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Use normalized cross correlation instead of normal cross correlation

pull/21/head
Pieter Robyns 2016-09-13 16:43:41 +02:00
rodzic e9a3025340
commit 0a157780a7
2 zmienionych plików z 27 dodań i 4 usunięć
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30
lib/decoder_impl.cc
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@ -25,6 +25,7 @@
#include <gnuradio/io_signature.h>
#include <gnuradio/expj.h>
#include <liquid/liquid.h>
#include <numeric>
#include "decoder_impl.h"
#include "tables.h"
#include "utilities.h"
@ -205,14 +206,30 @@ namespace gr {
instantaneous_freq_down[i-1] = instantaneous_phase_down[i] - instantaneous_phase_down[i-1];
}
double average = std::accumulate(instantaneous_freq, instantaneous_freq + window, 0.0) / window;
double average_down = std::accumulate(instantaneous_freq_down, instantaneous_freq_down + window, 0.0) / window;
double sd = stddev(instantaneous_freq, window, average);
double sd_down = stddev(instantaneous_freq_down, window, average_down);
for (int i = 0; i < window-1; i++) {
result += instantaneous_freq[i] * instantaneous_freq_down[i];
result += (instantaneous_freq[i] - average) * (instantaneous_freq_down[i] - average_down) / (sd * sd_down);
}
result = result / window;
return result;
}
double decoder_impl::stddev(float *values, int len, float mean) {
double variance = 0.0f;
for (unsigned int i = 0; i < len; i++) {
variance += std::pow(values[i] - mean, 2);
}
variance /= len;
return std::sqrt(variance);
}
double decoder_impl::sliding_freq_cross_correlate(const gr_complex *samples_1, const gr_complex *samples_2, int window, int slide, int* index) {
float instantaneous_phase[window];
float instantaneous_phase_down[window];
@ -238,10 +255,15 @@ namespace gr {
instantaneous_freq_down[i-1] = instantaneous_phase_down[i] - instantaneous_phase_down[i-1];
}
double average = std::accumulate(instantaneous_freq, instantaneous_freq + window, 0.0) / window;
double average_down = std::accumulate(instantaneous_freq_down, instantaneous_freq_down + window, 0.0) / window;
double sd = stddev(instantaneous_freq, window, average);
double sd_down = stddev(instantaneous_freq_down, window, average_down);
for(int i = 0; i < 2*slide; i++) {
double result = 0.0f;
for (int j = 0; j < window-1; j++) {
result += instantaneous_freq[i+j] * instantaneous_freq_down[j];
result += (instantaneous_freq[i+j] - average) * (instantaneous_freq_down[j] - average_down) / (sd * sd_down);
}
correlations[i] = result / (window-1);
}
@ -577,7 +599,7 @@ namespace gr {
int c_window = std::min(2*d_samples_per_symbol - i, d_samples_per_symbol);
int index_correction = 0;
double c = sliding_freq_cross_correlate(&input[i], &d_upchirp[0], c_window, 128, &index_correction);
if(c > 0.02f) {
if(c > 0.8f) {
d_debug << "Cu: " << c << std::endl;
samples_to_file("/tmp/detectb", &input[i], d_samples_per_symbol, sizeof(gr_complex));
samples_to_file("/tmp/detect", &input[i+index_correction], d_samples_per_symbol, sizeof(gr_complex));
@ -594,7 +616,7 @@ namespace gr {
double c = freq_cross_correlate(&input[0], &d_downchirp[0], d_samples_per_symbol);
d_debug << "Cd: " << c << std::endl;
if(c > 0.045f) {
if(c > 0.8f) {
d_debug << "SYNC: " << c << std::endl;
// Debug stuff
samples_to_file("/tmp/sync", &input[0], CORRELATION_SEARCH_RANGE, sizeof(gr_complex));

1
lib/decoder_impl.h
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@ -99,6 +99,7 @@ namespace gr {
void dewhiten(const uint8_t* prng);
void hamming_decode(uint8_t* out_data);
void nibble_reverse(uint8_t* out_data, int len);
double stddev(float *values, int len, float mean);
inline void phase(gr_complex* in_samples, float* out_phase, int window);