mirror of
https://github.com/DSheirer/sdrtrunk.git
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#90 [WIP] Resolves issue with MPT-1327 decoder which has apparently been broken for a long time.
This commit is contained in:
Denny
@@ -1,296 +1,302 @@
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/*******************************************************************************
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* SDR Trunk
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* Copyright (C) 2014 Dennis Sheirer
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*
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>
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******************************************************************************/
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package dsp.fsk;
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import buffer.BooleanAveragingBuffer;
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import dsp.symbol.SymbolEvent;
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import dsp.symbol.SymbolEvent.Shift;
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import instrument.Instrumentable;
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import instrument.tap.Tap;
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import instrument.tap.TapGroup;
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import instrument.tap.stream.SymbolEventTap;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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import sample.Listener;
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import sample.real.RealBuffer;
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import java.util.ArrayList;
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import java.util.BitSet;
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import java.util.List;
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import sample.Listener;
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import sample.real.RealBuffer;
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import buffer.BooleanAveragingBuffer;
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import dsp.symbol.SymbolEvent;
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import dsp.symbol.SymbolEvent.Shift;
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/**
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* Binary Frequency Shift Keying (FSK) decoder. Implements a BFSK correlation
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* decoder. Provides normal or inverted decoded output. Requires the symbol
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* rate to be an integer multiple of the sample rate.
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*
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* Implements a correlation decoder that correlates a modulated FSK signal upon
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* against a one-baud delayed version of itself, converting all float samples to
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* binary (0 or 1), and uses XOR to produce the correlation value. Low pass
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*
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* Implements a correlation decoder that correlates a modulated FSK signal upon
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* against a one-baud delayed version of itself, converting all float samples to
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* binary (0 or 1), and uses XOR to produce the correlation value. Low pass
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* filtering smoothes the correlated output.
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*
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*
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* Automatically aligns to symbol timing during symbol transitions (0 to 1, or
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* 1 to 0) by inspecting the samples at the symbol edges and advancing or
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* 1 to 0) by inspecting the samples at the symbol edges and advancing or
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* retarding symbol window to maintain continuous symbol alignment.
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*
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*
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* Use a DC-removal filter prior to this decoder to ensure samples don't have
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* a DC component.
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*
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*
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* Implements instrumentable interface, so that slice events can be received
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* externally to analyze decoder performance.
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*/
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public class FSK2Decoder implements Instrumentable, Listener<RealBuffer>
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{
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public enum Output{ NORMAL, INVERTED };
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private final static Logger mLog = LoggerFactory.getLogger(FSK2Decoder.class);
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/* Instrumentation taps */
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private static final String INSTRUMENT_DECISION =
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"Tap Point: FSK2 Symbol Decision";
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private List<TapGroup> mAvailableTaps;
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private ArrayList<SymbolEventTap> mTaps = new ArrayList<SymbolEventTap>();
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private Listener<Boolean> mListener;
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private BooleanAveragingBuffer mDelayBuffer;
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private BooleanAveragingBuffer mLowPassFilter;
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private Slicer mSlicer;
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private boolean mNormalOutput;
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private int mSamplesPerSymbol;
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private int mSymbolRate;
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public FSK2Decoder( int sampleRate, int symbolRate, Output output )
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{
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/* Ensure we're using an integral symbolRate of the sampleRate */
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assert( sampleRate % symbolRate == 0 );
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mSamplesPerSymbol = (int)( sampleRate / symbolRate );
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mNormalOutput = ( output == Output.NORMAL );
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mSymbolRate = symbolRate;
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mDelayBuffer = new BooleanAveragingBuffer( mSamplesPerSymbol );
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mLowPassFilter = new BooleanAveragingBuffer( mSamplesPerSymbol );
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mSlicer = new Slicer( mSamplesPerSymbol );
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}
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/**
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* Disposes of all references to prepare for garbage collection
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*/
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public void dispose()
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{
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mListener = null;
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}
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public enum Output
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{
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NORMAL, INVERTED
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}
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/**
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* Primary sample input
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*/
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@Override
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public void receive( RealBuffer buffer )
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{
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for( float sample: buffer.getSamples() )
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{
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/* Instrumentation taps */
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private static final String INSTRUMENT_DECISION =
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"Tap Point: FSK2 Symbol Decision";
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private List<TapGroup> mAvailableTaps;
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private ArrayList<SymbolEventTap> mTaps = new ArrayList<SymbolEventTap>();
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private Listener<Boolean> mListener;
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private BooleanAveragingBuffer mDelayBuffer;
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private BooleanAveragingBuffer mLowPassFilter;
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private Slicer mSlicer;
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private boolean mNormalOutput;
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private int mSamplesPerSymbol;
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private int mSymbolRate;
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public FSK2Decoder(int sampleRate, int symbolRate, Output output)
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{
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/* Ensure we're using an integral symbolRate of the sampleRate */
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assert (sampleRate % symbolRate == 0);
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mSamplesPerSymbol = (int) (sampleRate / symbolRate);
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mNormalOutput = (output == Output.NORMAL);
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mSymbolRate = symbolRate;
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mDelayBuffer = new BooleanAveragingBuffer(mSamplesPerSymbol);
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mLowPassFilter = new BooleanAveragingBuffer(mSamplesPerSymbol);
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mSlicer = new Slicer(mSamplesPerSymbol);
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}
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/**
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* Disposes of all references to prepare for garbage collection
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*/
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public void dispose()
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{
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mListener = null;
