300 lines
No EOL
9.6 KiB
C++
300 lines
No EOL
9.6 KiB
C++
#include <cstdlib>
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#include <cstring>
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#include <cstdio>
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#include <cmath>
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#include "common/wave.h"
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#include "ft8/pack.h"
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#include "ft8/encode.h"
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#include "ft8/pack_v2.h"
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#include "ft8/encode_v2.h"
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#include "ft8/ldpc.h"
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#include "fft/kiss_fftr.h"
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void usage() {
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printf("Decode a 15-second WAV file.\n");
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}
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float hann_i(int i, int N) {
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float x = sinf((float)M_PI * i / (N - 1));
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return x*x;
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}
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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_sub;
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uint8_t freq_sub;
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};
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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 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 Costas symbols (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 = ((time_offset + k + m) * 4 + alt) * num_bins + freq_offset;
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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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power[offset + 4] - power[offset + 5] -
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power[offset + 6] - power[offset + 7];
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}
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}
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// If the heap is full AND the current candidate is better than
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// the worst of the heap, we remove the worst and make space
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if (heap_size == num_candidates && score > heap[0].score) {
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heap[0] = heap[heap_size - 1];
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--heap_size;
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heapify_down(heap, heap_size);
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}
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// If there's free space in the heap, we add the current candidate
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if (heap_size < num_candidates) {
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heap[heap_size].score = score;
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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_up(heap, heap_size);
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}
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}
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}
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}
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}
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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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float window[nfft];
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for (int i = 0; i < nfft; ++i) {
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window[i] = hann_i(i, nfft);
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}
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size_t fft_work_size;
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kiss_fftr_alloc(nfft, 0, 0, &fft_work_size);
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printf("N_FFT = %d\n", nfft);
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printf("FFT work area = %lu\n", fft_work_size);
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void * fft_work = malloc(fft_work_size);
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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_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_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 = 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_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_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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int scaled = (int)(2 * (db + 100));
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power[offset] = (scaled < 0) ? 0 : ((scaled > 255) ? 255 : scaled);
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++offset;
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}
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}
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}
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}
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free(fft_work);
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}
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uint8_t max2(uint8_t a, uint8_t b) {
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return (a >= b) ? a : b;
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}
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uint8_t max4(uint8_t a, uint8_t b, uint8_t c, uint8_t d) {
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return max2(max2(a, b), max2(c, d));
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}
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// Compute log likelihood log(p(0) / p(1)) of 174 message bits
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// for later use in soft-decision LDPC decoding
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void extract_likelihood(const uint8_t * power, int num_bins, const Candidate & c, float * log174) {
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int offset = (c.time_offset * 4 + c.time_sub * 2 + c.freq_sub) * num_bins + c.freq_offset;
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int k = 0;
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// Go over FSK tones and skip Costas sync symbols
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for (int i = 7; i < NN - 7; ++i) {
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if (i == 36) i += 7;
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// Pointer to 8 bins of the current symbol
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const uint8_t * ps = power + (offset + i * 4 * num_bins);
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// Extract bit significance (and convert them to float)
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// 8 FSK tones = 3 bits
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log174[k + 0] = -(int)max4(ps[4], ps[5], ps[6], ps[7]) + (int)max4(ps[0], ps[1], ps[2], ps[3]);
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log174[k + 1] = -(int)max4(ps[2], ps[3], ps[6], ps[7]) + (int)max4(ps[0], ps[1], ps[4], ps[5]);
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log174[k + 2] = -(int)max4(ps[1], ps[3], ps[5], ps[7]) + (int)max4(ps[0], ps[2], ps[4], ps[6]);
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// printf("%d %d %d %d %d %d %d %d : %.0f %.0f %.0f\n",
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// ps[0], ps[1], ps[2], ps[3], ps[4], ps[5], ps[6], ps[7],
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// log174[k + 0], log174[k + 1], log174[k + 2]);
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k += 3;
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}
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// Compute the variance of log174
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float sum = 0;
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float sum2 = 0;
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float inv_n = 1.0f / (3 * ND);
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for (int i = 0; i < 3 * ND; ++i) {
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sum += log174[i];
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sum2 += log174[i] * log174[i];
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}
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float var = (sum2 - sum * sum * inv_n) * inv_n;
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// Normalize log174 such that sigma = 2.83 (Why? It's in WSJT-X)
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float norm_factor = 2.83f / sqrtf(var);
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for (int i = 0; i < 3 * ND; ++i) {
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log174[i] *= norm_factor;
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//printf("%.1f ", log174[i]);
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}
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//printf("\n");
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}
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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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int sample_rate = 12000;
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int num_samples = 15 * sample_rate;
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float signal[num_samples];
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int rc = load_wav(signal, num_samples, sample_rate, wav_path);
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if (rc < 0) {
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return -1;
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}
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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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printf("%d blocks, %d bins\n", num_blocks, num_bins);
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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_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_hz = (heap[i].freq_offset + heap[i].freq_sub / 2.0f) * fsk_dev;
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float time_sec = (heap[i].time_offset + heap[i].time_sub / 2.0f) / fsk_dev;
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// printf("%03d: score = %d freq = %.1f time = %.2f\n", i,
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// heap[i].score, freq_hz, time_sec);
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float log174[3 * ND];
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extract_likelihood(power, num_bins, heap[i], log174);
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const int num_iters = 10;
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int plain[3 * ND];
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int ok;
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ldpc_decode(log174, num_iters, plain, &ok);
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//printf("ldpc_decode() = %d\n", ok);
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if (ok == 87) {
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printf("%03d: score = %d freq = %.1f time = %.2f\n", i,
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heap[i].score, freq_hz, time_sec);
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}
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}
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return 0;
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} |