UE: Fix if target cell has SSB at a different offset as in source cell

Actual problem is that SYNC does not happen on the target cell as frame parameters is not updated
and ssb start carrier is not correct in the UE frame parameters
function nr_get_ssb_start_sc to determine ssb_start_subcarrier

executables/nr-ue.c

@@ -486,12 +486,13 @@ static int handle_sync_req_from_mac(PHY_VARS_NR_UE *UE)
       UE->UE_scan_carrier = false;
     UE->target_Nid_cell = UE->synch_request.synch_req.target_Nid_cell;
 
-    const fapi_nr_ue_carrier_config_t *cfg = &UE->nrUE_config.carrier_config;
+    const fapi_nr_config_request_t *config = &UE->nrUE_config;
+    const fapi_nr_ue_carrier_config_t *cfg = &config->carrier_config;
     uint64_t dl_CarrierFreq = get_carrier_frequency(fp->N_RB_DL, fp->numerology_index, cfg->dl_frequency);
     uint64_t ul_CarrierFreq = get_carrier_frequency(fp->N_RB_UL, fp->numerology_index, cfg->uplink_frequency);
     if (dl_CarrierFreq != fp->dl_CarrierFreq || ul_CarrierFreq != fp->ul_CarrierFreq) {
       LOG_I(NR_PHY,
-            "[UE %d] RF frequency change: dl %lu->%lu Hz, ul %lu->%lu Hz (from dl_frequency=%u kHz, target_Nid_cell=%d)\n",
+            "[UE %d] SYNC REQ: RF frequency change: dl %lu->%lu Hz, ul %lu->%lu Hz (from dl_frequency=%u kHz, target_Nid_cell=%d)\n",
             UE->Mod_id,
             fp->dl_CarrierFreq,
             dl_CarrierFreq,
@@ -505,6 +506,16 @@ static int handle_sync_req_from_mac(PHY_VARS_NR_UE *UE)
       init_symbol_rotation(fp);
     }
 
+    int ssb_start_subcarrier = nr_get_ssb_start_sc(fp->numerology_index,
+                                                   config->ssb_table.ssb_offset_point_a,
+                                                   config->ssb_table.ssb_subcarrier_offset,
+                                                   fp->freq_range);
+    // SSB location can change during for ex: handover on the target cell
+    if (ssb_start_subcarrier != fp->ssb_start_subcarrier) {
+      fp->ssb_start_subcarrier = ssb_start_subcarrier;
+      LOG_I(NR_PHY, "SYNC REQ: SSB location changed:%d\n", fp->ssb_start_subcarrier);
+    }
+
     // Apply Doppler based on NTN-Config for target cell
     if (UE->nrUE_config.ntn_config.is_targetcell)
       apply_ntn_timing_advance_and_doppler(UE, fp, -1);

openair1/PHY/INIT/nr_parms.c

@@ -24,6 +24,7 @@
 #include "common/utils/LOG/log.h"
 #include "executables/softmodem-common.h"
 #include "PHY/MODULATION/nr_modulation.h"
+#include "PHY/nr_phy_common/inc/nr_phy_common.h"
 
 /// Subcarrier spacings in Hz indexed by numerology index
 static const uint32_t nr_subcarrier_spacing[MAX_NUM_SUBCARRIER_SPACING] = {15e3, 30e3, 60e3, 120e3, 240e3};
@@ -421,16 +422,11 @@ int nr_init_frame_parms_ue(NR_DL_FRAME_PARMS *fp, fapi_nr_config_request_t* conf
   fp->samples_per_frame = 10 * fp->samples_per_subframe;
   fp->freq_range = get_freq_range_from_freq(fp->dl_CarrierFreq);
 