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}
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/**
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* Primary sample input
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*/
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@Override
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public void receive(RealBuffer buffer)
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{
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for(float sample : buffer.getSamples())
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{
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/* Square the sample. Greater than zero is a 1 (true) and less than
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* zero is a 0 (false) */
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boolean bitSample = ( sample >= 0.0f );
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boolean bitSample = (sample >= 0.0f);
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/* Feed the delay buffer and fetch the one-baud delayed sample */
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boolean delayedBitSample = mDelayBuffer.get( bitSample );
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boolean delayedBitSample = mDelayBuffer.get(bitSample);
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/* Correlation: xor current bit with delayed bit */
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boolean softBit = bitSample ^ delayedBitSample;
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boolean softBit = bitSample ^ delayedBitSample;
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/* Low pass filter to smooth the correlated values */
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boolean filteredSoftBit = mLowPassFilter.getAverage( softBit );
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boolean filteredSoftBit = mLowPassFilter.getAverage(softBit);
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/* Send the filtered correlated bit to the slicer */
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mSlicer.receive( filteredSoftBit );
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}
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}
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mSlicer.receive(filteredSoftBit);
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}
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}
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/**
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* Registers a listener to receive the decoded FSK bits
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*/
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public void setListener( Listener<Boolean> listener )
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{
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mListener = listener;
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}
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/**
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* Registers a listener to receive the decoded FSK bits
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*/
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public void setListener(Listener<Boolean> listener)
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{
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mListener = listener;
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}
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/**
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* Removes the listener
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*/
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public void removeListener( Listener<Boolean> listener )
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{
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mListener = null;
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}
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/**
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* Removes the listener
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*/
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public void removeListener(Listener<Boolean> listener)
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{
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mListener = null;
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}
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/**
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* Symbol slicer with auto-aligning baud timing
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*/
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public class Slicer
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{
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private BitSet mBitSet = new BitSet();
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private int mSymbolLength;
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private int mDecisionThreshold;
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private int mSampleCounter;
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public Slicer( int samplesPerSymbol )
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{
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mSymbolLength = samplesPerSymbol;
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mDecisionThreshold = (int)( mSymbolLength / 2 );
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/**
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* Symbol slicer with auto-aligning baud timing
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*/
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public class Slicer
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{
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private BitSet mBitSet = new BitSet();
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private int mSymbolLength;
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private int mDecisionThreshold;
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private int mSampleCounter;
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public Slicer(int samplesPerSymbol)
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{
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mSymbolLength = samplesPerSymbol;
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mDecisionThreshold = (int) (mSymbolLength / 2);
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/* Adjust for an odd number of samples per baud */
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if( mSymbolLength % 2 == 1 )
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{
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mDecisionThreshold++;
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}
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}
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public void receive( boolean softBit )
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{
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if( mSampleCounter >= 0 )
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{
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if( softBit )
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{
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mBitSet.set( mSampleCounter );
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}
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else
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{
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mBitSet.clear( mSampleCounter );
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}
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}
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mSampleCounter++;
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if( mSampleCounter >= mSymbolLength )
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{
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boolean decision = mBitSet.cardinality() >= mDecisionThreshold;
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send( decision );
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if(mSymbolLength % 2 == 1)
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{
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mDecisionThreshold++;
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}
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}
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public void receive(boolean softBit)
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{
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if(mSampleCounter >= 0)
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{
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if(softBit)
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{
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mBitSet.set(mSampleCounter);
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}
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else
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{
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mBitSet.clear(mSampleCounter);
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}
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}
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mSampleCounter++;
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if(mSampleCounter >= mSymbolLength)
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{
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boolean decision = mBitSet.cardinality() >= mDecisionThreshold;
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send(decision);
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/* Shift timing left if the left bit in the bitset is opposite
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* the decision and the right bit is the same */
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if( ( mBitSet.get( 0 ) ^ decision ) &&
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( !( mBitSet.get( mSymbolLength - 1 ) ^ decision ) ) )
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{
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sendTapEvent( mBitSet, Shift.LEFT, decision );
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reset();
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mSampleCounter--;
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}
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if((mBitSet.get(0) ^ decision) &&
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(!(mBitSet.get(mSymbolLength - 1) ^ decision)))
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{
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sendTapEvent(mBitSet, Shift.LEFT, decision);
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reset();
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mSampleCounter--;
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}
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/* Shift timing right if the left bit is the same as the
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* decision and the right bit is opposite */
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else if( ( !( mBitSet.get( 0 ) ^ decision ) ) &&
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( mBitSet.get( mSymbolLength - 1 ) ^ decision ) )
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{
