Set DL MCS when receiving CQI report

- Introduce generic get_mcs_from_cqi() that gets MCS for a particular
  CQI
- Set MCS after receiving CQI
- Distinguish "global" max MCS from UE-measured max MCS

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_dlsch.c

@@ -404,13 +404,9 @@ int get_mcs_from_bler(module_id_t mod_id, int CC_id, frame_t frame, sub_frame_t
   const NR_ServingCellConfigCommon_t *scc = nrmac->common_channels[CC_id].ServingCellConfigCommon;
   const int n = nr_slots_per_frame[*scc->ssbSubcarrierSpacing];
   int max_allowed_mcs = (mcs_table == 1) ? 27 : 28;
-  int max_mcs = nrmac->dl_max_mcs;
-
-  if (nrmac->dl_max_mcs>max_allowed_mcs)
-    max_mcs = max_allowed_mcs;
-
-  NR_DL_bler_stats_t *bler_stats = &nrmac->UE_info.UE_sched_ctrl[UE_id].dl_bler_stats;
 
+  NR_UE_sched_ctrl_t *sched_ctrl = &nrmac->UE_info.UE_sched_ctrl[UE_id];
+  NR_DL_bler_stats_t *bler_stats = &sched_ctrl->dl_bler_stats;
   /* first call: everything is zero. Initialize to sensible default */
   if (bler_stats->last_frame_slot == 0 && bler_stats->mcs == 0) {
     bler_stats->last_frame_slot = frame * n + slot;
@@ -458,6 +454,7 @@ int get_mcs_from_bler(module_id_t mod_id, int CC_id, frame_t frame, sub_frame_t
   if (bler_stats->rd2_bler > nrmac->dl_rd2_bler_threshold && old_mcs > 6) {
     new_mcs -= 2;
   } else if (bler_stats->rd2_bler < nrmac->dl_rd2_bler_threshold) {*/
+  const int max_mcs = min(max_allowed_mcs, min(sched_ctrl->dl_max_mcs, nrmac->dl_max_mcs));
   if (bler_stats->bler < nrmac->dl_bler_target_lower && old_mcs < max_mcs && dtx > 9)
     new_mcs += 1;
   else if (bler_stats->bler > nrmac->dl_bler_target_upper && old_mcs > 6)
@@ -772,7 +769,6 @@ void pf_dl(module_id_t module_id,
         continue;
 
       /* Calculate coeff */
-      set_dl_mcs(sched_pdsch,sched_ctrl,&mac->dl_max_mcs,ps->mcsTableIdx);
       sched_pdsch->mcs = get_mcs_from_bler(module_id, /* CC_id = */ 0, frame, slot, UE_id, ps->mcsTableIdx);
       layers[UE_id] = set_dl_nrOfLayers(sched_ctrl);
       const uint8_t Qm = nr_get_Qm_dl(sched_pdsch->mcs, ps->mcsTableIdx);

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_primitives.c

@@ -145,7 +145,6 @@ uint8_t set_dl_nrOfLayers(NR_UE_sched_ctrl_t *sched_ctrl) {
 
 }
 
-
 uint16_t set_pm_index(NR_UE_sched_ctrl_t *sched_ctrl,
                       int layers,
                       int N1, int N2,
@@ -169,20 +168,19 @@ uint16_t set_pm_index(NR_UE_sched_ctrl_t *sched_ctrl,
     AssertFatal(1==0,"More than 2 antenna ports not yet supported\n");
 }
 
+uint8_t get_mcs_from_cqi(int mcs_table, int cqi_table, int cqi_idx)
+{
+  if (cqi_idx <= 0) {
+    LOG_E(NR_MAC, "invalid cqi_idx %d, default to MCS 9\n", cqi_idx);
+    return 9;
+  }
+
+  if (mcs_table != cqi_table) {
+    LOG_E(NR_MAC, "indices of CQI (%d) and MCS (%d) tables don't correspond yet\n", cqi_table, mcs_table);
+    return 9;
+  }
 
