DL HARQ feedback processing: check frame/slot

Due to real-time issue, we might miss HARQ feedbacks. Similarly, I
observed that we get feedback for HARQ processes scheduled for a future
frame (don't know how this can happen).

This commit introduces a function that checks whether the first HARQ
process in the queue corresponds due the current frame/slot combination.
If not, it marks old feedbacks for retransmission.  Furthermore, it also
checks whether the feedback is too early, by not considering this
feedback.

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_dlsch.c

@@ -748,6 +748,7 @@ void nr_schedule_ue_spec(module_id_t module_id,
     DevAssert(!harq->is_waiting);
     add_tail_nr_list(&sched_ctrl->feedback_dl_harq, current_harq_pid);
     NR_sched_pucch_t *pucch = &sched_ctrl->sched_pucch[0];
+    harq->feedback_frame = pucch->frame;
     harq->feedback_slot = pucch->ul_slot;
     harq->is_waiting = true;
     UE_info->mac_stats[UE_id].dlsch_rounds[harq->round]++;

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_uci.c

@@ -948,7 +948,50 @@ void extract_pucch_csi_report (NR_CSI_MeasConfig_t *csi_MeasConfig,
 
   if ( !(reportQuantity_type)) 
     AssertFatal(reportQuantity_type, "reportQuantity is not configured");
+}
 
+static NR_UE_harq_t *find_harq(module_id_t mod_id, frame_t frame, sub_frame_t slot, int UE_id)
+{
+  /* In case of realtime problems: we can only identify a HARQ process by
+   * timing. If the HARQ process's feedback_frame/feedback_slot is not the one we
+   * expected, we assume that processing has been aborted and we need to
+   * skip this HARQ process, which is what happens in the loop below.
+   * Similarly, we might be "in advance", in which case we need to skip
+   * this result. */
+  NR_UE_sched_ctrl_t *sched_ctrl = &RC.nrmac[mod_id]->UE_info.UE_sched_ctrl[UE_id];
+  int8_t pid = sched_ctrl->feedback_dl_harq.head;
+  if (pid < 0)
+    return NULL;
+  NR_UE_harq_t *harq = &sched_ctrl->harq_processes[pid];
+  /* old feedbacks we missed: mark for retransmission */
+  while (harq->feedback_frame != frame
+         || (harq->feedback_frame == frame && harq->feedback_slot < slot)) {
+    LOG_W(MAC,
+          "expected HARQ pid %d feedback at %d.%d, but is at %d.%d instead (HARQ feedback is in the past)\n",
+          pid,
+          harq->feedback_frame,
+          harq->feedback_slot,
+          frame,
+          slot);
+    remove_front_nr_list(&sched_ctrl->feedback_dl_harq);
+    handle_dl_harq(mod_id, UE_id, pid, 0);
+    pid = sched_ctrl->feedback_dl_harq.head;
+    if (pid < 0)
+      return NULL;
+    harq = &sched_ctrl->harq_processes[pid];
+  }
+  /* feedbacks that we wait for in the future: don't do anything */
+  if (harq->feedback_slot > slot) {
+    LOG_W(MAC,
+          "expected HARQ pid %d feedback at %d.%d, but is at %d.%d instead (HARQ feedback is in the future)\n",
+          pid,
+          harq->feedback_frame,
+          harq->feedback_slot,
+          frame,
+          slot);
+    return NULL;
+  }
+  return harq;
 }
 
