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Improved sync, automatic CFO correction

pull/21/head
Pieter Robyns 2016-09-12 14:23:25 +02:00
rodzic be8cba4ddb
commit 4a6b45c809
2 zmienionych plików z 35 dodań i 22 usunięć
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54
lib/decoder_impl.cc
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@ -174,6 +174,17 @@ namespace gr {
}
}
double decoder_impl::cross_correlate(const gr_complex *samples_1, const gr_complex *samples_2, int window) {
double result = 0.0f;
for (int i = 0; i < window; i++) {
result += real(samples_1[i] * conj(samples_2[i]));
}
result = result / window;
return result;
}
double decoder_impl::freq_cross_correlate(const gr_complex *samples_1, const gr_complex *samples_2, int window) {
double result = 0.0f;
float instantaneous_phase[window];
@ -207,27 +218,27 @@ namespace gr {
float fft_mag[d_number_of_bins];
gr_complex mult_hf[d_samples_per_symbol];
#ifdef CFO_CORRECT
/*#ifdef CFO_CORRECT
determine_cfo(&samples[0]);
std::cout << "CFO: " << d_cfo_estimation << std::endl;
correct_cfo(&samples[0], d_samples_per_symbol);
#endif
#endif*/
//samples_to_file("/tmp/data", &samples[0], d_samples_per_symbol, sizeof(gr_complex));
samples_to_file("/tmp/data", &samples[0], d_samples_per_symbol, sizeof(gr_complex));
// Multiply with ideal downchirp
for(uint32_t i = 0; i < d_samples_per_symbol; i++) {
mult_hf[i] = conj(samples[i] * d_downchirp[i]);
}
//samples_to_file("/tmp/mult", &mult_hf[0], d_samples_per_symbol, sizeof(gr_complex));
samples_to_file("/tmp/mult", &mult_hf[0], d_samples_per_symbol, sizeof(gr_complex));
// Perform decimation
for (uint32_t i = 0; i < d_number_of_bins; i++) {
firdecim_crcf_execute(d_decim, &mult_hf[d_decim_factor*i], &d_mult[i]);
}
//samples_to_file("/tmp/resampled", &d_mult[0], d_number_of_bins, sizeof(gr_complex));
samples_to_file("/tmp/resampled", &d_mult[0], d_number_of_bins, sizeof(gr_complex));
// Perform FFT
fft_execute(d_q);
@ -237,7 +248,7 @@ namespace gr {
fft_mag[i] = abs(d_fft[i]);
}
//samples_to_file("/tmp/fft", &d_fft[0], d_number_of_bins, sizeof(gr_complex));
samples_to_file("/tmp/fft", &d_fft[0], d_number_of_bins, sizeof(gr_complex));
// Return argmax here
return (std::max_element(fft_mag,fft_mag+d_number_of_bins) - fft_mag);
@ -286,8 +297,8 @@ namespace gr {
}
bool decoder_impl::demodulate(gr_complex* samples, bool is_header) {
//unsigned int bin_idx = max_frequency_gradient_idx(samples);
unsigned int bin_idx = sync_fft(samples);
unsigned int bin_idx = max_frequency_gradient_idx(samples);
//unsigned int bin_idx = sync_fft(samples);
//unsigned int bin_idx_test = sync_fft(samples);
unsigned int bin_idx_test = 0;
@ -467,6 +478,8 @@ namespace gr {
sum /= d_samples_per_symbol;
d_cfo_estimation = sum;
/*d_cfo_estimation = (*std::max_element(instantaneous_freq, instantaneous_freq+d_samples_per_symbol-1) + *std::min_element(instantaneous_freq, instantaneous_freq+d_samples_per_symbol-1)) / 2;*/
}
void decoder_impl::correct_cfo(gr_complex* samples, int num_samples) {
@ -485,9 +498,9 @@ namespace gr {
}
}
int decoder_impl::find_preamble_start_fast(gr_complex* samples) {
int decoder_impl::find_preamble_start_fast(gr_complex* samples, uint32_t len) {
int step_size = d_samples_per_symbol / 8;
