fix: do NR only if at least one gNB is connected to the eNB

We used to set 'does_nr' of an UE if we detect ENDC supported in the
UE capabilities.

Then we activate NR measurements if 'does_nr' is true.

The problem is that if the eNB is not connected to a gNB but the UE
reports some NR measurements (because a gNB is running somewhere near)
then the eNB will crash when starting the switch to NR.

A (quick) solution is to set 'does_nr' only if there is a gNB connected to
the eNB.

Maybe not the best solution. To be changed if needed.

openair2/RRC/LTE/rrc_defs.h

@@ -67,6 +67,8 @@
 
 #define MAX_NUM_NEIGH_CELLs 6 /* maximum neighbouring cells number */
 
+#define MAX_NUM_GNB_CELLs 1   /* maximum gNB cells number */
+
 #define UE_STATE_NOTIFICATION_INTERVAL      50
 
 #define IPV4_ADDR    "%u.%u.%u.%u"
@@ -804,8 +806,13 @@ typedef struct eNB_RRC_INST_s {
   int num_neigh_cells_cc[MAX_NUM_CCs];
   uint32_t neigh_cells_id[MAX_NUM_NEIGH_CELLs][MAX_NUM_CCs];
 
+  // gNB cells connected to this eNB
+  int num_gnb_cells;
+  int num_gnb_cells_cc[MAX_NUM_GNB_CELLs];
+  uint32_t gnb_cells_id[MAX_NUM_GNB_CELLs][MAX_NUM_CCs];
+
   // Nr scc freq band and SSB absolute frequency
-  uint32_t nr_neigh_freq_band[MAX_NUM_NEIGH_CELLs][MAX_NUM_CCs];
+  uint32_t nr_gnb_freq_band[MAX_NUM_GNB_CELLs][MAX_NUM_CCs];
   int nr_scg_ssb_freq;
 
   // other RAN parameters

openair2/RRC/LTE/rrc_eNB.c

@@ -1283,7 +1283,7 @@ rrc_eNB_generate_UECapabilityEnquiry(
   T(T_ENB_RRC_UE_CAPABILITY_ENQUIRY, T_INT(ctxt_pP->module_id), T_INT(ctxt_pP->frame),
     T_INT(ctxt_pP->subframe), T_INT(ctxt_pP->rnti));
   int16_t eutra_band = RC.rrc[ctxt_pP->module_id]->configuration.eutra_band[0];
-  uint32_t nr_band = RC.rrc[ctxt_pP->module_id]->nr_neigh_freq_band[0][0];
+  uint32_t nr_band = RC.rrc[ctxt_pP->module_id]->nr_gnb_freq_band[0][0];
   size = do_UECapabilityEnquiry(
            ctxt_pP,
            buffer,
@@ -1333,7 +1333,7 @@ rrc_eNB_generate_NR_UECapabilityEnquiry(
   T(T_ENB_RRC_UE_CAPABILITY_ENQUIRY, T_INT(ctxt_pP->module_id), T_INT(ctxt_pP->frame),
     T_INT(ctxt_pP->subframe), T_INT(ctxt_pP->rnti));
   int16_t eutra_band = RC.rrc[ctxt_pP->module_id]->configuration.eutra_band[0];
-  uint32_t nr_band = RC.rrc[ctxt_pP->module_id]->nr_neigh_freq_band[0][0];
+  uint32_t nr_band = RC.rrc[ctxt_pP->module_id]->nr_gnb_freq_band[0][0];
   size = do_NR_UECapabilityEnquiry(
            ctxt_pP,
            buffer,
@@ -7588,8 +7588,8 @@ is_en_dc_supported(
 )
 //-----------------------------------------------------------------------------
 {
-  /* to be refined - check that the eNB is connected to a gNB, check that
-   * the bands supported by the UE include the band of the gNB
+  /* to be refined - check that the bands supported by the UE include
+   * the band of the gNB
    */
 #define NCE nonCriticalExtension
   return c != NULL
@@ -8289,8 +8289,13 @@ rrc_eNB_decode_dcch(
           ue_context_p->ue_context.UE_Capability = 0;
         }
 
-        if (dec_rval.code == RC_OK)
-          ue_context_p->ue_context.does_nr = is_en_dc_supported(ue_context_p->ue_context.UE_Capability);
+        if (dec_rval.code == RC_OK) {
+          /* do NR only if at least one gNB connected */
+          if (RC.rrc[ctxt_pP->module_id]->num_gnb_cells != 0)
+            ue_context_p->ue_context.does_nr = is_en_dc_supported(ue_context_p->ue_context.UE_Capability);
+          else
+            ue_context_p->ue_context.does_nr = 0;
+        }
 
         if (EPC_MODE_ENABLED) {
           rrc_eNB_send_S1AP_UE_CAPABILITIES_IND(ctxt_pP,
@@ -9029,22 +9034,22 @@ void rrc_subframe_process(protocol_ctxt_t *const ctxt_pP, const int CC_id) {
 }
 
 void rrc_eNB_process_ENDC_x2_setup_request(int mod_id, x2ap_ENDC_setup_req_t *m) {
-  if (RC.rrc[mod_id]->num_neigh_cells > MAX_NUM_NEIGH_CELLs) {
-    LOG_E(RRC, "Error: number of neighbouring cells is exceeded \n");
+  if (RC.rrc[mod_id]->num_gnb_cells >= MAX_NUM_GNB_CELLs) {
+    LOG_E(RRC, "Error: number of gNB cells is exceeded\n");
     return;
   }
 
   if (m->num_cc > MAX_NUM_CCs) {
-    LOG_E(RRC, "Error: number of neighbouring cells carriers is exceeded \n");
+    LOG_E(RRC, "Error: number of gNB cells carriers is exceeded \n");
     return;
   }
 
-  RC.rrc[mod_id]->num_neigh_cells++;
-  RC.rrc[mod_id]->num_neigh_cells_cc[RC.rrc[mod_id]->num_neigh_cells-1] = m->num_cc;
+  RC.rrc[mod_id]->num_gnb_cells++;
+  RC.rrc[mod_id]->num_gnb_cells_cc[RC.rrc[mod_id]->num_gnb_cells-1] = m->num_cc;
 
   for (int i=0; i<m->num_cc; i++) {
-    RC.rrc[mod_id]->neigh_cells_id[RC.rrc[mod_id]->num_neigh_cells-1][i] = m->Nid_cell[i];
-    RC.rrc[mod_id]->nr_neigh_freq_band[RC.rrc[mod_id]->num_neigh_cells-1][i] = m->servedNrCell_band[i];
+    RC.rrc[mod_id]->gnb_cells_id[RC.rrc[mod_id]->num_gnb_cells-1][i] = m->Nid_cell[i];
+    RC.rrc[mod_id]->nr_gnb_freq_band[RC.rrc[mod_id]->num_gnb_cells-1][i] = m->servedNrCell_band[i];
   }
 
 }