82 lines
2.5 KiB
C++
82 lines
2.5 KiB
C++
#include "fft-beacon-finder.h"
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FFTBeaconFinder::FFTBeaconFinder(int samplingrate) {
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this->samplingrate = samplingrate;
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coarse_correction = nco_crcf_create(LIQUID_NCO);
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nco_crcf_set_frequency(coarse_correction, 0.0f);
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fft = fft_create_plan(FFT_LEN, fft_in, fft_out, LIQUID_FFT_FORWARD, 0);
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pos = 0;
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next_fft_in = 0;
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}
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std::complex<float> FFTBeaconFinder::work(std::complex<float> in) {
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if (next_fft_in <= 0) {
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fft_in[pos] = in;
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pos += 1;
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if (pos == FFT_LEN) {
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pos = 0;
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fft_execute(fft);
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float fft_max = std::abs(fft_out[0]);
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for (int i = 0; i < FFT_LEN; i++) {
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float mag = std::abs(fft_out[i]);
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if (mag > fft_max) {
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fft_max = mag;
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}
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}
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float max_levels = 0;
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int max_center = 0;
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for (int bin = -50; bin <= 50; bin++) {
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int center_idx = spectral_bin_to_fft_idx(bin);
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float center_val = std::abs(fft_out[center_idx]) / fft_max;
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if (center_val > 0.25) {
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printf("Found peak candidate at %d\n", bin);
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int left_idx = spectral_bin_to_fft_idx(bin - 127);
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int right_idx = spectral_bin_to_fft_idx(bin + 127);
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float left_val = std::abs(fft_out[left_idx]) / fft_max;
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float right_val = std::abs(fft_out[right_idx]) / fft_max;
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if (center_val + left_val + right_val > max_levels) {
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max_levels = center_val + left_val + right_val;
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max_center = bin;
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}
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}
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}
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if (max_levels > 0.0) {
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float center_freq = max_center * samplingrate / FFT_LEN;
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printf("Found center at %f\n", center_freq);
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nco_crcf_set_frequency(
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coarse_correction,
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-(2 * M_PI * center_freq) / samplingrate);
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}
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next_fft_in = samplingrate / 4;
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}
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} else {
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next_fft_in--;
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}
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std::complex<float> y;
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// increment internal phase
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nco_crcf_step(coarse_correction);
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// compute complex exponential
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nco_crcf_cexpf(coarse_correction, &y);
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return y * in;
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}
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int FFTBeaconFinder::spectral_bin_to_fft_idx(int bin) {
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if (bin == 0) {
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return FFT_LEN / 2;
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} else if (bin > 0) {
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return bin - 1;
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} else {
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return bin + FFT_LEN;
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}
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}
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