From 0c2e35b998328d5dcf016e983281c15b93510ea1 Mon Sep 17 00:00:00 2001 From: Karlis Goba Date: Tue, 25 Dec 2018 14:01:51 +0200 Subject: [PATCH] Improved decode by extending search in time and better windowing --- decode_ft8.cpp | 222 +++++++++++++++++++++++++++++++------------------ 1 file changed, 143 insertions(+), 79 deletions(-) diff --git a/decode_ft8.cpp b/decode_ft8.cpp index 5c850f3..9c13390 100644 --- a/decode_ft8.cpp +++ b/decode_ft8.cpp @@ -10,6 +10,12 @@ #include "common/wave.h" #include "fft/kiss_fftr.h" +const int kMax_candidates = 100; +const int kLDPC_iterations = 20; + +const int kMax_decoded_messages = 50; +const int kMax_message_length = 20; + void usage() { printf("Decode a 15-second WAV file.\n"); } @@ -21,16 +27,38 @@ float hann_i(int i, int N) { } +float hamming_i(int i, int N) { + const float a0 = (float)25 / 46; + const float a1 = 1 - a0; + + float x1 = cosf(2 * (float)M_PI * i / (N - 1)); + return a0 - a1*x1; +} + + +float blackman_i(int i, int N) { + const float alpha = 0.16f; // or 2860/18608 + const float a0 = (1 - alpha) / 2; + const float a1 = 1.0f / 2; + const float a2 = alpha / 2; + + float x1 = cosf(2 * (float)M_PI * i / (N - 1)); + float x2 = cosf(4 * (float)M_PI * i / (N - 1)); + + return a0 - a1*x1 + a2*x2; +} + + struct Candidate { int16_t score; - uint16_t time_offset; - uint16_t freq_offset; + int16_t time_offset; + int16_t freq_offset; uint8_t time_sub; uint8_t freq_sub; }; -void heapify_down(Candidate * heap, int heap_size) { +void heapify_down(Candidate *heap, int heap_size) { // heapify from the root down int current = 0; while (true) { @@ -56,7 +84,7 @@ void heapify_down(Candidate * heap, int heap_size) { } -void heapify_up(Candidate * heap, int heap_size) { +void heapify_up(Candidate *heap, int heap_size) { // heapify from the last node up int current = heap_size - 1; while (current > 0) { @@ -79,21 +107,26 @@ int find_sync(const uint8_t *power, int num_blocks, int num_bins, const uint8_t int heap_size = 0; for (int alt = 0; alt < 4; ++alt) { - for (int time_offset = 0; time_offset < num_blocks - FT8_NN; ++time_offset) { + for (int time_offset = -7; time_offset < num_blocks - FT8_NN + 7; ++time_offset) { for (int freq_offset = 0; freq_offset < num_bins - 8; ++freq_offset) { int score = 0; // Compute score over Costas symbols (0-7, 36-43, 72-79) + int num_scores = 0; for (int m = 0; m <= 72; m += 36) { for (int k = 0; k < 7; ++k) { + if (time_offset + k + m < 0) continue; + if (time_offset + k + m >= num_blocks) break; int offset = ((time_offset + k + m) * 4 + alt) * num_bins + freq_offset; score += 8 * (int)power[offset + sync_map[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]; + ++num_scores; } } + score /= num_scores; // If the heap is full AND the current candidate is better than // the worst in the heap, we remove the worst and make space @@ -124,17 +157,14 @@ int find_sync(const uint8_t *power, int num_blocks, int num_bins, const uint8_t // Compute FFT magnitudes (log power) for each timeslot in the signal -void extract_power(const float * signal, int num_blocks, int num_bins, uint8_t * power) { +void extract_power(const float *signal, int num_blocks, 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 float window[nfft]; for (int i = 0; i < nfft; ++i) { - window[i] = hann_i(i, nfft); + window[i] = blackman_i(i, nfft); } - // for (int i = 0; i < nfft; ++i) { - // window[i] = (i < block_size) ? 