plateau_detector_fb.h

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/* -*- c++ -*- */
/*
 * Copyright 2012-2013 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_BLOCKS_PLATEAU_DETECTOR_FB_H
#define INCLUDED_BLOCKS_PLATEAU_DETECTOR_FB_H
 
#include <gnuradio/blocks/api.h>
#include <gnuradio/sync_block.h>
 
namespace gr {
namespace blocks {
 
/*!
 * \brief Detects a plateau and marks the middle.
 * \ingroup peak_detectors_blk
 *
 * \details
 * Detect a plateau of a-priori known height. Input is a stream of floats,
 * the output is a stream of bytes. Whenever a plateau is detected, the
 * middle of that plateau is marked with a '1' on the output stream (all
 * other samples are left at zero).
 *
 * You can use this in a Schmidl & Cox synchronisation algorithm to interpret
 * the output of the normalized correlator. Just pass the length of the cyclic
 * prefix (in samples) as the max_len parameter).
 *
 * Unlike the peak detectors, you must the now the absolute height of the plateau.
 * Whenever the amplitude exceeds the given threshold, it starts assuming the
 * presence of a plateau.
 *
 * An implicit hysteresis is provided by the fact that after detecting one plateau,
 * it waits at least max_len samples before the next plateau can be detected.
 */
class BLOCKS_API plateau_detector_fb : virtual public block
{
public:
    typedef boost::shared_ptr<plateau_detector_fb> sptr;
 
    /*!
     * \param max_len Maximum length of the plateau
     * \param threshold Anything above this value is considered a plateau
     */
    static sptr make(int max_len, float threshold = 0.9);
 
    virtual void set_threshold(float threshold) = 0;
    virtual float threshold() const = 0;
};
 
} // namespace blocks
} // namespace gr
 
#endif /* INCLUDED_BLOCKS_PLATEAU_DETECTOR_FB_H */