Fix downsampler producing incorrect output when ratio 0.5 < x < 1.0

Add I/Q support to timing error detector Fix PSK/QAM generator not applying constant doppler effects properly Replace Integrator.Preload() with Integrator.SetValue(), as they do the same thing

Author: TylerAdkisson

SignalTest/AGC.cs

@@ -69,7 +69,7 @@ public AGC(float targetAmplitude, float maxGain)
  _isAdaptAllowed = true;
 
  _gainIntegrator = new Integrator(1f, (1f / 44100f) * 1500f);
- _gainIntegrator.Preload(1.0f);
+ _gainIntegrator.SetValue(1.0f);
  _gain = 1.0f;
  }
 

SignalTest/Downsampler.cs

@@ -14,87 +14,48 @@ public class Downsampler
  private float _invRatio;
  private float _lastSample;
  private float _sampleCounter;
- private bool _needsMoreInput;
 
 
  public Downsampler(double inputSampleRate)
  {
  _inputSampleRate = inputSampleRate;
  _firBuffer = new float[9];
 
- _needsMoreInput = true;
-
  _sampleCounter = 0f;
  SetRatio(1f);
  }
 
 
  public void SupplyInput(float sample)
  {
- if (!_needsMoreInput)
- return;
-
  ShiftArrayLeft(_firBuffer, sample);
- _needsMoreInput = false;
  }
 
  public bool Next()
  {
- if (_needsMoreInput)
- return false;
-
  bool returnVal = false;
  if (_ratio <= 1f)
  {
- //Console.WriteLine("{0:F4}", _sampleCounter);
-
  if (_sampleCounter < 1f)
  {
  float result = 0f;
- //for (int i = 0; i < _firBuffer.Length; i++)
- //{
- // result += (float)(Sinc((i - (_firBuffer.Length / 2)) - (_sampleCounter - (int)_sampleCounter), 1.0) * _firBuffer[i]);
- //}
-
- // Linear decimation seems to perform better than the sinc-based decimation from above
- float dist = (_sampleCounter - (int)_sampleCounter);
- result = (_firBuffer[_firBuffer.Length - 2] * (1f - dist)) + (_firBuffer[_firBuffer.Length - 1] * dist);
+ for (int i = 0; i < _firBuffer.Length; i++)
+ {
+ result += (float)(Sinc((i - (_firBuffer.Length / 2)) - (_sampleCounter - (int)_sampleCounter), 1.0) * _firBuffer[i]);
+ }
 
  _lastSample = result;
 
  _sampleCounter += _invRatio;
  returnVal = true;
  }
- //else
- {
- _sampleCounter--;
- }
-
-
-
- //// If the counter is 0 < x < 1, we need more input
- //if (_sampleCounter == 0f || _sampleCounter >= 1f)
- //{
- // _sampleCounter -= (int)_sampleCounter;
- // returnVal = true;
- //}
- ////else
-
- //{
- // if (_sampleCounter == -1)
- // _sampleCounter = 0f;
- // else
- // _sampleCounter += _ratio;
- //}
+ _sampleCounter--;
  }
  else
  {
  throw new NotImplementedException("Raising the sampling rate is currently not supported");
  }
 
- _needsMoreInput = !returnVal;
- //Console.WriteLine(returnVal);
-
  return returnVal;
  }
 

SignalTest/Gardner.cs

@@ -9,38 +9,65 @@ namespace SignalTest
  class Gardner
  {
  private bool _flipFlop;
- private float _prevSample;
- private float _currentSample;
- private float _middleSample;
+ private float _prevSampleI;
+ private float _prevSampleQ;
+ private float _currentSampleI;
+ private float _currentSampleQ;
+ private float _middleSampleI;
+ private float _middleSampleQ;
 
 
- public Gardner(float baudRate)
+ public Gardner()
  {
  }
 
 
  public float Process(float sample)
+ {
+ return Process(sample, 0);
+ }
+
+ public float Process(float sampleI, float sampleQ)
  {
  // Shift symbol samples over
- _prevSample = _middleSample;
- _middleSample = _currentSample;
- _currentSample = sample;
+ _prevSampleI = _middleSampleI;
+ _prevSampleQ = _middleSampleQ;
+ _middleSampleI = _currentSampleI;
+ _middleSampleQ = _currentSampleQ;
+ _currentSampleI = sampleI;
+ _currentSampleQ = sampleQ;
 
  if ((_flipFlop ^= true))
  {
  // Every other sample, calculate error, but only if there is a transition
  // using Jonti's (modified gardner) method for M-QAM and M-PAM timing recovery
  // This method also works for QPSK and BPSK, and 2-PAM as well
- if (Math.Sign(_prevSample) != Math.Sign(_currentSample))
+ float error = 0f;
+
+ // Calculate for I
+ if (Math.Sign(_prevSampleI) != Math.Sign(_currentSampleI))
+ {
+ float localError = 0.5f * (_currentSampleI + _prevSampleI) - _middleSampleI;
+ if (_currentSampleI > _prevSampleI)
+ {
+ localError = -localError;
+ }
+
+ error += localError;
+ }
+
+ // Calculate for Q
+ if (Math.Sign(_prevSampleQ) != Math.Sign(_currentSampleQ))
  {
- float error = 0.5f * (_currentSample + _prevSample) - _middleSample;
- if (_currentSample > _prevSample)
+ float localError = 0.5f * (_currentSampleQ + _prevSampleQ) - _middleSampleQ;
+ if (_currentSampleQ > _prevSampleQ)
  {
- error = -error;
+ localError = -localError;
  }
 
- return error;
+ error += localError;
  }
+ return error;
  }
 
  return 0;

SignalTest/Integrator.cs

@@ -42,7 +42,7 @@ public Integrator(float pGain, float iGain, float preloadValue)
  {
  _iGain = iGain;
  _pGain = pGain;
- Preload(preloadValue);
+ SetValue(preloadValue);
  }
 
 
@@ -54,10 +54,6 @@ public float Process(float sample)
  return _lastValue = (pTerm + (_iState * _iGain));
  }
 
- public void Preload(float value)
- {
- _iState = (value / _iGain);
- }
 
  public float GetValue()
  {
@@ -73,5 +69,10 @@ public void SetValue(float value)
  {
  _iState = (value / _iGain);
  }
+
+ public void Reset()
+ {
+ _iState = 0f;
+ }
  }
 }