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Integrate preamble search

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This commit is contained in:
Thomas Kolb 2022-02-01 21:35:43 +01:00
parent b6713909f7
commit c17c7e060f
2 changed files with 90 additions and 56 deletions
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2
impl/CMakeLists.txt
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@ -19,6 +19,8 @@ set(sources
src/preamble.c src/preamble.c
src/transmission.h src/transmission.h
src/transmission.c src/transmission.c
src/correlator.h
src/correlator.c
) )
include_directories( include_directories(

144
impl/src/main.c
View file

@ -4,11 +4,19 @@
#include <math.h> #include <math.h>
#include <liquid/liquid.h> #include <liquid/liquid.h>
#include "results.h"
#include "utils.h" #include "utils.h"
#include "packet_mod.h" #include "packet_mod.h"
#include "config.h" #include "config.h"
#include "preamble.h" #include "preamble.h"
#include "transmission.h" #include "transmission.h"
#include "correlator.h"
typedef enum {
RX_STATE_ACQUISITION,
RX_STATE_HEADER,
RX_STATE_DATA,
} rx_state_t;
int main(void) int main(void)
{ {
@ -93,6 +101,13 @@ int main(void)
float phase_history[FREQ_EST_L]; float phase_history[FREQ_EST_L];
memset(phase_history, 0, sizeof(phase_history)); memset(phase_history, 0, sizeof(phase_history));
// General receiver state
rx_state_t rx_state = RX_STATE_ACQUISITION;
// Correlator for preamble search
correlator_ctx_t preamble_correlator;
correlator_init(&preamble_correlator, preamble_get_symbols(), preamble_get_symbol_count());
for(unsigned int i = 0; i < burst_len; i++) { for(unsigned int i = 0; i < burst_len; i++) {
// Mix the input signal with the carrier NCO, which oscillates at the // Mix the input signal with the carrier NCO, which oscillates at the
// frequency estimated so far. // frequency estimated so far.
@ -100,68 +115,85 @@ int main(void)
nco_crcf_step(carrier_nco); nco_crcf_step(carrier_nco);
nco_crcf_mix_down(carrier_nco, msg_received[i], &mixed_sample); nco_crcf_mix_down(carrier_nco, msg_received[i], &mixed_sample);
// run the timing synchronizer (works even with shifted frequency // run the timing synchronizer (works even with shifted frequency)
unsigned int out_len; unsigned int out_len;
symsync_crcf_execute(symsync, &mixed_sample, 1, symsync_out + symsync_out_len, &out_len); symsync_crcf_execute(symsync, &mixed_sample, 1, symsync_out + symsync_out_len, &out_len);
if(out_len != 0) { switch(rx_state) {
// for all the output samples produced, run the frequency case RX_STATE_ACQUISITION:
// estimator. This is an implementation that works with unknown if(out_len != 0) {
// BPSK symbols and therefore can be used during ramp-up and // for all the output samples produced, run the frequency
// preamble. // estimator. This is an implementation that works with unknown
// BPSK symbols and therefore can be used during ramp-up and
// preamble.
if(out_len < FREQ_EST_L) { if(out_len < FREQ_EST_L) {
memmove(phase_history, memmove(phase_history,
phase_history + out_len, phase_history + out_len,
(FREQ_EST_L-out_len) * sizeof(phase_history[0])); (FREQ_EST_L-out_len) * sizeof(phase_history[0]));
} }
for(unsigned int j = 0; j < out_len; j++) { for(unsigned int j = 0; j < out_len; j++) {
