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NR UE: improve initial timing advance calculation from SIB19

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Before, we only considered ta_Common_r17 and the SAT position from SIB19 to compute the initial timing advance value.
This is good enough if the satellite does not move too fast (e.g. GEO satellite).

Now we also consider ta_CommonDrift_r17 and the SAT velocity together with the epoch time from SIB19.
This improves the accuracy of the initial TA computation, esp. for LEO satellite scenarios.
This commit is contained in:
Thomas Schlichter
2025-04-23 12:49:16 +00:00
parent 42bc0d4eb3
commit f1d612c01b
7 changed files with 135 additions and 55 deletions
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36
executables/nr-ue.c
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@@ -905,7 +905,8 @@ static inline int get_readBlockSize(uint16_t slot, NR_DL_FRAME_PARMS *fp) {
static inline void apply_ntn_config(PHY_VARS_NR_UE *UE,
NR_DL_FRAME_PARMS *fp,
int slot_nr,
int frame_rx,
int slot_rx,
int *duration_rx_to_tx,
int *timing_advance,
int *ntn_koffset)
@@ -913,22 +914,33 @@ static inline void apply_ntn_config(PHY_VARS_NR_UE *UE,
if (UE->ntn_config_message->update) {
UE->ntn_config_message->update = false;
double total_ta_ms = UE->ntn_config_message->ntn_config_params.ntn_total_time_advance_ms;
UE->timing_advance = fp->samples_per_subframe * total_ta_ms;
const int mu = fp->numerology_index;
const int koffset = UE->ntn_config_message->ntn_config_params.cell_specific_k_offset;
int mu = fp->numerology_index;
int koffset = UE->ntn_config_message->ntn_config_params.cell_specific_k_offset;
if (*ntn_koffset != koffset) {
*duration_rx_to_tx = NR_UE_CAPABILITY_SLOT_RX_TO_TX + (koffset << mu);
*timing_advance += fp->get_samples_slot_timestamp(slot_nr, fp, (koffset - *ntn_koffset) << mu);
*ntn_koffset = koffset;
}
*duration_rx_to_tx = NR_UE_CAPABILITY_SLOT_RX_TO_TX + (koffset << mu);
if (koffset > *ntn_koffset)
*timing_advance += fp->get_samples_slot_timestamp(slot_rx, fp, (koffset - *ntn_koffset) << mu);
else if (koffset < *ntn_koffset)
*timing_advance -= fp->get_samples_slot_timestamp(slot_rx, fp, (*ntn_koffset - koffset) << mu);
*ntn_koffset = koffset;
const int abs_subframe_tx = 10 * frame_rx + ((slot_rx + *duration_rx_to_tx) >> mu);
const int abs_subframe_epoch =
10 * UE->ntn_config_message->ntn_config_params.epoch_sfn + UE->ntn_config_message->ntn_config_params.epoch_subframe;
const int ms_since_epoch = (abs_subframe_tx - abs_subframe_epoch + 10240) % 10240;
const double total_ta_ms = UE->ntn_config_message->ntn_config_params.ntn_total_time_advance_ms;
const double total_ta_drift = UE->ntn_config_message->ntn_config_params.ntn_total_time_advance_drift; // µs/s
UE->timing_advance = fp->samples_per_subframe * (total_ta_ms + (total_ta_drift / 1000.0) * (ms_since_epoch / 1000.0));
LOG_I(PHY,
"k_offset = %d ms (%d slots), ntn_total_time_advance_ms = %f ms (%d samples)\n",
"k_offset = %d ms (%d slots), total_ta_ms = %f ms, total_ta_drift = %f µs/s, ms_since_epoch = %d ms, computed "
"timing_advance = %d samples\n",
*ntn_koffset,
*ntn_koffset << mu,
total_ta_ms,
total_ta_drift,
ms_since_epoch,
UE->timing_advance);
}
}
@@ -1227,7 +1239,7 @@ void *UE_thread(void *arg)
}
// apply new NTN timing information
apply_ntn_config(UE, fp, slot_nr, &duration_rx_to_tx, &timing_advance, &ntn_koffset);
apply_ntn_config(UE, fp, curMsg.proc.frame_rx, curMsg.proc.nr_slot_rx, &duration_rx_to_tx, &timing_advance, &ntn_koffset);
// Start TX slot processing here. It runs in parallel with RX slot processing
// in current code, DURATION_RX_TO_TX constant is the limit to get UL data to encode from a RX slot