Procedures for Contention Resolution

openair2/LAYER2/NR_MAC_UE/mac_proto.h

@@ -300,12 +300,9 @@ void configure_csi_resource_mapping(fapi_nr_dl_config_csirs_pdu_rel15_t *csirs_c
 */
 void nr_ue_msg3_scheduler(NR_UE_MAC_INST_t *mac, frame_t current_frame, slot_t current_slot, uint8_t Msg3_tda_id);
 
-void nr_ue_contention_resolution(NR_UE_MAC_INST_t *mac, int cc_id, frame_t frame, int slot, NR_PRACH_RESOURCES_t *prach_resources);
-
-void nr_ra_failed(NR_UE_MAC_INST_t *mac, uint8_t CC_id, NR_PRACH_RESOURCES_t *prach_resources, frame_t frame, int slot);
-
+void nr_ra_contention_resolution_failed(RA_config_t *ra);
 void nr_ra_succeeded(NR_UE_MAC_INST_t *mac, const uint8_t gNB_index, const frame_t frame, const int slot);
-
+void nr_ra_backoff_setting(RA_config_t *ra);
 void nr_get_RA_window(NR_UE_MAC_INST_t *mac);
 
 /*@mac pointer to MAC instance

openair2/LAYER2/NR_MAC_UE/nr_ra_procedures.c

@@ -1174,8 +1174,6 @@ void nr_get_Msg3_MsgA_PUSCH_payload(NR_UE_MAC_INST_t *mac, uint8_t *buf, int TBS
 void nr_ue_manage_ra_procedure(NR_UE_MAC_INST_t *mac, int CC_id, frame_t frame, uint8_t gNB_id, int nr_slot_tx)
 {
   RA_config_t *ra = &mac->ra;
-  NR_PRACH_RESOURCES_t *prach_resources = &ra->prach_resources;
-
   if (ra->ra_state == nrRA_UE_IDLE) {
     bool init_success = init_RA(mac, frame);
     if (!init_success)
@@ -1199,30 +1197,6 @@ void nr_ue_manage_ra_procedure(NR_UE_MAC_INST_t *mac, int CC_id, frame_t frame,
       ra_resource_selection(mac);
     }
   }
-
-  if (nr_timer_is_active(&ra->contention_resolution_timer)) {
-    nr_ue_contention_resolution(mac, CC_id, frame, nr_slot_tx, prach_resources);
-  }
-}
-
-////////////////////////////////////////////////////////////////////////////
-/////////* Random Access Contention Resolution (5.1.35 TS 38.321) */////////
-////////////////////////////////////////////////////////////////////////////
-// Handling contention resolution timer
-// WIP todo:
-// - beam failure recovery
-// - RA completed
-void nr_ue_contention_resolution(NR_UE_MAC_INST_t *mac, int cc_id, frame_t frame, int slot, NR_PRACH_RESOURCES_t *prach_resources)
-{
-  RA_config_t *ra = &mac->ra;
-
-  if (nr_timer_expired(&ra->contention_resolution_timer)) {
-    ra->t_crnti = 0;
-    nr_timer_stop(&ra->contention_resolution_timer);
-    // Signal PHY to quit RA procedure
-    LOG_E(MAC, "[UE %d] 4-Step CBRA: Contention resolution timer has expired, RA procedure has failed...\n", mac->ue_id);
-    nr_ra_failed(mac, cc_id, prach_resources, frame, slot);
-  }
 }
 
 // Handlig successful RA completion @ MAC layer
@@ -1250,7 +1224,6 @@ void nr_ra_succeeded(NR_UE_MAC_INST_t *mac, const uint8_t gNB_index, const frame
           mac->ue_id,
           frame,
           slot);
-    nr_timer_stop(&ra->contention_resolution_timer);
     mac->crnti = ra->t_crnti;
     ra->t_crnti = 0;
     LOG_D(MAC, "[UE %d][%d.%d] CBRA: cleared contention resolution timer...\n", mac->ue_id, frame, slot);
@@ -1264,6 +1237,33 @@ void nr_ra_succeeded(NR_UE_MAC_INST_t *mac, const uint8_t gNB_index, const frame
   nr_mac_rrc_ra_ind(mac->ue_id, frame, true);
 }
 