for(int i = 0; i < d_samples_per_symbol; i++) {
for(int i = 0; i < len; i += 8) {
bool higher = true;
float last_ifreq = -999999999;
@ -501,7 +514,7 @@ namespace gr {
float ifreq = (s[1] - s[0]) / (2.0f * M_PI) * d_samples_per_second;
d_debug << "F: " << ifreq << std::endl;
if(ifreq - last_ifreq < (d_bw / 8) - 3000) { // Make sure it rises fast enough
if(ifreq - last_ifreq < (d_bw / 8) / 1.5) { // Make sure it rises fast enough
higher = false;
d_debug << "NOPE" << std::endl;
break;
@ -528,23 +541,24 @@ namespace gr {
switch(d_state) {
case DETECT: {
if(calc_energy_threshold(input, noutput_items, 0.002)) {
//d_debug << "Got something\n";
// Attempt to synchronize to an upchirp of the preamble
int chirp_start_pos = -1;
d_cfo_estimation = 0;
// Find rough position of preamble
int i = find_preamble_start_fast(&input[0]);
int i = find_preamble_start_fast(&input[0], noutput_items);
// After this step, if i != -1 we know that we are in a rising chirp, starting from i.
// Calculate the CFO here, and correct for it. Then perform sync_fft until we get a 0
// The final position where this is the case indicates the start of the preamble.
if(i != -1) {
//samples_to_file("/tmp/bcfo", &input[i], noutput_items, sizeof(gr_complex));
// TODO: Find algorithm to reliably determine CFO
samples_to_file("/tmp/bcfo", &input[0], noutput_items, sizeof(gr_complex));
i = find_preamble_start(&input[0]);
determine_cfo(&input[i]);
//d_debug << "CFO " << d_cfo_estimation << std::endl;
d_debug << "CFO " << d_cfo_estimation << std::endl;
correct_cfo(&input[0], noutput_items);
//samples_to_file("/tmp/acfo", &input[i], noutput_items, sizeof(gr_complex));
samples_to_file("/tmp/acfo", &input[0], noutput_items, sizeof(gr_complex));
// Sync
i = find_preamble_start(&input[0]);
@ -565,8 +579,8 @@ namespace gr {
break;
}
case SYNC: {
double c = freq_cross_correlate(&input[0], &d_downchirp[0], CORRELATION_SEARCH_RANGE);
//d_debug << "C: " << c << std::endl;
double c = freq_cross_correlate(&input[0], &d_downchirp[0], d_samples_per_symbol);
d_debug << "C: " << c << std::endl;
if(c > 0.045f) {
d_debug << "SYNC: " << c << std::endl;
@ -579,7 +593,6 @@ namespace gr {
d_corr_fails++;
if(d_corr_fails > 32) {
d_state = DETECT;
d_cfo_estimation = 0;
}
consume_each(d_samples_per_symbol);
}
@ -626,7 +639,6 @@ namespace gr {
decode(decoded, false);
d_state = DETECT;
d_cfo_estimation = 0;
}
}

3
lib/decoder_impl.h
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@ -84,11 +84,12 @@ namespace gr {
void samples_to_file(const std::string path, const gr_complex* v, int length, int elem_size);
void samples_debug(const gr_complex* v, int length);
double freq_cross_correlate(const gr_complex *samples_1, const gr_complex *samples_2, int window);
double cross_correlate(const gr_complex *samples_1, const gr_complex *samples_2, int window);
unsigned int sync_fft(gr_complex* samples);
void determine_cfo(const gr_complex* samples);
void correct_cfo(gr_complex* samples, int num_samples);
int find_preamble_start(gr_complex* samples);
int find_preamble_start_fast(gr_complex* samples);
int find_preamble_start_fast(gr_complex* samples, uint32_t len);
unsigned int max_frequency_gradient_idx(gr_complex* samples);
bool demodulate(gr_complex* samples, bool is_header);
void deinterleave(int ppm);