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qpsk-demod: Exclude trailing noise from level and confidence #210

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qpsk-demod: Exclude trailing noise from level and confidence #210

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57 changes: 34 additions & 23 deletions lib/iridium_qpsk_demod_impl.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -183,50 +183,61 @@ float iridium_qpsk_demod_impl::qpskFirstOrderPLL(const gr_complex* x,
size_t iridium_qpsk_demod_impl::demod_qpsk(
const gr_complex* burst, size_t n_symbols, int* out, float* level, int* confidence)
{
int index;
float sum = 0;
float max = 0;
int low_count = 0;
int n_ok = 0;
int n = 0;
float offsets[n_symbols];

volk_32fc_magnitude_32f(d_magnitude_f, burst, n_symbols);

for (index = 0; index < n_symbols; index++) {
sum += d_magnitude_f[index];
if (max < d_magnitude_f[index]) {
max = d_magnitude_f[index];
for (int i = 0; i < n_symbols; i++) {
if (max < d_magnitude_f[i]) {
max = d_magnitude_f[i];
}

// demodulating circuit
if (burst[index].real() >= 0 && burst[index].imag() >= 0) {
out[index] = d_symbol_mapping[0];
} else if (burst[index].real() >= 0 && burst[index].imag() < 0) {
out[index] = d_symbol_mapping[3];
} else if (burst[index].real() < 0 && burst[index].imag() < 0) {
out[index] = d_symbol_mapping[2];
if (burst[i].real() >= 0 && burst[i].imag() >= 0) {
out[i] = d_symbol_mapping[0];
} else if (burst[i].real() >= 0 && burst[i].imag() < 0) {
out[i] = d_symbol_mapping[3];
} else if (burst[i].real() < 0 && burst[i].imag() < 0) {
out[i] = d_symbol_mapping[2];
} else {
out[index] = d_symbol_mapping[1];
out[i] = d_symbol_mapping[1];
}

// Keep some quality estimate
// If the phase is off too much, we lower the reported confidence
int phase = (gr::fast_atan2f(burst[index]) + M_PI) * 180 / M_PI;
int phase = (gr::fast_atan2f(burst[i]) + M_PI) * 180 / M_PI;
int offset = 45 - (phase % 90);
if (abs(offset) <= 22) {
n_ok++;
}
offsets[i] = offset;

if (d_magnitude_f[index] < max / 8.) {
n++;
if (d_magnitude_f[i] < max / 8.) {
low_count++;
if (low_count > 2) {
if (low_count == 3) {
// We don't want to consider noise at the end of the frame
n -= 3;
break;
}
} else {
low_count = 0;
}
}

int n_ok = 0;
float sum = 0;

for (int i=0; i < n; i++) {
if (abs(offsets[i]) <= 22) {
n_ok++;
}
sum += d_magnitude_f[i];
}

*level = sum / index;
*confidence = (int)(100. * n_ok / index);
return index;
*level = sum / n;
*confidence = (int)(100. * n_ok / n);
return n;
}

void iridium_qpsk_demod_impl::decode_deqpsk(int* demodulated_burst, size_t n_symbols)
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