kopia lustrzana https://github.com/kgoba/ft8_lib
Tested sync candidate search
Karlis Goba
rodzic
8397509c85
commit
b1a1d1edc6
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@ -1,2 +1,3 @@
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*.o
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gen_ft8
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decode_ft8
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173
decode_ft8.cpp
173
decode_ft8.cpp
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@ -28,28 +28,71 @@ struct Candidate {
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int16_t score;
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uint16_t time_offset;
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uint16_t freq_offset;
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uint8_t time_alt;
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uint8_t freq_alt;
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uint8_t time_sub;
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uint8_t freq_sub;
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};
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void find_candidates(int num_blocks, int num_bins, const uint8_t * power,
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int num_candidates, Candidate heap[num_candidates]) {
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void heapify_down(Candidate * heap, int heap_size) {
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// heapify from the root down
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int current = 0;
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while (true) {
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int largest = current;
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int left = 2 * current + 1;
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int right = left + 1;
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if (left < heap_size && heap[left].score < heap[largest].score) {
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largest = left;
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}
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if (right < heap_size && heap[right].score < heap[largest].score) {
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largest = right;
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}
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if (largest == current) {
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break;
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}
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Candidate tmp = heap[largest];
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heap[largest] = heap[current];
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heap[current] = tmp;
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current = largest;
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}
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}
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void heapify_up(Candidate * heap, int heap_size) {
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// heapify from the last node up
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int current = heap_size - 1;
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while (current > 0) {
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int parent = (current - 1) / 2;
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if (heap[current].score >= heap[parent].score) {
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break;
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}
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Candidate tmp = heap[parent];
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heap[parent] = heap[current];
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heap[current] = tmp;
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current = parent;
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}
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}
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// Find top N candidates in frequency and time according to their sync strength (looking at Costas symbols)
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void find_sync(const uint8_t * power, int num_blocks, int num_bins, int num_candidates, Candidate * heap) {
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// Costas 7x7 tone pattern
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const uint8_t ICOS7[] = { 2,5,6,0,4,1,3 };
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int heap_size = 0;
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for (int alt = 0; alt < 4; ++alt) {
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for (int i = 0; i < num_blocks - NN; ++i) {
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for (int j = 0; j < num_bins - 8; ++j) {
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for (int time_offset = 0; time_offset < num_blocks - NN; ++time_offset) {
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for (int freq_offset = 0; freq_offset < num_bins - 8; ++freq_offset) {
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int score = 0;
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// Compute score over bins 0-7, 36-43, 72-79
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for (int m = 0; m <= 72; m += 36) {
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for (int k = 0; k < 7; ++k) {
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int offset = ((i + k + m) * 4 + alt) * num_bins + j;
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// score += 8 * (int)power[i + k + m][alt][j + ICOS7[k]] -
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int offset = ((time_offset + k + m) * 4 + alt) * num_bins + freq_offset;
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// score += 8 * (int)power[time_offset + k + m][alt][freq_offset + ICOS7[k]] -
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score += 8 * (int)power[offset + ICOS7[k]] -
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power[offset + 0] - power[offset + 1] -
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power[offset + 2] - power[offset + 3] -
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@ -60,56 +103,23 @@ void find_candidates(int num_blocks, int num_bins, const uint8_t * power,
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// update the candidate list
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if (heap_size == num_candidates && score > heap[0].score) {
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//printf("Removing score %d\n", heap[0].score);
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// extract the least promising candidate
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heap[0] = heap[heap_size - 1];
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--heap_size;
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// heapify from the root down
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int current = 0;
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while (true) {
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int largest = current;
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int left = 2 * current + 1;
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int right = left + 1;
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if (left < heap_size && heap[left].score < heap[largest].score) {
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largest = left;
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}
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if (right < heap_size && heap[right].score < heap[largest].score) {
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largest = right;
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}
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if (largest == current) {
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break;
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}
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Candidate tmp = heap[largest];
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heap[largest] = heap[current];
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heap[current] = tmp;
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current = largest;
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}
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heapify_down(heap, heap_size);
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}
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if (heap_size < num_candidates) {
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// add the current candidate
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//printf("Adding score %d\n", score);
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heap[heap_size].score = score;
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heap[heap_size].time_offset = i;
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heap[heap_size].freq_offset = j;
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heap[heap_size].time_offset = time_offset;
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heap[heap_size].freq_offset = freq_offset;
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heap[heap_size].time_sub = alt / 2;
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heap[heap_size].freq_sub = alt % 2;
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++heap_size;
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// heapify from the last node up
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int current = heap_size - 1;
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while (current > 0) {
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int parent = (current - 1) / 2;
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if (heap[current].score >= heap[parent].score) {
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break;
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}
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Candidate tmp = heap[parent];
