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https://github.com/f4exb/sdrangel.git
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437 lines
12 KiB
C++
437 lines
12 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2026 //
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// //
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// Experimental FT4 decoder scaffold derived from FT8 decoder architecture. //
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///////////////////////////////////////////////////////////////////////////////////
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#include <array>
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#include <cmath>
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#include <algorithm>
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#include <QThread>
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#include "ft4.h"
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#include "fft.h"
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#include "libldpc.h"
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#include "osd.h"
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namespace FT8 {
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namespace {
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constexpr int kFT4SymbolSamples = 576;
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constexpr int kFT4TotalSymbols = 103;
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constexpr int kFT4FrameSamples = kFT4TotalSymbols * kFT4SymbolSamples;
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const std::array<std::array<int, 4>, 4> kFT4SyncTones = {{
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{{0, 1, 3, 2}},
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{{1, 0, 2, 3}},
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{{2, 3, 1, 0}},
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{{3, 2, 0, 1}}
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}};
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const std::array<int, 77> kFT4Rvec = {{
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0,1,0,0,1,0,1,0,0,1,0,1,1,1,1,0,1,0,0,0,1,0,0,1,1,0,1,1,0,
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1,0,0,1,0,1,1,0,0,0,0,1,0,0,0,1,0,1,0,0,1,1,1,1,0,0,1,0,1,
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0,1,0,1,0,1,1,0,1,1,1,1,1,0,0,0,1,0,1
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}};
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struct FT4Candidate
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{
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int frameIndex;
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int start;
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int toneBin;
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float sync;
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float noise;
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float score;
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};
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class FT4Worker : public QObject
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{
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public:
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FT4Worker(
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const std::vector<float>& samples,
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float minHz,
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float maxHz,
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int start,
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int rate,
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CallbackInterface *cb,
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const FT4Params& params
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) :
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m_samples(samples),
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m_minHz(minHz),
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m_maxHz(maxHz),
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m_start(start),
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m_rate(rate),
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m_cb(cb),
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m_params(params)
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{}
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void start_work()
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{
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decode();
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}
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private:
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static float binPower(const FFTEngine::ffts_t& bins, int symbolIndex, int toneBin)
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{
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return std::abs(bins[symbolIndex][toneBin]);
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}
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void collectSyncMetrics(const FFTEngine::ffts_t& bins, int toneBin, float& sync, float& noise) const
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{
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sync = 0.0f;
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noise = 0.0f;
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for (int block = 0; block < 4; block++)
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{
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const int symbolOffset = block * 33;
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for (int index = 0; index < 4; index++)
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{
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const int symbolIndex = symbolOffset + index;
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const int expectedTone = kFT4SyncTones[block][index];
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for (int tone = 0; tone < 4; tone++)
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{
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const float power = binPower(bins, symbolIndex, toneBin + tone);
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if (tone == expectedTone) {
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sync += power;
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} else {
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noise += power;
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}
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}
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}
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}
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}
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int refineToneBin(const FFTEngine::ffts_t& bins, int toneBin) const
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{
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float bestSync = -1.0f;
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int bestToneBin = toneBin;
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for (int delta = -1; delta <= 1; delta++)
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{
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int candidateToneBin = toneBin + delta;
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if (candidateToneBin < 0) {
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continue;
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}
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float sync = 0.0f;
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float noise = 0.0f;
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collectSyncMetrics(bins, candidateToneBin, sync, noise);
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if (sync > bestSync)
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{
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bestSync = sync;
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bestToneBin = candidateToneBin;
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}
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}
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return bestToneBin;
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}
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void buildBitMetrics(const FFTEngine::ffts_t& bins, int toneBin, std::array<float, 174>& bitMetrics) const
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{
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int bitIndex = 0;
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for (int symbolIndex = 0; symbolIndex < kFT4TotalSymbols; symbolIndex++)
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{
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const bool inSync = (symbolIndex < 4)
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|| (symbolIndex >= 33 && symbolIndex < 37)
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|| (symbolIndex >= 66 && symbolIndex < 70)
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|| (symbolIndex >= 99);
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if (inSync) {
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continue;
