+/* -*- c++ -*- */

+/* Copyright 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_CHANEST_VCVC_H

+#define INCLUDED_DIGITAL_OFDM_CHANEST_VCVC_H

+

+#include <digital/api.h>

+#include <gr_block.h>

+

+class digital_ofdm_chanest_vcvc;

+

+typedef boost::shared_ptr<digital_ofdm_chanest_vcvc> digital_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.

+ */

+DIGITAL_API digital_ofdm_chanest_vcvc_sptr

+digital_make_ofdm_chanest_vcvc (

+ 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);

+

+/*!

+ * \brief Estimate channel and coarse frequency offset for OFDM from preambles

+ * \ingroup ofdm_blk

+ * \ingroup sync_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 normally.

+ *

+ * 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 digital_ofdm_chanest_vcvc : public gr_block

+{

+ private:

+ friend DIGITAL_API digital_ofdm_chanest_vcvc_sptr digital_make_ofdm_chanest_vcvc (const std::vector<gr_complex> &sync_symbol1, const std::vector<gr_complex> &sync_symbol2, int n_data_symbols, int eq_noise_red_len, int max_carr_offset, bool force_one_sync_symbol);

+

+ int d_fft_len; //! FFT length

+ int d_n_data_syms; //! Number of data symbols following the sync symbol(s)

+ int d_n_sync_syms; //! Number of sync symbols (1 or 2)

+ //! 0 if no noise reduction is done for the initial channel state estimation. Otherwise, the maximum length of the channel delay in samples.

+ int d_eq_noise_red_len;

+ //! Is sync_symbol1 if d_n_sync_syms == 1, otherwise sync_symbol2. Used as a reference symbol to estimate the channel.

+ std::vector<gr_complex> d_ref_sym;

+ //! If d_n_sync_syms == 2 this is used as a differential correlation vector (called 'v' in [1]).

+ std::vector<gr_complex> d_corr_v;

+ //! If d_n_sync_syms == 1 we use this instead of d_corr_v to estimate the coarse freq. offset

+ std::vector<float> d_known_symbol_diffs;

+ //! If d_n_sync_syms == 1 we use this instead of d_corr_v to estimate the coarse freq. offset (temp. variable)

+ std::vector<float> d_new_symbol_diffs;

+ //! The index of the first carrier with data (index 0 is not DC here, but the lowest frequency)

+ int d_first_active_carrier;

+ //! The index of the last carrier with data

+ int d_last_active_carrier;

+ //! If true, the channel estimation must be interpolated

+ bool d_interpolate;

+ //! Maximum carrier offset (negative value!)

+ int d_max_neg_carr_offset;

+ //! Maximum carrier offset (positive value!)

+ int d_max_pos_carr_offset;

+

+

+ digital_ofdm_chanest_vcvc(const std::vector<gr_complex> &sync_symbol1, const std::vector<gr_complex> &sync_symbol2, int n_data_symbols, int eq_noise_red_len, int max_carr_offset, bool force_one_sync_symbol);

+

+ //! Calculate the coarse frequency offset in number of carriers

+ int get_carr_offset(const gr_complex *sync_sym1, const gr_complex *sync_sym2);

+ //! Estimate the channel (phase and amplitude offset per carrier)

+ void get_chan_taps(const gr_complex *sync_sym1, const gr_complex *sync_sym2, int carr_offset, std::vector<gr_complex> &taps);

+

+ public:

+ ~digital_ofdm_chanest_vcvc();

+

+ void forecast (int noutput_items, gr_vector_int &ninput_items_required);

+ 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 /* INCLUDED_DIGITAL_OFDM_CHANEST_VCVC_H */

+