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Diffstat (limited to 'gr-digital/include/digital_ofdm_frame_acquisition.h')
| -rw-r--r-- | gr-digital/include/digital_ofdm_frame_acquisition.h | 116 |
1 files changed, 116 insertions, 0 deletions
diff --git a/gr-digital/include/digital_ofdm_frame_acquisition.h b/gr-digital/include/digital_ofdm_frame_acquisition.h new file mode 100644 index 000000000..971202099 --- /dev/null +++ b/gr-digital/include/digital_ofdm_frame_acquisition.h @@ -0,0 +1,116 @@ +/* -*- c++ -*- */ +/* + * Copyright 2006,2007,2011 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 <gr_block.h> +#include <vector> + +class digital_ofdm_frame_acquisition; +typedef boost::shared_ptr<digital_ofdm_frame_acquisition> digital_ofdm_frame_acquisition_sptr; + +digital_ofdm_frame_acquisition_sptr +digital_make_ofdm_frame_acquisition (unsigned int occupied_carriers, unsigned int fft_length, + unsigned int cplen, + const std::vector<gr_complex> &known_symbol, + unsigned int max_fft_shift_len=10); + +/*! + * \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_ofdm_frame_acquisition : public gr_block +{ + /*! + * \brief Build 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 + */ + friend digital_ofdm_frame_acquisition_sptr + digital_make_ofdm_frame_acquisition (unsigned int occupied_carriers, unsigned int fft_length, + unsigned int cplen, + const std::vector<gr_complex> &known_symbol, + unsigned int max_fft_shift_len); + +protected: + digital_ofdm_frame_acquisition (unsigned int occupied_carriers, unsigned int fft_length, + unsigned int cplen, + const std::vector<gr_complex> &known_symbol, + unsigned int max_fft_shift_len); + + private: + unsigned char slicer(gr_complex x); + void correlate(const gr_complex *symbol, int zeros_on_left); + void calculate_equalizer(const gr_complex *symbol, int zeros_on_left); + gr_complex coarse_freq_comp(int freq_delta, int count); + + unsigned int d_occupied_carriers; // !< \brief number of subcarriers with data + unsigned int d_fft_length; // !< \brief length of FFT vector + unsigned int d_cplen; // !< \brief length of cyclic prefix in samples + unsigned int d_freq_shift_len; // !< \brief number of surrounding bins to look at for correlation + std::vector<gr_complex> d_known_symbol; // !< \brief known symbols at start of frame + std::vector<float> d_known_phase_diff; // !< \brief factor used in correlation from known symbol + std::vector<float> d_symbol_phase_diff; // !< \brief factor used in correlation from received symbol + std::vector<gr_complex> d_hestimate; // !< channel estimate + int d_coarse_freq; // !< \brief search distance in number of bins + unsigned int d_phase_count; // !< \brief accumulator for coarse freq correction + float d_snr_est; // !< an estimation of the signal to noise ratio + + gr_complex *d_phase_lut; // !< look-up table for coarse frequency compensation + + void forecast(int noutput_items, gr_vector_int &ninput_items_required); + + public: + /*! + * \brief Return an estimate of the SNR of the channel + */ + float snr() { return d_snr_est; } + + ~digital_ofdm_frame_acquisition(void); + 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 |