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[fix](trx-rs): improve FT2 coherent decoding

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Add coherent FT2 sync and likelihood extraction.
Align FT2 frequency and DT reporting with the reference decoder.
Fix vendored monitor phase-mode type mismatches.

Co-authored-by: OpenAI Codex <codex@openai.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>
This commit is contained in:
Stan Grams
2026-03-14 20:25:59 +01:00
parent 2570fe739e
commit 27de75cf79
5 changed files with 192 additions and 9 deletions
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external/ft8_lib/ft8/decode.c
Vendored
+158 -2
View File
@@ -5,6 +5,7 @@
#include <stdbool.h>
#include <math.h>
#include <complex.h>
// #define LOG_LEVEL LOG_DEBUG
// #include "debug.h"
@@ -30,6 +31,7 @@ static const float db_power_sum[40] = {
/// @param[in] code_map Symbol encoding map
/// @param[out] log174 Output of decoded log likelihoods for each of the 174 message bits
static void ft4_extract_likelihood(const ftx_waterfall_t* wf, const ftx_candidate_t* cand, float* log174);
static void ft2_extract_likelihood(const ftx_waterfall_t* wf, const ftx_candidate_t* cand, float* log174);
static void ft8_extract_likelihood(const ftx_waterfall_t* wf, const ftx_candidate_t* cand, float* log174);
/// Packs a string of bits each represented as a zero/non-zero byte in bit_array[],
@@ -46,9 +48,17 @@ static void heapify_up(ftx_candidate_t heap[], int heap_size);
static void ftx_normalize_logl(float* log174);
static void ft4_extract_symbol(const WF_ELEM_T* wf, float* logl);
static void ft2_extract_logl_sequence(const float complex symbols[4][FT2_NN - FT2_NR], int start_sym, int n_syms, float* metrics);
static void ft8_extract_symbol(const WF_ELEM_T* wf, float* logl);
static void ft8_decode_multi_symbols(const WF_ELEM_T* wf, int num_bins, int n_syms, int bit_idx, float* log174);
static inline float complex wf_elem_to_complex(const WF_ELEM_T elem)
{
float mag = WF_ELEM_MAG(elem);
float amplitude = powf(10.0f, mag / 20.0f);
return amplitude * cexpf(I * elem.phase);
}
static const WF_ELEM_T* get_cand_mag(const ftx_waterfall_t* wf, const ftx_candidate_t* candidate)
{
int offset = candidate->time_offset;
@@ -124,6 +134,44 @@ static int ft8_sync_score(const ftx_waterfall_t* wf, const ftx_candidate_t* cand
return score;
}
static int ft2_sync_score(const ftx_waterfall_t* wf, const ftx_candidate_t* candidate)
{
const WF_ELEM_T* mag_cand = get_cand_mag(wf, candidate);
float score = 0.0f;
int groups = 0;
for (int m = 0; m < FT2_NUM_SYNC; ++m)
{
float complex sum = 0.0f;
bool complete = true;
for (int k = 0; k < FT2_LENGTH_SYNC; ++k)
{
int block = 1 + (FT2_SYNC_OFFSET * m) + k;
int block_abs = candidate->time_offset + block;
if ((block_abs < 0) || (block_abs >= wf->num_blocks))
{
complete = false;
break;
}
const WF_ELEM_T* sym = mag_cand + (block * wf->block_stride);
int tone = kFT4_Costas_pattern[m][k];
sum += wf_elem_to_complex(sym[tone]);
}
if (!complete)
continue;
score += cabsf(sum);
++groups;
}
if (groups == 0)
return 0;
return (int)lroundf((score / groups) * 8.0f);
}
static int ft4_sync_score(const ftx_waterfall_t* wf, const ftx_candidate_t* candidate)
{
int score = 0;
@@ -191,7 +239,7 @@ int ftx_find_candidates(const ftx_waterfall_t* wf, int num_candidates, ftx_candi
{
bool is_ft2 = (wf->protocol == FTX_PROTOCOL_FT2);
int (*sync_fun)(const ftx_waterfall_t*, const ftx_candidate_t*) =
ftx_protocol_uses_ft4_layout(wf->protocol) ? ft4_sync_score : ft8_sync_score;
is_ft2 ? ft2_sync_score : (ftx_protocol_uses_ft4_layout(wf->protocol) ? ft4_sync_score : ft8_sync_score);
int num_tones = ftx_protocol_uses_ft4_layout(wf->protocol) ? 4 : 8;
int time_offset_min = -10;
int time_offset_max = 20;
@@ -290,6 +338,74 @@ static void ft4_extract_likelihood(const ftx_waterfall_t* wf, const ftx_candidat
}
}
