Add MCS from HARQ BLER

- Estimates correct MCS using EMA, kept between target thresholds
  dl_bler_target_upper and dl_bler_target_lower (conf options) for 1st
  retx and below dl_rd2_bler_threshold for 2nd retx
- Maximum MCS configurable
- on 3rd retx, reduce MCS by 5

openair2/GNB_APP/MACRLC_nr_paramdef.h

@@ -60,6 +60,11 @@
 #define CONFIG_STRING_MACRLC_PUCCHTARGETSNRX10             "pucch_TargetSNRx10"
 #define CONFIG_STRING_MACRLC_PUCCHFAILURETHRES             "pucch_FailureThres"
 #define CONFIG_STRING_MACRLC_PUSCHFAILURETHRES             "pusch_FailureThres"
+#define CONFIG_STRING_MACRLC_DL_BLER_TARGET_UPPER          "dl_bler_target_upper"
+#define CONFIG_STRING_MACRLC_DL_BLER_TARGET_LOWER          "dl_bler_target_lower"
+#define CONFIG_STRING_MACRLC_DL_RD2_BLER_THRESHOLD         "dl_rd2_bler_threshold"
+#define CONFIG_STRING_MACRLC_DL_MAX_MCS                    "dl_max_mcs"
+
 
 /*-------------------------------------------------------------------------------------------------------------------------------------------------------*/
 /*                                            MacRLC  configuration parameters                                                                           */
@@ -88,6 +93,10 @@
 {CONFIG_STRING_MACRLC_PUCCHTARGETSNRX10,                 NULL,     0,          iptr:NULL,           defintval:150,             TYPE_INT,      0},        \
 {CONFIG_STRING_MACRLC_PUCCHFAILURETHRES,                 NULL,     0,          iptr:NULL,           defintval:10,              TYPE_INT,      0},        \
 {CONFIG_STRING_MACRLC_PUSCHFAILURETHRES,                 NULL,     0,          iptr:NULL,           defintval:10,              TYPE_INT,      0},        \
+{CONFIG_STRING_MACRLC_DL_BLER_TARGET_UPPER,   "Upper threshold of BLER to decrease DL MCS",   0, dblptr:NULL,  defdblval:0.15,  TYPE_DOUBLE,  0},        \
+{CONFIG_STRING_MACRLC_DL_BLER_TARGET_LOWER,   "Lower threshold of BLER to increase DL MCS",   0, dblptr:NULL,  defdblval:0.05,  TYPE_DOUBLE,  0},        \
+{CONFIG_STRING_MACRLC_DL_RD2_BLER_THRESHOLD,  "Threshold of RD2/RETX2 BLER to decrease DL MCS", 0, dblptr:NULL,  defdblval:0.01,  TYPE_DOUBLE,  0},      \
+{CONFIG_STRING_MACRLC_DL_MAX_MCS,             "Maximum DL MCS that should be used", 0, u8ptr:NULL,  defintval:20,  TYPE_UINT8,  0},      \
 }
 #define MACRLC_CC_IDX                                          0
 #define MACRLC_TRANSPORT_N_PREFERENCE_IDX                      1
@@ -111,5 +120,10 @@
 #define MACRLC_PUCCHTARGETSNRX10_IDX                           19
 #define MACRLC_PUCCHFAILURETHRES_IDX                           20
 #define MACRLC_PUSCHFAILURETHRES_IDX                           21
+#define MACRLC_DL_BLER_TARGET_UPPER_IDX                        22
+#define MACRLC_DL_BLER_TARGET_LOWER_IDX                        23
+#define MACRLC_DL_RD2_BLER_THRESHOLD_IDX                       24
+#define MACRLC_DL_MAX_MCS_IDX                                  25
+
 /*---------------------------------------------------------------------------------------------------------------------------------------------------------*/
 #endif

openair2/GNB_APP/gnb_config.c

@@ -697,6 +697,10 @@ void RCconfig_nr_macrlc() {
         AssertFatal(1==0,"MACRLC %d: %s unknown southbound midhaul\n",j,*(MacRLC_ParamList.paramarray[j][MACRLC_TRANSPORT_S_PREFERENCE_IDX].strptr));
       } 
       RC.nrmac[j]->ulsch_max_slots_inactivity = *(MacRLC_ParamList.paramarray[j][MACRLC_ULSCH_MAX_SLOTS_INACTIVITY].uptr);
+      RC.nrmac[j]->dl_bler_target_upper = *(MacRLC_ParamList.paramarray[j][MACRLC_DL_BLER_TARGET_UPPER_IDX].dblptr);
+      RC.nrmac[j]->dl_bler_target_lower = *(MacRLC_ParamList.paramarray[j][MACRLC_DL_BLER_TARGET_LOWER_IDX].dblptr);
+      RC.nrmac[j]->dl_rd2_bler_threshold = *(MacRLC_ParamList.paramarray[j][MACRLC_DL_RD2_BLER_THRESHOLD_IDX].dblptr);
+      RC.nrmac[j]->dl_max_mcs = *(MacRLC_ParamList.paramarray[j][MACRLC_DL_MAX_MCS_IDX].u8ptr);
     }//  for (j=0;j<RC.nb_nr_macrlc_inst;j++)
   }else {// MacRLC_ParamList.numelt > 0
     LOG_E(PHY,"No %s configuration found\n", CONFIG_STRING_MACRLC_LIST);

