ft8_lib/decode_ft8.cpp

283 lines
8.8 KiB
C++
Raw Permalink Normal View History

#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <cmath>
#include "ft8/unpack.h"
#include "ft8/ldpc.h"
#include "ft8/decode.h"
2018-12-24 20:22:26 +08:00
#include "ft8/constants.h"
#include "ft8/encode.h"
2018-12-24 20:22:26 +08:00
#include "common/wave.h"
#include "common/debug.h"
2018-12-24 20:22:26 +08:00
#include "fft/kiss_fftr.h"
#define LOG_LEVEL LOG_INFO
const int kMin_score = 40; // Minimum sync score threshold for candidates
2019-11-11 19:36:22 +08:00
const int kMax_candidates = 120;
const int kLDPC_iterations = 25;
const int kMax_decoded_messages = 50;
const int kMax_message_length = 25;
const int kFreq_osr = 2;
const int kTime_osr = 2;
const float kFSK_dev = 6.25f; // tone deviation in Hz and symbol rate
void usage() {
fprintf(stderr, "Decode a 15-second WAV file.\n");
}
float hann_i(int i, int N) {
float x = sinf((float)M_PI * i / (N - 1));
return x*x;
}
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));
float x2 = 2*x1*x1 - 1; // Use double angle formula
return a0 - a1*x1 + a2*x2;
}
static float max2(float a, float b) {
return (a >= b) ? a : b;
}
2018-11-13 19:04:36 +08:00
// Compute FFT magnitudes (log power) for each timeslot in the signal
void extract_power(const float signal[], ft8::MagArray * power) {
const int block_size = 2 * power->num_bins; // Average over 2 bins per FSK tone
const int subblock_size = block_size / power->time_osr;
const int nfft = block_size * power->freq_osr; // We take FFT of two blocks, advancing by one
const float fft_norm = 2.0f / nfft;
2018-11-12 18:49:35 +08:00
float window[nfft];
for (int i = 0; i < nfft; ++i) {
window[i] = hann_i(i, nfft);
2018-11-12 18:49:35 +08:00
}
size_t fft_work_size;
kiss_fftr_alloc(nfft, 0, 0, &fft_work_size);
LOG(LOG_INFO, "Block size = %d\n", block_size);
LOG(LOG_INFO, "Subblock size = %d\n", subblock_size);
LOG(LOG_INFO, "N_FFT = %d\n", nfft);
LOG(LOG_INFO, "FFT work area = %lu\n", fft_work_size);
2018-11-12 18:49:35 +08:00
void *fft_work = malloc(fft_work_size);
2018-11-12 18:49:35 +08:00
kiss_fftr_cfg fft_cfg = kiss_fftr_alloc(nfft, 0, fft_work, &fft_work_size);
int offset = 0;
2018-12-24 20:22:26 +08:00
float max_mag = -100.0f;
for (int i = 0; i < power->num_blocks; ++i) {
2018-11-12 18:49:35 +08:00
// Loop over two possible time offsets (0 and block_size/2)
for (int time_sub = 0; time_sub < power->time_osr; ++time_sub) {
2018-11-12 18:49:35 +08:00
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_sub * subblock_size)];
2018-11-12 18:49:35 +08:00
}
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 * log10f(1E-10f + mag2 * fft_norm * fft_norm);
2018-11-12 18:49:35 +08:00
}
// Loop over two possible frequency bin offsets (for averaging)
for (int freq_sub = 0; freq_sub < power->freq_osr; ++freq_sub) {
for (int j = 0; j < power->num_bins; ++j) {
float db1 = mag_db[j * power->freq_osr + freq_sub];
//float db2 = mag_db[j * 2 + freq_sub + 1];
//float db = (db1 + db2) / 2;
float db = db1;
//float db = sqrtf(db1 * db2);
2018-11-12 18:49:35 +08:00
2018-12-24 20:22:26 +08:00
// Scale decibels to unsigned 8-bit range and clamp the value
int scaled = (int)(2 * (db + 120));
power->mag[offset] = (scaled < 0) ? 0 : ((scaled > 255) ? 255 : scaled);
2018-11-12 18:49:35 +08:00
++offset;
2018-12-24 20:22:26 +08:00
if (db > max_mag) max_mag = db;
2018-11-12 18:49:35 +08:00
}
}
}
}
LOG(LOG_INFO, "Max magnitude: %.1f dB\n", max_mag);
2018-11-12 18:49:35 +08:00
free(fft_work);
}
void normalize_signal(float *signal, int num_samples) {
float max_amp = 1E-5f;
for (int i = 0; i < num_samples; ++i) {
float amp = fabsf(signal[i]);
if (amp > max_amp) {
max_amp = amp;
}
}
for (int i = 0; i < num_samples; ++i) {
signal[i] /= max_amp;
}
}
2018-12-24 20:22:26 +08:00
void print_tones(const uint8_t *code_map, const float *log174) {
for (int k = 0; k < ft8::N; k += 3) {
2018-12-24 20:22:26 +08:00
uint8_t max = 0;
if (log174[k + 0] > 0) max |= 4;
