packet_header_ofdm.h

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/* -*- 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_PACKET_HEADER_OFDM_H
#define INCLUDED_DIGITAL_PACKET_HEADER_OFDM_H

#include <vector>
#include <gnuradio/digital/api.h>
#include <gnuradio/digital/packet_header_default.h>

namespace gr {
  namespace digital {

    /*!
     * \brief Header utility for OFDM signals.
     * \ingroup ofdm_blk
     */
    class DIGITAL_API packet_header_ofdm : public packet_header_default
    {
     public:
      typedef boost::shared_ptr<packet_header_ofdm> sptr;

      packet_header_ofdm(
                      const std::vector<std::vector<int> > &occupied_carriers,
                      int n_syms,
                      const std::string &len_tag_key,
                      const std::string &frame_len_tag_key,
                      const std::string &num_tag_key,
                      int bits_per_header_sym,
                      int bits_per_payload_sym,
                      bool scramble_header);
      ~packet_header_ofdm();

      /*!
       * \brief Header formatter.
       *
       * Does the same as packet_header_default::header_formatter(), but
       * optionally scrambles the bits (this is more important for OFDM to avoid
       * PAPR spikes).
       */
      bool header_formatter(
          long packet_len,
          unsigned char *out,
          const std::vector<tag_t> &tags
      );

      /*!
       * \brief Inverse function to header_formatter().
       *
       * Does the same as packet_header_default::header_parser(), but
       * adds another tag that stores the number of OFDM symbols in the
       * packet.
       * Note that there is usually no linear connection between the number
       * of OFDM symbols and the packet length because a packet might
       * finish mid-OFDM-symbol.
       */
      bool header_parser(
        const unsigned char *header,
        std::vector<tag_t> &tags);

      /*!
       * \param occupied_carriers See carrier allocator
       * \param n_syms The number of OFDM symbols the header should be (usually 1)
       * \param len_tag_key The tag key used for the packet length (number of bytes)
       * \param frame_len_tag_key The tag key used for the frame length (number of
       *                          OFDM symbols, this is the tag key required for the
       *                          frame equalizer etc.)
       * \param num_tag_key The tag key used for packet numbering.
       * \param bits_per_header_sym Bits per complex symbol in the header, e.g. 1 if
       *                            the header is BPSK modulated, 2 if it's QPSK
       *                            modulated etc.
       * \param bits_per_payload_sym Bits per complex symbol in the payload. This is
       *                             required to figure out how many OFDM symbols
       *                             are necessary to encode the given number of
       *                             bytes.
       * \param scramble_header Set this to true to scramble the bits. This is highly
       *                        recommended, as it reduces PAPR spikes.
       */
      static sptr make(
            const std::vector<std::vector<int> > &occupied_carriers,
            int n_syms,
            const std::string &len_tag_key="packet_len",
            const std::string &frame_len_tag_key="frame_len",
            const std::string &num_tag_key="packet_num",
            int bits_per_header_sym=1,
            int bits_per_payload_sym=1,
            bool scramble_header=false
      );


     protected:
      pmt::pmt_t d_frame_len_tag_key; //!< Tag key of the additional frame length tag
      const std::vector<std::vector<int> > d_occupied_carriers; //!< Which carriers/symbols carry data
      int d_syms_per_set; //!< Helper variable: Total number of elements in d_occupied_carriers
      int d_bits_per_payload_sym;
      std::vector<unsigned char> d_scramble_mask; //!< Bits are xor'd with this before tx'ing
    };

  } // namespace digital
} // namespace gr

#endif /* INCLUDED_DIGITAL_PACKET_HEADER_OFDM_H */