sched,nr: force R<0.9 by reducing mcs

srsenb/hdr/stack/mac/nr/sched_nr_harq.h

@@ -58,7 +58,7 @@ public:
   bool new_retx(slot_point slot_tx, slot_point slot_ack);
 
   // NOTE: Has to be used before first tx is dispatched
-  bool set_tbs(uint32_t tbs);
+  bool set_tbs(uint32_t tbs, int mcs = -1);
 
   const uint32_t pid;
 

srsenb/src/stack/mac/nr/sched_nr_grant_allocator.cc

@@ -243,6 +243,8 @@ alloc_result bwp_slot_allocator::alloc_pdsch(slot_ue& ue, const prb_grant& dl_gr
 
   // Allocation Successful
 
+  int mcs = ue.cfg->ue_cfg()->fixed_dl_mcs;
+  do {
     // Generate PDCCH
     pdcch_dl_t& pdcch = bwp_pdcch_slot.dl_pdcchs.back();
     fill_dl_dci_ue_fields(ue, *bwp_grid.cfg, ss_id, pdcch.dci.ctx.location, pdcch.dci);
@@ -267,6 +269,7 @@ alloc_result bwp_slot_allocator::alloc_pdsch(slot_ue& ue, const prb_grant& dl_gr
     slot_cfg.idx = ue.pdsch_slot.to_uint();
     bool ret     = ue.cfg->phy().get_pdsch_cfg(slot_cfg, pdcch.dci, pdsch.sch);
     srsran_assert(ret, "Error converting DCI to grant");
+
     pdsch.sch.grant.tb[0].softbuffer.tx = ue.h_dl->get_softbuffer().get();
     pdsch.data[0]                       = ue.h_dl->get_tx_pdu()->get();
     if (ue.h_dl->nof_retx() == 0) {
@@ -274,6 +277,18 @@ alloc_result bwp_slot_allocator::alloc_pdsch(slot_ue& ue, const prb_grant& dl_gr
     } else {
       srsran_assert(pdsch.sch.grant.tb[0].tbs == (int)ue.h_dl->tbs(), "The TBS did not remain constant in retx");
     }
+    if (bwp_pdsch_slot.pdschs.back().sch.grant.tb[0].R < 0.9 or mcs == 0) {
+      break;
+    }
+    // Decrease MCS if rate is too high
+    mcs--;
+    ue.h_dl->set_tbs(100, mcs);
+    bwp_pdsch_slot.pdschs.pop_back();
+    bwp_uci_slot.pending_acks.pop_back();
+  } while (true);
+  if (mcs == 0) {
+    logger.warning("Couldn't find mcs that leads to R<0.9");
+  }
 
   return alloc_result::success;
 }

srsenb/src/stack/mac/nr/sched_nr_harq.cc

@@ -66,12 +66,15 @@ bool harq_proc::new_tx(slot_point       slot_tx_,
   return true;
 }
 
-bool harq_proc::set_tbs(uint32_t tbs)
+bool harq_proc::set_tbs(uint32_t tbs, int mcs)
 {
   if (empty() or nof_retx() > 0) {
     return false;
   }
   tb[0].tbs = tbs;
+  if (mcs >= 0) {
+    tb[0].mcs = mcs;
+  }
   return true;
 }