-  uint8_t sco = 0;
-  if (((fp->freq_range == FR1) && (config->ssb_table.ssb_subcarrier_offset < 24)) ||
-      ((fp->freq_range == FR2) && (config->ssb_table.ssb_subcarrier_offset < 12))) {
-    if (fp->freq_range == FR1)
-      sco = config->ssb_table.ssb_subcarrier_offset>>config->ssb_config.scs_common;
-    else
-      sco = config->ssb_table.ssb_subcarrier_offset;
-  }
+  fp->ssb_start_subcarrier = nr_get_ssb_start_sc(config->ssb_config.scs_common,
+                                                 config->ssb_table.ssb_offset_point_a,
+                                                 config->ssb_table.ssb_subcarrier_offset,
+                                                 fp->freq_range);
 
-  fp->ssb_start_subcarrier = (12 * config->ssb_table.ssb_offset_point_a + sco);
   set_Lmax(fp);
 
   fp->L_ssb = (((uint64_t) config->ssb_table.ssb_mask_list[0].ssb_mask)<<32) | config->ssb_table.ssb_mask_list[1].ssb_mask;

openair1/PHY/nr_phy_common/inc/nr_phy_common.h

@@ -389,4 +389,9 @@ void nr_generate_csi_rs(const NR_DL_FRAME_PARMS *frame_parms,
                         const uint8_t cdm_type,
                         c16_t **dataF);
 
+int nr_get_ssb_start_sc(int scs,
+                        int ssb_offset_point_a,
+                        int ssb_sco,
+                        frequency_range_t freq_range);
+
 #endif

openair1/PHY/nr_phy_common/src/nr_phy_common.c

@@ -481,3 +481,26 @@ void nr_fo_compensation(double fo_Hz, int samples_per_ms, int sample_offset, con
   mult_complex_vectors(rxdata_in, rot, rxdata_out, size, 14);
 #endif
 }
+
+/*!
+* Setting the first subcarrier
+* 3GPP TS 38.211 sections 7.4.3.1 and 4.4.4.2
+* for FR1 offsetToPointA and k_SSB are expressed in terms of 15 kHz SCS
+* for FR2 offsetToPointA is expressed in terms of 60 kHz SCS and k_SSB expressed in terms of the SCS provided
+* by the higher-layer parameter subCarrierSpacingCommon
+*/
+int nr_get_ssb_start_sc(int scs, int ssb_offset_point_a, int ssb_sco, frequency_range_t freq_range)
+{
+  const int prb_offset =
+      (freq_range == FR1) ? ssb_offset_point_a >> scs : ssb_offset_point_a >> (scs - 2);
+  const int sc_offset =
+      (freq_range == FR1) ? ssb_sco >> scs : ssb_sco;
+
+  int ssb_start_subcarrier = (12 * prb_offset + sc_offset);
+
+  LOG_D(NR_PHY, "prb_offset:%d, ssb_subcarrier_offset:%d,scs :%d, Fr:%d, ssb_start_subcarrier:%d\n",
+                        prb_offset, ssb_sco, scs, freq_range, ssb_start_subcarrier);
+
+  return ssb_start_subcarrier;
+
+}

openair1/SCHED_NR/phy_procedures_nr_gNB.c

@@ -118,9 +118,10 @@ void nr_common_signal_procedures(PHY_VARS_gNB *gNB, int frame, int slot, const n
   // by the higher-layer parameter subCarrierSpacingCommon
   nfapi_nr_config_request_scf_t *cfg = &gNB->gNB_config;
   const int scs = cfg->ssb_config.scs_common.value;
-  const int prb_offset = (fp->freq_range == FR1) ? pdu->ssbOffsetPointA >> scs : pdu->ssbOffsetPointA >> (scs - 2);
-  const int sc_offset = (fp->freq_range == FR1) ? pdu->SsbSubcarrierOffset >> scs : pdu->SsbSubcarrierOffset;
-  fp->ssb_start_subcarrier = (12 * prb_offset + sc_offset);
+  fp->ssb_start_subcarrier = nr_get_ssb_start_sc(scs,
+                                                 pdu->ssbOffsetPointA,
+                                                 pdu->SsbSubcarrierOffset,
+                                                 fp->freq_range);
 
