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330 - updates P25 C4FM decoder to use the new DQPSK demodulator and

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removes the previous FM demodulator based decoder.
This commit is contained in:
Denny
2018-03-17 09:45:23 -04:00
parent 646bd78037
commit 8868c1f954
10 changed files with 181 additions and 462 deletions
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2
src/main/java/io/github/dsheirer/dsp/psk/DQPSKSymbolEvaluator.java
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@@ -32,7 +32,7 @@ public class DQPSKSymbolEvaluator implements IDQPSKSymbolEvaluator
private Dibit mSymbolDecision = Dibit.D00_PLUS_1;
/**
* Data-directed symbol phase and timing error detector and symbol decision slicer.
* Decision-directed symbol phase and timing error detector and symbol decision slicer.
*
* Symbol decision is based on the closest reference quadrant for the sampled symbol.
*

37
src/main/java/io/github/dsheirer/dsp/psk/DQPSKSymbolPhaseErrorCalculator.java
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@@ -1,37 +0,0 @@
/*******************************************************************************
* sdr-trunk
* Copyright (C) 2014-2018 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.dsp.psk;
import io.github.dsheirer.sample.complex.Complex;
public class DQPSKSymbolPhaseErrorCalculator extends QPSKSymbolPhaseErrorCalculator
{
//45 degrees rotation to orient the symbol to a polar axis to make error calculation easy/efficient
public static final Complex DIFFERENTIAL_OFFSET = Complex.fromAngle(Math.PI / 4.0d);
private Complex mSymbol = new Complex(0, 0);
public DQPSKSymbolPhaseErrorCalculator()
{
}
@Override
public float getPhaseError(Complex symbol)
{
mSymbol.setValues(symbol);
mSymbol.multiply(DIFFERENTIAL_OFFSET);
return super.getPhaseError(mSymbol);
}
}

89
src/main/java/io/github/dsheirer/dsp/psk/DQPSKTimingErrorDetector.java
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@@ -1,89 +0,0 @@
/*******************************************************************************
* sdr-trunk
* Copyright (C) 2014-2018 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.dsp.psk;
import io.github.dsheirer.sample.complex.Complex;
public class DQPSKTimingErrorDetector
{
private static final float PI_4_ROTATION = (float)(Math.PI / 4.0);
/**
* Custom early/late symbol timing error detector designed to optimize the sample timing point such that the
* current symbol's inphase and quadrature approach the optimal 45 degree (.707) sampling instant.
*/
public DQPSKTimingErrorDetector()
{
}
/**
* Calculates a symbol sampling time error by comparing the current complex sample against a normal QPSK or
* Pi/4 rotated four symbol constellation. The error signal (advance/retard) is determined by the slope
* of each of the inphase and quadrature legs as detected by comparing an immediately preceding sample against
* the current sample and then calculating the error distance of the sampled symbol from the ideal Pi/4 sampling
* location.
*
* Note: both the preceding and the current symbols MUST be normalized (ie symbol.normalize()) to the unit circle
* prior to invoking this method.
*
* @param precedingSymbol
* @param currentSymbol
* @return timing error signal used to advance (positive) or retard (negative) the sampling point
*/
public float getError(Complex precedingSymbol, Complex currentSymbol)
{
return getError(precedingSymbol.inphase(), currentSymbol.inphase()) +
getError(precedingSymbol.quadrature(), currentSymbol.quadrature());
}
/**
* Calculates timing error of current value relative to an ideal 45 degree or Pi/4 radians (.707) value.
*
* @param early sample that closely precedes the current sampling instant - used to determine slope
* @param current sampling value
* @return error as the distance of the current value from an ideal value and the sign (advance/retard)
* appropriate for the detected slope
*/
private float getError(float early, float current)
{
if(early < current) //Ascending slope
{
if(current > 0.0)
{
//Positive quadrature hemisphere, ascending slope
return PI_4_ROTATION - current;
}
else
{
//Negative quadrature hemisphere, ascending slope
return -PI_4_ROTATION - current;
}
}
else //Descending slope
{
if(current > 0.0)
{
//Positive quadrature hemisphere, descending slope
return current - PI_4_ROTATION;
}
else
{
//Negative quadrature hemisphere, descending slope
return current + PI_4_ROTATION;
}
}
}
}