Implement DL HARQ using NR_list_t

openair1/SIMULATION/NR_PHY/dlsim.c

@@ -207,6 +207,20 @@ void nr_dlsim_preprocessor(module_id_t module_id,
   sched_ctrl->mcs = g_mcsIndex;
   sched_ctrl->time_domain_allocation = 2;
   sched_ctrl->mcsTableIdx = g_mcsTableIdx;
+  /* the simulator assumes the HARQ PID is equal to the slot number */
+  sched_ctrl->dl_harq_pid = slot;
+  /* The scheduler uses lists to track whether a HARQ process is
+   * free/busy/awaiting retransmission, and updates the HARQ process states.
+   * However, in the simulation, we never get ack or nack for any HARQ process,
+   * thus the list and HARQ states don't match what the scheduler expects.
+   * Therefore, below lines just "repair" everything so that the scheduler
+   * won't remark that there is no HARQ feedback */
+  sched_ctrl->feedback_dl_harq.head = -1; // always overwrite feedback HARQ process
+  if (sched_ctrl->harq_processes[slot].round == 0) // depending on round set in simulation ...
+    add_front_nr_list(&sched_ctrl->available_dl_harq, slot); // ... make PID available
+  else
+    add_front_nr_list(&sched_ctrl->retrans_dl_harq, slot);   // ... make PID retransmission
+  sched_ctrl->harq_processes[slot].is_waiting = false;
   AssertFatal(sched_ctrl->rbStart >= 0, "invalid rbStart %d\n", sched_ctrl->rbStart);
   AssertFatal(sched_ctrl->rbSize > 0, "invalid rbSize %d\n", sched_ctrl->rbSize);
   AssertFatal(sched_ctrl->mcs >= 0, "invalid sched_ctrl->mcs %d\n", sched_ctrl->mcs);

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_dlsch.c

@@ -418,14 +418,13 @@ void nr_simple_dlsch_preprocessor(module_id_t module_id,
   }
 
   uint16_t *vrb_map = RC.nrmac[module_id]->common_channels[CC_id].vrb_map;
-  // for now HARQ PID is fixed and should be the same as in post-processor
-  const int current_harq_pid = slot % 8;
-  NR_UE_harq_t *harq = &sched_ctrl->harq_processes[current_harq_pid];
-  NR_UE_ret_info_t *retInfo = &sched_ctrl->retInfo[current_harq_pid];
+  /* get the PID of a HARQ process awaiting retransmission, or -1 otherwise */
+  sched_ctrl->dl_harq_pid = sched_ctrl->retrans_dl_harq.head;
   const uint16_t bwpSize = NRRIV2BW(sched_ctrl->active_bwp->bwp_Common->genericParameters.locationAndBandwidth, MAX_BWP_SIZE);
   int rbStart = NRRIV2PRBOFFSET(sched_ctrl->active_bwp->bwp_Common->genericParameters.locationAndBandwidth, MAX_BWP_SIZE);
 
-  if (harq->round != 0) { /* retransmission */
+  if (sched_ctrl->dl_harq_pid >= 0) { /* retransmission */
+    NR_UE_ret_info_t *retInfo = &sched_ctrl->retInfo[sched_ctrl->dl_harq_pid];
     sched_ctrl->time_domain_allocation = retInfo->time_domain_allocation;
 
     /* ensure that there is a free place for RB allocation */
@@ -563,11 +562,29 @@ void nr_schedule_ue_spec(module_id_t module_id,
                        nrOfLayers)
         >> 3;
 
-    const int current_harq_pid = slot % 8;
+    int8_t current_harq_pid = sched_ctrl->dl_harq_pid;
+    if (current_harq_pid < 0) {
+      /* PP has not selected a specific HARQ Process, get a new one */
+      current_harq_pid = sched_ctrl->available_dl_harq.head;
+      AssertFatal(current_harq_pid >= 0,
+                  "no free HARQ process available for UE %d\n",
+                  UE_id);
+      remove_front_nr_list(&sched_ctrl->available_dl_harq);
+    } else {
+      /* PP selected a specific HARQ process. Check whether it will be a new
+       * transmission or a retransmission, and remove from the corresponding
+       * list */
+      if (sched_ctrl->harq_processes[current_harq_pid].round == 0)
+        remove_nr_list(&sched_ctrl->available_dl_harq, current_harq_pid);
+      else
+        remove_nr_list(&sched_ctrl->retrans_dl_harq, current_harq_pid);
+    }
     NR_UE_harq_t *harq = &sched_ctrl->harq_processes[current_harq_pid];
+    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_slot = pucch->ul_slot;
-    harq->is_waiting = 1;
+    harq->is_waiting = true;
     UE_info->mac_stats[UE_id].dlsch_rounds[harq->round]++;
 
     LOG_D(MAC,

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_phytest.c

@@ -360,6 +360,8 @@ void nr_preprocessor_phytest(module_id_t module_id,
   }
   sched_ctrl->mcs = 9;
   sched_ctrl->numDmrsCdmGrpsNoData = 1;
+  /* get the PID of a HARQ process awaiting retransmission, or -1 otherwise */
+  sched_ctrl->dl_harq_pid = sched_ctrl->retrans_dl_harq.head;
 