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}
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std::array<float, 4> tonePower;
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for (int tone = 0; tone < 4; tone++) {
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tonePower[tone] = binPower(bins, symbolIndex, toneBin + tone);
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}
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const float b0Zero = std::max(tonePower[0], tonePower[1]);
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const float b0One = std::max(tonePower[2], tonePower[3]);
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const float b1Zero = std::max(tonePower[0], tonePower[3]);
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const float b1One = std::max(tonePower[1], tonePower[2]);
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bitMetrics[bitIndex++] = b0Zero - b0One;
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bitMetrics[bitIndex++] = b1Zero - b1One;
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}
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}
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FFTEngine::ffts_t makeFrameBins(int start)
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{
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return m_fftEngine.ffts(m_samples, start, kFT4SymbolSamples);
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}
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void decode()
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{
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if (m_samples.size() < kFT4FrameSamples) {
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return;
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}
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const int maxStart = static_cast<int>(m_samples.size()) - kFT4FrameSamples;
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const float binSpacing = static_cast<float>(m_rate) / static_cast<float>(kFT4SymbolSamples);
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if (m_maxHz <= m_minHz) {
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return;
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}
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std::vector<int> startCandidates;
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auto addStartCandidate = [&](int start)
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{
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start = std::max(0, std::min(start, maxStart));
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if (std::find(startCandidates.begin(), startCandidates.end(), start) == startCandidates.end()) {
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startCandidates.push_back(start);
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}
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};
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for (int start = 0; start <= std::min(maxStart, 14000); start += kFT4SymbolSamples) {
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addStartCandidate(start);
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}
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const int nominalStart = maxStart / 2;
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addStartCandidate(std::max(0, nominalStart - 2 * kFT4SymbolSamples));
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addStartCandidate(std::max(0, nominalStart - kFT4SymbolSamples));
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addStartCandidate(nominalStart);
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addStartCandidate(std::min(maxStart, nominalStart + kFT4SymbolSamples));
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addStartCandidate(std::min(maxStart, nominalStart + 2 * kFT4SymbolSamples));
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addStartCandidate(maxStart);
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struct FT4Frame
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{
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int start;
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FFTEngine::ffts_t bins;
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};
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std::vector<FT4Frame> frames;
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frames.reserve(startCandidates.size());
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for (int start : startCandidates)
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{
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FFTEngine::ffts_t bins = makeFrameBins(start);
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if (bins.size() < kFT4TotalSymbols) {
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continue;
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}
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if (bins[0].size() < 8) {
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continue;
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}
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frames.push_back(FT4Frame{start, std::move(bins)});
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}
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if (frames.empty()) {
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return;
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}
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const int minToneBin = std::max(0, static_cast<int>(std::ceil(m_minHz / binSpacing)));
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const int maxToneBinByHz = static_cast<int>(std::floor(m_maxHz / binSpacing)) - 3;
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if (maxToneBinByHz < minToneBin) {
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return;
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}
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std::vector<FT4Candidate> candidates;
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for (int frameIndex = 0; frameIndex < static_cast<int>(frames.size()); frameIndex++)
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{
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const FT4Frame& frame = frames[frameIndex];
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const int maxToneBin = std::min(maxToneBinByHz, static_cast<int>(frame.bins[0].size()) - 4);
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for (int toneBin = minToneBin; toneBin <= maxToneBin; toneBin++)
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{
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float sync = 0.0f;
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float noise = 0.0f;
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collectSyncMetrics(frame.bins, toneBin, sync, noise);
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const float score = sync - 1.25f * (noise / 3.0f);
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candidates.push_back(FT4Candidate{frameIndex, frame.start, toneBin, sync, noise, score});
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}
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}
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if (candidates.empty()) {
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return;
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}
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std::sort(candidates.begin(), candidates.end(), [](const FT4Candidate& lhs, const FT4Candidate& rhs) {
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return lhs.score > rhs.score;
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});
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const int maxDecodeCandidates = std::min(m_params.max_candidates, static_cast<int>(candidates.size()));
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const int ldpcThreshold = std::max(48, m_params.osd_ldpc_thresh - 18);
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for (int candidateIndex = 0; candidateIndex < maxDecodeCandidates; candidateIndex++)
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{
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const FT4Candidate& candidate = candidates[candidateIndex];
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const FT4Frame& frame = frames[candidate.frameIndex];
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const int refinedToneBin = refineToneBin(frame.bins, candidate.toneBin);
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std::array<float, 174> llr;
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buildBitMetrics(frame.bins, refinedToneBin, llr);
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int plain[174];
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int ldpcOk = 0;
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LDPC::ldpc_decode(llr.data(), m_params.ldpc_iters, plain, &ldpcOk);
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if (ldpcOk < ldpcThreshold) {
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continue;
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}
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int a174[174];
