nr,gnb,rrc: fix ssb frequency derivation when coreset0 is active

lib/include/srsran/phy/common/phy_common_nr.h

@@ -704,6 +704,16 @@ SRSRAN_API int srsran_coreset_zero(uint32_t                    n_cell_id,
                                    uint32_t                    idx,
                                    srsran_coreset_t*           coreset);
 
+/**
+ * @brief Obtain offset in RBs between CoresetZero and SSB. See TS 38.213, Tables 13-{1,...,10}
+ * @param idx Index of 13-{1,...10} table
+ * @param ssb_scs SS/PBCH block subcarrier spacing
+ * @param pdcch_scs PDCCH subcarrier spacing
+ * @return offset in RBs, or -1 in case of invalid inputs
+ */
+SRSRAN_API int
+srsran_coreset0_ssb_offset(uint32_t idx, srsran_subcarrier_spacing_t ssb_scs, srsran_subcarrier_spacing_t pdcch_scs);
+
 /**
  * @brief Convert SSB pattern to string
  * @param pattern

lib/src/common/band_helper.cc

@@ -163,7 +163,7 @@ uint32_t srsran_band_helper::get_abs_freq_ssb_arfcn(uint16_t
   double freq_point_a_hz    = nr_arfcn_to_freq(freq_point_a_arfcn);
   double ssb_bw_hz          = SRSRAN_SSB_BW_SUBC * SRSRAN_SUBC_SPACING_NR(scs);
   double coreset0_offset_hz = coreset0_offset_rb * SRSRAN_NRE * SRSRAN_SUBC_SPACING_NR(scs);
-  return find_lower_bound_abs_freq_ssb(band, scs, freq_point_a_hz + coreset0_offset_hz / 2 + ssb_bw_hz / 2);
+  return find_lower_bound_abs_freq_ssb(band, scs, freq_point_a_hz + coreset0_offset_hz + ssb_bw_hz / 2);
 }
 
 srsran_ssb_patern_t srsran_band_helper::get_ssb_pattern(uint16_t band, srsran_subcarrier_spacing_t scs) const

lib/src/common/test/band_helper_test.cc

@@ -51,7 +51,7 @@ int bands_test_nr()
   TESTASSERT(bands.nr_arfcn_to_freq(376000) == 1880.0e6);
   TESTASSERT(bands.get_abs_freq_point_a_arfcn(52, 368500) == 367564);
   TESTASSERT(bands.get_abs_freq_ssb_arfcn(3, srsran_subcarrier_spacing_15kHz, 367564) > 367924);
-  TESTASSERT_EQ(368410, bands.get_abs_freq_ssb_arfcn(3, srsran_subcarrier_spacing_15kHz, 367564, 16));
+  TESTASSERT_EQ(368410, bands.get_abs_freq_ssb_arfcn(3, srsran_subcarrier_spacing_15kHz, 367564, 12));
   // n5
   TESTASSERT(bands.get_duplex_mode(5) == SRSRAN_DUPLEX_MODE_FDD);
   TESTASSERT(bands.nr_arfcn_to_freq(176300) == 881.5e6);

lib/src/phy/common/phy_common_nr.c

@@ -682,6 +682,48 @@ int srsran_coreset_zero(uint32_t                    n_cell_id,
   return SRSRAN_SUCCESS;
 }
 
