Provide TBS lookup table for PF coefficient

The TBS calculation is necessary to implement the PF coefficient. To
avoid having to recalculate TDA and DMRS parameters for every UE that we
compare, we pre-calculate (approximate) TB sizes which can be used to
calculate the coefficient.

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_dlsch.c

@@ -438,6 +438,7 @@ bool allocate_dl_retransmission(module_id_t module_id,
 }
 
 float thr_ue[MAX_MOBILES_PER_GNB];
+uint32_t pf_tbs[3][28]; // pre-computed, approximate TBS values for PF coefficient
 
 void pf_dl(module_id_t module_id,
            frame_t frame,
@@ -483,25 +484,9 @@ void pf_dl(module_id_t module_id,
         continue;
 
       /* Calculate coeff */
-      sched_pdsch->time_domain_allocation = 2;
       sched_pdsch->mcsTableIdx = 0;
       sched_pdsch->mcs = 9;
-      sched_pdsch->numDmrsCdmGrpsNoData = 1;
-      sched_pdsch->Qm = nr_get_Qm_dl(sched_pdsch->mcs, sched_pdsch->mcsTableIdx);
-      sched_pdsch->R = nr_get_code_rate_dl(sched_pdsch->mcs, sched_pdsch->mcsTableIdx);
-      int nrOfSymbols = getNrOfSymbols(sched_ctrl->active_bwp, sched_pdsch->time_domain_allocation);
-      const uint8_t N_PRB_DMRS = getN_PRB_DMRS(sched_ctrl->active_bwp, sched_ctrl->sched_pdsch.numDmrsCdmGrpsNoData);
-      const uint8_t N_DMRS_SLOT = get_num_dmrs_symbols(
-          sched_ctrl->active_bwp->bwp_Dedicated->pdsch_Config->choice.setup, scc->dmrs_TypeA_Position, nrOfSymbols);
-      uint32_t tbs = nr_compute_tbs(sched_pdsch->Qm,
-                                    sched_pdsch->R,
-                                    1, // rbSize
-                                    nrOfSymbols,
-                                    N_PRB_DMRS * N_DMRS_SLOT,
-                                    0 /* N_PRB_oh, 0 for initialBWP */,
-                                    0 /* tb_scaling */,
-                                    1 /* nrOfLayers */)
-                     >> 3;
+      uint32_t tbs = pf_tbs[sched_pdsch->mcsTableIdx][sched_pdsch->mcs];
       coeff_ue[UE_id] = (float) tbs / thr_ue[UE_id];
       LOG_D(MAC,"b %d, thr_ue[%d] %f, tbs %d, coeff_ue[%d] %f\n",
             b, UE_id, thr_ue[UE_id], tbs, UE_id, coeff_ue[UE_id]);
@@ -564,23 +549,24 @@ void pf_dl(module_id_t module_id,
       return;
     }
 
-    /* MCS, TDA, etc. has been set above */
-
     // Freq-demain allocation
     while (rbStart < bwpSize && !rballoc_mask[rbStart]) rbStart++;
 
-    const uint8_t N_PRB_DMRS = getN_PRB_DMRS(sched_ctrl->active_bwp, sched_ctrl->sched_pdsch.numDmrsCdmGrpsNoData);
+    /* MCS has been set above */
+    NR_sched_pdsch_t *sched_pdsch = &sched_ctrl->sched_pdsch;
+    sched_pdsch->time_domain_allocation = 2;
+    sched_pdsch->numDmrsCdmGrpsNoData = 1;
+    sched_pdsch->Qm = nr_get_Qm_dl(sched_pdsch->mcs, sched_pdsch->mcsTableIdx);
+    sched_pdsch->R = nr_get_code_rate_dl(sched_pdsch->mcs, sched_pdsch->mcsTableIdx);
     const int nrOfSymbols = getNrOfSymbols(sched_ctrl->active_bwp, sched_ctrl->sched_pdsch.time_domain_allocation);
+    const uint8_t N_PRB_DMRS = getN_PRB_DMRS(sched_ctrl->active_bwp, sched_pdsch->numDmrsCdmGrpsNoData);
     const uint8_t N_DMRS_SLOT = get_num_dmrs_symbols(
-        sched_ctrl->active_bwp->bwp_Dedicated->pdsch_Config->choice.setup,
-        scc->dmrs_TypeA_Position,
-        nrOfSymbols);
+        sched_ctrl->active_bwp->bwp_Dedicated->pdsch_Config->choice.setup, scc->dmrs_TypeA_Position, nrOfSymbols);
 
     int rbSize = 0;
     uint32_t TBS = 0;
     const int oh = 2 + (sched_ctrl->num_total_bytes >= 256)
                  + 2 * (frame == (sched_ctrl->ta_frame + 10) % 1024);
-    NR_sched_pdsch_t *sched_pdsch = &sched_ctrl->sched_pdsch;
     do {
       rbSize++;
       TBS = nr_compute_tbs(sched_pdsch->Qm,
@@ -644,6 +630,29 @@ void nr_fr1_dlsch_preprocessor(module_id_t module_id, frame_t frame, sub_frame_t
 
 nr_pp_impl_dl nr_init_fr1_dlsch_preprocessor(module_id_t module_id, int CC_id)
 {
+  /* in the PF algorithm, we have to use the TBsize to compute the coefficient.
+   * This would include the number of DMRS symbols, which in turn depends on
+   * the time domain allocation. In case we are in a mixed slot, we do not want
+   * to recalculate all these values just, and therefore we provide a look-up
+   * table which should approximately give us the TBsize */
+  for (int mcsTableIdx = 0; mcsTableIdx < 3; ++mcsTableIdx) {
+    for (int mcs = 0; mcs < 29; ++mcs) {
+      if (mcs > 27 && mcsTableIdx == 1)
+        continue;
+      const uint8_t Qm = nr_get_Qm_dl(mcs, mcsTableIdx);
+      const uint16_t R = nr_get_code_rate_dl(mcs, mcsTableIdx);
+      pf_tbs[mcsTableIdx][mcs] = nr_compute_tbs(Qm,
+                                                R,
+                                                1, /* rbSize */
+                                                10, /* hypothetical number of slots */
+                                                0, /* N_PRB_DMRS * N_DMRS_SLOT */
+                                                0 /* N_PRB_oh, 0 for initialBWP */,
+                                                0 /* tb_scaling */,
+                                                1 /* nrOfLayers */)
+                                 >> 3;
+    }
+  }
+
   return nr_fr1_dlsch_preprocessor;
 }