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FT4 decoder: use FFT (3)

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f4exb
2026-03-04 22:27:06 +01:00
parent 831f0e16d3
commit 31a1fb8f9e
1 changed files with 23 additions and 22 deletions
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ft8/ft4.cpp
+23 -22
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@@ -175,16 +175,15 @@ private:
tonePower[tone] = binPowerInterpolated(bins, symbolIndex, toneBin + tone);
}
const float symbolAvg = 0.25f * (tonePower[0] + tonePower[1] + tonePower[2] + tonePower[3]) + 1.0e-6f;
const float llrScale = 6.0f / symbolAvg;
const float epsilon = 1.0e-6f;
const float b0Zero = std::max(tonePower[0], tonePower[1]) + epsilon;
const float b0One = std::max(tonePower[2], tonePower[3]) + epsilon;
const float b1Zero = std::max(tonePower[0], tonePower[3]) + epsilon;
const float b1One = std::max(tonePower[1], tonePower[2]) + epsilon;
const float b0Zero = std::max(tonePower[0], tonePower[1]);
const float b0One = std::max(tonePower[2], tonePower[3]);
const float b1Zero = std::max(tonePower[0], tonePower[3]);
const float b1One = std::max(tonePower[1], tonePower[2]);
const float llr0 = std::log(b0Zero / b0One);
const float llr1 = std::log(b1Zero / b1One);
const float llr0 = (b0Zero - b0One) * llrScale;
const float llr1 = (b1Zero - b1One) * llrScale;
bitMetrics[bitIndex++] = llr0;
bitMetrics[bitIndex++] = llr1;
llrAbsSum += std::fabs(llr0) + std::fabs(llr1);
@@ -200,10 +199,19 @@ private:
return;
}
const float globalScale = 4.0f / meanAbs;
const float targetMean = 3.0f;
const float globalScale = targetMean / meanAbs;
for (int i = 0; i < bitIndex; i++) {
bitMetrics[i] *= globalScale;
float scaled = bitMetrics[i] * globalScale;
if (scaled > 8.0f) {
scaled = 8.0f;
} else if (scaled < -8.0f) {
scaled = -8.0f;
}
bitMetrics[i] = scaled;
}
}
@@ -325,11 +333,11 @@ private:
float sync = 0.0f;
float noise = 0.0f;
collectSyncMetrics(frame.bins, toneBin, sync, noise);
if (sync < 1.8f) {
continue;
}
const float score = sync - 1.0f * (noise / 3.0f);
candidates.push_back(FT4Candidate{frameIndex, frame.start, toneBin, sync, noise, score});
}
@@ -358,15 +366,8 @@ private:
int ldpcOk = 0;
LDPC::ldpc_decode(llr.data(), m_params.ldpc_iters, plain, &ldpcOk);
const float candidateHz = candidate.toneBin * binSpacing;
if (ldpcOk < ldpcThreshold)
{
if (candidateHz >= 1400 && candidateHz <= 2500)
{
qDebug("FT4Worker::decode: Candidate at %.1f Hz rejected: ldpcOk=%d < threshold=%d",
candidateHz, ldpcOk, ldpcThreshold);
}
continue;
}
@@ -407,13 +408,13 @@ private:
const float snrLinear = (candidate.sync + 1.0e-9f) / ((candidate.noise / 3.0f) + 1.0e-9f);
const float snr = 10.0f * std::log10(snrLinear) - 12.0f;
const float tone0 = refinedToneBin * binSpacing;
if (snr < -26.0f) {
continue;
}
const float off = static_cast<float>(m_start) / m_rate + static_cast<float>(candidate.start) / m_rate;
const float tone0 = refinedToneBin * binSpacing;
m_cb->hcb(a91, tone0, off, "FT4-EXP", snr, 0, ldpcOk);
}
}