+void nr_ra_backoff_setting(RA_config_t *ra)
+{
+  // select a random backoff time according to a uniform distribution
+  // between 0 and the PREAMBLE_BACKOFF
+  uint32_t seed = (unsigned int)(rdtsc_oai() & ~0);
+  uint32_t random_backoff = ra->RA_backoff_limit ? rand_r(&seed) % ra->RA_backoff_limit : 0; // in slots
+  nr_timer_setup(&ra->RA_backoff_timer, random_backoff, 1);
+  nr_timer_start(&ra->RA_backoff_timer);
+}
+
+void nr_ra_contention_resolution_failed(RA_config_t *ra)
+{
+  // discard the TEMPORARY_C-RNTI
+  ra->t_crnti = 0;
+  // flush MSG3 buffer
+  free_and_zero(ra->Msg3_buffer);
+  NR_PRACH_RESOURCES_t *prach_resources = &ra->prach_resources;
+  prach_resources->preamble_tx_counter++;
+  if (prach_resources->preamble_tx_counter == ra->preambleTransMax + 1) {
+    // TODO indicate a Random Access problem to upper layers
+  } else {
+    // TODO handle msgA-TransMax (go back to 4-step if the threshold is reached)
+    // starting backoff time
+    nr_ra_backoff_setting(ra);
+  }
+}
+
 void nr_rar_not_successful(NR_UE_MAC_INST_t *mac)
 {
   LOG_W(MAC, "[UE %d] RAR reception failed\n", mac->ue_id);
@@ -1284,44 +1284,7 @@ void nr_rar_not_successful(NR_UE_MAC_INST_t *mac)
     }
   }
   if (!ra_completed) {
-    // select a random backoff time according to a uniform distribution
-    // between 0 and the PREAMBLE_BACKOFF
-    uint32_t seed = (unsigned int)(rdtsc_oai() & ~0);
-    uint32_t random_backoff = rand_r(&seed) % ra->RA_backoff_limit; // in slots
-    nr_timer_setup(&ra->RA_backoff_timer, random_backoff, 1);
-    nr_timer_start(&ra->RA_backoff_timer);
-  }
-}
-
-// Handling failure of RA procedure @ MAC layer
-// according to section 5 of 3GPP TS 38.321 version 16.2.1 Release 16
-// todo:
-// - complete handling of received contention-based RA preamble
-void nr_ra_failed(NR_UE_MAC_INST_t *mac, uint8_t CC_id, NR_PRACH_RESOURCES_t *prach_resources, frame_t frame, int slot)
-{
-  RA_config_t *ra = &mac->ra;
-  ra->ra_PreambleIndex = -1;
-  ra->ra_state = nrRA_UE_IDLE;
-
-  prach_resources->preamble_tx_counter++;
-
-  // when the Contention Resolution is considered not successful
-  // stop timeAlignmentTimer
-  nr_timer_stop(&mac->time_alignment_timer);
-
-  if (prach_resources->preamble_tx_counter == ra->preambleTransMax + 1) {
-
-    LOG_D(NR_MAC,
-          "[UE %d][%d.%d] Maximum number of RACH attempts (%d) reached, selecting backoff time...\n",
-          mac->ue_id,
-          frame,
-          slot,
-          ra->preambleTransMax);
-
-    prach_resources->preamble_tx_counter = 1;
-    prach_resources->preamble_power_ramping_step += 2; // 2 dB increment
-    prach_resources->ra_preamble_rx_target_power = get_ra_preamble_rx_target_power(ra, mac->current_UL_BWP->scs);
-
+    nr_ra_backoff_setting(ra);
   }
 }
 

openair2/LAYER2/NR_MAC_UE/nr_ue_procedures.c

@@ -3501,9 +3501,7 @@ static int nr_ue_validate_successrar(uint8_t *pduP,
           nr_timer_stop(&ra->response_window_timer);
           nr_ra_succeeded(mac, gNB_index, frameP, slot);
         } else if (!ra_success) {
-          // nr_ra_failed(mac, CC_id, &ra->prach_resources, frameP, slot);
-          ra->ra_state = nrRA_UE_IDLE;
-          ra->RA_active = 0;
+          nr_ra_backoff_setting(ra);
         }
       }
     } else { // RAPID
@@ -3706,7 +3704,8 @@ void nr_ue_process_mac_pdu(NR_UE_MAC_INST_t *mac, nr_downlink_indication_t *dl_i
         mac_len = 6;
 
         if (ra->ra_state == nrRA_WAIT_CONTENTION_RESOLUTION) {
-          LOG_I(MAC, "[UE %d]Frame %d Contention resolution identity: 0x%02x%02x%02x%02x%02x%02x Terminating RA procedure\n",
+          LOG_D(NR_MAC,
+                "[UE %d]Frame %d Contention resolution identity: 0x%02x%02x%02x%02x%02x%02x Terminating RA procedure\n",
                 mac->ue_id,
                 frameP,
                 pduP[1],
@@ -3716,15 +3715,15 @@ void nr_ue_process_mac_pdu(NR_UE_MAC_INST_t *mac, nr_downlink_indication_t *dl_i
                 pduP[5],
                 pduP[6]);
 
+          nr_timer_stop(&ra->contention_resolution_timer);
           bool ra_success = check_ra_contention_resolution(&pduP[1], ra->cont_res_id);
 
           if (ra->RA_active && ra_success) {
             nr_ra_succeeded(mac, gNB_index, frameP, slot);
           } else if (!ra_success) {
-            // TODO: Handle failure of RA procedure @ MAC layer
-            //  nr_ra_failed(module_idP, CC_id, prach_resources, frameP, slot); // prach_resources is a PHY structure
-            ra->ra_state = nrRA_UE_IDLE;
-            ra->RA_active = false;
+            // consider this Contention Resolution not successful and discard the successfully decoded MAC PDU
+            nr_ra_contention_resolution_failed(ra);
+            return;
           }
         }
         break;

openair2/LAYER2/NR_MAC_UE/nr_ue_scheduler.c

@@ -192,7 +192,9 @@ void update_mac_timers(NR_UE_MAC_INST_t *mac)
   bool alignment_timer_expired = nr_timer_tick(&mac->time_alignment_timer);
   if (alignment_timer_expired)
     handle_time_alignment_timer_expired(mac);
-  nr_timer_tick(&mac->ra.contention_resolution_timer);
+  bool contention_resolution_expired = nr_timer_tick(&mac->ra.contention_resolution_timer);
+  if (contention_resolution_expired)
+    nr_ra_contention_resolution_failed(&mac->ra);
   for (int j = 0; j < NR_MAX_SR_ID; j++)
     nr_timer_tick(&mac->scheduling_info.sr_info[j].prohibitTimer);
   nr_timer_tick(&mac->scheduling_info.sr_DelayTimer);