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[fix](trx-ft8): align FT2 decoder thresholds and LLR scaling with reference

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The FT2 decoder was failing to decode valid signals due to thresholds
and LLR parameters that were significantly stricter than the reference
implementation (Decodium/raptor ft2_triggered_decode).

Thresholds aligned with reference at depth>=3:
- Peak detection: 1.08 -> 1.03 (reference uses 0.50 on normalized spectrum)
- Scan sync: 0.60 -> 0.50 (reference at depth>=3)
- Decode sync: 0.80 -> 0.65 (reference at depth>=3)
- Sync quality min: 13 -> 10 (reference at depth>=3)

LLR parameters aligned:
- Scale factor: 2.83 -> 3.2 (matches reference scalefac)
- Normalization: sqrt(24/var) -> 1/sigma (matches reference normalizebmet)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>
This commit is contained in:
Stan Grams
2026-03-17 21:38:48 +01:00
parent 7844cb65c8
commit 8aa1884d2d
1 changed files with 10 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/decoders/trx-ft8/src/ft8_wrapper.c
+10 -10
View File
@@ -368,7 +368,7 @@ static int ft2_find_frequency_peaks(
if (baseline[bin] <= 0.0f) if (baseline[bin] <= 0.0f)
continue; continue;
float value = smooth[bin] / baseline[bin]; float value = smooth[bin] / baseline[bin];
if (value < 1.08f) if (value < 1.03f)
continue; continue;
if (!(value >= (smooth[bin - 1] / fmaxf(baseline[bin - 1], 1e-9f)) && if (!(value >= (smooth[bin - 1] / fmaxf(baseline[bin - 1], 1e-9f)) &&
value >= (smooth[bin + 1] / fmaxf(baseline[bin + 1], 1e-9f)))) value >= (smooth[bin + 1] / fmaxf(baseline[bin + 1], 1e-9f))))
@@ -676,7 +676,7 @@ static int ft2_find_scan_hits(
} }
} }
} }
if (best_score < 0.60f) if (best_score < 0.50f)
continue; continue;
for (int idf = best_idf - 4; idf <= best_idf + 4; ++idf) for (int idf = best_idf - 4; idf <= best_idf + 4; ++idf)
@@ -694,7 +694,7 @@ static int ft2_find_scan_hits(
} }
} }
} }
if (best_score < 0.60f) if (best_score < 0.50f)
continue; continue;
out[count].freq_hz = peaks[peak].freq_hz; out[count].freq_hz = peaks[peak].freq_hz;
@@ -755,9 +755,9 @@ static void ft2_normalize_log174(float* log174)
if (variance <= 1.0e-12f) if (variance <= 1.0e-12f)
return; return;
float norm_factor = sqrtf(24.0f / variance); float sigma = sqrtf(variance);
for (int i = 0; i < FTX_LDPC_N; ++i) for (int i = 0; i < FTX_LDPC_N; ++i)
log174[i] *= norm_factor; log174[i] /= sigma;
} }
static bool ft2_extract_bitmetrics_raw(const float complex* signal, float bitmetrics[2 * FT2_FRAME_SYMBOLS][3]) static bool ft2_extract_bitmetrics_raw(const float complex* signal, float bitmetrics[2 * FT2_FRAME_SYMBOLS][3])
@@ -1286,7 +1286,7 @@ static bool ft2_decode_hit(
} }
} }
} }
if (best_score < 0.80f) if (best_score < 0.65f)
{ {
if (fail_stage) if (fail_stage)
*fail_stage = FT2_FAIL_REFINED_SYNC; *fail_stage = FT2_FAIL_REFINED_SYNC;
@@ -1338,7 +1338,7 @@ static bool ft2_decode_hit(
sync_qual += ((bitmetrics[132 + i][0] >= 0.0f) ? 1 : 0) == sync_bits_c[i]; sync_qual += ((bitmetrics[132 + i][0] >= 0.0f) ? 1 : 0) == sync_bits_c[i];
sync_qual += ((bitmetrics[198 + i][0] >= 0.0f) ? 1 : 0) == sync_bits_d[i]; sync_qual += ((bitmetrics[198 + i][0] >= 0.0f) ? 1 : 0) == sync_bits_d[i];
} }
if (sync_qual < 13) if (sync_qual < 10)
{ {
if (fail_stage) if (fail_stage)
*fail_stage = FT2_FAIL_SYNC_QUAL; *fail_stage = FT2_FAIL_SYNC_QUAL;
@@ -1362,9 +1362,9 @@ static bool ft2_decode_hit(
} }
for (int i = 0; i < FTX_LDPC_N; ++i) for (int i = 0; i < FTX_LDPC_N; ++i)
{ {
llr_passes[0][i] *= 2.83f; llr_passes[0][i] *= 3.2f;
llr_passes[1][i] *= 2.83f; llr_passes[1][i] *= 3.2f;
llr_passes[2][i] *= 2.83f; llr_passes[2][i] *= 3.2f;
float a = llr_passes[0][i]; float a = llr_passes[0][i];
float b = llr_passes[1][i]; float b = llr_passes[1][i];
float c = llr_passes[2][i]; float c = llr_passes[2][i];