UE changes: Handle T430 expiry in RRC, MAC

SPEC 38.331 section 5.2.2.6
Inform MAC that UL SYNC got lost because of T430 expiry
- Send message NR_MAC_RRC_CONFIG_RESET with cause UL_SYNC_LOST_T430_EXPIRY to MAC
Reacquire SIB19 after T430 expiry

This is not checked in this commit
- RACH needs to be performed through probably PDCCH order to reobtain UL-SYNC
- system usecase involving Recovery from T430 expiry not tested yet as that requires changes on gNB side.

openair2/LAYER2/NR_MAC_UE/config_ue.c

@@ -1718,6 +1718,11 @@ void nr_rrc_mac_config_req_reset(module_id_t module_id, NR_UE_MAC_reset_cause_t
       sync_req.ssb_bw_scan = false;
       nr_ue_send_synch_request(mac, module_id, 0, &sync_req);
       break;
+    case UL_SYNC_LOST_T430_EXPIRED:
+      // TS 38.331 Section 5.2.2.6, TS 38.321 Section 5.2a
+      // Flush all HARQ buffers and Stop UL transmissions
+      handle_ulsync_loss(mac);
+      break;
     default:
       AssertFatal(false, "Invalid MAC reset cause %d\n", cause);
   }

openair2/LAYER2/NR_MAC_UE/mac_defs.h

@@ -196,7 +196,8 @@ typedef enum {
   GO_TO_IDLE,
   DETACH,
   T300_EXPIRY,
-  RE_ESTABLISHMENT
+  RE_ESTABLISHMENT,
+  UL_SYNC_LOST_T430_EXPIRED
 } NR_UE_MAC_reset_cause_t;
 
 typedef struct {

openair2/LAYER2/NR_MAC_UE/mac_proto.h

@@ -323,6 +323,7 @@ void nr_Msg3_transmitted(NR_UE_MAC_INST_t *mac, uint8_t CC_id, frame_t frameP, s
 void trigger_MAC_UE_RA(NR_UE_MAC_INST_t *mac, dci_pdu_rel15_t *pdcch_order);
 void nr_get_Msg3_MsgA_PUSCH_payload(NR_UE_MAC_INST_t *mac, uint8_t *buf, int TBS_max);
 void handle_time_alignment_timer_expired(NR_UE_MAC_INST_t *mac);
+void handle_ulsync_loss(NR_UE_MAC_INST_t *mac);
 int8_t nr_ue_process_dci_freq_dom_resource_assignment(nfapi_nr_ue_pusch_pdu_t *pusch_config_pdu,
                                                       fapi_nr_dl_config_dlsch_pdu_rel15_t *dlsch_config_pdu,
                                                       NR_PDSCH_Config_t *pdsch_Config,

openair2/LAYER2/NR_MAC_UE/nr_ue_scheduler.c

@@ -182,6 +182,27 @@ void handle_time_alignment_timer_expired(NR_UE_MAC_INST_t *mac)
   // TODO not sure what to do here
 }
 
+void handle_ulsync_loss(NR_UE_MAC_INST_t *mac)
+{
+  // flush all HARQ buffers for all Serving Cells
+  for (int k = 0; k < NR_MAX_HARQ_PROCESSES; k++) {
+    memset(&mac->dl_harq_info[k], 0, sizeof(*mac->dl_harq_info));
+    memset(&mac->ul_harq_info[k], 0, sizeof(*mac->ul_harq_info));
+    mac->dl_harq_info[k].last_ndi = -1; // initialize to invalid value
+    mac->ul_harq_info[k].last_ndi = -1; // initialize to invalid value
+  }
+  // clear any configured downlink assignments and uplink grants;
+  if (mac->dl_config_request)
+    memset(mac->dl_config_request, 0, sizeof(*mac->dl_config_request));
+  if (mac->ul_config_request)
+    clear_ul_config_request(mac);
+
+  // Need to receive SIB19 again after loosing UL SYNC
+  mac->state = UE_RECEIVING_SIB;
+  // gNB needs to send PDCCH ORDER triggering RA after detecting ULSYNC LOSS
+  LOG_W(NR_MAC, "Wait for PDCCH ORDER, RACH needs to performed to obtain ULSYNC.\n");
+}
+
 void update_mac_dl_timers(NR_UE_MAC_INST_t *mac)
 {
   bool ra_window_expired = nr_timer_tick(&mac->ra.response_window_timer);

openair2/RRC/NR_UE/rrc_UE.c

@@ -2801,6 +2801,22 @@ void handle_t300_expiry(NR_UE_RRC_INST_t *rrc)
   // TODO inform upper layers about the failure to establish the RRC connection
 }
 
+void handle_t430_expiry(NR_UE_RRC_INST_t *rrc)
+{
+  // SPEC 38.331 section 5.2.2.6
+  // Reacquire SIB19 after T430 expiry
+  for (int i = 0; i < NB_CNX_UE; i++) {
+    rrcPerNB_t *nb = &rrc->perNB[i];
+    NR_UE_RRC_SI_INFO *SI_info = &nb->SInfo;
+    SI_info->SInfo_r17.sib19_validity = false;
+  }
+  // Indicate MAC that UL SYNC is LOST
+  NR_UE_MAC_reset_cause_t cause = UL_SYNC_LOST_T430_EXPIRED;
+  MessageDef *msg = itti_alloc_new_message(TASK_RRC_NRUE, 0, NR_MAC_RRC_CONFIG_RESET);
+  NR_MAC_RRC_CONFIG_RESET(msg).cause = cause;
+  itti_send_msg_to_task(TASK_MAC_UE, rrc->ue_id, msg);
+}
+
 //This calls the sidelink preconf message after RRC, MAC instances are created.
 void start_sidelink(int instance)
 {

openair2/RRC/NR_UE/rrc_proto.h

@@ -80,6 +80,7 @@ void init_SI_timers(NR_UE_RRC_SI_INFO *SInfo);
 
 void nr_ue_rrc_timer_trigger(int module_id, int frame, int gnb_id);
 void handle_t300_expiry(NR_UE_RRC_INST_t *rrc);
+void handle_t430_expiry(NR_UE_RRC_INST_t *rrc);
 
 void reset_rlf_timers_and_constants(NR_UE_Timers_Constants_t *tac);
 void set_default_timers_and_constants(NR_UE_Timers_Constants_t *tac);

openair2/RRC/NR_UE/rrc_timers_and_constants.c

@@ -172,10 +172,10 @@ void nr_rrc_handle_timers(NR_UE_RRC_INST_t *rrc)
 
   bool t430_expired = nr_timer_tick(&rrc->timers_and_constants.T430);
   if (t430_expired && rrc->nrRrcState == RRC_STATE_CONNECTED_NR && rrc->is_NTN_UE) {
-    LOG_W(NR_RRC, "Timer T430 expired! NTN UL SYNC FAILURE\n");
+    LOG_W(NR_RRC, "Timer T430 expired! Indicate UL SYNC LOSS to MAC\n");
     // Upon T430 expiry, the UE shall reacquire SIB19 and re-obtain UL-SYNC
     // Spec 38.331 Section 5.2.2.6
-    AssertFatal(1 == 0, "UL-Sync Lost. Read SIB19, perform RACH and obtain UL-SYNC. NOT YET Implemented.\n");
+    handle_t430_expiry(rrc);
   }
 }