puncture_bb.h

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/* -*- c++ -*- */
/*
 * Copyright 2014 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_FEC_PUNCTURE_BB_H
#define INCLUDED_FEC_PUNCTURE_BB_H

#include <gnuradio/block.h>
#include <gnuradio/fec/api.h>

namespace gr {
namespace fec {

/*!
 * \brief Puncture a stream of unpacked bits.
 * \ingroup error_coding_blk
 *
 * \details
 * Puncture a given block of input samples of \p puncsize. The
 * items produced is based on pattern \p puncpat. Basically, if:
 *
 * \code
 *    k = 0
 *    if _puncpat[i] == 1:
 *       out[k++] = input[i]
 * \endcode
 *
 * This block is designed for unpacked bits - that is, every
 * input sample is a bit, either a 1 or 0. It's possible to use
 * packed bits as symbols, but the puncturing will be done on
 * the symbol level, not the bit level.
 *
 * \p puncpat is specified as a 32-bit integer that we can
 * convert into the vector _puncpat used in the algorithm above:
 *
 * \code
 *    _puncpat = [0,...]
 *    for i in puncsize:
 *        _puncpat[i] = puncpat >> (puncsize-1-i)
 * \endcode
 *
 * Example:
 * \code
 *    puncsize = 8
 *    puncpat = 0xEF  -->  [1,1,1,0,1,1,1,1]
 *    input = [a, b, c, d, e, f, g, h]
 *    output = [a, b, c, e, f, g, h]
 * \endcode
 *
 * The gr.fec Python module provides a read_bitlist function
 * that can turn a string of a puncture pattern into the correct
 * integer form. The pattern of 0xEF could be specified as
 * fec.readbitlist("11101111"). Also, this allows us to use
 * puncsize=len("11101111") to make sure that our sizes are set
 * up correctly for the pattern we want.
 *
 * The fec.extended_encoder takes in the puncture pattern
 * directly as a string and uses the readbitlist inside to do
 * the conversion.
 *
 * Note that due to the above concept, the default setting in the
 * extended encoder of '11' translates into no puncturing.
 *
 * The \p delay parameter delays the application of the puncture
 * pattern. This is equivalent to circularly rotating the \p
 * puncpat by \p delay. Note that because of the circular shift,
 * the delay should be between 0 and \p puncsize, but this is
 * not enforced; the effective delay will simply be \p delay mod
 * \p puncsize. A negative value here is ignored.
 */
class FEC_API puncture_bb : virtual public block
{
public:
    // gr::fec::puncture_bb::sptr
    typedef boost::shared_ptr<puncture_bb> sptr;

    /*!
     * \brief Constructs a puncture block for unpacked bits.
     *
     * \param puncsize Size of block of bits to puncture
     * \param puncpat The puncturing pattern
     * \param delay Delayed the puncturing pattern by shifting it
     */
    static sptr make(int puncsize, int puncpat, int delay = 0);
};

} /* namespace fec */
} /* namespace gr */

#endif /* INCLUDED_FEC_PUNCTURE_BB_H */