-void set_dl_mcs(NR_sched_pdsch_t *sched_pdsch,
-                NR_UE_sched_ctrl_t *sched_ctrl,
-                uint8_t *target_mcs,
-                uint8_t mcs_table_idx) {
-
-  if (sched_ctrl->set_mcs) {
-    // TODO for wideband case and multiple TB
-    int cqi_idx = sched_ctrl->CSI_report.cri_ri_li_pmi_cqi_report.wb_cqi_1tb;
-    uint16_t target_coderate,target_qm;
-    if (cqi_idx>0) {
-      int cqi_table = sched_ctrl->CSI_report.cri_ri_li_pmi_cqi_report.cqi_table;
-      if (cqi_table != mcs_table_idx)
-       LOG_W(NR_MAC,"Indices of MCS tables don't correspond yet, cri_ri_li_pmi_cqi_report.cqi_table %d, mcs_table_index %d\n",cqi_table,mcs_table_idx);
+  uint16_t target_coderate, target_qm;
   switch (cqi_table) {
     case 0:
       target_qm = cqi_table1[cqi_idx][0];
@@ -199,21 +197,16 @@ void set_dl_mcs(NR_sched_pdsch_t *sched_pdsch,
     default:
       AssertFatal(1==0,"Invalid cqi table index %d\n",cqi_table);
   }
-      int max_mcs = 28;
-      int R,Qm;
-      if (mcs_table_idx == 1)
-        max_mcs = 27;
-      for (int i=0; i<=max_mcs; i++) {
-        R = nr_get_code_rate_dl(i, mcs_table_idx);
-        Qm = nr_get_Qm_dl(i, mcs_table_idx);
-        if ((Qm == target_qm) && (target_coderate <= R)) {
-          *target_mcs = i;
-          break;
-        }
-      }
-    }
-    sched_ctrl->set_mcs = false;
+  const int max_mcs = mcs_table == 1 ? 27 : 28;
+  for (int i = 0; i <= max_mcs; i++) {
+    const int R = nr_get_code_rate_dl(i, mcs_table);
+    const int Qm = nr_get_Qm_dl(i, mcs_table);
+    if (Qm == target_qm && target_coderate <= R)
+      return i;
   }
+
+  LOG_E(NR_MAC, "could not find maximum MCS from cqi_idx %d, default to 9\n", cqi_idx);
+  return 9;
 }
 
 void set_dl_dmrs_ports(NR_pdsch_semi_static_t *ps) {
@@ -2359,7 +2352,7 @@ int add_new_nr_ue(module_id_t mod_idP, rnti_t rntiP, NR_CellGroupConfig_t *CellG
       compute_csi_bitlen (CellGroup->spCellConfig->spCellConfigDedicated->csi_MeasConfig->choice.setup, UE_info, UE_id, mod_idP);
     NR_UE_sched_ctrl_t *sched_ctrl = &UE_info->UE_sched_ctrl[UE_id];
     memset(sched_ctrl, 0, sizeof(*sched_ctrl));
-    sched_ctrl->set_mcs = true;
+    sched_ctrl->dl_max_mcs = 28; /* do not limit MCS for individual UEs */
     sched_ctrl->set_pmi = false;
     sched_ctrl->ta_frame = 0;
     sched_ctrl->ta_update = 31;

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_uci.c

@@ -1250,7 +1250,12 @@ void evaluate_cqi_report(uint8_t *payload,
     sched_ctrl->CSI_report.cri_ri_li_pmi_cqi_report.wb_cqi_2tb = temp_cqi;
     LOG_D(MAC,"Wide-band CQI for the second TB %d\n", temp_cqi);
   }
-  sched_ctrl->set_mcs = true;
+
+  // TODO for wideband case and multiple TB
+  const int cqi_idx = sched_ctrl->CSI_report.cri_ri_li_pmi_cqi_report.wb_cqi_1tb;
+  const int mcs_table = sched_ctrl->pdsch_semi_static.mcsTableIdx;
+  const int cqi_table = sched_ctrl->CSI_report.cri_ri_li_pmi_cqi_report.cqi_table;
+  sched_ctrl->dl_max_mcs = get_mcs_from_cqi(mcs_table, cqi_table, cqi_idx);
 }
 
 

openair2/LAYER2/NR_MAC_gNB/mac_proto.h

@@ -514,10 +514,7 @@ uint16_t set_pm_index(NR_UE_sched_ctrl_t *sched_ctrl,
                       int xp_pdsch_antenna_ports,
                       int codebook_mode);
 
-void set_dl_mcs(NR_sched_pdsch_t *sched_pdsch,
-                NR_UE_sched_ctrl_t *sched_ctrl,
-                uint8_t *target_mcs,
-                uint8_t mcs_table_idx);
+uint8_t get_mcs_from_cqi(int mcs_table, int cqi_table, int cqi_idx);
 
 uint8_t set_dl_nrOfLayers(NR_UE_sched_ctrl_t *sched_ctrl);
 

openair2/LAYER2/NR_MAC_gNB/nr_mac_gNB.h

@@ -613,6 +613,9 @@ typedef struct {
   NR_pdsch_semi_static_t pdsch_semi_static;
   /// Sched PDSCH: scheduling decisions, copied into HARQ and cleared every TTI
   NR_sched_pdsch_t sched_pdsch;
+  /// UE-estimated maximum MCS (from CSI-RS)
+  uint8_t dl_max_mcs;
+
   /// For UL synchronization: store last UL scheduling grant
   frame_t last_ul_frame;
   sub_frame_t last_ul_slot;
@@ -641,7 +644,6 @@ typedef struct {
   int ul_failure;
   struct CSI_Report CSI_report;
   bool SR;
-  bool set_mcs;
   bool set_pmi;
   /// information about every HARQ process
   NR_UE_harq_t harq_processes[NR_MAX_NB_HARQ_PROCESSES];