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[fix](trx-rs): normalize FT2 bitmetrics before LDPC

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This commit is contained in:
Stan Grams
2026-03-14 21:05:55 +01:00
parent 5b168fd6d5
commit 0b97329f63
1 changed files with 21 additions and 21 deletions
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src/decoders/trx-ft8/src/ft8_wrapper.c
+21 -21
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@@ -763,29 +763,30 @@ static bool ft2_extract_bitmetrics_raw(const float complex* signal, float bitmet
bitmetrics[i][1] = metric2[i];
bitmetrics[i][2] = metric4[i];
}
for (int metric = 0; metric < 3; ++metric)
{
float sum = 0.0f;
float sum2 = 0.0f;
for (int i = 0; i < 2 * FT2_FRAME_SYMBOLS; ++i)
{
float v = bitmetrics[i][metric];
sum += v;
sum2 += v * v;
}
float mean = sum / (2 * FT2_FRAME_SYMBOLS);
float variance = (sum2 / (2 * FT2_FRAME_SYMBOLS)) - (mean * mean);
float sigma = (variance > 0.0f) ? sqrtf(variance) : sqrtf(fmaxf(sum2 / (2 * FT2_FRAME_SYMBOLS), 0.0f));
if (sigma > 1.0e-6f)
{
for (int i = 0; i < 2 * FT2_FRAME_SYMBOLS; ++i)
{
bitmetrics[i][metric] /= sigma;
}
}
}
return true;
}
static void ft2_normalize_logl(float* log174)
{
float sum = 0.0f;
float sum2 = 0.0f;
for (int i = 0; i < FTX_LDPC_N; ++i)
{
sum += log174[i];
sum2 += log174[i] * log174[i];
}
float inv_n = 1.0f / FTX_LDPC_N;
float variance = (sum2 - (sum * sum * inv_n)) * inv_n;
if (variance <= 1.0e-6f)
return;
float norm_factor = sqrtf(24.0f / variance);
for (int i = 0; i < FTX_LDPC_N; ++i)
{
log174[i] *= norm_factor;
}
}
static void ft2_pack_bits(const uint8_t bit_array[], int num_bits, uint8_t packed[])
{
int num_bytes = (num_bits + 7) / 8;
@@ -977,7 +978,6 @@ static bool ft2_decode_hit(
{
float log174[FTX_LDPC_N];
memcpy(log174, llr_passes[pass], sizeof(log174));
ft2_normalize_logl(log174);
int ldpc_errors = 0;
bp_decode(log174, 50, plain174, &ldpc_errors);
if (ldpc_errors > 0)