Over-estimate short and long BSR

38.321 6.1.3.1 says: "The size of the RLC headers and MAC subheaders are
not considered in the buffer size computation" [for BSR]. However, prior
to this commit, we take the size signaled of the BSR and schedule the UE
with that amount of data, making it impossible for the UE to transmit
all its data at once (because it is the size signaled + headers).

In this commit, over-estimate the buffer status size. As we cannot know
the exact number and size of headers, we simply use "BSR size + n", as
done in function overestim_bsr_index().

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_ulsch.c

@@ -111,6 +111,65 @@ static int compute_ph_factor(int mu, int tbs_bits, int rb, int n_layers, int n_s
   return ((int)roundf(delta_tf + bw_factor));
 }
 
+/* \brief over-estimate the BSR index, given real_index.
+ *
+ * BSR does not account for headers, so we need to estimate. See 38.321
+ * 6.1.3.1: "The size of the RLC headers and MAC subheaders are not considered
+ * in the buffer size computation." */
+static int overestim_bsr_index(int real_index)
+{
+  /* if UE reports BSR 0, it means "no data"; otherwise, overestimate to
+   * account for headers */
+  const int add_overestim = 1;
+  return real_index > 0 ? real_index + add_overestim : real_index;
+}
+
+static int estimate_ul_buffer_short_bsr(const NR_BSR_SHORT *bsr)
+{
+  /* NOTE: the short BSR might be for different LCGID than 0, but we do not
+   * differentiate them */
+  int rep_idx = bsr->Buffer_size;
+  int estim_idx = overestim_bsr_index(rep_idx);
+  int max = sizeofArray(NR_SHORT_BSR_TABLE);
+  int idx = min(estim_idx, max);
+  int estim_size = NR_SHORT_BSR_TABLE[idx];
+  LOG_D(NR_MAC, "short BSR LCGID %d index %d estim index %d size %d\n", bsr->LcgID, rep_idx, estim_idx, estim_size);
+  return estim_size;
+}
+
+static int estimate_ul_buffer_long_bsr(const NR_BSR_LONG *bsr)
+{
+  LOG_D(NR_MAC,
+        "LONG BSR, LCG ID(7-0) %d/%d/%d/%d/%d/%d/%d/%d\n",
+        bsr->LcgID7,
+        bsr->LcgID6,
+        bsr->LcgID5,
+        bsr->LcgID4,
+        bsr->LcgID3,
+        bsr->LcgID2,
+        bsr->LcgID1,
+        bsr->LcgID0);
+  bool bsr_active[8] = {bsr->LcgID0 != 0, bsr->LcgID1 != 0, bsr->LcgID2 != 0, bsr->LcgID3 != 0, bsr->LcgID4 != 0, bsr->LcgID5 != 0, bsr->LcgID6 != 0, bsr->LcgID7 != 0};
+
+  int estim_size = 0;
+  int max = sizeofArray(NR_LONG_BSR_TABLE);
+  uint8_t *payload = ((uint8_t*) bsr) + 1;
+  int m = 0;
+  const int total_lcgids = 8; /* see 38.321 6.1.3.1 */
+  for (int n = 0; n < total_lcgids; n++) {
+    if (!bsr_active[n])
+      continue;
+    int rep_idx = payload[m];
+    int estim_idx = overestim_bsr_index(rep_idx);
+    int idx = min(estim_idx, max);
+    estim_size += NR_LONG_BSR_TABLE[idx];
+
+    LOG_D(NR_MAC, "LONG BSR LCGID/m %d/%d Index %d estim index %d size %d", n, m, rep_idx, estim_idx, estim_size);
+    m++;
+  }
+  return estim_size;
+}
+
 //  For both UL-SCH except:
 //   - UL-SCH: fixed-size MAC CE(known by LCID)
 //   - UL-SCH: padding
@@ -166,7 +225,6 @@ static int nr_process_mac_pdu(instance_t module_idP,
     LOG_D(NR_MAC, "In %s: received UL-SCH sub-PDU with LCID 0x%x in %d.%d (remaining PDU length %d)\n", __func__, rx_lcid, frameP, slot, pdu_len);
 
