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Added more comments for better understanding in NR PDCCH DMRS

This commit is contained in:
Xavier Arteaga 2021-04-12 10:20:31 +02:00 committed by Andre Puschmann
parent bc1b14efea
commit dd26c6a90e
1 changed files with 27 additions and 17 deletions
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44
lib/src/phy/ch_estimation/dmrs_pdcch.c
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@ -437,20 +437,23 @@ int srsran_dmrs_pdcch_get_measure(const srsran_dmrs_pdcch_estimator_t* q,
uint32_t pilot_idx = (dci_location->ncce * 18) / q->coreset.duration; uint32_t pilot_idx = (dci_location->ncce * 18) / q->coreset.duration;
uint32_t nof_pilots = (L * 18) / q->coreset.duration; uint32_t nof_pilots = (L * 18) / q->coreset.duration;
float rsrp = 0.0f; // Initialise measurements
float epre = 0.0f; float rsrp = 0.0f; //< Averages linear RSRP
float cfo = 0.0f; float epre = 0.0f; //< Averages linear EPRE
float sync_err = 0.0f; float cfo_avg_Hz = 0.0f; //< Averages CFO in Radians
cf_t corr[SRSRAN_CORESET_DURATION_MAX] = {}; float sync_err_avg = 0.0f; //< Averages synchronization
cf_t corr[SRSRAN_CORESET_DURATION_MAX] = {}; //< Saves correlation for the different symbols
// Iterate the CORESET duration
for (uint32_t l = 0; l < q->coreset.duration; l++) { for (uint32_t l = 0; l < q->coreset.duration; l++) {
if (SRSRAN_DEBUG_ENABLED && srsran_verbose >= SRSRAN_VERBOSE_DEBUG && !handler_registered) { if (SRSRAN_DEBUG_ENABLED && srsran_verbose >= SRSRAN_VERBOSE_DEBUG && !handler_registered) {
DMRS_PDCCH_DEBUG_RX("Measuring PDCCH l=%d; lse=", l); DMRS_PDCCH_DEBUG_RX("Measuring PDCCH l=%d; lse=", l);
srsran_vec_fprint_c(stdout, &q->lse[l][pilot_idx], nof_pilots); srsran_vec_fprint_c(stdout, &q->lse[l][pilot_idx], nof_pilots);
} }
// Measure synchronization error // Measure synchronization error and accumulate for average
float tmp_sync_err = srsran_vec_estimate_frequency(&q->lse[l][pilot_idx], nof_pilots); float tmp_sync_err = srsran_vec_estimate_frequency(&q->lse[l][pilot_idx], nof_pilots);
sync_err += tmp_sync_err; sync_err_avg += tmp_sync_err;
#if DMRS_PDCCH_SYNC_PRECOMPENSATE_MEAS #if DMRS_PDCCH_SYNC_PRECOMPENSATE_MEAS
cf_t tmp[DMRS_PDCCH_MAX_NOF_PILOTS_CANDIDATE]; cf_t tmp[DMRS_PDCCH_MAX_NOF_PILOTS_CANDIDATE];
@ -472,26 +475,33 @@ int srsran_dmrs_pdcch_get_measure(const srsran_dmrs_pdcch_estimator_t* q,
// Measure CFO only from the second and third symbols // Measure CFO only from the second and third symbols
if (l != 0) { if (l != 0) {
cfo += cargf(corr[l] * conjf(corr[l - 1])); // Calculates the time between the previous and the current symbol
float Ts = srsran_symbol_distance_s(l - 1, l, q->carrier.numerology);
if (isnormal(Ts)) {
// Compute phase difference between symbols and convert to Hz
cfo_avg_Hz += cargf(corr[l] * conjf(corr[l - 1])) / (2.0f * (float)M_PI * Ts);
}
} }
} }
// Store results
measure->rsrp = rsrp / (float)q->coreset.duration;
measure->epre = epre / (float)q->coreset.duration;
if (q->coreset.duration > 1) { if (q->coreset.duration > 1) {
cfo /= (float)(q->coreset.duration - 1); // Protected zero division
measure->cfo_hz /= (float)(q->coreset.duration - 1);
} else {
// There are not enough symbols for computing CFO, set to NAN
measure->cfo_hz = NAN;
} }
// Symbol time, including cyclic prefix. Required for CFO estimation
float Ts = (71.3541666667f / (float)(1 << q->carrier.numerology));
measure->rsrp = rsrp / (float)q->coreset.duration;
measure->epre = epre / (float)q->coreset.duration;
measure->cfo_hz = cfo / (2.0f * (float)M_PI * Ts);
measure->sync_error_us = measure->sync_error_us =
sync_err / (4.0e-6f * (float)q->coreset.duration * SRSRAN_SUBC_SPACING_NR(q->carrier.numerology)); sync_err_avg / (4.0e-6f * (float)q->coreset.duration * SRSRAN_SUBC_SPACING_NR(q->carrier.numerology));
// Convert power measurements into logarithmic scale
measure->rsrp_dBfs = srsran_convert_power_to_dB(measure->rsrp); measure->rsrp_dBfs = srsran_convert_power_to_dB(measure->rsrp);
measure->epre_dBfs = srsran_convert_power_to_dB(measure->epre); measure->epre_dBfs = srsran_convert_power_to_dB(measure->epre);
// Store DMRS correlation
if (isnormal(measure->rsrp) && isnormal(measure->epre)) { if (isnormal(measure->rsrp) && isnormal(measure->epre)) {
measure->norm_corr = measure->rsrp / measure->epre; measure->norm_corr = measure->rsrp / measure->epre;
} else { } else {