Fix RA-RNTI computation according to 3GPP

t_id for long prach formats is computed with mu = 0.

openair2/LAYER2/NR_MAC_COMMON/nr_mac_common.c

@@ -1755,6 +1755,27 @@ int get_nr_prach_occasion_info_from_index(uint8_t index,
   }
 }
 
+uint16_t get_nr_prach_format_from_index(uint8_t index, uint32_t pointa, uint8_t unpaired)
+{
+  uint8_t format2 = 0xff;
+  uint16_t format;
+  if (pointa > 2016666) { // FR2
+    if (table_6_3_3_2_4_prachConfig_Index[index][1] != -1)
+      format2 = (uint8_t)table_6_3_3_2_4_prachConfig_Index[index][1];
+    format = ((uint8_t)table_6_3_3_2_4_prachConfig_Index[index][0]) | (format2 << 8);
+  } else {
+    if (unpaired) {
+      if (table_6_3_3_2_3_prachConfig_Index[index][1] != -1)
+        format2 = (uint8_t)table_6_3_3_2_3_prachConfig_Index[index][1];
+      format = ((uint8_t)table_6_3_3_2_3_prachConfig_Index[index][0]) | (format2 << 8);
+    } else {
+      if (table_6_3_3_2_2_prachConfig_Index[index][1] != -1)
+        format2 = (uint8_t)table_6_3_3_2_2_prachConfig_Index[index][1];
+      format = ((uint8_t)table_6_3_3_2_2_prachConfig_Index[index][0]) | (format2 << 8);
+    }
+  }
+  return format;
+}
 
 int get_nr_prach_info_from_index(uint8_t index,
                                  int frame,

openair2/LAYER2/NR_MAC_COMMON/nr_mac_common.h

@@ -141,6 +141,8 @@ void find_aggregation_candidates(uint8_t *aggregation_level,
                                  const NR_SearchSpace_t *ss,
                                  int maxL);
 
+uint16_t get_nr_prach_format_from_index(uint8_t index, uint32_t pointa, uint8_t unpaired);
+
 int get_nr_prach_info_from_index(uint8_t index,
                                  int frame,
                                  int slot,

openair2/LAYER2/NR_MAC_UE/nr_ue_scheduler.c

@@ -2956,10 +2956,16 @@ static void nr_ue_prach_scheduler(NR_UE_MAC_INST_t *mac, frame_t frameP, sub_fra
       nr_get_prach_resources(mac, 0, 0, &ra->prach_resources, ra->rach_ConfigDedicated);
       pdu->prach_config_pdu.ra_PreambleIndex = ra->ra_PreambleIndex;
       pdu->prach_config_pdu.prach_tx_power = get_prach_tx_power(mac);
-      mac->ra.ra_rnti = nr_get_ra_rnti(pdu->prach_config_pdu.prach_start_symbol,
-                                       pdu->prach_config_pdu.prach_slot,
-                                       pdu->prach_config_pdu.num_ra,
-                                       0);
+      unsigned int slot_RA;
+      // 3GPP TS 38.321 Section 5.1.3 says t_id for RA-RNTI depends on mu as specified in clause 5.3.2 in TS 38.211
+      // so mu = 0 for prach format < 4.
+      if (pdu->prach_config_pdu.prach_format < 4) {
+        unsigned int slots_per_sf = (1 << mac->current_UL_BWP->scs);
+        slot_RA = pdu->prach_config_pdu.prach_slot / slots_per_sf;
+      } else {
+        slot_RA = pdu->prach_config_pdu.prach_slot;
+      }
+      mac->ra.ra_rnti = nr_get_ra_rnti(pdu->prach_config_pdu.prach_start_symbol, slot_RA, pdu->prach_config_pdu.num_ra, 0);
       release_ul_config(pdu, false);
       nr_scheduled_response_t scheduled_response = {.ul_config = mac->ul_config_request + slotP,
                                                     .mac = mac,
@@ -3007,7 +3013,7 @@ static void nr_ue_prach_scheduler(NR_UE_MAC_INST_t *mac, frame_t frameP, sub_fra
 
