--- /dev/null
+/* -*- c++ -*- */
+/*
+ * Copyright 2006, 2007 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_GR_OFDM_FRAME_ACQUISITION_H
+#define INCLUDED_GR_OFDM_FRAME_ACQUISITION_H
+
+
+#include <gr_block.h>
+#include <vector>
+
+class gr_ofdm_frame_acquisition;
+typedef boost::shared_ptr<gr_ofdm_frame_acquisition> gr_ofdm_frame_acquisition_sptr;
+
+gr_ofdm_frame_acquisition_sptr
+gr_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 gr_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 gr_ofdm_frame_acquisition_sptr
+ gr_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:
+ gr_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; }
+
+ ~gr_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
projects / debian / gnuradio / blobdiff