NR_UE: add PI controller to time sync

this allows to compensate larger continuous time drift in DL (e.g. large Doppler from LEO satellite)

executables/nr-ue.c

@@ -947,7 +947,7 @@ void *UE_thread(void *arg)
     if (slot_nr == nb_slot_frame - 1) {
       // we shift of half of measured drift, at each beginning of frame for both rx and tx
       iq_shift_to_apply = shiftForNextFrame;
-      shiftForNextFrame = 0; // We will get a new measured offset if we decode PBCH
+      shiftForNextFrame = -round(UE->max_pos_acc * get_nrUE_params()->time_sync_I);
     }
 
     const int readBlockSize = get_readBlockSize(slot_nr, fp) - iq_shift_to_apply;