         // Compute MsgB RNTI
         ra->MsgB_rnti =
-            nr_get_MsgB_rnti(prach_occasion_info_p->start_symbol, prach_occasion_info_p->slot, prach_occasion_info_p->fdm, 0);
+            nr_get_MsgB_rnti(prach_occasion_info_p->start_symbol, slot_RA, prach_occasion_info_p->fdm, 0);
         LOG_D(NR_MAC, "ra->ra_state %s\n", nrra_ue_text[ra->ra_state]);
         ra->ra_state = nrRA_WAIT_MSGB;
         ra->t_crnti = 0;

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_RA.c

@@ -761,17 +761,37 @@ void nr_initiate_ra_proc(module_id_t module_idP,
   ra->preamble_index = preamble_index;
   ra->timing_offset = timing_offset;
   ra->msg3_TPC = nr_get_msg3_tpc(preamble_power);
-  uint8_t ul_carrier_id = 0; // 0 for NUL 1 for SUL
-  ra->RA_rnti = nr_get_ra_rnti(symbol, slotP, freq_index, ul_carrier_id);
 
   NR_ServingCellConfigCommon_t *scc = cc->ServingCellConfigCommon;
-  if (scc->uplinkConfigCommon->initialUplinkBWP->ext1 && scc->uplinkConfigCommon->initialUplinkBWP->ext1->msgA_ConfigCommon_r16) {
-    ra->ra_type = RA_2_STEP;
-    ra->ra_state = nrRA_WAIT_MsgA_PUSCH;
-    ra->MsgB_rnti = nr_get_MsgB_rnti(symbol, slotP, freq_index, ul_carrier_id);
-  } else {
-    ra->ra_type = RA_4_STEP;
-    ra->ra_state = nrRA_Msg2;
+  {
+    // 3GPP TS 38.321 Section 5.1.3(a) says t_id for RA-RNTI depends on mu as specified in clause 5.3.2 in TS 38.211
+    // so mu = 0 for prach format < 4.
+    NR_RACH_ConfigCommon_t *rach_ConfigCommon = scc->uplinkConfigCommon->initialUplinkBWP->rach_ConfigCommon->choice.setup;
+    NR_MsgA_ConfigCommon_r16_t *msgacc = NULL;
+    if (scc->uplinkConfigCommon->initialUplinkBWP->ext1 && scc->uplinkConfigCommon->initialUplinkBWP->ext1->msgA_ConfigCommon_r16)
+      msgacc = scc->uplinkConfigCommon->initialUplinkBWP->ext1->msgA_ConfigCommon_r16->choice.setup;
+    const int ul_mu = scc->uplinkConfigCommon->frequencyInfoUL->scs_SpecificCarrierList.list.array[0]->subcarrierSpacing;
+    const int mu = nr_get_prach_or_ul_mu(msgacc, rach_ConfigCommon, ul_mu);
+    uint8_t index = rach_ConfigCommon->rach_ConfigGeneric.prach_ConfigurationIndex;
+    uint16_t prach_format =
+        get_nr_prach_format_from_index(index, scc->downlinkConfigCommon->frequencyInfoDL->absoluteFrequencyPointA, cc->frame_type);
+    unsigned int slot_RA;
+    if ((prach_format & 0xff) < 4) {
+      unsigned int slots_per_sf = (1 << mu);
+      slot_RA = slotP / slots_per_sf;
+    } else {
+      slot_RA = slotP;
+    }
+    uint8_t ul_carrier_id = 0; // 0 for NUL 1 for SUL
+    ra->RA_rnti = nr_get_ra_rnti(symbol, slot_RA, freq_index, ul_carrier_id);
+    if (scc->uplinkConfigCommon->initialUplinkBWP->ext1 && scc->uplinkConfigCommon->initialUplinkBWP->ext1->msgA_ConfigCommon_r16) {
+      ra->ra_type = RA_2_STEP;
+      ra->ra_state = nrRA_WAIT_MsgA_PUSCH;
+      ra->MsgB_rnti = nr_get_MsgB_rnti(symbol, slot_RA, freq_index, ul_carrier_id);
+    } else {
+      ra->ra_type = RA_4_STEP;
+      ra->ra_state = nrRA_Msg2;
+    }
   }
 
   int index = ra - cc->ra;