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Resolves 1122. Adds decimation to NBFMDecoder so that channel bandwidth is reduced to min sample rate needed. This reduces the impact on channel power measurement from adjacent channels. (#1129)

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Co-authored-by: Dennis Sheirer <dsheirer@github.com>
This commit is contained in:
Denny Sheirer
2022-01-02 08:35:19 -05:00
committed by GitHub
parent 2a0427c559
commit 8413343e76
9 changed files with 234 additions and 58 deletions
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79
src/main/java/io/github/dsheirer/module/decode/nbfm/NBFMDecoder.java
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@@ -1,20 +1,21 @@
/*******************************************************************************
* SDR Trunk
* Copyright (C) 2014,2015 Dennis Sheirer
*
* This program 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 of the License, or
* (at your option) any later version.
*
* This program 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 this program. If not, see <http://www.gnu.org/licenses/>
******************************************************************************/
/*
* *****************************************************************************
* Copyright (C) 2014-2022 Dennis Sheirer
*
* This program 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 of the License, or
* (at your option) any later version.
*
* This program 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 this program. If not, see <http://www.gnu.org/licenses/>
* ****************************************************************************
*/
package io.github.dsheirer.module.decode.nbfm;
import io.github.dsheirer.channel.state.DecoderStateEvent;
@@ -22,6 +23,8 @@ import io.github.dsheirer.channel.state.IDecoderStateEventProvider;
import io.github.dsheirer.channel.state.State;
import io.github.dsheirer.dsp.filter.FilterFactory;
import io.github.dsheirer.dsp.filter.Window;
import io.github.dsheirer.dsp.filter.decimate.DecimationFilterFactory;
import io.github.dsheirer.dsp.filter.decimate.IComplexDecimationFilter;
import io.github.dsheirer.dsp.filter.design.FilterDesignException;
import io.github.dsheirer.dsp.filter.fir.FIRFilterSpecification;
import io.github.dsheirer.dsp.filter.fir.complex.ComplexFIRFilter2;
@@ -49,11 +52,12 @@ public class NBFMDecoder extends PrimaryDecoder implements ISourceEventListener,
{
private final static Logger mLog = LoggerFactory.getLogger(NBFMDecoder.class);
private static final double DEMODULATED_AUDIO_SAMPLE_RATE = 8000.0;
private static final double POWER_SQUELCH_ALPHA_DECAY = 0.0002;
private static final double POWER_SQUELCH_ALPHA_DECAY = 0.0004;
private static final double POWER_SQUELCH_THRESHOLD_DB = -78.0;
private static final int POWER_SQUELCH_RAMP = 4;
private ComplexFIRFilter2 mIQFilter;
private IComplexDecimationFilter mDecimationFilter;
private SquelchingFMDemodulator mDemodulator = new SquelchingFMDemodulator(POWER_SQUELCH_ALPHA_DECAY,
POWER_SQUELCH_THRESHOLD_DB, POWER_SQUELCH_RAMP);
private RealResampler mResampler;
@@ -131,7 +135,9 @@ public class NBFMDecoder extends PrimaryDecoder implements ISourceEventListener,
"event before it can process complex sample buffers");
}
ReusableComplexBuffer basebandFilteredBuffer = mIQFilter.filter(reusableComplexBuffer);
ReusableComplexBuffer decimatedBuffer = mDecimationFilter.decimate(reusableComplexBuffer);
ReusableComplexBuffer basebandFilteredBuffer = mIQFilter.filter(decimatedBuffer);
ReusableFloatBuffer demodulatedBuffer = mDemodulator.demodulate(basebandFilteredBuffer);
if(mResampler != null)
@@ -268,11 +274,31 @@ public class NBFMDecoder extends PrimaryDecoder implements ISourceEventListener,
double sampleRate = sourceEvent.getValue().doubleValue();
if((sampleRate < (2.0 * mChannelBandwidth)))
int decimationRate = 0;
double decimatedSampleRate = sampleRate;
if(sampleRate / 2 > mChannelBandwidth)
{
decimationRate = 2;
while(sampleRate / decimationRate / 2 > mChannelBandwidth)
{
decimationRate *= 2;
}
}
if(decimationRate > 0)
{
decimatedSampleRate /= decimationRate;
}
mDecimationFilter = DecimationFilterFactory.getComplexDecimationFilter(decimationRate);
if((decimatedSampleRate < (2.0 * mChannelBandwidth)))
{
throw new IllegalStateException("FM Demodulator with channel bandwidth [" + mChannelBandwidth +
"] requires a channel sample rate of [" + (2.0 * mChannelBandwidth + "] - sample rate of [" +
sampleRate + "] is not supported"));
decimatedSampleRate + "] is not supported"));
}
int passBandStop = (int)(mChannelBandwidth * .8);
@@ -281,7 +307,7 @@ public class NBFMDecoder extends PrimaryDecoder implements ISourceEventListener,
float[] filterTaps = null;
FIRFilterSpecification specification = FIRFilterSpecification.lowPassBuilder()
.sampleRate(sampleRate)
.sampleRate(decimatedSampleRate * 2)
.gridDensity(16)
.oddLength(true)
.passBandCutoff(passBandStop)
@@ -300,18 +326,21 @@ public class NBFMDecoder extends PrimaryDecoder implements ISourceEventListener,
{
mLog.error("Couldn't design FM demodulator remez filter for sample rate [" + sampleRate +
"] pass frequency [" + passBandStop + "] and stop frequency [" + stopBandStart +
"] - using sinc filter");
"] - will proceed using sinc (low-pass) filter");
}
if(filterTaps == null)
{
filterTaps = FilterFactory.getLowPass(sampleRate, passBandStop, stopBandStart, 60,
mLog.info("Unable to use remez filter designer for sample rate [" + decimatedSampleRate +
"] pass band stop [" + passBandStop +
"] and stop band start [" + stopBandStart + "] - will proceed using simple low pass filter design");
filterTaps = FilterFactory.getLowPass(decimatedSampleRate, passBandStop, stopBandStart, 60,
Window.WindowType.HAMMING, true);
}
mIQFilter = new ComplexFIRFilter2(filterTaps);
mResampler = new RealResampler(sampleRate, mOutputSampleRate, 2000, 1000);
mResampler = new RealResampler(decimatedSampleRate, mOutputSampleRate, 2000, 1000);
mResampler.setListener(reusableFloatBuffer ->
{