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Transceiver: Compansate for frequency error.

This commit is contained in:
Alexander Chemeris 2015-06-29 22:42:32 -04:00
parent 8f01fd659e
commit 7a82180778
1 changed files with 43 additions and 0 deletions
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43
Transceiver52M/Transceiver.cpp
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@ -1041,11 +1041,41 @@ inline float vectorRMS(const Vector<float> &vec)
return sqrt(rms/vec.size());
}
bool vectorLinearFit(const Vector<float> &y, float &slope, float &interceptor)
{
int len_y = y.size();
float numerator = 0.0;
float denominator = 0.0;
float avg_x = len_y/2.0;
float avg_y = 0.0;
if (len_y==0)
return false;
for (int i=0; i<len_y; i++)
avg_y += y[i];
avg_y /= len_y;
for (int i=0; i<len_y; i++) {
numerator += (i - avg_x) * (y[i] - avg_y);
denominator += (i - avg_x) * (i - avg_x);
}
if (denominator == 0.0)
return false;
slope = numerator/denominator;
interceptor = avg_y - avg_x*slope;
return true;
}
void Transceiver::estimateBurstQuality(const BitVector &wBits, signalVector *received,
const GSM::Time &wTime, size_t chan,
Transceiver::BurstQuality &qual)
{
signalVector *burst;
float slope, interceptor;
// this code supports only 4 SPS modulation
// we also assume that received vector is 1 SPS
@ -1065,11 +1095,24 @@ void Transceiver::estimateBurstQuality(const BitVector &wBits, signalVector *rec
// calculate phase error for each bit
for (size_t i=0; i<qual.phase_err.size(); i++) {
float rx_phase = (*received)[i].arg();
// modulated data is 4SPS and is 1/4 bit shifted
float mod_phase = (*burst)[1+(2+i)*4].arg();
qual.phase_err[i] = wrapAnglePi(rx_phase - mod_phase);
qual.phase_err_deg[i] = rad2deg(qual.phase_err[i]);
}
// compensate for frequency error
if (vectorLinearFit(qual.phase_err, slope, interceptor)) {
for (size_t i=0; i<qual.phase_err.size(); i++) {
qual.phase_err[i] -= i*slope + interceptor;
}
}
// convert to degrees
for (size_t i=0; i<qual.phase_err.size(); i++) {
qual.phase_err_deg[i] = rad2deg(qual.phase_err[i]);
}
// calculate Peak and RMS values
qual.phase_err_max_idx = vectorMaxAbs(qual.phase_err);
qual.phase_err_max = qual.phase_err[qual.phase_err_max_idx];