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heap[parent] = heap[current];
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heap[current] = tmp;
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current = parent;
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}
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heapify_up(heap, heap_size);
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}
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}
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}
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@ -117,10 +127,10 @@ void find_candidates(int num_blocks, int num_bins, const uint8_t * power,
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}
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void extract_power(const float *signal, int num_samples, int num_bins, uint8_t * power) {
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// Compute FFT magnitudes (log power) for each timeslot in the signal
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void extract_power(const float * signal, int num_blocks, int num_bins, uint8_t * power) {
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const int block_size = 2 * num_bins; // Average over 2 bins per FSK tone
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const int nfft = 2 * block_size; // We take FFT of two blocks, advancing by one
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const int num_blocks = (num_samples - (block_size/2) - block_size) / block_size;
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float window[nfft];
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for (int i = 0; i < nfft; ++i) {
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@ -137,31 +147,32 @@ void extract_power(const float *signal, int num_samples, int num_bins, uint8_t *
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kiss_fftr_cfg fft_cfg = kiss_fftr_alloc(nfft, 0, fft_work, &fft_work_size);
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int offset = 0;
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float fft_norm = 1.0f / nfft;
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for (int i = 0; i < num_blocks; ++i) {
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// Loop over two possible time offsets (0 and block_size/2)
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for (int time_offset = 0; time_offset <= block_size/2; time_offset += block_size/2) {
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for (int time_sub = 0; time_sub <= block_size/2; time_sub += block_size/2) {
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kiss_fft_scalar timedata[nfft];
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kiss_fft_cpx freqdata[nfft/2 + 1];
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float mag_db[nfft/2 + 1];
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// Extract windowed signal block
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for (int j = 0; j < nfft; ++j) {
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timedata[j] = window[j] * signal[i * block_size + j + time_offset];
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timedata[j] = window[j] * signal[(i * block_size) + (j + time_sub)];
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}
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kiss_fftr(fft_cfg, timedata, freqdata);
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// Compute log magnitude in decibels
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for (int j = 0; j < nfft/2 + 1; ++j) {
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float mag2 = (freqdata[j].i * freqdata[j].i + freqdata[j].r * freqdata[j].r);
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mag_db[j] = 10.0f * logf(1.0E-10f + mag2);
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float mag2 = fft_norm * (freqdata[j].i * freqdata[j].i + freqdata[j].r * freqdata[j].r);
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mag_db[j] = 10.0f * log10f(1.0E-10f + mag2);
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}
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// Loop over two possible frequency bin offsets (for averaging)
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for (int freq_offset = 0; freq_offset <= 1; ++freq_offset) {
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for (int freq_sub = 0; freq_sub < 2; ++freq_sub) {
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for (int j = 0; j < num_bins; ++j) {
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float db1 = mag_db[j * 2 + freq_offset];
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float db2 = mag_db[j * 2 + freq_offset + 1];
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float db1 = mag_db[j * 2 + freq_sub];
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float db2 = mag_db[j * 2 + freq_sub + 1];
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float db = (db1 + db2) / 2;
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// Scale decibels to unsigned 8-bit range
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@ -177,14 +188,14 @@ void extract_power(const float *signal, int num_samples, int num_bins, uint8_t *
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}
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int main(int argc, char **argv) {
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int main(int argc, char ** argv) {
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// Expect one command-line argument
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if (argc < 2) {
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usage();
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return -1;
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}
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const char *wav_path = argv[1];
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const char * wav_path = argv[1];
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int sample_rate = 12000;
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int num_samples = 15 * sample_rate;
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return -1;
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}
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const int num_bins = (int)(sample_rate / 2 / 6.25);
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const float fsk_dev = 6.25f;
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const int num_bins = (int)(sample_rate / (2 * fsk_dev));
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const int block_size = 2 * num_bins;
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const int num_blocks = (num_samples - (block_size/2) - block_size) / block_size;
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uint8_t power[num_blocks * 4 * num_bins]; // [num_blocks][4][num_bins] ~ 200 KB
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extract_power(signal, num_samples, num_bins, power);
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printf("%d blocks, %d bins\n", num_blocks, num_bins);
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const int num_candidates = 200;
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extract_power(signal, num_blocks, num_bins, power);
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const int num_candidates = 250;
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Candidate heap[num_candidates];
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find_candidates(num_blocks, num_bins, power, num_candidates, heap);
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find_sync(power, num_blocks, num_bins, num_candidates, heap);
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for (int i = 0; i < num_candidates; ++i) {
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float freq_offset = (heap[i].freq_offset + heap[i].freq_sub / 2.0f) * fsk_dev;
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float time_offset = (heap[i].time_offset + heap[i].time_sub / 2.0f) / fsk_dev;
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// int offset = (heap[i].time_offset * 4 + heap[i].time_sub * 2 + heap[i].freq_sub) * num_bins + heap[i].freq_offset;
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printf("%03d: score = %.1f freq = %.1f time = %.2f\n", i, heap[i].score / 7.0f / 2, freq_offset, time_offset);
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}
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/*
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// take absolute magnitude
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s2(0:7,k)=abs(csymb(1:8))/1e3
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// skip Costas sync symbols
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s1(0:7,j)=s2(0:7,k)
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// Normalize by median magnitude
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s1=s1/xmeds1
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// Extract bit significance
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ps=s1(0:7,j)
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bmeta(i4)=max(ps(4),ps(5),ps(6),ps(7))-max(ps(0),ps(1),ps(2),ps(3))
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bmeta(i2)=max(ps(2),ps(3),ps(6),ps(7))-max(ps(0),ps(1),ps(4),ps(5))
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bmeta(i1)=max(ps(1),ps(3),ps(5),ps(7))-max(ps(0),ps(2),ps(4),ps(6))
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// Normalize by std. deviation
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call normalizebmet(bmeta,3*ND)
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// Magical fudge/scale factor
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scalefac=2.83
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llr0=scalefac*bmeta
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*/
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return 0;
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}
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