sdrtrunk/src/main/java/io/github/dsheirer/dsp/squelch/PowerSquelch.java

package io.github.dsheirer.dsp.squelch;

import io.github.dsheirer.dsp.filter.iir.SinglePoleIirFilter;
import io.github.dsheirer.sample.Listener;
import io.github.dsheirer.source.SourceEvent;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Power squelch
 *
 * Modeled after gnuradio complex power squelch:
 * https://github.com/gnuradio/gnuradio/blob/master/gr-analog/lib/pwr_squelch_cc_impl.cc
 */
public class PowerSquelch implements Listener<SourceEvent>
{
    private static final Logger mLog = LoggerFactory.getLogger(PowerSquelch.class);
    private State mState = State.MUTE;
    private SinglePoleIirFilter mFilter;
    private double mPower = 0.0f;
    private double mSquelchThreshold;
    private int mRampThreshold;
    private int mRampCount;
    private boolean mSquelchChanged = false;
    private boolean mStateChange = false;
    private int mPowerLevelBroadcastCount = 0;
    private int mPowerLevelBroadcastThreshold;
    private Listener<SourceEvent> mSourceEventListener;

    /**
     * Constructs an instance
     *
     * Testing against a 12.5 kHz analog FM modulated signal, the following parameters provided a
     * good responsiveness.  A threshold of -80.0 dB seemed to trigger significant flapping during un-squelching.
     *   - alpha: 0.0001
     *   - threshold: 78.0 dB
     *   - ramp: 4 (samples)
     *
     * @param alpha decay value of the single pole IIR filter in range: 0.0 - 1.0.  The smaller the alpha value,
     * the slower the squelch response.
     * @param squelchThreshold in decibels.  Signal power must exceed this threshold value for unsquelch.
     * @param ramp count of samples before transition between mute and unmute.  Setting this value to zero
     * causes immediate mute and unmute.  Set to higher count to prevent mute/unmute flapping.
     */
    public PowerSquelch(double alpha, double squelchThreshold, int ramp)
    {
        mFilter = new SinglePoleIirFilter(alpha);
        setSquelchThreshold(squelchThreshold);
        mRampThreshold = ramp;
        mPowerLevelBroadcastThreshold = 25000; //Based on a default sample rate of 50 kHz
    }

    /**
     * Sets the sample rate to effect the frequency of power level notifications where the notifications are
     * sent twice a second.
     * @param sampleRate in hertz
     */
    public void setSampleRate(int sampleRate)
    {
        mPowerLevelBroadcastThreshold = sampleRate / 2;
    }

    /**
     * Squelch threshold value
     * @return value in decibels
     */
    public double getSquelchThreshold()
    {
        return 10.0 * Math.log10(mSquelchThreshold);
    }

    /**
     * Sets the squelch threshold
     * @param squelchThreshold in decibels
     */
    public void setSquelchThreshold(double squelchThreshold)
    {
        mSquelchThreshold = Math.pow(10.0, squelchThreshold / 10.0);
        broadcast(SourceEvent.squelchThreshold(null, squelchThreshold));
    }

    /**
     * Processes a complex IQ sample and changes squelch state when the signal power is above or below the
     * threshold value.
     * @param inphase complex sample component
     * @param quadrature complex sample component
     */
    public void process(double inphase, double quadrature)
    {
        mPower = mFilter.filter(inphase * inphase + quadrature * quadrature);

        mPowerLevelBroadcastCount++;
        if(mPowerLevelBroadcastCount % mPowerLevelBroadcastThreshold == 0)
        {
            mPowerLevelBroadcastCount = 0;
            broadcast(SourceEvent.channelPowerLevel(null, 10.0 * Math.log10(mPower)));
        }

        mStateChange = false;

        switch(mState)
        {
            case MUTE -> {
                if(!mute())
                {
                    if(mRampThreshold > 0)
                    {
                        mState = State.ATTACK;
                        mRampCount++;
                    }
                    else
                    {
                        mState = State.UNMUTE;
                        mStateChange = true;
                    }
                }
            }
            case ATTACK -> {
                if(mRampCount >= mRampThreshold)
                {
                    mState = State.UNMUTE;
                    mStateChange = true;
                }
                else
                {
                    mRampCount++;
                }
            }
            case DECAY -> {
                if(mRampCount <= 0)
                {
                    mState = State.MUTE;
                    mStateChange = true;
                }
                else
                {
                    mRampCount--;
                }
            }
            case UNMUTE -> {
                if(mute())
                {
                    if(mRampThreshold > 0)
                    {
                        mState = State.DECAY;
                        mRampCount--;
                    }
                    else
                    {
                        mState = State.MUTE;
                        mStateChange = true;
                    }
                }
            }
        }

        //Signal that the squelch state has changed if we modified the squelch state above.
        setSquelchChanged(mStateChange);
    }

    /**
     * Indicates if the current state is muted
     */
    public boolean isMuted()
    {
        return mState == State.MUTE;
    }

    /**
     * Indicates if the current state is unmuted
     */
    public boolean isUnmuted()
    {
        return mState == State.UNMUTE;
    }

    /**
     * Indicates if the current state is fading in (attach) or fading out (decay)
     */
    public boolean isFading()
    {
        return isAttack() || isDecay();
    }

    /**
     * Indicates the squelch is in a ramp up attack state
     */
    public boolean isAttack()
    {
        return mState == State.ATTACK;
    }

    /**
     * Indicates the squelch is in a ramp down decay state
     */
    public boolean isDecay()
    {
        return mState == State.DECAY;
    }

    /**
     * Current power level
     * @return current power level in dB
     */
    public float getPower()
    {
        return (float)(10.0 * Math.log10(mPower));
    }

    /**
     * Indicates if the current power level is below the threshold, indicating that the state should be muted.
     */
    private boolean mute()
    {
        return mPower < mSquelchThreshold;
    }

    /**
     * Indicates if the squelch state has changed (muted > unmuted, or vice-versa)
     */
    public boolean isSquelchChanged()
    {
        return mSquelchChanged;
    }

    /**
     * Sets or resets the squelch changed flag
     */
    public void setSquelchChanged(boolean changed)
    {
        mSquelchChanged = changed;
    }

    /**
     * Registers the listener to receive power level notifications and squelch threshold requests
     */
    public void setSourceEventListener(Listener<SourceEvent> listener)
    {
        mSourceEventListener = listener;
    }

    /**
     * Broadcasts the source event to an optional register listener
     */
    private void broadcast(SourceEvent event)
    {
        if(mSourceEventListener != null)
        {
            mSourceEventListener.receive(event);
        }
    }

    /**
     * Primary method to receive requests for squelch threshold change
     */
    @Override
    public void receive(SourceEvent sourceEvent)
    {
        if(sourceEvent.getEvent() == SourceEvent.Event.REQUEST_CHANGE_SQUELCH_THRESHOLD)
        {
            setSquelchThreshold(sourceEvent.getValue().doubleValue());
        }
        else if(sourceEvent.getEvent() == SourceEvent.Event.REQUEST_CURRENT_SQUELCH_THRESHOLD)
        {
            broadcast(SourceEvent.squelchThreshold(null, getSquelchThreshold()));
        }
    }

    /**
     * State of squelch processing
     */
    private enum State
    {
        ATTACK,
        DECAY,
        MUTE,
        UNMUTE;
    }
}