2 * hann_i(i, block_size) : 0.0f; - // } size_t fft_work_size; kiss_fftr_alloc(nfft, 0, 0, &fft_work_size); @@ -187,18 +217,17 @@ void extract_power(const float * signal, int num_blocks, int num_bins, uint8_t * } printf("Max magnitude: %.1f dB\n", max_mag); - free(fft_work); } -uint8_t max2(uint8_t a, uint8_t b) { +float max2(float a, float b) { return (a >= b) ? a : b; } -uint8_t max4(uint8_t a, uint8_t b, uint8_t cand, uint8_t d) { - return max2(max2(a, b), max2(cand, d)); +float max4(float a, float b, float c, float d) { + return max2(max2(a, b), max2(c, d)); } @@ -207,45 +236,61 @@ uint8_t max4(uint8_t a, uint8_t b, uint8_t cand, uint8_t d) { void extract_likelihood(const uint8_t *power, int num_bins, const Candidate & cand, const uint8_t *code_map, float *log174) { int offset = (cand.time_offset * 4 + cand.time_sub * 2 + cand.freq_sub) * num_bins + cand.freq_offset; - int k = 0; // Go over FSK tones and skip Costas sync symbols - for (int i = 7; i < FT8_NN - 7; ++i) { - if (i == 36) i += 7; + const int n_syms = 1; + const int n_bits = 3 * n_syms; + const int n_tones = (1 << n_bits); + for (int k = 0; k < FT8_ND; k += n_syms) { + int sym_idx = (k < FT8_ND / 2) ? (k + 7) : (k + 14); // Pointer to 8 bins of the current symbol - const uint8_t * ps = power + (offset + i * 4 * num_bins); - uint8_t s2[8]; + const uint8_t *ps = power + (offset + sym_idx * 4 * num_bins); + float s2[n_tones]; - for (int i = 0; i < 8; ++i) { - s2[i] = ps[code_map[i]]; + for (int j = 0; j < n_tones; ++j) { + int j1 = j & 0x07; + s2[j] = (float)ps[code_map[j1]]; + //int j2 = (j >> 3) & 0x07; + //s2[j] = (float)ps[code_map[j2]]; + //s2[j] += (float)ps[code_map[j1] + 4 * num_bins]; } // Extract bit significance (and convert them to float) // 8 FSK tones = 3 bits - log174[k + 0] = (int)max4(s2[4], s2[5], s2[6], s2[7]) - (int)max4(s2[0], s2[1], s2[2], s2[3]); - log174[k + 1] = (int)max4(s2[2], s2[3], s2[6], s2[7]) - (int)max4(s2[0], s2[1], s2[4], s2[5]); - log174[k + 2] = (int)max4(s2[1], s2[3], s2[5], s2[7]) - (int)max4(s2[0], s2[2], s2[4], s2[6]); - // printf("%d %d %d %d %d %d %d %d : %.0f %.0f %.0f\n", - // ps[0], ps[1], ps[2], ps[3], ps[4], ps[5], ps[6], ps[7], - // log174[k + 0], log174[k + 1], log174[k + 2]); + int bit_idx = 3 * k; + for (int i = 0; i < n_bits; ++i) { + uint16_t mask = (n_tones >> (i + 1)); - k += 3; + float max_zero = -1000, max_one = -1000; + for (int n = 0; n < n_tones; ++n) { + if (n & mask) { + max_one = max2(max_one, s2[n]); + } + else { + max_zero = max2(max_zero, s2[n]); + } + } + if (bit_idx + i >= 174) break; + log174[bit_idx + i] = max_one - max_zero; + } + // log174[bit_idx + 0] = max4(s2[4], s2[5], s2[6], s2[7]) - max4(s2[0], s2[1], s2[2], s2[3]); + // log174[bit_idx + 1] = max4(s2[2], s2[3], s2[6], s2[7]) - max4(s2[0], s2[1], s2[4], s2[5]); + // log174[bit_idx + 2] = max4(s2[1], s2[3], s2[5], s2[7]) - max4(s2[0], s2[2], s2[4], s2[6]); } // Compute the variance of log174 float sum = 0; float sum2 = 0; - float inv_n = 1.0f / (3 * FT8_ND); - for (int i = 0; i < 3 * FT8_ND; ++i) { + float inv_n = 1.0f / FT8_N; + for (int i = 0; i < FT8_N; ++i) { sum += log174[i]; sum2 += log174[i] * log174[i]; } float variance = (sum2 - sum * sum * inv_n) * inv_n; // Normalize log174 such that sigma = 2.83 (Why? It's in WSJT-X) - float norm_factor = 2.83f / sqrtf(variance); - - for (int i = 0; i < 3 * FT8_ND; ++i) { + float norm_factor = 3.83f / sqrtf(variance); + for (int i = 0; i < FT8_N; ++i) { log174[i] *= norm_factor; //printf("%.1f ", log174[i]); } @@ -282,14 +327,14 @@ void print_tones(const uint8_t *code_map, const float *log174) { } -int main(int argc, char ** argv) { +int main(int argc, char **argv) { // Expect one command-line argument if (argc < 2) { usage(); return -1; } - const char * wav_path = argv[1]; + const char *wav_path = argv[1]; int sample_rate = 12000; int num_samples = 15 * sample_rate; @@ -300,78 +345,97 @@ int main(int argc, char ** argv) { return -1; } - const float fsk_dev = 6.25f; + const float fsk_dev = 6.25f; // tone deviation in Hz and symbol rate + // Compute DSP parameters that depend on the sample rate const int num_bins = (int)(sample_rate / (2 * fsk_dev)); const int block_size = 2 * num_bins; const int num_blocks = (num_samples - (block_size/2) - block_size) / block_size; - uint8_t power[num_blocks * 4 * num_bins]; // [num_blocks][4][num_bins] ~ 200 KB printf("%d blocks, %d bins\n", num_blocks, num_bins); + // Compute FFT over the whole signal and store it + uint8_t power[num_blocks * 4 * num_bins]; extract_power(signal, num_blocks, num_bins, power); - int num_candidates = 100; - Candidate heap[num_candidates]; + Candidate heap[kMax_candidates]; + char decoded[kMax_decoded_messages][kMax_message_length]; + int num_decoded = 0; - find_sync(power, num_blocks, num_bins, kCostas_map, num_candidates, heap); + int num_candidates = find_sync(power, num_blocks, num_bins, kCostas_map, kMax_candidates, heap); for (int idx = 0; idx < num_candidates; ++idx) { Candidate &cand = heap[idx]; - float log174[3 * FT8_ND]; + float log174[FT8_N]; extract_likelihood(power, num_bins, cand, kGray_map, log174); - const int num_iters = 25; - uint8_t plain[3 * FT8_ND]; - int n_errors = 0; - - float freq_hz = (cand.freq_offset + cand.freq_sub / 2.0f) * fsk_dev; - float time_sec = (cand.time_offset + cand.time_sub / 2.0f) / fsk_dev; - - printf("%03d: score = %d freq = %.1f time = %.2f\n", idx, - cand.score, freq_hz, time_sec); - - bp_decode(log174, num_iters, plain, &n_errors); + // bp_decode() produces better decodes, uses way less memory + uint8_t plain[FT8_N]; + int n_errors = 0; + bp_decode(log174, kLDPC_iterations, plain, &n_errors); //ldpc_decode(log174, num_iters, plain, &n_errors); - printf("ldpc_decode() = %d\n", n_errors); - if (n_errors == 0) { + if (n_errors > 0) { + //printf("ldpc_decode() = %d\n", n_errors); + continue; + } - //print_tones(kGray_map, log174); - - // Extract payload + CRC - uint8_t a91[12]; - uint8_t mask = 0x80; - uint8_t position = 0; - for (int i = 0; i < 12; ++i) { - a91[i] = 0; + float freq_hz = (cand.freq_offset + cand.freq_sub / 2.0f) * fsk_dev; + float time_sec = (cand.time_offset + cand.time_sub / 2.0f) / fsk_dev; + + // printf("%03d: score = %d freq = %.1f time = %.2f\n", idx, + // cand.score, freq_hz, time_sec); + + //print_tones(kGray_map, log174); + + // Extract payload + CRC + uint8_t a91[12]; + uint8_t mask = 0x80; + int byte_idx = 0; + for (int i = 0; i < 12; ++i) { + a91[i] = 0; + } + for (int i = 0; i < FT8_K; ++i) { + if (plain[i]) { + a91[byte_idx] |= mask; } - for (int i = 0; i < FT8_K; ++i) { - if (plain[i]) { - a91[position] |= mask; - } - mask >>= 1; - if (!mask) { - mask = 0x80; - ++position; - } + mask >>= 1; + if (!mask) { + mask = 0x80; + ++byte_idx; } + } - // TODO: check CRC + // TODO: check CRC - // for (int i = 0; i < 12; ++i) { - // printf("%02x ", a91[i]); - // } - // printf("\n"); + // for (int i = 0; i < 12; ++i) { + // printf("%02x ", a91[i]); + // } + // printf("\n"); - char message[20]; - unpack77(a91, message); + char message[kMax_message_length]; + unpack77(a91, message); + + // Check for duplicate messages + bool found = false; + for (int i = 0; i < num_decoded; ++i) { + if (0 == strcmp(decoded[i], message)) { + found = true; + break; + } + } + + if (!found && num_decoded < kMax_decoded_messages) { + strcpy(decoded[num_decoded], message); + ++num_decoded; // Fake WSJT-X-like output for now - printf("000000 0 %4.1f %4d ~ %s\n", time_sec, (int)(freq_hz + 0.5f), message); + int snr = 0; // TODO: compute SNR + printf("000000 %3d %4.1f %4d ~ %s\n", snr, time_sec, (int)(freq_hz + 0.5f), message); } } + printf("Decoded %d messages\n", num_decoded); return 0; } \ No newline at end of file