static void DemodulateOffsetQPSK()
{
// Manual adjust values
int sampleRate = 8000;
float symbolRate = 250; // Symbols per second
int carrierHz = 1005;
string inputPath = Path.Combine(LocalPath, "oqpsk_output.8k.3ch.pcm32f");
string outputPath = Path.Combine(LocalPath, "oqpsk_output_demodulate.8k.2ch.pcm32f");
int inputChannelCount = 3;
// Fixed values
float symbolPeriod = 1f / symbolRate;
int symbolLengthSamples = sampleRate / (int)symbolRate;
Costas costas = new Costas(sampleRate, carrierHz, Costas.LoopType.QPSK);
// Downsamplers for bit slicing
Downsampler dsI = new Downsampler(sampleRate);
Downsampler dsQ = new Downsampler(sampleRate);
dsI.SetRatio((symbolRate * 2) / sampleRate);
dsQ.SetRatio((symbolRate * 2) / sampleRate);
// Integrator to track symbol rate
Integrator intRatio = new Integrator(0.3f, (1f / (symbolRate * 2)) * 0.5f, (symbolRate * 2) / sampleRate);
// Modified gardner timing error detector
Gardner gardner = new Gardner();
// Tweakable parameters
costas.ArmFilterHz = symbolRate * 1.5f;
using (Stream input = File.OpenRead(inputPath))
{
using (Stream output = File.Create(outputPath))
{
// Data input buffer
byte[] buffer = new byte[sizeof(float) * inputChannelCount];
bool flipFlop = false;
float sampleBufferI = 0;
int bytesRead = 0;
while ((bytesRead = input.Read(buffer, 0, buffer.Length)) == buffer.Length)
{
// Get input sample as a float
float sampleInput = BitConverter.ToSingle(buffer, 0);
// Process sample with costas loop
costas.Process(sampleInput);
// Get samples for I and Q channels
float sampleI = costas.Inphase();
float sampleQ = costas.Quadrature();
// Downsample to 2x symbol rate for timing recovery
dsQ.Next();
if (dsI.Next())
{
// Compute timing error
float error = gardner.Process(sampleBufferI);
float ratio = intRatio.Process(error * 0.1f);
// Adjust ratio
dsI.SetRatio(ratio);
dsQ.SetRatio(ratio);
// Output every other sample
if (flipFlop ^= true)
{
// Output timing bits to file
output.Write(BitConverter.GetBytes(sampleBufferI), 0, sizeof(float));
output.Write(BitConverter.GetBytes(dsQ.GetSample()), 0, sizeof(float));
}
// Buffer the I channel by half a symbol period because we delayed Q during modulation
// This puts I and Q back in sync resulting in our original data stream
// NOTE: This assumption only holds if the demodulated phase is correct and the
// constellation is not rotated the wrong way around
sampleBufferI = dsI.GetSample();
}
// Supply data to downsamplers
dsI.SupplyInput(sampleI);
dsQ.SupplyInput(sampleQ);
//// Output full-rate samples to file instead
//output.Write(BitConverter.GetBytes(sampleI), 0, sizeof(float));
//output.Write(BitConverter.GetBytes(sampleQ), 0, sizeof(float));
}
}
}
}
static void DemodulateQPSK()
{
// Manual adjust values
int sampleRate = 8000;
float symbolRate = 250; // Symbols per second
int carrierHz = 1005;
string inputPath = Path.Combine(LocalPath, "qpsk_output.8k.3ch.pcm32f");
string outputPath = Path.Combine(LocalPath, "qpsk_output_demodulate.8k.2ch.pcm32f");
// Fixed values
float symbolPeriod = 1f / symbolRate;
int symbolLengthSamples = sampleRate / (int)symbolRate;
Costas costas = new Costas(sampleRate, carrierHz, Costas.LoopType.QPSK);
Gardner gardner = new Gardner();
Downsampler dsI = new Downsampler(sampleRate);
Downsampler dsQ = new Downsampler(sampleRate);
dsI.SetRatio((symbolRate * 2) / sampleRate);
dsQ.SetRatio((symbolRate * 2) / sampleRate);
Integrator intRatio = new Integrator(0.3f, (1f / (symbolRate * 2)) * 0.5f, (symbolRate * 2) / sampleRate);
// Tweakable parameters
costas.ArmFilterHz = symbolRate * 1.5f;
using (Stream input = File.OpenRead(inputPath))
{
// Data input buffer
byte[] buffer = new byte[sizeof(float) * 3];
bool flipFlop = false;
using (Stream output = File.Create(outputPath))
{
int bytesRead = 0;
while ((bytesRead = input.Read(buffer, 0, buffer.Length)) == buffer.Length)
{
// Get input sample as a float
float sampleInput = BitConverter.ToSingle(buffer, 0);
// Process sample with costas loop
costas.Process(sampleInput);
float sampleI = costas.Inphase();
float sampleQ = costas.Quadrature();
// Downsample to 2x symbol rate for timing recovery
dsQ.Next();
if (dsI.Next())
{
// Compute timing error
float error = gardner.Process(dsI.GetSample(), dsQ.GetSample());
float ratio = intRatio.Process(error * 0.01f);// ((symbolRate * 16) / sampleRate) + (0.7f * error);
// Adjust ratio
dsI.SetRatio(ratio);
dsQ.SetRatio(ratio);
// Output every other sample
if (flipFlop ^= true)
{
// Output timing bits to file
output.Write(BitConverter.GetBytes(dsI.GetSample()), 0, sizeof(float));
output.Write(BitConverter.GetBytes(dsQ.GetSample()), 0, sizeof(float));
}
}
dsI.SupplyInput(sampleI);
dsQ.SupplyInput(sampleQ);
//// Output sample to file
//output.Write(BitConverter.GetBytes(sampleI), 0, sizeof(float));
//output.Write(BitConverter.GetBytes(sampleQ), 0, sizeof(float));
}
}
}
}