshold) = 0;
      virtual float threshold() const = 0;
    };

  } // namespace digital
} // namespace gr

#endif /* INCLUDED_DIGITAL_OFDM_SYNC_SC_CFB_H */