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler.c

@@ -77,25 +77,28 @@ void dump_mac_stats(gNB_MAC_INST *gNB)
   int stroff=0;
   for (int UE_id = UE_info->list.head; UE_id >= 0; UE_id = UE_info->list.next[UE_id]) {
     stroff = sprintf(output,"UE ID %d RNTI %04x (%d/%d)\n", UE_id, UE_info->rnti[UE_id], num++, UE_info->num_UEs);
-    LOG_I(NR_MAC, "UE ID %d RNTI %04x (%d/%d) PH %d dB PCMAX %d dBm\n",
-      UE_id,
-      UE_info->rnti[UE_id],
-      num++,
-      UE_info->num_UEs,
-      UE_info->UE_sched_ctrl[UE_id].ph,
-      UE_info->UE_sched_ctrl[UE_id].pcmax);
     NR_mac_stats_t *stats = &UE_info->mac_stats[UE_id];
+    const NR_UE_sched_ctrl_t *sched_ctrl = &UE_info->UE_sched_ctrl[UE_id];
     const int avg_rsrp = stats->num_rsrp_meas > 0 ? stats->cumul_rsrp / stats->num_rsrp_meas : 0;
-    stroff+=sprintf(output+stroff,"UE %d: dlsch_rounds %d/%d/%d/%d, dlsch_errors %d, average RSRP %d (%d meas)\n",
+    LOG_I(MAC, "UE ID %d RNTI %04x (%d/%d) PH %d dB PCMAX %d dBm, average RSRP %d (%d meas)\n",
+          UE_id,
+          UE_info->rnti[UE_id],
+          num++,
+          UE_info->num_UEs,
+          sched_ctrl->ph,
+          sched_ctrl->pcmax,
+          avg_rsrp,
+          stats->num_rsrp_meas);
+    stroff+=sprintf(output+stroff,"UE %d: dlsch_rounds %d/%d/%d/%d, dlsch_errors %d, BLER %.5f MCS %d\n",
+          UE_id,
+          stats->dlsch_rounds[0], stats->dlsch_rounds[1],
+          stats->dlsch_rounds[2], stats->dlsch_rounds[3], stats->dlsch_errors,
+          sched_ctrl->dl_bler_stats.bler, sched_ctrl->dl_bler_stats.mcs);
+    LOG_I(MAC, "UE %d: dlsch_rounds %d/%d/%d/%d, dlsch_errors %d, BLER %.5f MCS %d\n",
           UE_id,
           stats->dlsch_rounds[0], stats->dlsch_rounds[1],
           stats->dlsch_rounds[2], stats->dlsch_rounds[3], stats->dlsch_errors,
-          avg_rsrp, stats->num_rsrp_meas);
-    LOG_I(NR_MAC, "UE %d: dlsch_rounds %d/%d/%d/%d, dlsch_errors %d, average RSRP %d (%d meas)\n",
-      UE_id,
-      stats->dlsch_rounds[0], stats->dlsch_rounds[1],
-      stats->dlsch_rounds[2], stats->dlsch_rounds[3], stats->dlsch_errors,
-      avg_rsrp, stats->num_rsrp_meas);
+          sched_ctrl->dl_bler_stats.bler, sched_ctrl->dl_bler_stats.mcs);
     stats->num_rsrp_meas = 0;
     stats->cumul_rsrp = 0 ;
     stroff+=sprintf(output+stroff,"UE %d: dlsch_total_bytes %d\n", UE_id, stats->dlsch_total_bytes);

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_dlsch.c

@@ -381,6 +381,71 @@ int nr_write_ce_dlsch_pdu(module_id_t module_idP,
   return offset;
 }
 