static void ft2_extract_likelihood(const ftx_waterfall_t* wf, const ftx_candidate_t* cand, float* log174)
{
const WF_ELEM_T* mag = get_cand_mag(wf, cand);
float complex symbols[4][FT2_NN - FT2_NR];
float metric1[2 * (FT2_NN - FT2_NR)] = { 0 };
float metric2[2 * (FT2_NN - FT2_NR)] = { 0 };
float metric4[2 * (FT2_NN - FT2_NR)] = { 0 };
for (int frame_sym = 0; frame_sym < (FT2_NN - FT2_NR); ++frame_sym)
{
int sym_idx = frame_sym + 1; // skip ramp-up symbol
int block = cand->time_offset + sym_idx;
if ((block < 0) || (block >= wf->num_blocks))
{
for (int tone = 0; tone < 4; ++tone)
{
symbols[tone][frame_sym] = 0.0f;
}
continue;
}
const WF_ELEM_T* sym = mag + (sym_idx * wf->block_stride);
for (int tone = 0; tone < 4; ++tone)
{
symbols[tone][frame_sym] = wf_elem_to_complex(sym[tone]);
}
}
for (int start = 0; start <= (FT2_NN - FT2_NR) - 1; start += 1)
{
ft2_extract_logl_sequence(symbols, start, 1, metric1 + (2 * start));
}
for (int start = 0; start <= (FT2_NN - FT2_NR) - 2; start += 2)
{
ft2_extract_logl_sequence(symbols, start, 2, metric2 + (2 * start));
}
for (int start = 0; start <= (FT2_NN - FT2_NR) - 4; start += 4)
{
ft2_extract_logl_sequence(symbols, start, 4, metric4 + (2 * start));
}
metric2[204] = metric1[204];
metric2[205] = metric1[205];
metric4[200] = metric2[200];
metric4[201] = metric2[201];
metric4[202] = metric2[202];
metric4[203] = metric2[203];
metric4[204] = metric1[204];
metric4[205] = metric1[205];
for (int data_sym = 0; data_sym < FT2_ND; ++data_sym)
{
int frame_sym = data_sym + ((data_sym < 29) ? 4 : ((data_sym < 58) ? 8 : 12));
int src_bit = 2 * frame_sym;
int dst_bit = 2 * data_sym;
float a0 = metric1[src_bit + 0];
float b0 = metric2[src_bit + 0];
float c0 = metric4[src_bit + 0];
float a1 = metric1[src_bit + 1];
float b1 = metric2[src_bit + 1];
float c1 = metric4[src_bit + 1];
log174[dst_bit + 0] = (fabsf(a0) >= fabsf(b0) && fabsf(a0) >= fabsf(c0)) ? a0 : ((fabsf(b0) >= fabsf(c0)) ? b0 : c0);
log174[dst_bit + 1] = (fabsf(a1) >= fabsf(b1) && fabsf(a1) >= fabsf(c1)) ? a1 : ((fabsf(b1) >= fabsf(c1)) ? b1 : c1);
}
}
static void ft8_extract_likelihood(const ftx_waterfall_t* wf, const ftx_candidate_t* cand, float* log174)
{
const WF_ELEM_T* mag = get_cand_mag(wf, cand); // Pointer to 8 magnitude bins of the first symbol
@@ -341,7 +457,11 @@ static void ftx_normalize_logl(float* log174)
bool ftx_decode_candidate(const ftx_waterfall_t* wf, const ftx_candidate_t* cand, int max_iterations, ftx_message_t* message, ftx_decode_status_t* status)
{
float log174[FTX_LDPC_N]; // message bits encoded as likelihood
if (ftx_protocol_uses_ft4_layout(wf->protocol))
if (wf->protocol == FTX_PROTOCOL_FT2)
{
ft2_extract_likelihood(wf, cand, log174);
}
else if (ftx_protocol_uses_ft4_layout(wf->protocol))
{
ft4_extract_likelihood(wf, cand, log174);
}
@@ -479,6 +599,42 @@ static void ft4_extract_symbol(const WF_ELEM_T* wf, float* logl)
logl[1] = max2(s2[1], s2[3]) - max2(s2[0], s2[2]);
}
static void ft2_extract_logl_sequence(const float complex symbols[4][FT2_NN - FT2_NR], int start_sym, int n_syms, float* metrics)
{
const int n_bits = 2 * n_syms;
const int n_sequences = 1 << n_bits;
for (int bit = 0; bit < n_bits; ++bit)
{
float max_zero = -INFINITY;
float max_one = -INFINITY;
for (int seq = 0; seq < n_sequences; ++seq)
{
float complex sum = 0.0f;
for (int sym = 0; sym < n_syms; ++sym)
{
int shift = 2 * (n_syms - sym - 1);
int dibit = (seq >> shift) & 0x3;
int tone = kFT4_Gray_map[dibit];
sum += symbols[tone][start_sym + sym];
}
float strength = cabsf(sum);
int mask_bit = n_bits - bit - 1;
if (((seq >> mask_bit) & 0x1) != 0)
{
if (strength > max_one)
max_one = strength;
}
else
{
if (strength > max_zero)
max_zero = strength;
}
}
metrics[bit] = max_one - max_zero;
}
}
// Compute unnormalized log likelihood log(p(1) / p(0)) of 3 message bits (1 FSK symbol)
static void ft8_extract_symbol(const WF_ELEM_T* wf, float* logl)
{