ofdm_chanest_vcvc.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_CHANEST_VCVC_H
#define INCLUDED_DIGITAL_OFDM_CHANEST_VCVC_H

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

namespace gr {
namespace digital {

/*!
 * \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 ofdm_chanest_vcvc : virtual public block
{
public:
    typedef boost::shared_ptr<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.
     */
    static sptr make(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);
};

} // namespace digital
} // namespace gr

#endif /* INCLUDED_DIGITAL_OFDM_CHANEST_VCVC_H */