ue_dl: reference point for DMRS varies for SIB

lib/include/srsran/phy/phch/phch_cfg_nr.h

@@ -77,6 +77,8 @@ typedef struct {
   srsran_dmrs_sch_typeA_pos_t typeA_pos;
   bool                        lte_CRS_to_match_around;
 
+  uint32_t reference_point_k_rb;
+
   /// Parameters provided by FeatureSetDownlink-v1540
   bool additional_DMRS_DL_Alt;
 

lib/src/phy/ch_estimation/dmrs_sch.c

@@ -216,7 +216,8 @@ static int srsran_dmrs_sch_put_symbol(srsran_dmrs_sch_t*           q,
         // ... save first consecutive PRB in the group
         prb_start = prb_idx;
 
-        // ... discard unused pilots and reset counter
+        // ... discard unused pilots and reset counter unless the PDSCH transmission carries SIB
+        prb_skip = SRSRAN_MAX(0, (int)prb_skip - (int)dmrs_cfg->reference_point_k_rb);
         srsran_sequence_state_advance(&sequence_state, prb_skip * nof_pilots_x_prb * 2);
         prb_skip = 0;
       }
@@ -704,7 +705,8 @@ static int srsran_dmrs_sch_get_symbol(srsran_dmrs_sch_t*           q,
         // ... save first consecutive PRB in the group
         prb_start = prb_idx;
 
-        // ... discard unused pilots and reset counter
+        // ... discard unused pilots and reset counter unless the PDSCH transmission carries SIB
+        prb_skip = SRSRAN_MAX(0, (int)prb_skip - (int)dmrs_cfg->reference_point_k_rb);
         srsran_sequence_state_advance(&sequence_state, prb_skip * nof_pilots_x_prb * 2);
         prb_skip = 0;
       }

lib/src/phy/ue/test/ue_dl_nr_file_test.cc

@@ -205,6 +205,14 @@ static int work_ue_dl(srsran_ue_dl_nr_t* ue_dl, srsran_slot_cfg_t* slot)
   srsran_pdsch_res_nr_t pdsch_res = {};
   pdsch_res.tb[0].payload         = data;
 
+  // See 7.4.1.1.2 38.211 The reference point for k is
+  // - for PDSCH transmission carrying SIB1, subcarrier 0 of the lowest-numbered common resource block in the
+  //  CORESET configured by the PBCH
+  //- otherwise, subcarrier 0 in common resource block 0
+  if (rnti_type == srsran_rnti_type_si) {
+    pdsch_cfg.dmrs.reference_point_k_rb = pdcch_cfg.coreset[0].offset_rb;
+  }
+
   // Decode PDSCH
   if (srsran_ue_dl_nr_decode_pdsch(ue_dl, slot, &pdsch_cfg, &pdsch_res) < SRSRAN_SUCCESS) {
     ERROR("Error decoding PDSCH search");