HACK: cut PUSCH and PDSCH OFDM symbol after complete CP

Currently we cute the PUSCH and PDSCH OFDM symbols starting within the last 1/8th of the CP to avoid ISI.
This time shift leads to a rotation in frequency domain.
The current PRB based channel estimation does not compensate for the rotation _within_ a PRB, leading to bad performance.

This commit should _not_ make it into develop branch, it is just for testing!
Instead, we should do some compensating rotation before channel estimation.

openair1/PHY/MODULATION/slot_fep_nr.c

@@ -107,7 +107,7 @@ int nr_slot_fep(PHY_VARS_NR_UE *ue,
   rx_offset += frame_parms->ofdm_symbol_size * symbol;
 
   // use OFDM symbol from within 1/8th of the CP to avoid ISI
-  rx_offset -= nb_prefix_samples / 8;
+  //rx_offset -= nb_prefix_samples / 8;
 
 #ifdef DEBUG_FEP
   //  if (ue->frame <100)
@@ -296,7 +296,7 @@ int nr_slot_fep_ul(NR_DL_FRAME_PARMS *frame_parms,
   // offset of n-th OFDM symbol
   rxdata_offset += symbol * (frame_parms->ofdm_symbol_size + nb_prefix_samples);
   // use OFDM symbol from within 1/8th of the CP to avoid ISI
-  rxdata_offset -= nb_prefix_samples / 8;
+  //rxdata_offset -= nb_prefix_samples / 8;
 
   int16_t *rxdata_ptr;
 

openair1/PHY/NR_ESTIMATION/nr_measurements_gNB.c

@@ -45,7 +45,7 @@ int nr_est_timing_advance_pusch(PHY_VARS_gNB* gNB, int UE_id)
   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 / 8;
+  int sync_pos = 0; // frame_parms->nb_prefix_samples / 8;
 
   for (i = 0; i < frame_parms->ofdm_symbol_size; i++) {
     int temp = 0;

openair1/PHY/NR_UE_ESTIMATION/nr_adjust_synch_ue.c

@@ -82,7 +82,7 @@ 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>>3);
+      diff = max_pos_fil; // - (frame_parms->nb_prefix_samples>>3);
 
       if (frame_parms->freq_range==nr_FR2) 
 		sync_offset = 2;