NR UE: improve physical layer for NTN (esp. LEO) reestablishment and HO

executables/nr-ue.c

@@ -497,6 +497,8 @@ static uint64_t get_carrier_frequency(const int N_RB, const int mu, const uint32
   return carrier_freq;
 }
 
+static void apply_ntn_timing_advance_and_doppler(PHY_VARS_NR_UE *UE, const NR_DL_FRAME_PARMS *fp, int abs_subframe_tx);
+
 static int handle_sync_req_from_mac(PHY_VARS_NR_UE *UE)
 {
   NR_DL_FRAME_PARMS *fp = &UE->frame_parms;
@@ -521,6 +523,12 @@ static int handle_sync_req_from_mac(PHY_VARS_NR_UE *UE)
       init_symbol_rotation(fp);
     }
 
+    // Apply Doppler based on NTN-Config for target cell
+    if (UE->target_Nid_cell != fp->Nid_cell)
+      apply_ntn_timing_advance_and_doppler(UE, fp, -1);
+    // Apply NTN DL Doppler as initial FO
+    UE->initial_fo = UE->dl_Doppler_shift;
+
     /* Clearing UE harq while DL actors are active causes race condition.
         So we let the current execution to complete here.*/
     for (int i = 0; i < get_nrUE_params()->num_dl_actors; i++) {
@@ -727,13 +735,39 @@ static inline int get_readBlockSize(uint16_t slot, NR_DL_FRAME_PARMS *fp) {
   return rem_samples + next_slot_first_symbol;
 }
 
+static void fix_ntn_epoch_hfn(PHY_VARS_NR_UE *UE, int hfn, int frame)
+{
+  const int epoch_frame = UE->ntn_config_message->ntn_config_params.epoch_sfn;
+  const int diff1 = (frame - epoch_frame + 1024) % 1024;
+  const int diff2 = (epoch_frame - frame + 1024) % 1024;
+
+  int *epoch_hfn = &UE->ntn_config_message->ntn_config_params.epoch_hfn;
+  if (diff1 < diff2) { // epoch_frame in the past
+    LOG_I(PHY, "epoch is %d frames in the past\n", diff1);
+    if (epoch_frame <= frame)
+      *epoch_hfn = hfn;
+    else
+      *epoch_hfn = hfn - 1;
+  } else { // epoch_frame in the future
+    LOG_I(PHY, "epoch is %d frames in the future\n", diff2);
+    if (epoch_frame >= frame)
+      *epoch_hfn = hfn;
+    else
+      *epoch_hfn = hfn + 1;
+  }
+  LOG_I(PHY, "setting epoch_hfn = %d\n", *epoch_hfn);
+}
+
 #define SPEED_OF_LIGHT 299792458
+
+// calculate TA and Doppler based on the NTN-Config, if abs_subframe_tx < 0 then apply only Doppler
 static void apply_ntn_timing_advance_and_doppler(PHY_VARS_NR_UE *UE, const NR_DL_FRAME_PARMS *fp, int abs_subframe_tx)
 {
   const fapi_nr_dl_ntn_config_command_pdu *ntn_config_params = &UE->ntn_config_message->ntn_config_params;
 
   // Handle terrestrial networks
   if (ntn_config_params->cell_specific_k_offset == 0) {
+    if (abs_subframe_tx >= 0)
       UE->timing_advance_ntn = 0;
     UE->dl_Doppler_shift = 0;
     UE->ul_Doppler_shift = 0;
@@ -743,7 +777,7 @@ static void apply_ntn_timing_advance_and_doppler(PHY_VARS_NR_UE *UE, const NR_DL
   const int abs_subframe_epoch = ntn_config_params->epoch_subframe
                                + ntn_config_params->epoch_sfn * 10
                                + ntn_config_params->epoch_hfn * 10240;
-  const int ms_since_epoch = abs_subframe_tx - abs_subframe_epoch;
+  const int ms_since_epoch = abs_subframe_tx < 0 ? 0 : abs_subframe_tx - abs_subframe_epoch;
 
   const position_t pos_sat_0 = ntn_config_params->pos_sat_0;
   const position_t vel_sat_0 = ntn_config_params->vel_sat_0;
@@ -797,22 +831,26 @@ static void apply_ntn_timing_advance_and_doppler(PHY_VARS_NR_UE *UE, const NR_DL
   const double N_common_ta_drift = ntn_config_params->N_common_ta_drift;
   const double N_common_ta_drift_variant = ntn_config_params->N_common_ta_drift_variant;
 
-  UE->timing_advance_ntn = (N_UE_TA_adj + N_common_ta_adj
-                          + N_common_ta_drift * ms_since_epoch / 1e6
+  if (abs_subframe_tx >= 0) {
+    UE->timing_advance_ntn = (N_UE_TA_adj + N_common_ta_adj + N_common_ta_drift * ms_since_epoch / 1e6
                               + N_common_ta_drift_variant * ((int64_t)ms_since_epoch * ms_since_epoch) / 1e9)
                              * fp->samples_per_subframe;
+  }
 
   UE->freq_offset -= dl_Doppler_shift - UE->dl_Doppler_shift;
   UE->dl_Doppler_shift = dl_Doppler_shift;
   UE->ul_Doppler_shift = ul_Doppler_shift;
 
-  LOG_D(PHY,
+  if (abs_subframe_tx < 0) {
+    LOG_I(PHY,
           "satellite velocity towards UE = %f m/s, DL Doppler shift = %f kHz, UL Doppler shift = %f kHz\n",
           vel_sat_ue,
           dl_Doppler_shift / 1000,
           ul_Doppler_shift / 1000);
+  }
 }
 
