NR UE: continuously estimate the frequency offset using PBCH DMRS

openair1/PHY/NR_UE_TRANSPORT/nr_pbch.c

@@ -525,3 +525,21 @@ int nr_rx_pbch(PHY_VARS_NR_UE *ue,
   TracyCZoneEnd(ctx);
   return 0;
 }
+
+double nr_ue_pbch_freq_offset(const NR_DL_FRAME_PARMS *frame_parms,
+                              int estimateSz,
+                              const c16_t dl_ch_estimates[][estimateSz])
+{
+  const int i_ssb = frame_parms->ssb_index;
+  const int symbol_offset = nr_get_ssb_start_symbol(frame_parms, i_ssb) % frame_parms->symbols_per_slot;
+  const c16_t *dl_ch_est_symb1 = &dl_ch_estimates[0][(symbol_offset + 1) * frame_parms->ofdm_symbol_size];
+  const c16_t *dl_ch_est_symb3 = &dl_ch_estimates[0][(symbol_offset + 3) * frame_parms->ofdm_symbol_size];
+  const int nb_re = 240;
+  const c32_t dot_prod_res = dot_product(dl_ch_est_symb1, dl_ch_est_symb3, nb_re, 8);
+  const double res_phase = atan2(dot_prod_res.i, dot_prod_res.r);
+  const int samples_per_symbol = frame_parms->ofdm_symbol_size + frame_parms->nb_prefix_samples;
+  const double t_ofdm = samples_per_symbol / (frame_parms->samples_per_subframe * 1000.0); // symbol duration in sec
+  const double freq_offset = res_phase / (2 * M_PI * (3 - 1) * t_ofdm);
+
+  return freq_offset;
+}

openair1/PHY/NR_UE_TRANSPORT/nr_transport_proto_ue.h

@@ -204,6 +204,10 @@ int nr_rx_pbch(PHY_VARS_NR_UE *ue,
                int rxdataFSize,
                const struct complex16 rxdataF[][rxdataFSize]);
 
+double nr_ue_pbch_freq_offset(const NR_DL_FRAME_PARMS *frame_parms,
+                              int estimateSz,
+                              const c16_t dl_ch_estimates[][estimateSz]);
+
 #ifndef modOrder
 #define modOrder(I_MCS,I_TBS) ((I_MCS-I_TBS)*2+2) // Find modulation order from I_TBS and I_MCS
 #endif

openair1/SCHED_NR_UE/phy_procedures_nr_ue.c

@@ -929,6 +929,11 @@ int pbch_pdcch_processing(PHY_VARS_NR_UE *ue, const UE_nr_rxtx_proc_t *proc, nr_
               sampleShift =
                   nr_adjust_synch_ue(fp, ue, gNB_id, fp->ofdm_symbol_size, dl_ch_estimates_time, frame_rx, nr_slot_rx, 16384);
             }
+
+            if (/*ue->continuous_freq_correction &&*/ pbchSuccess == 0) {
+              double freq_offset = nr_ue_pbch_freq_offset(fp, estimateSz, dl_ch_estimates);
+              LOG_I(PHY,"detected frequency offset = %.3f Hz\n", freq_offset);
+            }
           }
           LOG_D(PHY, "Doing N0 measurements in %s\n", __FUNCTION__);
           nr_ue_rrc_measurements(ue, proc, rxdataF);