5G NR: move CIR peak to 0

The rotation compensating the shifted OFDM position _before_ the channel estimation makes the CIR peak move back to 0.
We have to take this into account on gNB side when calculating the timing advance command, and on UE side in the time adjustment.

openair1/PHY/NR_ESTIMATION/nr_measurements_gNB.c

@@ -39,20 +39,20 @@ extern openair0_config_t openair0_cfg[MAX_CARDS];
 
 int nr_est_timing_advance_pusch(PHY_VARS_gNB* gNB, int UE_id)
 {
-  int i, aa, max_pos = 0, max_val = 0;
+  int max_pos = 0, max_val = 0;
 
   NR_DL_FRAME_PARMS *frame_parms = &gNB->frame_parms;
   NR_gNB_PUSCH *gNB_pusch_vars   = gNB->pusch_vars[UE_id];
   int32_t **ul_ch_estimates_time = gNB_pusch_vars->ul_ch_estimates_time;
 
-  int sync_pos = frame_parms->nb_prefix_samples / frame_parms->ofdm_offset_divisor;
+  const int sync_pos = 0;
 
-  for (i = 0; i < frame_parms->ofdm_symbol_size; i++) {
+  for (int i = 0; i < frame_parms->ofdm_symbol_size; i++) {
     int temp = 0;
 
-    for (aa = 0; aa < frame_parms->nb_antennas_rx; aa++) {
-      short Re = ((int16_t*)ul_ch_estimates_time[aa])[(i<<1)];
-      short Im = ((int16_t*)ul_ch_estimates_time[aa])[1+(i<<1)];
+    for (int aa = 0; aa < frame_parms->nb_antennas_rx; aa++) {
+      int Re = ((int16_t*)ul_ch_estimates_time[aa])[(i<<1)];
+      int Im = ((int16_t*)ul_ch_estimates_time[aa])[1+(i<<1)];
       temp += (Re*Re/2) + (Im*Im/2);      
     }
 
@@ -65,7 +65,6 @@ int nr_est_timing_advance_pusch(PHY_VARS_gNB* gNB, int UE_id)
   if (max_pos > frame_parms->ofdm_symbol_size/2)
     max_pos = max_pos - frame_parms->ofdm_symbol_size;
 
-
   return max_pos - sync_pos;
 }
 

openair1/PHY/NR_UE_ESTIMATION/nr_adjust_synch_ue.c

@@ -45,25 +45,23 @@ void nr_adjust_synch_ue(NR_DL_FRAME_PARMS *frame_parms,
   static int max_pos_fil = 0;
   static int count_max_pos_ok = 0;
   static int first_time = 1;
-  int temp = 0, i, aa, max_val = 0, max_pos = 0;
-  int diff;
-  short Re,Im,ncoef;
+  int max_val = 0, max_pos = 0;
+  const int sync_pos = 0;
   uint8_t sync_offset = 0;
 
   VCD_SIGNAL_DUMPER_DUMP_FUNCTION_BY_NAME(VCD_SIGNAL_DUMPER_FUNCTIONS_UE_ADJUST_SYNCH, VCD_FUNCTION_IN);
 
-  ncoef = 32767 - coef;
+  short ncoef = 32767 - coef;
 
   LOG_D(PHY,"AbsSubframe %d: rx_offset (before) = %d\n",subframe,ue->rx_offset);
 
-
   // we only use channel estimates from tx antenna 0 here
-  for (i = 0; i < frame_parms->nb_prefix_samples; i++) {
-    temp = 0;
+  for (int i = 0; i < frame_parms->nb_prefix_samples; i++) {
+    int temp = 0;
 
-    for (aa=0; aa<frame_parms->nb_antennas_rx; aa++) {
-      Re = ((int16_t*)ue->pbch_vars[gNB_id]->dl_ch_estimates_time[aa])[(i<<1)];
-      Im = ((int16_t*)ue->pbch_vars[gNB_id]->dl_ch_estimates_time[aa])[1+(i<<1)];
+    for (int aa = 0; aa < frame_parms->nb_antennas_rx; aa++) {
+      int Re = ((int16_t*)ue->pbch_vars[gNB_id]->dl_ch_estimates_time[aa])[(i<<1)];
+      int Im = ((int16_t*)ue->pbch_vars[gNB_id]->dl_ch_estimates_time[aa])[1+(i<<1)];
       temp += (Re*Re/2) + (Im*Im/2);
     }
 
@@ -73,6 +71,9 @@ void nr_adjust_synch_ue(NR_DL_FRAME_PARMS *frame_parms,
     }
   }
 
+  if (max_pos > frame_parms->ofdm_symbol_size/2)
+    max_pos = max_pos - frame_parms->ofdm_symbol_size;
+
   // filter position to reduce jitter
   if (clear == 1)
     max_pos_fil = max_pos;
@@ -82,7 +83,7 @@ void nr_adjust_synch_ue(NR_DL_FRAME_PARMS *frame_parms,
   // do not filter to have proactive timing adjustment
   //max_pos_fil = max_pos;
 
-      diff = max_pos_fil - (frame_parms->nb_prefix_samples / frame_parms->ofdm_offset_divisor);
+  int diff = max_pos_fil - sync_pos;
 
   if (frame_parms->freq_range==nr_FR2) 
     sync_offset = 2;
@@ -123,20 +124,17 @@ void nr_adjust_synch_ue(NR_DL_FRAME_PARMS *frame_parms,
   if (ue->rx_offset >= frame_parms->samples_per_frame)
     ue->rx_offset -= frame_parms->samples_per_frame;
 
-
-
-      #ifdef DEBUG_PHY
-      LOG_D(PHY,"AbsSubframe %d: diff =%i rx_offset (final) = %i : clear %d,max_pos = %d,max_pos_fil = %d (peak %d) max_val %d target_pos %d \n",
+#ifdef DEBUG_PHY
+  LOG_D(PHY,"AbsSubframe %d: diff = %i, rx_offset (final) = %i : clear = %d, max_pos = %d, max_pos_fil = %d, max_val = %d, sync_pos %d\n",
         subframe,
         diff,
         ue->rx_offset,
         clear,
         max_pos,
         max_pos_fil,
-              temp,max_val,
-              (frame_parms->nb_prefix_samples>>3));
-      #endif //DEBUG_PHY
+        max_val,
+        sync_pos);
+#endif //DEBUG_PHY
 
   VCD_SIGNAL_DUMPER_DUMP_FUNCTION_BY_NAME(VCD_SIGNAL_DUMPER_FUNCTIONS_UE_ADJUST_SYNCH, VCD_FUNCTION_OUT);
-
 }