if (log174[k + 1] > 0) max |= 2;
if (log174[k + 2] > 0) max |= 1;
LOG(LOG_DEBUG, "%d", code_map[max]);
2018-12-24 20:22:26 +08:00
}
LOG(LOG_DEBUG, "\n");
2018-12-24 20:22:26 +08:00
}
int main(int argc, char **argv) {
// Expect one command-line argument
if (argc < 2) {
usage();
return -1;
}
const char *wav_path = argv[1];
int sample_rate = 12000;
int num_samples = 15 * sample_rate;
float signal[num_samples];
int rc = load_wav(signal, num_samples, sample_rate, wav_path);
if (rc < 0) {
return -1;
}
normalize_signal(signal, num_samples);
// Compute DSP parameters that depend on the sample rate
const int num_bins = (int)(sample_rate / (2 * kFSK_dev));
2018-11-12 18:49:35 +08:00
const int block_size = 2 * num_bins;
const int subblock_size = block_size / kTime_osr;
const int nfft = block_size * kFreq_osr;
const int num_blocks = (num_samples - nfft + subblock_size) / block_size;
LOG(LOG_INFO, "Sample rate %d Hz, %d blocks, %d bins\n", sample_rate, num_blocks, num_bins);
2018-11-13 19:04:36 +08:00
// Compute FFT over the whole signal and store it
uint8_t mag_power[num_blocks * kFreq_osr * kTime_osr * num_bins];
ft8::MagArray power = {
.num_blocks = num_blocks,
.num_bins = num_bins,
.time_osr = kTime_osr,
.freq_osr = kFreq_osr,
.mag = mag_power
};
extract_power(signal, &power);
// Find top candidates by Costas sync score and localize them in time and frequency
ft8::Candidate candidate_list[kMax_candidates];
2019-11-12 21:50:59 +08:00
int num_candidates = ft8::find_sync(&power, ft8::kCostas_map, kMax_candidates, candidate_list, kMin_score);
// TODO: sort the candidates by strongest sync first?
2018-11-13 19:04:36 +08:00
// Go over candidates and attempt to decode messages
char decoded[kMax_decoded_messages][kMax_message_length];
int num_decoded = 0;
for (int idx = 0; idx < num_candidates; ++idx) {
ft8::Candidate &cand = candidate_list[idx];
if (cand.score < kMin_score) continue;
float freq_hz = (cand.freq_offset + (float)cand.freq_sub / kFreq_osr) * kFSK_dev;
float time_sec = (cand.time_offset + (float)cand.time_sub / kTime_osr) / kFSK_dev;
2018-11-13 23:16:24 +08:00
float log174[ft8::N];
ft8::extract_likelihood(&power, cand, ft8::kGray_map, log174);
2018-11-13 23:16:24 +08:00
// bp_decode() produces better decodes, uses way less memory
uint8_t plain[ft8::N];
int n_errors = 0;
ft8::bp_decode(log174, kLDPC_iterations, plain, &n_errors);
//ft8::ldpc_decode(log174, kLDPC_iterations, plain, &n_errors);
if (n_errors > 0) {
2019-01-03 02:24:44 +08:00
LOG(LOG_DEBUG, "ldpc_decode() = %d (%.0f Hz)\n", n_errors, freq_hz);
continue;
}
int sum_plain = 0;
for (int i = 0; i < ft8::N; ++i) {
sum_plain += plain[i];
}
if (sum_plain == 0) {
// All zeroes message
continue;
}
// Extract payload + CRC (first ft8::K bits)
uint8_t a91[ft8::K_BYTES];
ft8::pack_bits(plain, ft8::K, a91);
2019-01-03 02:24:44 +08:00
// Extract CRC and check it
uint16_t chksum = ((a91[9] & 0x07) << 11) | (a91[10] << 3) | (a91[11] >> 5);
a91[9] &= 0xF8;
a91[10] = 0;
a91[11] = 0;
uint16_t chksum2 = ft8::crc(a91, 96 - 14);
2019-01-03 02:24:44 +08:00
if (chksum != chksum2) {
LOG(LOG_DEBUG, "Checksum: message = %04x, CRC = %04x\n", chksum, chksum2);
continue;
}
2018-12-24 20:22:26 +08:00
char message[kMax_message_length];
2019-11-11 19:36:22 +08:00
if (ft8::unpack77(a91, message) < 0) {
continue;
}
// Check for duplicate messages (TODO: use hashing)
bool found = false;
for (int i = 0; i < num_decoded; ++i) {
if (0 == strcmp(decoded[i], message)) {
found = true;
break;
}
}
2018-11-20 23:04:05 +08:00
if (!found && num_decoded < kMax_decoded_messages) {
strcpy(decoded[num_decoded], message);
++num_decoded;
2018-11-20 23:04:05 +08:00
2018-12-24 20:22:26 +08:00
// Fake WSJT-X-like output for now
int snr = 0; // TODO: compute SNR
printf("000000 %3d %4.1f %4d ~ %s\n", cand.score, time_sec, (int)(freq_hz + 0.5f), message);
2018-11-13 23:16:24 +08:00
}
2018-11-13 19:04:36 +08:00
}
LOG(LOG_INFO, "Decoded %d messages\n", num_decoded);
2018-11-13 19:04:36 +08:00
return 0;
}