   if (fp->print_ue_help_cmdline_log && IS_SA_MODE(get_softmodem_params())) {
     fp->print_ue_help_cmdline_log = false;
@@ -142,15 +143,6 @@ void nr_common_signal_procedures(PHY_VARS_gNB *gNB, int frame, int slot, const n
             fp->ssb_start_subcarrier,
             fp->threequarter_fs ? "-E" : "");
   }
-  LOG_D(PHY,
-        "ssbOffsetPointA %d SSB SsbSubcarrierOffset %d  prb_offset %d sc_offset %d scs %d ssb_start_subcarrier %d\n",
-        pdu->ssbOffsetPointA,
-        pdu->SsbSubcarrierOffset,
-        prb_offset,
-        sc_offset,
-        scs,
-        fp->ssb_start_subcarrier);
-
   LOG_D(PHY,"SS TX: frame %d, slot %d, start_symbol %d\n", frame, slot, ssb_start_symbol);
   const nfapi_nr_tx_precoding_and_beamforming_t *pb = &pdu->precoding_and_beamforming;
   c16_t ***txdataF = gNB->common_vars.txdataF;

openair2/LAYER2/NR_MAC_UE/config_ue.c

@@ -537,16 +537,15 @@ static void config_common_ue(NR_UE_MAC_INST_t *mac, NR_ServingCellConfigCommon_t
 
   // SSB Table config
   if (frequencyInfoDL && frequencyInfoDL->absoluteFrequencySSB) {
-    int scs_scaling = 1 << (cfg->ssb_config.scs_common);
-    if (frequencyInfoDL->absoluteFrequencyPointA < 600000)
-      scs_scaling = scs_scaling * 3;
-    if (frequencyInfoDL->absoluteFrequencyPointA > 2016666)
-      scs_scaling = scs_scaling >> 2;
-    uint32_t absolute_diff = (*frequencyInfoDL->absoluteFrequencySSB - frequencyInfoDL->absoluteFrequencyPointA);
-    cfg->ssb_table.ssb_offset_point_a = absolute_diff / (12 * scs_scaling) - 10;
+    cfg->ssb_table.ssb_offset_point_a = get_ssb_offset_to_pointA(*frequencyInfoDL->absoluteFrequencySSB,
+                                                                 frequencyInfoDL->absoluteFrequencyPointA,
+                                                                 cfg->ssb_config.scs_common,
+                                                                 mac->frequency_range);
     cfg->ssb_table.ssb_period = *scc->ssb_periodicityServingCell;
     // NSA -> take ssb offset from SCS
-    cfg->ssb_table.ssb_subcarrier_offset = absolute_diff % (12 * scs_scaling);
+    cfg->ssb_table.ssb_subcarrier_offset = get_ssb_subcarrier_offset(*frequencyInfoDL->absoluteFrequencySSB,
+                                                                     frequencyInfoDL->absoluteFrequencyPointA,
+                                                                     cfg->ssb_config.scs_common);
     cfg->ssb_table.ssb_case = set_ssb_case(*scc->ssbSubcarrierSpacing, mac->nr_band);
   }
 
@@ -2113,12 +2112,14 @@ static void handle_reconfiguration_with_sync(NR_UE_MAC_INST_t *mac,
   ra->ra_state = nrRA_UE_IDLE;
   nr_ue_mac_default_configs(mac);
 
+  // PHY CONFIG request should be sent, ahead of SYNC request
+  // As SYNC request processes the new config
+  mac->if_module->phy_config_request(&mac->phy_config);
+  mac->phy_config.config_req.ntn_config.params_changed = false;
   mac->synch_request.Mod_id = mac->ue_id;
   mac->synch_request.CC_id = cc_idP;
   mac->synch_request.synch_req.target_Nid_cell = mac->physCellId;
   mac->if_module->synch_request(&mac->synch_request);
-  mac->if_module->phy_config_request(&mac->phy_config);
-  mac->phy_config.config_req.ntn_config.params_changed = false;
 }
 
 static void configure_physicalcellgroup(NR_UE_MAC_INST_t *mac,