 void handle_nr_uci_pucch_0_1(module_id_t mod_id,
@@ -976,28 +1019,14 @@ void handle_nr_uci_pucch_0_1(module_id_t mod_id,
     for (int harq_bit = 0; harq_bit < uci_01->harq->num_harq; harq_bit++) {
       const uint8_t harq_value = uci_01->harq->harq_list[harq_bit].harq_value;
       const uint8_t harq_confidence = uci_01->harq->harq_confidence_level;
+      const int feedback_frame = slot == 0 ? (frame - 1 + 1024) % 1024 : frame;
       const int feedback_slot = (slot - 1 + num_slots) % num_slots;
-      /* In case of realtime problems: we can only identify a HARQ process by
-       * timing. If the HARQ process's feedback_slot is not the one we
-       * expected, we assume that processing has been aborted and we need to
-       * skip this HARQ process, which is what happens in the loop below. If
-       * you don't experience real-time problems, you might simply revert the
-       * commit that introduced these changes. */
-      int8_t pid = sched_ctrl->feedback_dl_harq.head;
-      DevAssert(pid >= 0);
-      while (sched_ctrl->harq_processes[pid].feedback_slot != feedback_slot) {
-        LOG_W(MAC,
-              "expected feedback slot %d, but found %d instead\n",
-              sched_ctrl->harq_processes[pid].feedback_slot,
-              feedback_slot);
-        remove_front_nr_list(&sched_ctrl->feedback_dl_harq);
-        handle_dl_harq(mod_id, UE_id, pid, 0);
-        pid = sched_ctrl->feedback_dl_harq.head;
-        DevAssert(pid >= 0);
-      }
-      remove_front_nr_list(&sched_ctrl->feedback_dl_harq);
-      NR_UE_harq_t *harq = &sched_ctrl->harq_processes[pid];
+      NR_UE_harq_t *harq = find_harq(mod_id, feedback_frame, feedback_slot, UE_id);
+      if (!harq)
+        break;
       DevAssert(harq->is_waiting);
+      const int8_t pid = sched_ctrl->feedback_dl_harq.head;
+      remove_front_nr_list(&sched_ctrl->feedback_dl_harq);
       handle_dl_harq(mod_id, UE_id, pid, harq_value == 1 && harq_confidence == 0);
     }
   }
@@ -1028,28 +1057,14 @@ void handle_nr_uci_pucch_2_3_4(module_id_t mod_id,
     // iterate over received harq bits
     for (int harq_bit = 0; harq_bit < uci_234->harq.harq_bit_len; harq_bit++) {
       const int acknack = ((uci_234->harq.harq_payload[harq_bit >> 3]) >> harq_bit) & 0x01;
+      const int feedback_frame = slot == 0 ? (frame - 1 + 1024) % 1024 : frame;
       const int feedback_slot = (slot - 1 + num_slots) % num_slots;
-      /* In case of realtime problems: we can only identify a HARQ process by
-       * timing. If the HARQ process's feedback_slot is not the one we
-       * expected, we assume that processing has been aborted and we need to
-       * skip this HARQ process, which is what happens in the loop below. If
-       * you don't experience real-time problems, you might simply revert the
-       * commit that introduced these changes. */
-      int8_t pid = sched_ctrl->feedback_dl_harq.head;
-      DevAssert(pid >= 0);
-      while (sched_ctrl->harq_processes[pid].feedback_slot != feedback_slot) {
-        LOG_W(MAC,
-              "expected feedback slot %d, but found %d instead\n",
-              sched_ctrl->harq_processes[pid].feedback_slot,
-              feedback_slot);
-        remove_front_nr_list(&sched_ctrl->feedback_dl_harq);
-        handle_dl_harq(mod_id, UE_id, pid, 0);
-        pid = sched_ctrl->feedback_dl_harq.head;
-        DevAssert(pid >= 0);
-      }
-      remove_front_nr_list(&sched_ctrl->feedback_dl_harq);
-      NR_UE_harq_t *harq = &sched_ctrl->harq_processes[pid];
+      NR_UE_harq_t *harq = find_harq(mod_id, feedback_frame, feedback_slot, UE_id);
+      if (!harq)
+        break;
       DevAssert(harq->is_waiting);
+      const int8_t pid = sched_ctrl->feedback_dl_harq.head;
+      remove_front_nr_list(&sched_ctrl->feedback_dl_harq);
       handle_dl_harq(mod_id, UE_id, pid, uci_234->harq.harq_crc != 1 && acknack);
     }
   }

openair2/LAYER2/NR_MAC_gNB/nr_mac_gNB.h

@@ -356,6 +356,7 @@ typedef struct NR_UE_harq {
   bool is_waiting;
   uint8_t ndi;
   uint8_t round;
+  uint16_t feedback_frame;
   uint16_t feedback_slot;
 
   /* Transport block to be sent using this HARQ process */