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main: restructure state management; evaluate a found preamble

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This commit is contained in:
Thomas Kolb 2022-02-03 22:18:24 +01:00
parent 423f1d6416
commit 465d9a1c26
1 changed files with 114 additions and 74 deletions
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188
impl/src/main.c
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@ -18,6 +18,17 @@ typedef enum {
RX_STATE_DATA,
} rx_state_t;
void print_complex_array(const char *varname, float complex const *array, size_t len)
{
printf("%s=np.array([%f%+fj", varname, crealf(array[0]), cimagf(array[0]));
for(size_t k = 1; k < len; k++) {
printf(", %f%+fj", crealf(array[k]), cimagf(array[k]));
}
printf("])\n");
}
int main(void)
{
uint8_t msg_org[] = "Hello Liquid! This is the message to transmit. Hopefully it can be decoded correctly...";
@ -28,7 +39,7 @@ int main(void)
channel_cccf channel = channel_cccf_create();
float snr = 50.0f;
float snr = 20.0f;
channel_cccf_add_awgn(channel, -snr, snr);
channel_cccf_add_carrier_offset(channel, 0.20f, 1.00f);
@ -119,81 +130,110 @@ int main(void)
unsigned int out_len;
symsync_crcf_execute(symsync, &mixed_sample, 1, symsync_out + symsync_out_len, &out_len);
switch(rx_state) {
case RX_STATE_ACQUISITION:
if(out_len != 0) {
// for all the output samples produced, run the frequency
// 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) {
memmove(phase_history,
phase_history + out_len,
(FREQ_EST_L-out_len) * sizeof(phase_history[0]));
}
for(unsigned int j = 0; j < out_len; j++) {
float complex *psymbol = symsync_out + symsync_out_len + j;
// square the symbol to remove BPSK ambiguity
float phase = cargf((*psymbol) * (*psymbol));
phase_history[FREQ_EST_L - out_len + j] = phase;
}
// update the frequency estimate
if(((i/RRC_SPS) % FREQ_EST_L) == 0) {
float unwrapped_phase_history[FREQ_EST_L];
memcpy(unwrapped_phase_history, phase_history, sizeof(unwrapped_phase_history));
liquid_unwrap_phase(unwrapped_phase_history, FREQ_EST_L);
// calculate slope of LMS-fitted line
float mean_index = (FREQ_EST_L-1) / 2.0f;
float mean_phase = 0.0f;
for(unsigned int j = 0; j < FREQ_EST_L; j++) {
mean_phase += unwrapped_phase_history[j];
}
mean_phase /= FREQ_EST_L;
float numerator = 0.0f;
float denominator = 0.0f;
for(unsigned int j = 0; j < FREQ_EST_L; j++) {
float delta_index = j - mean_index;
numerator += delta_index * (unwrapped_phase_history[j] - mean_phase);
denominator += delta_index*delta_index;
}
float lms_phase_change = numerator / denominator;
float freq_adjustment = (lms_phase_change / RRC_SPS / 2) * 0.3f;
nco_crcf_adjust_frequency(carrier_nco, freq_adjustment);
printf("Frequency adjustment: %.6f - carrier frequency: %.6f\n", freq_adjustment, nco_crcf_get_frequency(carrier_nco));
if(i/RRC_SPS == 2*FREQ_EST_L) {
float complex tmp[FREQ_EST_L];
for(unsigned int j = 0; j < FREQ_EST_L; j++) {
tmp[j] = unwrapped_phase_history[j];
}
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]);
float complex corr_out;
switch(rx_state) {
// Try to acquire packets by synchronizing the frequency
// (symbol-independent search) and correlating the preamble.
case RX_STATE_ACQUISITION:
// preamble search
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());
if(cabsf(corr_out) > 0.5f * preamble_get_symbol_count()) {
// Preamble found!
printf("Preamble found at symbol %u: %.3f > %.3f\n", i/RRC_SPS, cabsf(corr_out), 0.5f * preamble_get_symbol_count());
float mean_phase_error = correlator_get_mean_phase_deviation(&preamble_correlator);
float mean_frequency_error = correlator_get_mean_frequency_deviation(&preamble_correlator);
printf("Preamble phase deviation: %.6f rad\n", mean_phase_error);
printf("Preamble frequency deviation: %.6f rad/symbol\n", mean_frequency_error);
// adjust the frequency and phase of the NCO with the estimations from the preamble
nco_crcf_adjust_frequency(carrier_nco, -mean_frequency_error / RRC_SPS);
nco_crcf_adjust_phase(carrier_nco, mean_phase_error);
printf("New estimated carrier frequency: %.6f\n", nco_crcf_get_frequency(carrier_nco));
float complex input_history[preamble_get_symbol_count()];
correlator_get_input_history(&preamble_correlator, input_history);
printf("import numpy as np\n");
printf("import matplotlib.pyplot as pp\n");
print_complex_array("pre", preamble_get_symbols(), preamble_get_symbol_count());
print_complex_array("recv", input_history, preamble_get_symbol_count());
printf("pp.plot(recv * pre.conj())\n");
printf("pp.show()\n");
// receive and decode the header
rx_state = RX_STATE_HEADER;
} else {
// preamble not found.
// for all the output samples produced, run the frequency
// 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) {
memmove(phase_history,
phase_history + out_len,
(FREQ_EST_L-out_len) * sizeof(phase_history[0]));
}
for(unsigned int j = 0; j < out_len; j++) {
float complex *psymbol = symsync_out + symsync_out_len + j;
// square the symbol to remove BPSK ambiguity
float phase = cargf((*psymbol) * (*psymbol));
phase_history[FREQ_EST_L - out_len + j] = phase;
}
// update the frequency estimate
if(((i/RRC_SPS) % FREQ_EST_L) == 0) {
float unwrapped_phase_history[FREQ_EST_L];
memcpy(unwrapped_phase_history, phase_history, sizeof(unwrapped_phase_history));
liquid_unwrap_phase(unwrapped_phase_history, FREQ_EST_L);
// calculate slope of LMS-fitted line
float mean_index = (FREQ_EST_L-1) / 2.0f;
float mean_phase = 0.0f;
for(unsigned int j = 0; j < FREQ_EST_L; j++) {
mean_phase += unwrapped_phase_history[j];
}
mean_phase /= FREQ_EST_L;
float numerator = 0.0f;
float denominator = 0.0f;
for(unsigned int j = 0; j < FREQ_EST_L; j++) {
float delta_index = j - mean_index;
numerator += delta_index * (unwrapped_phase_history[j] - mean_phase);
denominator += delta_index*delta_index;
}
float lms_phase_change = numerator / denominator;
float freq_adjustment = (lms_phase_change / RRC_SPS / 2) * 0.5f;
nco_crcf_adjust_frequency(carrier_nco, freq_adjustment);
printf("Frequency adjustment: %.6f - carrier frequency: %.6f\n", freq_adjustment, nco_crcf_get_frequency(carrier_nco));
if(i/RRC_SPS == 2*FREQ_EST_L) {
float complex tmp[FREQ_EST_L];
for(unsigned int j = 0; j < FREQ_EST_L; j++) {
tmp[j] = unwrapped_phase_history[j];
}
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;
}
}