fix for computing ssb subcarrier offset

common/utils/nr/nr_common.c

@@ -755,11 +755,20 @@ void SLIV2SL(int SLIV,int *S,int *L) {
   }
 }
 
-int get_ssb_subcarrier_offset(uint32_t absoluteFrequencySSB, uint32_t absoluteFrequencyPointA)
+nr_sco_info_t get_ssb_subcarrier_offset(int scs, uint32_t absoluteFrequencySSB, uint32_t absoluteFrequencyPointA)
 {
-  uint32_t absolute_diff = (absoluteFrequencySSB - absoluteFrequencyPointA);
-  const int scaling_5khz = absoluteFrequencyPointA < 600000 ? 3 : 1;
-  return ((absolute_diff / scaling_5khz) % 24);
+  nr_sco_info_t sco;
+  // for FR1 k_SSB expressed in terms of 15kHz SCS
+  // for FR2 k_SSB expressed in terms of the subcarrier spacing provided by the higher-layer parameter subCarrierSpacingCommon
+  sco.absolute_diff = (absoluteFrequencySSB - absoluteFrequencyPointA);
+  sco.scaling = 1;
+  if (absoluteFrequencyPointA < 600000)
+    sco.scaling = 3;
+  if (scs > 2)
+    sco.scaling <<= (scs - 2);
+  int sco_limit = scs == 1 ? 24 : 12;
+  sco.subcarrier_offset = ((sco.absolute_diff / sco.scaling) % sco_limit);
+  return sco;
 }
 
 uint32_t get_ssb_offset_to_pointA(uint32_t absoluteFrequencySSB,
@@ -767,16 +776,14 @@ uint32_t get_ssb_offset_to_pointA(uint32_t absoluteFrequencySSB,
                                   int ssbSubcarrierSpacing,
                                   int frequency_range)
 {
-  uint32_t absolute_diff = (absoluteFrequencySSB - absoluteFrequencyPointA);
-  const int scaling_5khz = absoluteFrequencyPointA < 600000 ? 3 : 1;
-  int sco = get_ssb_subcarrier_offset(absoluteFrequencySSB, absoluteFrequencyPointA);
+  nr_sco_info_t sco = get_ssb_subcarrier_offset(ssbSubcarrierSpacing, absoluteFrequencySSB, absoluteFrequencyPointA);
   const int scs_scaling = frequency_range == FR2 ? 1 << (ssbSubcarrierSpacing - 2) : 1 << ssbSubcarrierSpacing;
-  const int scaled_abs_diff = absolute_diff / scaling_5khz;
-  const int ssb_offset_point_a =
-      (scaled_abs_diff - sco) / 12
-      - 10 * scs_scaling; // absoluteFrequencySSB is the central frequency of SSB which is made by 20RBs in total
+  const int scaled_abs_diff = sco.absolute_diff / sco.scaling;
+  // absoluteFrequencySSB is the central frequency of SSB which is made by 20RBs in total
+  const int cent_freq_comp = frequency_range == FR2 ? 10 : 10 * scs_scaling; // scaling taken into account in sco.scaling for FR2
+  const int ssb_offset_point_a = (scaled_abs_diff - sco.subcarrier_offset) / 12 - cent_freq_comp;
   AssertFatal(ssb_offset_point_a % scs_scaling == 0, "PRB offset %d can create frequency offset\n", ssb_offset_point_a);
-  AssertFatal(sco % scs_scaling == 0, "ssb offset %d can create frequency offset\n", sco);
+  AssertFatal(sco.subcarrier_offset % scs_scaling == 0, "ssb offset %d can create frequency offset\n", sco.subcarrier_offset);
   return ssb_offset_point_a;
 }
 

common/utils/nr/nr_common.h

@@ -81,6 +81,12 @@ typedef enum {
   nr_FR2
 } nr_frequency_range_e;
 
+typedef struct {
+  int subcarrier_offset;
+  uint32_t absolute_diff;
+  int scaling;
+} nr_sco_info_t;
+
 typedef struct nr_bandentry_s {
   int16_t band;
   uint64_t ul_min;
@@ -157,7 +163,7 @@ uint32_t get_ssb_offset_to_pointA(uint32_t absoluteFrequencySSB,
                                   uint32_t absoluteFrequencyPointA,
                                   int ssbSubcarrierSpacing,
                                   int frequency_range);
-int get_ssb_subcarrier_offset(uint32_t absoluteFrequencySSB, uint32_t absoluteFrequencyPointA);
+nr_sco_info_t get_ssb_subcarrier_offset(int scs, uint32_t absoluteFrequencySSB, uint32_t absoluteFrequencyPointA);
 int get_delay_idx(int delay, int max_delay_comp);
 
