/* -*- c++ -*- */ /* * Copyright 2006,2007,2011,2012 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_FRAME_ACQUISITION_H #define INCLUDED_DIGITAL_OFDM_FRAME_ACQUISITION_H #include <digital/api.h> #include <gr_block.h> #include <vector> namespace gr { namespace digital { /*! * \brief take a vector of complex constellation points in from an * FFT and performs a correlation and equalization. * \ingroup demodulation_blk * \ingroup ofdm_blk * * This block takes the output of an FFT of a received OFDM symbol * and finds the start of a frame based on two known symbols. It * also looks at the surrounding bins in the FFT output for the * correlation in case there is a large frequency shift in the * data. This block assumes that the fine frequency shift has * already been corrected and that the samples fall in the middle * of one FFT bin. * * It then uses one of those known symbols to estimate the channel * response over all subcarriers and does a simple 1-tap * equalization on all subcarriers. This corrects for the phase * and amplitude distortion caused by the channel. */ class DIGITAL_API ofdm_frame_acquisition : virtual public gr_block { public: // gr::digital::ofdm_frame_acquisition::sptr typedef boost::shared_ptr<ofdm_frame_acquisition> sptr; /*! * Make an OFDM correlator and equalizer. * * \param occupied_carriers The number of subcarriers with data in the received symbol * \param fft_length The size of the FFT vector (occupied_carriers + unused carriers) * \param cplen The length of the cycle prefix * \param known_symbol A vector of complex numbers representing a known symbol at the * start of a frame (usually a BPSK PN sequence) * \param max_fft_shift_len Set's the maximum distance you can look between bins for correlation */ static sptr make(unsigned int occupied_carriers, unsigned int fft_length, unsigned int cplen, const std::vector<gr_complex> &known_symbol, unsigned int max_fft_shift_len=4); /*! * \brief Return an estimate of the SNR of the channel */ virtual float snr() = 0; }; } /* namespace digital */ } /* namespace gr */ #endif /* INCLUDED_DIGITAL_OFDM_FRAME_ACQUISITION_H */