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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.
*/
static sptr make(int fft_len, int cp_len, bool use_even_carriers=false);
};
} // namespace digital
} // namespace gr
#endif /* INCLUDED_DIGITAL_OFDM_SYNC_SC_CFB_H */
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