   /* mark the corresponding RBs as used */
   for (int rb = 0; rb < sched_ctrl->rbSize; rb++)

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_uci.c

@@ -290,6 +290,31 @@ void nr_csi_meas_reporting(int Mod_idP,
   }
 }
 
+static void handle_dl_harq(module_id_t mod_id,
+                           int UE_id,
+                           int8_t harq_pid,
+                           bool success)
+{
+  NR_UE_info_t *UE_info = &RC.nrmac[mod_id]->UE_info;
+  NR_UE_harq_t *harq = &UE_info->UE_sched_ctrl[UE_id].harq_processes[harq_pid];
+  harq->feedback_slot = -1;
+  harq->is_waiting = false;
+  if (success) {
+    add_tail_nr_list(&UE_info->UE_sched_ctrl[UE_id].available_dl_harq, harq_pid);
+    harq->round = 0;
+    harq->ndi ^= 1;
+  } else if (harq->round == MAX_HARQ_ROUNDS) {
+    add_tail_nr_list(&UE_info->UE_sched_ctrl[UE_id].available_dl_harq, harq_pid);
+    harq->round = 0;
+    harq->ndi ^= 1;
+    NR_mac_stats_t *stats = &UE_info->mac_stats[UE_id];
+    stats->dlsch_errors++;
+    LOG_D(MAC, "retransmission error for UE %d (total %d)\n", UE_id, stats->dlsch_errors);
+  } else {
+    add_tail_nr_list(&UE_info->UE_sched_ctrl[UE_id].retrans_dl_harq, harq_pid);
+    harq->round++;
+  }
+}
 
 void handle_nr_uci_pucch_0_1(module_id_t mod_id,
                              frame_t frame,
@@ -309,50 +334,23 @@ void handle_nr_uci_pucch_0_1(module_id_t mod_id,
                                 uci_01->ul_cqi,
                                 30);
 
-  // TODO
-  int max_harq_rounds = 4; // TODO define macro
+  NR_ServingCellConfigCommon_t *scc = RC.nrmac[mod_id]->common_channels->ServingCellConfigCommon;
+  const int num_slots = nr_slots_per_frame[*scc->ssbSubcarrierSpacing];
   if (((uci_01->pduBitmap >> 1) & 0x01)) {
-    // handle harq
-    int harq_idx_s = 0;
-
     // iterate over received harq bits
     for (int harq_bit = 0; harq_bit < uci_01->harq->num_harq; harq_bit++) {
-      // search for the right harq process
-      for (int harq_idx = harq_idx_s; harq_idx < NR_MAX_NB_HARQ_PROCESSES; harq_idx++) {
-        // if the gNB received ack with a good confidence
-        if ((slot - 1) == sched_ctrl->harq_processes[harq_idx].feedback_slot) {
-          sched_ctrl->harq_processes[harq_idx].feedback_slot = -1;
-          if ((uci_01->harq->harq_list[harq_bit].harq_value == 1) &&
-              (uci_01->harq->harq_confidence_level == 0)) {
-            // toggle NDI and reset round
-            sched_ctrl->harq_processes[harq_idx].ndi ^= 1;
-            sched_ctrl->harq_processes[harq_idx].round = 0;
-          }
-          else
-            sched_ctrl->harq_processes[harq_idx].round++;
-          sched_ctrl->harq_processes[harq_idx].is_waiting = 0;
-          harq_idx_s = harq_idx + 1;
-          // if the max harq rounds was reached
-          if (sched_ctrl->harq_processes[harq_idx].round == max_harq_rounds) {
-            sched_ctrl->harq_processes[harq_idx].ndi ^= 1;
-            sched_ctrl->harq_processes[harq_idx].round = 0;
-            UE_info->mac_stats[UE_id].dlsch_errors++;
-          }
-          break;
-        }
-        // if feedback slot processing is aborted
-        else if (sched_ctrl->harq_processes[harq_idx].feedback_slot != -1
-                 && (slot - 1) > sched_ctrl->harq_processes[harq_idx].feedback_slot
-                 && sched_ctrl->harq_processes[harq_idx].is_waiting) {
-          sched_ctrl->harq_processes[harq_idx].feedback_slot = -1;
-          sched_ctrl->harq_processes[harq_idx].round++;
-          if (sched_ctrl->harq_processes[harq_idx].round == max_harq_rounds) {
-            sched_ctrl->harq_processes[harq_idx].ndi ^= 1;
-            sched_ctrl->harq_processes[harq_idx].round = 0;
-          }
-          sched_ctrl->harq_processes[harq_idx].is_waiting = 0;
-        }
-      }
+      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 int8_t 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];
+      const int feedback_slot = (slot - 1 + num_slots) % num_slots;
+      AssertFatal(harq->feedback_slot == feedback_slot,
+                  "expected feedback slot %d, but found %d instead\n",
+                  harq->feedback_slot, feedback_slot);
+      DevAssert(harq->is_waiting);
+      handle_dl_harq(mod_id, UE_id, pid, harq_value == 1 && harq_confidence == 0);
     }
   }
 }
@@ -375,50 +373,21 @@ void handle_nr_uci_pucch_2_3_4(module_id_t mod_id,
                                 uci_234->ul_cqi,
                                 30);
 