+int srsran_coreset0_ssb_offset(uint32_t idx, srsran_subcarrier_spacing_t ssb_scs, srsran_subcarrier_spacing_t pdcch_scs)
+{
+  // Verify inputs
+  if (idx >= 16) {
+    ERROR("Invalid CORESET Zero input. idx=%d", idx);
+    return SRSRAN_ERROR_INVALID_INPUTS;
+  }
+
+  // Default entry to NULL
+  const coreset_zero_entry_t* entry = NULL;
+
+  // Table 13-1: Set of resource blocks and slot symbols of CORESET for Type0-PDCCH search space set
+  // when {SS/PBCH block, PDCCH} SCS is {15, 15} kHz for frequency bands with minimum channel
+  // bandwidth 5 MHz or 10 MHz
+  if (ssb_scs == srsran_subcarrier_spacing_15kHz && pdcch_scs == srsran_subcarrier_spacing_15kHz) {
+    entry = &coreset_zero_15_15[idx];
+  }
+  // Table 13-2: Set of resource blocks and slot symbols of CORESET for Type0-PDCCH search space set
+  // when {SS/PBCH block, PDCCH} SCS is {15, 30} kHz for frequency bands with minimum channel
+  // bandwidth 5 MHz or 10 MHz
+  if (ssb_scs == srsran_subcarrier_spacing_15kHz && pdcch_scs == srsran_subcarrier_spacing_30kHz) {
+    entry = &coreset_zero_15_30[idx];
+  }
+
+  // Table 13-3: Set of resource blocks and slot symbols of CORESET for Type0-PDCCH search space set
+  // when {SS/PBCH block, PDCCH} SCS is {30, 15} kHz for frequency bands with minimum channel
+  // bandwidth 5 MHz or 10 MHz
+  if (ssb_scs == srsran_subcarrier_spacing_30kHz && pdcch_scs == srsran_subcarrier_spacing_15kHz) {
+    entry = &coreset_zero_30_15[idx];
+  }
+
+  // Check a valid entry has been selected
+  if (entry == NULL) {
+    ERROR("Unhandled case ssb_scs=%s, pdcch_scs=%s",
+          srsran_subcarrier_spacing_to_str(ssb_scs),
+          srsran_subcarrier_spacing_to_str(pdcch_scs));
+    return SRSRAN_ERROR;
+  }
+
+  return entry->offset_rb;
+}
+
 const char* srsran_ssb_pattern_to_str(srsran_ssb_patern_t pattern)
 {
   switch (pattern) {

srsenb/src/enb_cfg_parser.cc

@@ -1643,23 +1643,20 @@ int set_derived_args_nr(all_args_t* args_, rrc_nr_cfg_t* rrc_nr_cfg_, phy_cfg_t*
     }
 
     // fill remaining SSB fields
-    uint32_t coreset0_rb_offset = 0;
+    int coreset0_rb_offset = 0;
     if (rrc_nr_cfg_->is_standalone) {
-      // Taken from TS 38.213, Table 13-1
+      const uint32_t coreset0_idx           = 6; // See TS 38.331 - controlResourceSetZero / Table 13-1 index
-      if (cfg.phy_cell.carrier.nof_prb > 96) {
+      cfg.phy_cell.pdcch.coreset_present[0] = true;
-        coreset0_rb_offset = 96;
+      // Get offset in RBs between CORESET#0 and SSB
-      } else if (cfg.phy_cell.carrier.nof_prb > 48) {
+      coreset0_rb_offset = srsran_coreset0_ssb_offset(coreset0_idx, cfg.ssb_cfg.scs, cfg.phy_cell.carrier.scs);
-        coreset0_rb_offset = 16;
+      srsran_assert(coreset0_rb_offset >= 0, "Failed to compute RB offset between CORESET#0 and SSB");
-      } else {
-        coreset0_rb_offset = 4;
-      }
     }
     cfg.ssb_absolute_freq_point =
         band_helper.get_abs_freq_ssb_arfcn(cfg.band, cfg.ssb_cfg.scs, cfg.dl_absolute_freq_point_a, coreset0_rb_offset);
-    if (cfg.ssb_absolute_freq_point == 0) {
+    srsran_assert(cfg.ssb_absolute_freq_point > 0,
-      ERROR("Can't derive SSB freq point for dl_arfcn %d and band %d", cfg.dl_arfcn, cfg.band);
+                  "Can't derive SSB freq point for dl_arfcn %d and band %d",
-      return SRSRAN_ERROR;
+                  cfg.dl_arfcn,
-    }
+                  cfg.band);
 
     // Convert to frequency for PHY
     cfg.phy_cell.carrier.ssb_center_freq_hz = band_helper.nr_arfcn_to_freq(cfg.ssb_absolute_freq_point);

srsgnb/src/stack/rrc/rrc_nr.cc

@@ -51,7 +51,7 @@ int rrc_nr::init(const rrc_nr_cfg_t&         cfg_,
   cfg = cfg_;
   if (cfg.is_standalone) {
     // Generate parameters of Coreset#0 and SS#0
-    const uint32_t coreset0_idx                        = 6;
+    const uint32_t coreset0_idx                        = 6; // See TS 38.331 - controlResourceSetZero
     cfg.cell_list[0].phy_cell.pdcch.coreset_present[0] = true;
     // Get pointA and SSB absolute frequencies
     double pointA_abs_freq_Hz = cfg.cell_list[0].phy_cell.carrier.dl_center_frequency_hz -