 void freq2time(uint16_t ofdm_symbol_size,

openair1/PHY/INIT/nr_parms.c

@@ -347,10 +347,12 @@ int nr_init_frame_parms_ue(NR_DL_FRAME_PARMS *fp,
   fp->freq_range = (fp->dl_CarrierFreq < 6e9)? nr_FR1 : nr_FR2;
 
   uint8_t sco = 0;
-  if (((fp->freq_range == nr_FR1) && (config->ssb_table.ssb_subcarrier_offset<24)) ||
-      ((fp->freq_range == nr_FR2) && (config->ssb_table.ssb_subcarrier_offset<12)) ) {
+  if (((fp->freq_range == nr_FR1) && (config->ssb_table.ssb_subcarrier_offset < 24)) ||
+      ((fp->freq_range == nr_FR2) && (config->ssb_table.ssb_subcarrier_offset < 12))) {
     if (fp->freq_range == nr_FR1)
-      sco = config->ssb_table.ssb_subcarrier_offset>>config->ssb_config.scs_common;
+      sco = config->ssb_table.ssb_subcarrier_offset >> config->ssb_config.scs_common;
+    else
+      sco = config->ssb_table.ssb_subcarrier_offset;
   }
 
   fp->ssb_start_subcarrier = (12 * config->ssb_table.ssb_offset_point_a + sco);

openair1/PHY/NR_TRANSPORT/nr_pbch.c

@@ -228,7 +228,8 @@ int nr_generate_pbch(nfapi_nr_dl_tti_ssb_pdu *ssb_pdu,
                      uint8_t n_hf,
                      int sfn,
                      nfapi_nr_config_request_scf_t *config,
-                     NR_DL_FRAME_PARMS *frame_parms) {
+                     NR_DL_FRAME_PARMS *frame_parms)
+{
   int k,l,m;
   //int16_t a;
   int16_t mod_pbch_e[NR_POLAR_PBCH_E];

openair2/LAYER2/NR_MAC_gNB/config.c

@@ -329,9 +329,10 @@ static void config_common(gNB_MAC_INST *nrmac, int pdsch_AntennaPorts, int pusch
    cfg->ssb_table.ssb_period.value = *scc->ssb_periodicityServingCell;
    cfg->ssb_table.ssb_period.tl.tag = NFAPI_NR_CONFIG_SSB_PERIOD_TAG;
    cfg->num_tlv++;
-   cfg->ssb_table.ssb_subcarrier_offset.value =
-       get_ssb_subcarrier_offset(*scc->downlinkConfigCommon->frequencyInfoDL->absoluteFrequencySSB,
-                                 scc->downlinkConfigCommon->frequencyInfoDL->absoluteFrequencyPointA);
+   nr_sco_info_t sco = get_ssb_subcarrier_offset(*scc->ssbSubcarrierSpacing,
+                                                 *scc->downlinkConfigCommon->frequencyInfoDL->absoluteFrequencySSB,
+                                                 scc->downlinkConfigCommon->frequencyInfoDL->absoluteFrequencyPointA);
+   cfg->ssb_table.ssb_subcarrier_offset.value = sco.subcarrier_offset;
    AssertFatal(cfg->ssb_table.ssb_subcarrier_offset.value < 16,
                "cannot handle ssb_subcarrier_offset %d resulting from Point A %ld SSB %ld: please increase dl_absoluteFrequencyPointA "
                "in the config by 16\n",

openair2/RRC/NR/nr_rrc_config.c

@@ -1767,8 +1767,10 @@ NR_BCCH_BCH_Message_t *get_new_MIB_NR(const NR_ServingCellConfigCommon_t *scc)
   AssertFatal(scc->ssbSubcarrierSpacing != NULL, "scc->ssbSubcarrierSpacing is null\n");
   int ssb_subcarrier_offset = 31; // default value for NSA
   if (get_softmodem_params()->sa) {
-    ssb_subcarrier_offset = get_ssb_subcarrier_offset(*scc->downlinkConfigCommon->frequencyInfoDL->absoluteFrequencySSB,
-                                                      scc->downlinkConfigCommon->frequencyInfoDL->absoluteFrequencyPointA);
+    nr_sco_info_t sco = get_ssb_subcarrier_offset(*scc->ssbSubcarrierSpacing,
+                                                  *scc->downlinkConfigCommon->frequencyInfoDL->absoluteFrequencySSB,
+                                                  scc->downlinkConfigCommon->frequencyInfoDL->absoluteFrequencyPointA);
+    ssb_subcarrier_offset = sco.subcarrier_offset;
   }
   mib->message.choice.mib->ssb_SubcarrierOffset = ssb_subcarrier_offset & 15;