+// apply values based on the NTN-Config
 static void apply_ntn_config(PHY_VARS_NR_UE *UE,
                              NR_DL_FRAME_PARMS *fp,
                              int hfn_rx,
@@ -885,9 +923,14 @@ void *UE_thread(void *arg)
   notifiedFIFO_t freeBlocks;
   initNotifiedFIFO_nothreadSafe(&freeBlocks);
 
-  double ntn_init_time_drift = get_nrUE_params()->ntn_init_time_drift;
-  int ntn_koffset = 0;
+  const double ntn_init_time_drift = get_nrUE_params()->ntn_init_time_drift;
+  if (get_nrUE_params()->time_sync_I)
+    // ntn_init_time_drift is in µs/s, max_pos_acc * time_sync_I is in samples/frame
+    UE->max_pos_acc = ntn_init_time_drift * 1e-6 * fp->samples_per_frame / get_nrUE_params()->time_sync_I;
+  else
+    UE->max_pos_acc = 0;
 
+  int ntn_koffset = 0;
   int duration_rx_to_tx = NR_UE_CAPABILITY_SLOT_RX_TO_TX;
   int timing_advance = UE->timing_advance + UE->timing_advance_ntn;
   UE->N_TA_offset = determine_N_TA_offset(UE);
@@ -983,10 +1026,6 @@ void *UE_thread(void *arg)
       syncMsg->UE = UE;
       memset(&syncMsg->proc, 0, sizeof(syncMsg->proc));
       pushNotifiedFIFO(&UE->sync_actor.fifo, Msg);
-      if (ntn_koffset == 0) { // reset timing_advance for TN
-        timing_advance = 0;
-        UE->timing_advance = 0;
-      }
       trashed_frames = 0;
       syncRunning = true;
       continue;
@@ -996,13 +1035,8 @@ void *UE_thread(void *arg)
       stream_status = STREAM_STATUS_SYNCING;
       syncInFrame(UE, &sync_timestamp, duration_rx_to_tx, intialSyncOffset);
       openair0_write_reorder_clear_context(&UE->rfdevice);
-      if (get_nrUE_params()->time_sync_I)
-        // ntn_init_time_drift is in µs/s, max_pos_acc * time_sync_I is in samples/frame
-        UE->max_pos_acc = ntn_init_time_drift * 1e-6 * fp->samples_per_frame / get_nrUE_params()->time_sync_I;
-      else
-        UE->max_pos_acc = 0;
       shiftForNextFrame = -(UE->init_sync_frame + trashed_frames + 2) * UE->max_pos_acc * get_nrUE_params()->time_sync_I; // compensate for the time drift that happened during initial sync
-      LOG_D(PHY, "max_pos_acc = %d, shiftForNextFrame = %d\n", UE->max_pos_acc, shiftForNextFrame);
+      LOG_I(PHY, "max_pos_acc = %d, shiftForNextFrame = %d\n", UE->max_pos_acc, shiftForNextFrame);
       // read in first symbol
       AssertFatal(fp->ofdm_symbol_size + fp->nb_prefix_samples0
                       == UE->rfdevice.trx_read_func(&UE->rfdevice,
@@ -1020,6 +1054,18 @@ void *UE_thread(void *arg)
         // Set to the slot where the SL-SSB was decoded
         absolute_slot += UE->SL_UE_PHY_PARAMS.sync_params.slot_offset;
       }
+      // With the correct frame and slot numbers, we can now fix the UL timing
+      const int frame_rx = (absolute_slot / nb_slot_frame) % 1024;
+      const int hfn_rx = (absolute_slot / nb_slot_frame) / 1024;
+      fix_ntn_epoch_hfn(UE, hfn_rx, frame_rx);
+      if (UE->ntn_config_message->update) {
+        apply_ntn_config(UE, fp, hfn_rx, frame_rx, 0, &duration_rx_to_tx, &timing_advance, &ntn_koffset);
+      } else {
+        const int mu = fp->numerology_index;
+        const int abs_subframe_tx = 10240 * hfn_rx + 10 * frame_rx + (duration_rx_to_tx >> mu);
+        apply_ntn_timing_advance_and_doppler(UE, fp, abs_subframe_tx);
+      }
+      UE->timing_advance = 0;
       // We have resynchronized, maybe after RF loss so we need to purge any existing context
       memset(tx_wait_for_dlsch, 0, sizeof(tx_wait_for_dlsch));
       for (int i = 0; i < NUM_PROCESS_SLOT_TX_BARRIERS; i++) {
@@ -1134,6 +1180,11 @@ void *UE_thread(void *arg)
       writeBlockSize -= new_N_TA_offset - UE->N_TA_offset;
       UE->N_TA_offset = new_N_TA_offset;
     }
+    if (writeBlockSize < 0) {
+      timing_advance += writeBlockSize - 1;
+      LOG_I(PHY, "writeBlockSize is %d, setting it to 1 and changing timing_advance to %d\n", writeBlockSize, timing_advance);
+      writeBlockSize = 1;
+    }
 
     if (curMsg.proc.nr_slot_rx == 0)
       nr_ue_rrc_timer_trigger(UE->Mod_id, curMsg.proc.hfn_rx, curMsg.proc.frame_rx, curMsg.proc.gNB_id);
@@ -1166,7 +1217,7 @@ void *UE_thread(void *arg)
     curMsgTx->absolute_deadline_us = absolute_deadline_us;
 
     int slot = curMsgTx->proc.nr_slot_tx;
-    int slot_and_frame = slot + curMsgTx->proc.frame_tx * UE->frame_parms.slots_per_frame;
+    int slot_and_frame = slot + curMsgTx->proc.frame_tx * nb_slot_frame;
     int next_tx_slot_and_frame = absolute_slot + duration_rx_to_tx + 1;
     int wait_for_prev_slot = stream_status == STREAM_STATUS_SYNCED ? 1 : 0;