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sendTapEvent( mBitSet, Shift.RIGHT, decision );
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else if((!(mBitSet.get(0) ^ decision)) &&
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(mBitSet.get(mSymbolLength - 1) ^ decision))
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{
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sendTapEvent(mBitSet, Shift.RIGHT, decision);
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/* Last bit from previous symbol to pre-fill next symbol */
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boolean previousSoftBit = mBitSet.get( mSymbolLength - 1 );
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reset();
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if( previousSoftBit )
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{
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mBitSet.set( 0 );
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}
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mSampleCounter++;
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}
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boolean previousSoftBit = mBitSet.get(mSymbolLength - 1);
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reset();
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if(previousSoftBit)
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{
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mBitSet.set(0);
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}
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mSampleCounter++;
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}
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/* No shift */
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else
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{
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sendTapEvent( mBitSet, Shift.NONE, decision );
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reset();
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}
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}
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}
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/**
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* Sends the bit decision to the listener
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*/
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private void send( boolean decision )
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{
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if( mListener != null )
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{
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mListener.receive( mNormalOutput ? decision : !decision );
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}
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}
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private void reset()
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{
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mBitSet.clear();
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mSampleCounter = 0;
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}
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else
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{
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sendTapEvent(mBitSet, Shift.NONE, decision);
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/**
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* Sends instrumentation tap event to all registered listeners
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*/
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private void sendTapEvent( BitSet bitset, Shift shift, boolean decision )
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{
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for( SymbolEventTap tap: mTaps )
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{
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SymbolEvent event =
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new SymbolEvent( bitset.get( 0, mSymbolLength ),
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mSymbolLength,
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decision,
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shift );
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tap.receive( event );
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}
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}
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}
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reset();
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}
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}
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}
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/**
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* Get instrumentation taps
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*/
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@Override
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/**
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* Sends the bit decision to the listener
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*/
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private void send(boolean decision)
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{
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if(mListener != null)
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{
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mListener.receive(mNormalOutput ? decision : !decision);
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}
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}
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private void reset()
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{
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mBitSet.clear();
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mSampleCounter = 0;
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}
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/**
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* Sends instrumentation tap event to all registered listeners
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*/
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private void sendTapEvent(BitSet bitset, Shift shift, boolean decision)
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{
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for(SymbolEventTap tap : mTaps)
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{
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SymbolEvent event =
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new SymbolEvent(bitset.get(0, mSymbolLength),
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mSymbolLength,
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decision,
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shift);
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tap.receive(event);
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}
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}
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}
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/**
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* Get instrumentation taps
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*/
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@Override
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public List<TapGroup> getTapGroups()
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{
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if( mAvailableTaps == null )
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{
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mAvailableTaps = new ArrayList<TapGroup>();
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TapGroup tapGroup = new TapGroup( "FSK2 Decoder" );
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tapGroup.add( new SymbolEventTap( INSTRUMENT_DECISION, 0, .025f ) );
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mAvailableTaps.add( tapGroup );
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}
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return mAvailableTaps;
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if(mAvailableTaps == null)
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{
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mAvailableTaps = new ArrayList<TapGroup>();
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TapGroup tapGroup = new TapGroup("FSK2 Decoder");
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tapGroup.add(new SymbolEventTap(INSTRUMENT_DECISION, 0, .025f));
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mAvailableTaps.add(tapGroup);
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}
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return mAvailableTaps;
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}
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/**
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* Add instrumentation tap
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*/
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@Override
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public void registerTap( Tap tap )
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/**
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* Add instrumentation tap
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*/
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@Override
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public void registerTap(Tap tap)
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{
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if( tap instanceof SymbolEventTap && !mTaps.contains( tap ) )
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{
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mTaps.add( (SymbolEventTap)tap );
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}
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if(tap instanceof SymbolEventTap && !mTaps.contains(tap))
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{
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mTaps.add((SymbolEventTap) tap);
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}
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}
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/**
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* Remove instrumentation tap
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*/
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@Override
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public void unregisterTap( Tap tap )
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/**
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* Remove instrumentation tap
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*/
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@Override
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public void unregisterTap(Tap tap)
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{
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mTaps.remove( tap );
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mTaps.remove(tap);
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}
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}
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