float complex *psymbol = symsync_out + symsync_out_len + j; float complex *psymbol = symsync_out + symsync_out_len + j;
// square the symbol to remove BPSK ambiguity // square the symbol to remove BPSK ambiguity
float phase = cargf((*psymbol) * (*psymbol)); float phase = cargf((*psymbol) * (*psymbol));
phase_history[FREQ_EST_L - out_len + j] = phase; phase_history[FREQ_EST_L - out_len + j] = phase;
} }
// update the frequency estimate // update the frequency estimate
if(((i/RRC_SPS) % FREQ_EST_L) == 0) { if(((i/RRC_SPS) % FREQ_EST_L) == 0) {
float unwrapped_phase_history[FREQ_EST_L]; float unwrapped_phase_history[FREQ_EST_L];
memcpy(unwrapped_phase_history, phase_history, sizeof(unwrapped_phase_history)); memcpy(unwrapped_phase_history, phase_history, sizeof(unwrapped_phase_history));
liquid_unwrap_phase(unwrapped_phase_history, FREQ_EST_L); liquid_unwrap_phase(unwrapped_phase_history, FREQ_EST_L);
// calculate slope of LMS-fitted line // calculate slope of LMS-fitted line
float mean_index = (FREQ_EST_L-1) / 2.0f; float mean_index = (FREQ_EST_L-1) / 2.0f;
float mean_phase = 0.0f; float mean_phase = 0.0f;
for(unsigned int j = 0; j < FREQ_EST_L; j++) { for(unsigned int j = 0; j < FREQ_EST_L; j++) {
mean_phase += unwrapped_phase_history[j]; mean_phase += unwrapped_phase_history[j];
} }
mean_phase /= FREQ_EST_L; mean_phase /= FREQ_EST_L;
float numerator = 0.0f; float numerator = 0.0f;
float denominator = 0.0f; float denominator = 0.0f;
for(unsigned int j = 0; j < FREQ_EST_L; j++) { for(unsigned int j = 0; j < FREQ_EST_L; j++) {
float delta_index = j - mean_index; float delta_index = j - mean_index;
numerator += delta_index * (unwrapped_phase_history[j] - mean_phase); numerator += delta_index * (unwrapped_phase_history[j] - mean_phase);
denominator += delta_index*delta_index; denominator += delta_index*delta_index;
} }
float lms_phase_change = numerator / denominator; float lms_phase_change = numerator / denominator;
float freq_adjustment = (lms_phase_change / RRC_SPS / 2) * 0.3f; float freq_adjustment = (lms_phase_change / RRC_SPS / 2) * 0.3f;
nco_crcf_adjust_frequency(carrier_nco, freq_adjustment); nco_crcf_adjust_frequency(carrier_nco, freq_adjustment);
printf("Frequency adjustment: %.6f - carrier frequency: %.6f\n", freq_adjustment, nco_crcf_get_frequency(carrier_nco)); printf("Frequency adjustment: %.6f - carrier frequency: %.6f\n", freq_adjustment, nco_crcf_get_frequency(carrier_nco));
if(i/RRC_SPS == 2*FREQ_EST_L) { if(i/RRC_SPS == 2*FREQ_EST_L) {
float complex tmp[FREQ_EST_L]; float complex tmp[FREQ_EST_L];
for(unsigned int j = 0; j < FREQ_EST_L; j++) { for(unsigned int j = 0; j < FREQ_EST_L; j++) {
tmp[j] = unwrapped_phase_history[j]; tmp[j] = unwrapped_phase_history[j];
}
dump_array_cf(tmp, FREQ_EST_L, 1.0f, "/tmp/freq_est.cpx");
printf("MARK\n");
}
} }
dump_array_cf(tmp, FREQ_EST_L, 1.0f, "/tmp/freq_est.cpx");
printf("MARK\n");
} }
break;
case RX_STATE_HEADER:
case RX_STATE_DATA:
break;
}
// preamble search
if(out_len != 0) {
float complex corr_out = correlator_step(&preamble_correlator, symsync_out[symsync_out_len]);
if(cabsf(corr_out) > 0.5f * preamble_get_symbol_count()) {
printf("Preamble found at sample %u: %.3f > %.3f\n", i/RRC_SPS, cabsf(corr_out), 0.5f * preamble_get_symbol_count());
} }
} }