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Added candidate search for decoding

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This commit is contained in:
Karlis Goba 2018-11-12 12:49:35 +02:00
parent b8fc6e92d8
commit 8397509c85
2 changed files with 163 additions and 14 deletions
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4
Makefile
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@ -3,7 +3,7 @@ LDFLAGS = -lm
.PHONY: run_tests all
all: gen_ft8 wav_decode test
all: gen_ft8 decode_ft8 test
run_tests: test
@./test
@ -15,4 +15,4 @@ test: test.o ft8/encode.o ft8/pack.o ft8/text.o ft8/pack_v2.o ft8/encode_v2.o f
$(CXX) $(LDFLAGS) -o $@ $^
decode_ft8: decode_ft8.o fft/kiss_fftr.o fft/kiss_fft.o ft8/ldpc.o common/wave.o
$(CXX) $(LDFLAGS) -o $@ $^
$(CXX) $(LDFLAGS) -o $@ $^

173
decode_ft8.cpp
View file

@ -24,6 +24,159 @@ float hann_i(int i, int N) {
}
struct Candidate {
int16_t score;
uint16_t time_offset;
uint16_t freq_offset;
uint8_t time_alt;
uint8_t freq_alt;
};
void find_candidates(int num_blocks, int num_bins, const uint8_t * power,
int num_candidates, Candidate heap[num_candidates]) {
// Costas 7x7 tone pattern
const uint8_t ICOS7[] = { 2,5,6,0,4,1,3 };
int heap_size = 0;
for (int alt = 0; alt < 4; ++alt) {
for (int i = 0; i < num_blocks - NN; ++i) {
for (int j = 0; j < num_bins - 8; ++j) {
int score = 0;
// Compute score over bins 0-7, 36-43, 72-79
for (int m = 0; m <= 72; m += 36) {
for (int k = 0; k < 7; ++k) {
int offset = ((i + k + m) * 4 + alt) * num_bins + j;
// score += 8 * (int)power[i + k + m][alt][j + ICOS7[k]] -
score += 8 * (int)power[offset + ICOS7[k]] -
power[offset + 0] - power[offset + 1] -
power[offset + 2] - power[offset + 3] -
power[offset + 4] - power[offset + 5] -
power[offset + 6] - power[offset + 7];
}
}
// update the candidate list
if (heap_size == num_candidates && score > heap[0].score) {
//printf("Removing score %d\n", heap[0].score);
// extract the least promising candidate
heap[0] = heap[heap_size - 1];
--heap_size;
// heapify from the root down
int current = 0;
while (true) {
int largest = current;
int left = 2 * current + 1;
int right = left + 1;
if (left < heap_size && heap[left].score < heap[largest].score) {
largest = left;
}
if (right < heap_size && heap[right].score < heap[largest].score) {
largest = right;
}
if (largest == current) {
break;
}
Candidate tmp = heap[largest];
heap[largest] = heap[current];
heap[current] = tmp;
current = largest;
}
}
if (heap_size < num_candidates) {
// add the current candidate
//printf("Adding score %d\n", score);
heap[heap_size].score = score;
heap[heap_size].time_offset = i;
heap[heap_size].freq_offset = j;
++heap_size;
// heapify from the last node up
int current = heap_size - 1;
while (current > 0) {
int parent = (current - 1) / 2;
if (heap[current].score >= heap[parent].score) {
break;
}
Candidate tmp = heap[parent];
heap[parent] = heap[current];
heap[current] = tmp;
current = parent;
}
}
}
}
}
}
void extract_power(const float *signal, int num_samples, int num_bins, uint8_t * power) {
const int block_size = 2 * num_bins; // Average over 2 bins per FSK tone
const int nfft = 2 * block_size; // We take FFT of two blocks, advancing by one
const int num_blocks = (num_samples - (block_size/2) - block_size) / block_size;
float window[nfft];
for (int i = 0; i < nfft; ++i) {
window[i] = hann_i(i, nfft);
}
size_t fft_work_size;
kiss_fftr_alloc(nfft, 0, 0, &fft_work_size);
printf("N_FFT = %d\n", nfft);
printf("FFT work area = %lu\n", fft_work_size);
void * fft_work = malloc(fft_work_size);
kiss_fftr_cfg fft_cfg = kiss_fftr_alloc(nfft, 0, fft_work, &fft_work_size);
int offset = 0;
for (int i = 0; i < num_blocks; ++i) {
// Loop over two possible time offsets (0 and block_size/2)
for (int time_offset = 0; time_offset <= block_size/2; time_offset += block_size/2) {
kiss_fft_scalar timedata[nfft];
kiss_fft_cpx freqdata[nfft/2 + 1];
float mag_db[nfft/2 + 1];
// Extract windowed signal block
for (int j = 0; j < nfft; ++j) {
timedata[j] = window[j] * signal[i * block_size + j + time_offset];
}
kiss_fftr(fft_cfg, timedata, freqdata);
// Compute log magnitude in decibels
for (int j = 0; j < nfft/2 + 1; ++j) {
float mag2 = (freqdata[j].i * freqdata[j].i + freqdata[j].r * freqdata[j].r);
mag_db[j] = 10.0f * logf(1.0E-10f + mag2);
}
// Loop over two possible frequency bin offsets (for averaging)
for (int freq_offset = 0; freq_offset <= 1; ++freq_offset) {
for (int j = 0; j < num_bins; ++j) {
float db1 = mag_db[j * 2 + freq_offset];
float db2 = mag_db[j * 2 + freq_offset + 1];
float db = (db1 + db2) / 2;
// Scale decibels to unsigned 8-bit range
int scaled = (int)(0.5f + 2 * (db + 100));
power[offset] = (scaled < 0) ? 0 : ((scaled > 255) ? 255 : scaled);
++offset;
}
}
}
}
free(fft_work);
}
int main(int argc, char **argv) {
// Expect one command-line argument
if (argc < 2) {
@ -42,22 +195,18 @@ int main(int argc, char **argv) {
return -1;
}
//return 0;
const int num_bins = (int)(sample_rate / 2 / 6.25);
const int block_size = 2 * num_bins;
const int num_blocks = (num_samples - (block_size/2) - block_size) / block_size;
const int nfft = 2 * (int)(sample_rate / 6.25); // 2 bins per FSK tone
uint8_t power[num_blocks * 4 * num_bins]; // [num_blocks][4][num_bins] ~ 200 KB
size_t fft_work_size;
kiss_fftr_alloc(nfft, 0, 0, &fft_work_size);
extract_power(signal, num_samples, num_bins, power);
printf("N_FFT = %d\n", nfft);
printf("FFT work area = %lu\n", fft_work_size);
const int num_candidates = 200;
Candidate heap[num_candidates];
void *fft_work = malloc(fft_work_size);
kiss_fftr_cfg fft_cfg = kiss_fftr_alloc(nfft, 0, fft_work, &fft_work_size);
kiss_fft_scalar timedata[nfft];
kiss_fft_cpx freqdata[nfft/2 + 1];
kiss_fftr(fft_cfg, timedata, freqdata);
find_candidates(num_blocks, num_bins, power, num_candidates, heap);
return 0;
}