srsgnb,sched: mark as occupied the resources used by SSB before scheduling other PDSCH (eg SIB1). Prevents overlapping SIB1 PDSCH with SSB

srsgnb/hdr/stack/mac/sched_nr_grant_allocator.h

@@ -57,6 +57,8 @@ struct bwp_slot_grid {
   explicit bwp_slot_grid(const bwp_params_t& bwp_params, uint32_t slot_idx_);
   void reset();
 
+  void reserve_pdsch(const prb_grant& grant) { pdschs.reserve_prbs(grant); }
+
   bool is_dl() const { return cfg->slots[slot_idx].is_dl; }
   bool is_ul() const { return cfg->slots[slot_idx].is_ul; }
 };

srsgnb/hdr/stack/mac/sched_nr_sch.h

@@ -46,6 +46,9 @@ public:
     return dl_prbs.prbs();
   }
 
+  /// Marks a range of PRBS as occupied, preventing further allocations
+  void reserve_prbs(const prb_grant& grant) { dl_prbs |= grant; }
+
   /// Verifies if the input arguments are valid for an SI allocation and grant doesnt collide with other grants
   alloc_result is_si_grant_valid(uint32_t ss_id, const prb_grant& grant) const;
 

srsgnb/src/stack/mac/sched_nr_signalling.cc

@@ -96,6 +96,17 @@ void sched_dl_signalling(bwp_slot_allocator& bwp_alloc)
   // Schedule SSB
   sched_ssb_basic(sl_pdcch, bwp_params.cell_cfg.ssb.periodicity_ms, bwp_params.cell_cfg.mib, sl_grid.dl.phy.ssb);
 
+  // Mark SSB region as occupied
+  if (!sl_grid.dl.phy.ssb.empty()) {
+    float ssb_offset_hz =
+        bwp_params.cell_cfg.carrier.ssb_center_freq_hz - bwp_params.cell_cfg.carrier.dl_center_frequency_hz;
+    int      ssb_offset_rb = ceil(ssb_offset_hz / (15000.0f * 12));
+    int      ssb_start_rb  = bwp_params.cell_cfg.carrier.nof_prb / 2 + ssb_offset_rb - 10;
+    uint32_t ssb_len_rb    = 20;
+    assert(ssb_start_rb >= 0 && ssb_start_rb + ssb_len_rb < bwp_params.cell_cfg.carrier.nof_prb);
+    sl_grid.reserve_pdsch(prb_grant({(uint32_t)ssb_start_rb, ssb_start_rb + ssb_len_rb}));
+  }
+
   // Schedule NZP-CSI-RS
   sched_nzp_csi_rs(bwp_params.cfg.pdsch.nzp_csi_rs_sets, cfg, sl_grid.dl.phy.nzp_csi_rs);
 }
@@ -150,12 +161,10 @@ void si_sched::run_slot(bwp_slot_allocator& bwp_alloc)
       }
     } else if (si.win_start + si.win_len_slots >= sl_pdcch) {
       // If end of SI message window
-      if (si.n == 0) {
-        logger.error("SCHED: Could not allocate SIB1, len=%d. Cause: %s", si.len_bytes, to_string(si.result));
-      } else {
-        logger.warning(
-            "SCHED: Could not allocate SI message idx=%d, len=%d. Cause: %s", si.n, si.len_bytes, to_string(si.result));
-      }
+      srsran_always_assert(
+          si.n == 0, "SCHED: Could not allocate SIB1, len=%d. Cause: %s", si.len_bytes, to_string(si.result));
+      logger.warning(
+          "SCHED: Could not allocate SI message idx=%d, len=%d. Cause: %s", si.n, si.len_bytes, to_string(si.result));
       si.win_start.clear();
     }
   }

srsgnb/src/stack/mac/sched_nr_worker.cc

@@ -74,9 +74,15 @@ dl_sched_res_t* cc_worker::run_slot(slot_point tx_sl, ue_map_t& ue_db)
   // Log UEs state for slot
   log_sched_slot_ues(logger, tx_sl, cfg.cc, slot_ues);
 
+  const uint32_t ss_id    = 0;
+  slot_point     sl_pdcch = bwp_alloc.get_pdcch_tti();
+
+  prb_bitmap prbs_before = bwp_alloc.res_grid()[sl_pdcch].pdschs.occupied_prbs(ss_id, srsran_dci_format_nr_1_0);
   // Allocate cell DL signalling
   sched_dl_signalling(bwp_alloc);
 
+  prb_bitmap prbs_after = bwp_alloc.res_grid()[sl_pdcch].pdschs.occupied_prbs(ss_id, srsran_dci_format_nr_1_0);
+
   // Allocate pending SIBs
   bwps[0].si.run_slot(bwp_alloc);