-  // TODO
-  int max_harq_rounds = 4; // TODO define macro
+  NR_ServingCellConfigCommon_t *scc = RC.nrmac[mod_id]->common_channels->ServingCellConfigCommon;
+  const int num_slots = nr_slots_per_frame[*scc->ssbSubcarrierSpacing];
   if ((uci_234->pduBitmap >> 1) & 0x01) {
-    int harq_idx_s = 0;
-    int acknack;
-
     // iterate over received harq bits
     for (int harq_bit = 0; harq_bit < uci_234->harq.harq_bit_len; harq_bit++) {
-      acknack = ((uci_234->harq.harq_payload[harq_bit>>3])>>harq_bit)&0x01;
-      for (int harq_idx = harq_idx_s; harq_idx < NR_MAX_NB_HARQ_PROCESSES-1; harq_idx++) {
-        // if the gNB received ack with a good confidence or if the max harq rounds was reached
-        if ((slot - 1) == sched_ctrl->harq_processes[harq_idx].feedback_slot) {
-          // TODO add some confidence level for when there is no CRC
-          sched_ctrl->harq_processes[harq_idx].feedback_slot = -1;
-          if ((uci_234->harq.harq_crc != 1) && acknack) {
-            // toggle NDI and reset round
-            sched_ctrl->harq_processes[harq_idx].ndi ^= 1;
-            sched_ctrl->harq_processes[harq_idx].round = 0;
-          }
-          else
-            sched_ctrl->harq_processes[harq_idx].round++;
-          sched_ctrl->harq_processes[harq_idx].is_waiting = 0;
-          harq_idx_s = harq_idx + 1;
-          // if the max harq rounds was reached
-          if (sched_ctrl->harq_processes[harq_idx].round == max_harq_rounds) {
-            sched_ctrl->harq_processes[harq_idx].ndi ^= 1;
-            sched_ctrl->harq_processes[harq_idx].round = 0;
-            UE_info->mac_stats[UE_id].dlsch_errors++;
-          }
-          break;
-        }
-        // if feedback slot processing is aborted
-        else if (sched_ctrl->harq_processes[harq_idx].feedback_slot != -1
-                 && (slot - 1) > sched_ctrl->harq_processes[harq_idx].feedback_slot
-                 && sched_ctrl->harq_processes[harq_idx].is_waiting) {
-          sched_ctrl->harq_processes[harq_idx].feedback_slot = -1;
-          sched_ctrl->harq_processes[harq_idx].round++;
-          if (sched_ctrl->harq_processes[harq_idx].round == max_harq_rounds) {
-            sched_ctrl->harq_processes[harq_idx].ndi ^= 1;
-            sched_ctrl->harq_processes[harq_idx].round = 0;
-          }
-          sched_ctrl->harq_processes[harq_idx].is_waiting = 0;
-        }
-      }
+      const int acknack = ((uci_234->harq.harq_payload[harq_bit >> 3]) >> harq_bit) & 0x01;
+      const int8_t 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];
+      const int feedback_slot = (slot - 1 + num_slots) % num_slots;
+      AssertFatal(harq->feedback_slot == feedback_slot,
+                  "expected feedback slot %d, but found %d instead\n",
+                  harq->feedback_slot, feedback_slot);
+      handle_dl_harq(mod_id, UE_id, pid, uci_234->harq.harq_crc != 1 && acknack);
     }
   }
 }

openair2/LAYER2/NR_MAC_gNB/nr_mac_gNB.h

@@ -75,6 +75,7 @@
 #define MAX_NUM_BWP 2
 #define MAX_NUM_CORESET 2
 #define MAX_NUM_CCE 90
+#define MAX_HARQ_ROUNDS 4
 /*!\brief Maximum number of random access process */
 #define NR_NB_RA_PROC_MAX 4
 #define MAX_NUM_OF_SSB 64
@@ -338,7 +339,7 @@ typedef struct NR_sched_pusch {
 } NR_sched_pusch_t;
 
 typedef struct NR_UE_harq {
-  uint8_t is_waiting;
+  bool is_waiting;
   uint8_t ndi;
   uint8_t round;
   uint16_t feedback_slot;
@@ -425,6 +426,8 @@ typedef struct {
 
   /// Retransmission-related information
   NR_UE_ret_info_t retInfo[NR_MAX_NB_HARQ_PROCESSES];
+  /// DL HARQ PID to use for this UE, or -1 for "any new"
+  int8_t dl_harq_pid;
 
   uint16_t ta_frame;
   int16_t ta_update;