Make initial frequency sync much faster
The NCO frequency is now only adjusted every 8 symbols. That means that the frequency error over the last 8 symbols before the adjustment is (almost) constant, giving a good estimation result. Therefore, the adjustment factor can be much larger than previously, leading to faster acquisition time.
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@ -17,7 +17,7 @@
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#define RRC_DELAY 7 // delay in symbols
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#define RRC_BETA 0.2f
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#define TRANSMISSION_RAMP_UP_LEN 128 // symbols
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#define TRANSMISSION_RAMP_UP_LEN 64 // symbols
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#define TRANSMISSION_RAMP_DOWN_LEN 32 // symbols
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#endif // CONFIG_H
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@ -22,7 +22,7 @@ int main(void)
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float snr = 50.0f;
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channel_cccf_add_awgn(channel, -snr, snr);
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channel_cccf_add_carrier_offset(channel, 0.10f, 1.00f);
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channel_cccf_add_carrier_offset(channel, 0.20f, 1.00f);
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packet_mod_ctx_t pmod;
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@ -89,7 +89,7 @@ int main(void)
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float complex symsync_out[burst_len];
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unsigned int symsync_out_len = 0;
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#define FREQ_EST_L 16
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#define FREQ_EST_L 8
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float phase_history[FREQ_EST_L];
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memset(phase_history, 0, sizeof(phase_history));
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@ -126,46 +126,49 @@ int main(void)
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}
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// update the frequency estimate
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float unwrapped_phase_history[FREQ_EST_L];
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memcpy(unwrapped_phase_history, phase_history, sizeof(unwrapped_phase_history));
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liquid_unwrap_phase(unwrapped_phase_history, FREQ_EST_L);
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if(((i/RRC_SPS) % FREQ_EST_L) == 0) {
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float unwrapped_phase_history[FREQ_EST_L];
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memcpy(unwrapped_phase_history, phase_history, sizeof(unwrapped_phase_history));
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liquid_unwrap_phase(unwrapped_phase_history, FREQ_EST_L);
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// calculate slope of LMS-fitted line
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float mean_index = (FREQ_EST_L-1) / 2.0f;
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float mean_phase = 0.0f;
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for(unsigned int j = 0; j < FREQ_EST_L; j++) {
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mean_phase += unwrapped_phase_history[j];
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}
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mean_phase /= FREQ_EST_L;
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float numerator = 0.0f;
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float denominator = 0.0f;
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for(unsigned int j = 0; j < FREQ_EST_L; j++) {
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float delta_index = j - mean_index;
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numerator += delta_index * (unwrapped_phase_history[j] - mean_phase);
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denominator += delta_index*delta_index;
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}
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float lms_phase_change = numerator / denominator;
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nco_crcf_adjust_frequency(carrier_nco, lms_phase_change / RRC_SPS / 32);
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printf("Phase change: %.6f - carrier frequency: %.6f\n", lms_phase_change, nco_crcf_get_frequency(carrier_nco));
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if(i/RRC_SPS == 2*FREQ_EST_L) {
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float complex tmp[FREQ_EST_L];
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// calculate slope of LMS-fitted line
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float mean_index = (FREQ_EST_L-1) / 2.0f;
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float mean_phase = 0.0f;
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for(unsigned int j = 0; j < FREQ_EST_L; j++) {
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tmp[j] = unwrapped_phase_history[j];
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mean_phase += unwrapped_phase_history[j];
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}
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mean_phase /= FREQ_EST_L;
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float numerator = 0.0f;
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float denominator = 0.0f;
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for(unsigned int j = 0; j < FREQ_EST_L; j++) {
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float delta_index = j - mean_index;
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numerator += delta_index * (unwrapped_phase_history[j] - mean_phase);
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denominator += delta_index*delta_index;
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}
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float lms_phase_change = numerator / denominator;
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float freq_adjustment = (lms_phase_change / RRC_SPS / 2) * 0.3f;
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nco_crcf_adjust_frequency(carrier_nco, freq_adjustment);
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printf("Frequency adjustment: %.6f - carrier frequency: %.6f\n", freq_adjustment, nco_crcf_get_frequency(carrier_nco));
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if(i/RRC_SPS == 2*FREQ_EST_L) {
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float complex tmp[FREQ_EST_L];
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for(unsigned int j = 0; j < FREQ_EST_L; j++) {
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tmp[j] = unwrapped_phase_history[j];
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}
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dump_array_cf(tmp, FREQ_EST_L, 1.0f, "/tmp/freq_est.cpx");
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printf("MARK\n");
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}
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dump_array_cf(tmp, FREQ_EST_L, 1.0f, "/tmp/freq_est.cpx");
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printf("MARK\n");
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}
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}
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symsync_out_len += out_len;
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}
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dump_array_cf(symsync_out, symsync_out_len, 1.0f, "/tmp/rx.cpx");
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dump_array_cf(symsync_out, symsync_out_len, 1.0f, "/tmp/synced.cpx");
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#if 0
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// demodulate
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