static void ModulateQPSK()
{
// Manual adjust values
int sampleRate = 8000;
int symbolCount = 1000;
float symbolRate = 250; // Symbols per second
int carrierHz = 1000;
string outputPath = Path.Combine(LocalPath, "qpsk_output.8k.3ch.pcm32f");
// Fixed values
float symbolPeriod = 1f / symbolRate;
int symbolLengthSamples = sampleRate / (int)symbolRate;
Vco vco = new Vco(sampleRate, carrierHz);
PseudoRandom random = new PseudoRandom(23);
using (Stream output = File.Create(outputPath))
{
for (int i = 0; i < symbolCount; i++)
{
// Generate 2 data bits
int bits = (int)random.Next(0, 4);
// Generate symbol samples
for (int p = 0; p < symbolLengthSamples; p++)
{
// Generate symbol sample
float sampleI = (float)vco.Cos() * ((bits >> 1) * 2 - 1);
float sampleQ = (float)vco.Sin() * ((bits & 1) * 2 - 1);
vco.Next();
// Reduce amplitude so the sum equals 1.0
sampleI *= 0.707f;
sampleQ *= 0.707f;
// Combine I and Q samples
float sampleOutput = sampleI + sampleQ;
// Output sample to file
output.Write(BitConverter.GetBytes(sampleOutput), 0, 4);
output.Write(BitConverter.GetBytes(((bits >> 1) * 2f - 1)), 0, 4);
output.Write(BitConverter.GetBytes(((bits & 1) * 2f - 1)), 0, 4);
}
}
}
}
static void ModulateOffsetQPSK()
{
// Manual adjust values
int sampleRate = 8000;
int symbolCount = 1000;
float symbolRate = 250; // Symbols per second
int carrierHz = 1000;
string outputPath = Path.Combine(LocalPath, "oqpsk_output.8k.3ch.pcm32f");
// Fixed values
float symbolPeriod = 1f / symbolRate;
int symbolLengthSamples = sampleRate / (int)symbolRate;
Vco vco = new Vco(sampleRate, carrierHz);
PseudoRandom random = new PseudoRandom(23);
BiQuadraticFilter iFilter = new BiQuadraticFilter(BiQuadraticFilter.Type.LOWPASS, symbolRate, sampleRate, 0.707);
BiQuadraticFilter qFilter = new BiQuadraticFilter(BiQuadraticFilter.Type.LOWPASS, symbolRate, sampleRate, 0.707);
using (Stream output = File.Create(outputPath))
{
int bits = 0;
int nextBits = 0;
for (int i = 0; i < symbolCount * 2; i++)
{
bool even = i % 2 == 0;
// On each half-symbol period, shift in one data bit for transmission
// while keeping the previous other arm's bit transmitting
if (even)
{
nextBits = (int)random.Next(0, 4);
bits = (bits & 0x01) | (nextBits & 0x02);
}
else
{
bits = (bits & 0x02) | (nextBits & 0x01);
}
// Generate symbol samples
for (int p = 0; p < symbolLengthSamples / 2; p++)
{
// Generate symbol sample
// Also filter symbols with a low pass filter for basic pulse shaping
float sampleI = (float)vco.Cos() * (float)iFilter.filter((bits >> 1) * 2 - 1);
float sampleQ = (float)vco.Sin() * (float)qFilter.filter((bits & 1) * 2 - 1);
vco.Next();
// Reduce amplitude so the sum equals 1.0
sampleI *= 0.707f;
sampleQ *= 0.707f;
// Combine I and Q samples
float sampleOutput = sampleI + sampleQ;
// Output sample to file
output.Write(BitConverter.GetBytes(sampleOutput), 0, sizeof(float));
output.Write(BitConverter.GetBytes(((bits >> 1) * 2f - 1)), 0, sizeof(float));
output.Write(BitConverter.GetBytes(((bits & 1) * 2f - 1)), 0, sizeof(float));
}
}
}
}