+#define BLER_UPDATE_FRAME 10
+#define BLER_FILTER 0.9f
+int get_mcs_from_bler(module_id_t mod_id, int CC_id, frame_t frame, sub_frame_t slot, int UE_id)
+{
+  gNB_MAC_INST *nrmac = RC.nrmac[mod_id];
+  const NR_ServingCellConfigCommon_t *scc = nrmac->common_channels[CC_id].ServingCellConfigCommon;
+  const int n = nr_slots_per_frame[*scc->ssbSubcarrierSpacing];
+
+  NR_DL_bler_stats_t *bler_stats = &nrmac->UE_info.UE_sched_ctrl[UE_id].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;
+    bler_stats->mcs = 9;
+    bler_stats->bler = (nrmac->dl_bler_target_lower + nrmac->dl_bler_target_upper) / 2;
+    bler_stats->rd2_bler = nrmac->dl_rd2_bler_threshold;
+  }
+  const int now = frame * n + slot;
+  int diff = now - bler_stats->last_frame_slot;
+  if (diff < 0) // wrap around
+    diff += 1024 * n;
+
+  const uint8_t old_mcs = bler_stats->mcs;
+  const NR_mac_stats_t *stats = &nrmac->UE_info.mac_stats[UE_id];
+  const int dret3x = stats->dlsch_rounds[3] - bler_stats->dlsch_rounds[3];
+  if (dret3x > 0) {
+    /* if there is a third retransmission, decrease MCS for stabilization and
+     * restart averaging window to stabilize transmission */
+    bler_stats->last_frame_slot = now;
+    bler_stats->mcs = max(9, bler_stats->mcs - 5);
+    memcpy(bler_stats->dlsch_rounds, stats->dlsch_rounds, sizeof(stats->dlsch_rounds));
+    LOG_D(MAC, "%4d.%2d: %d retx in 3rd round, setting MCS to %d and restarting window\n", frame, slot, dret3x, bler_stats->mcs);
+    return bler_stats->mcs;
+  }
+  if (diff < BLER_UPDATE_FRAME * n)
+    return old_mcs; // no update
+
+  // last update is longer than x frames ago
+  const int dtx = stats->dlsch_rounds[0] - bler_stats->dlsch_rounds[0];
+  const int dretx = stats->dlsch_rounds[1] - bler_stats->dlsch_rounds[1];
+  const int dretx2 = stats->dlsch_rounds[2] - bler_stats->dlsch_rounds[2];
+  const float bler_window = dtx > 0 ? (float) dretx / dtx : bler_stats->bler;
+  const float rd2_bler_wnd = dtx > 0 ? (float) dretx2 / dtx : bler_stats->rd2_bler;
+  bler_stats->bler = BLER_FILTER * bler_stats->bler + (1 - BLER_FILTER) * bler_window;
+  bler_stats->rd2_bler = BLER_FILTER / 4 * bler_stats->rd2_bler + (1 - BLER_FILTER / 4) * rd2_bler_wnd;
+
+  int new_mcs = old_mcs;
+  /* first ensure that number of 2nd retx is below threshold. If this is the
+   * case, use 1st retx to adjust faster */
+  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) {
+    if (bler_stats->bler < nrmac->dl_bler_target_lower && old_mcs < nrmac->dl_max_mcs && dtx > 9)
+      new_mcs += 1;
+    else if (bler_stats->bler > nrmac->dl_bler_target_upper && old_mcs > 6)
+      new_mcs -= 1;
+    // else we are within threshold boundaries
+  }
+
+  bler_stats->last_frame_slot = now;
+  bler_stats->mcs = new_mcs;
+  memcpy(bler_stats->dlsch_rounds, stats->dlsch_rounds, sizeof(stats->dlsch_rounds));
+  LOG_D(MAC, "%4d.%2d MCS %d -> %d (dtx %d, dretx %d, BLER wnd %.3f avg %.6f, dretx2 %d, RD2 BLER wnd %.3f avg %.6f)\n", frame, slot, old_mcs, new_mcs, dtx, dretx, bler_window, bler_stats->bler, dretx2, rd2_bler_wnd, bler_stats->rd2_bler);
+  return new_mcs;
+}
+
 void nr_store_dlsch_buffer(module_id_t module_id,
                            frame_t frame,
                            sub_frame_t slot) {
@@ -600,8 +665,8 @@ void pf_dl(module_id_t module_id,
         continue;
 
       /* Calculate coeff */
-      sched_pdsch->mcs = 9;
       ps->nrOfLayers = 1;
+      sched_pdsch->mcs = get_mcs_from_bler(module_id, /* CC_id = */ 0, frame, slot, UE_id);
       uint32_t tbs = pf_tbs[ps->mcsTableIdx][sched_pdsch->mcs];
       coeff_ue[UE_id] = (float) tbs / thr_ue[UE_id];
       LOG_D(NR_MAC,"b %d, thr_ue[%d] %f, tbs %d, coeff_ue[%d] %f\n",

openair2/LAYER2/NR_MAC_gNB/nr_mac_gNB.h

@@ -420,6 +420,13 @@ typedef struct NR_UE_harq {
 
 //! fixme : need to enhace for the multiple TB CQI report
 
+typedef struct NR_DL_bler_stats {
+  frame_t last_frame_slot;
+  float bler;
+  float rd2_bler;
+  uint8_t mcs;
+  int dlsch_rounds[8];
+} NR_DL_bler_stats_t;
 
 //
 /*! As per spec 38.214 section 5.2.1.4.2
@@ -563,6 +570,10 @@ typedef struct {
   mac_rlc_status_resp_t rlc_status[MAX_NUM_LCID];
 
   int lcid_mask;
+
+  /// Estimation of HARQ from BLER
+  NR_DL_bler_stats_t dl_bler_stats;
+
   uint16_t ta_frame;
   int16_t ta_update;
   bool ta_apply;
@@ -754,6 +765,10 @@ typedef struct gNB_MAC_INST_s {
   NR_Type0_PDCCH_CSS_config_t type0_PDCCH_CSS_config[64];
 
   bool first_MIB;
+  double dl_bler_target_upper;
+  double dl_bler_target_lower;
+  double dl_rd2_bler_threshold;
+  uint8_t dl_max_mcs;
 } gNB_MAC_INST;
 
 #endif /*__LAYER2_NR_MAC_GNB_H__ */