slicer_agc_impl.h

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/* -*- c++ -*- */
/*
 * Copyright 2002 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 _ATSC_SLICER_AGC_H_
#define _ATSC_SLICER_AGC_H_

#include <gnuradio/atsc/api.h>
#include <gnuradio/filter/single_pole_iir.h>
#include <math.h>

/*!
 * \brief Automatic Gain Control class for atsc slicer
 *
 * Given perfect data, output values will be +/- {7, 5, 3, 1}
 */

class ATSC_API atsci_slicer_agc
{

public:
    atsci_slicer_agc() : _gain(1), dc(0.0025){};


    float gain() { return _gain; }

#if 1
    float scale(float input)
    {
        float t = input * _gain;
        float output = t - REFERENCE;
        float error = REFERENCE - dc.filter(t);
        _gain += error * RATE;
        return output;
    }
#else
    float scale(float input)
    {
        float avg = dc.filter(input);
        if (fabs(avg) < .1)
            avg = .1;
        _gain += _gain * .99 + .01 * REFERENCE / avg;
        return input * _gain - REFERENCE;
    }
#endif

protected:
    static const float REFERENCE = 1.25; // pilot reference value
    static const float RATE = 1.0e-5;    // adjustment rate
    float _gain;                         // current gain
    gr::filter::single_pole_iir<float, float, float> dc;
};

#endif /* _ATSC_SLICER_AGC_H_ */