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for (int i = 0; i < 174; i++) {
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a174[i] = plain[i];
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}
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bool crcOk = OSD::check_crc(a174);
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if (!crcOk && m_params.use_osd)
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{
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int oplain[91];
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int depth = -1;
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std::array<float, 174> llrCopy = llr;
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if (OSD::osd_decode(llrCopy.data(), m_params.osd_depth, oplain, &depth))
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{
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OSD::ldpc_encode(oplain, a174);
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crcOk = OSD::check_crc(a174);
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}
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}
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if (!crcOk) {
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continue;
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}
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int a91[91];
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for (int i = 0; i < 91; i++) {
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a91[i] = a174[i];
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}
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for (int i = 0; i < 77; i++) {
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a91[i] ^= kFT4Rvec[i];
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}
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const float snrLinear = (candidate.sync + 1.0e-9f) / ((candidate.noise / 3.0f) + 1.0e-9f);
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const float snr = 10.0f * std::log10(snrLinear) - 12.0f;
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const float off = static_cast<float>(m_start) / m_rate + static_cast<float>(candidate.start) / m_rate;
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const float tone0 = refinedToneBin * binSpacing;
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m_cb->hcb(a91, tone0, off, "FT4-EXP", snr, 0, ldpcOk);
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}
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}
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std::vector<float> m_samples;
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float m_minHz;
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float m_maxHz;
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int m_start;
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int m_rate;
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CallbackInterface *m_cb;
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FT4Params m_params;
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FFTEngine m_fftEngine;
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};
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} // namespace
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FT4Decoder::~FT4Decoder()
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{
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forceQuit();
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}
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void FT4Decoder::entry(
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float xsamples[],
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int nsamples,
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int start,
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int rate,
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float min_hz,
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float max_hz,
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int hints1[],
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int hints2[],
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double time_left,
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double total_time_left,
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CallbackInterface *cb,
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int nprevdecs,
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struct cdecode *xprevdecs
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)
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{
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(void) hints1;
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(void) hints2;
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(void) time_left;
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(void) total_time_left;
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(void) nprevdecs;
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(void) xprevdecs;
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std::vector<float> samples(nsamples);
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for (int i = 0; i < nsamples; i++) {
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samples[i] = xsamples[i];
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}
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if (min_hz < 0) {
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min_hz = 0;
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}
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if (max_hz > rate / 2) {
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max_hz = rate / 2;
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}
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const float per = (max_hz - min_hz) / params.nthreads;
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for (int i = 0; i < params.nthreads; i++)
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{
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float hz0 = min_hz + i * per;
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float hz1 = min_hz + (i + 1) * per;
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hz0 = std::max(hz0, 0.0f);
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hz1 = std::min(hz1, (rate / 2.0f) - 50.0f);
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FT4Worker *ft4 = new FT4Worker(samples, hz0, hz1, start, rate, cb, params);
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QThread *th = new QThread();
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th->setObjectName(QString("ft4:%1:%2").arg(cb->get_name()).arg(i));
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threads.push_back(th);
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ft4->moveToThread(th);
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QObject::connect(th, &QThread::started, ft4, [ft4, th]() {
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ft4->start_work();
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th->quit();
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});
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QObject::connect(th, &QThread::finished, ft4, &QObject::deleteLater);
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QObject::connect(th, &QThread::finished, th, &QObject::deleteLater);
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th->start();
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}
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}
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void FT4Decoder::wait(double time_left)
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{
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unsigned long thread_timeout = time_left * 1000;
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while (!threads.empty())
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{
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bool success = threads.front()->wait(thread_timeout);
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if (!success)
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{
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qDebug("FT8::FT4Decoder::wait: thread timed out");
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thread_timeout = 50;
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}
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threads.erase(threads.begin());
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}
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}
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void FT4Decoder::forceQuit()
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{
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while (!threads.empty())
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{
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threads.front()->quit();
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threads.front()->wait();
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threads.erase(threads.begin());
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}
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}
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} // namespace FT8
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