Integrate preamble search
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b6713909f7
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c17c7e060f
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@ -19,6 +19,8 @@ set(sources
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src/preamble.c
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src/transmission.h
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src/transmission.c
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src/correlator.h
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src/correlator.c
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)
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include_directories(
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144
impl/src/main.c
144
impl/src/main.c
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@ -4,11 +4,19 @@
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#include <math.h>
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#include <liquid/liquid.h>
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#include "results.h"
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#include "utils.h"
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#include "packet_mod.h"
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#include "config.h"
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#include "preamble.h"
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#include "transmission.h"
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#include "correlator.h"
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typedef enum {
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RX_STATE_ACQUISITION,
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RX_STATE_HEADER,
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RX_STATE_DATA,
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} rx_state_t;
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int main(void)
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{
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@ -93,6 +101,13 @@ int main(void)
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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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// General receiver state
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rx_state_t rx_state = RX_STATE_ACQUISITION;
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// Correlator for preamble search
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correlator_ctx_t preamble_correlator;
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correlator_init(&preamble_correlator, preamble_get_symbols(), preamble_get_symbol_count());
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for(unsigned int i = 0; i < burst_len; i++) {
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// Mix the input signal with the carrier NCO, which oscillates at the
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// frequency estimated so far.
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@ -100,68 +115,85 @@ int main(void)
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nco_crcf_step(carrier_nco);
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nco_crcf_mix_down(carrier_nco, msg_received[i], &mixed_sample);
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// run the timing synchronizer (works even with shifted frequency
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// run the timing synchronizer (works even with shifted frequency)
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unsigned int out_len;
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symsync_crcf_execute(symsync, &mixed_sample, 1, symsync_out + symsync_out_len, &out_len);
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if(out_len != 0) {
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// for all the output samples produced, run the frequency
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// estimator. This is an implementation that works with unknown
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// BPSK symbols and therefore can be used during ramp-up and
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// preamble.
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switch(rx_state) {
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case RX_STATE_ACQUISITION:
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if(out_len != 0) {
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// for all the output samples produced, run the frequency
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// estimator. This is an implementation that works with unknown
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// BPSK symbols and therefore can be used during ramp-up and
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// preamble.
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if(out_len < FREQ_EST_L) {
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memmove(phase_history,
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phase_history + out_len,
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(FREQ_EST_L-out_len) * sizeof(phase_history[0]));
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}
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for(unsigned int j = 0; j < out_len; j++) {
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float complex *psymbol = symsync_out + symsync_out_len + j;
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// square the symbol to remove BPSK ambiguity
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float phase = cargf((*psymbol) * (*psymbol));
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phase_history[FREQ_EST_L - out_len + j] = phase;
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}
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// update the frequency estimate
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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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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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if(out_len < FREQ_EST_L) {
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memmove(phase_history,
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phase_history + out_len,
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(FREQ_EST_L-out_len) * sizeof(phase_history[0]));
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}
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for(unsigned int j = 0; j < out_len; j++) {
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float complex *psymbol = symsync_out + symsync_out_len + j;
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// square the symbol to remove BPSK ambiguity
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float phase = cargf((*psymbol) * (*psymbol));
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phase_history[FREQ_EST_L - out_len + j] = phase;
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}
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// update the frequency estimate
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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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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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}
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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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break;
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case RX_STATE_HEADER:
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case RX_STATE_DATA:
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break;
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}
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// preamble search
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if(out_len != 0) {
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float complex corr_out = correlator_step(&preamble_correlator, symsync_out[symsync_out_len]);
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if(cabsf(corr_out) > 0.5f * preamble_get_symbol_count()) {
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printf("Preamble found at sample %u: %.3f > %.3f\n", i/RRC_SPS, cabsf(corr_out), 0.5f * preamble_get_symbol_count());
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}
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}
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