     unsigned char *ce_ptr;
-    int n_Lcg = 0;
 
     switch(rx_lcid){
       //  MAC CE
@@ -192,17 +250,8 @@ static int nr_process_mac_pdu(instance_t module_idP,
         }
         /* Extract short BSR value */
         ce_ptr = &pduP[mac_subheader_len];
-        NR_BSR_SHORT *bsr_s = (NR_BSR_SHORT *) ce_ptr;
-        sched_ctrl->estimated_ul_buffer = 0;
-        sched_ctrl->estimated_ul_buffer = NR_SHORT_BSR_TABLE[bsr_s->Buffer_size];
-        LOG_D(NR_MAC,
-              "SHORT BSR at %4d.%2d, LCG ID %d, BS Index %d, BS value < %d, est buf %d\n",
-              frameP,
-              slot,
-              bsr_s->LcgID,
-              bsr_s->Buffer_size,
-              NR_SHORT_BSR_TABLE[bsr_s->Buffer_size],
-              sched_ctrl->estimated_ul_buffer);
+        sched_ctrl->estimated_ul_buffer = estimate_ul_buffer_short_bsr((NR_BSR_SHORT *)ce_ptr);
+        LOG_D(NR_MAC, "SHORT BSR at %4d.%2d, est buf %d\n", frameP, slot, sched_ctrl->estimated_ul_buffer);
         break;
       case UL_SCH_LCID_L_BSR:
       case UL_SCH_LCID_L_TRUNCATED_BSR:
@@ -219,32 +268,8 @@ static int nr_process_mac_pdu(instance_t module_idP,
         }
         /* Extract long BSR value */
         ce_ptr = &pduP[mac_subheader_len];
-        NR_BSR_LONG *bsr_l = (NR_BSR_LONG *) ce_ptr;
-        sched_ctrl->estimated_ul_buffer = 0;
-
-        n_Lcg = bsr_l->LcgID7 + bsr_l->LcgID6 + bsr_l->LcgID5 + bsr_l->LcgID4 +
-                bsr_l->LcgID3 + bsr_l->LcgID2 + bsr_l->LcgID1 + bsr_l->LcgID0;
-
-        LOG_D(NR_MAC, "LONG BSR, LCG ID(7-0) %d/%d/%d/%d/%d/%d/%d/%d\n",
-              bsr_l->LcgID7, bsr_l->LcgID6, bsr_l->LcgID5, bsr_l->LcgID4,
-              bsr_l->LcgID3, bsr_l->LcgID2, bsr_l->LcgID1, bsr_l->LcgID0);
-
-        for (int n = 0; n < n_Lcg; n++){
-          LOG_D(NR_MAC, "LONG BSR, %d/%d (n/n_Lcg), BS Index %d, BS value < %d",
-                n, n_Lcg, pduP[mac_subheader_len + 1 + n],
-                NR_LONG_BSR_TABLE[pduP[mac_subheader_len + 1 + n]]);
-          sched_ctrl->estimated_ul_buffer += NR_LONG_BSR_TABLE[pduP[mac_subheader_len + 1 + n]];
-          LOG_D(NR_MAC,
-                "LONG BSR at %4d.%2d, %d/%d (n/n_Lcg), BS Index %d, BS value < %d, total %d\n",
-                frameP,
-                slot,
-                n,
-                n_Lcg,
-                pduP[mac_subheader_len + 1 + n],
-                NR_LONG_BSR_TABLE[pduP[mac_subheader_len + 1 + n]],
-                sched_ctrl->estimated_ul_buffer);
-        }
-
+        sched_ctrl->estimated_ul_buffer = estimate_ul_buffer_long_bsr((NR_BSR_LONG *)ce_ptr);
+        LOG_D(NR_MAC, "LONG BSR at %4d.%2d, estim buf %d\n", frameP, slot, sched_ctrl->estimated_ul_buffer);
         break;
 
       case UL_SCH_LCID_C_RNTI: