NR UE: add NTN specific parameter ta-Common and use it for initial timing advance, RA_contention_resolution_timer and RA_window_cnt

The value for this parameter can be set via UE command line parameter `--ntn-ta-common` in milliseconds.

executables/nr-ue.c

@@ -149,6 +149,7 @@ void init_nr_ue_vars(PHY_VARS_NR_UE *ue,
   ue->if_inst     = nr_ue_if_module_init(UE_id);
   ue->dci_thres   = 0;
   ue->target_Nid_cell = -1;
+  ue->timing_advance = ue->frame_parms.samples_per_subframe * get_nrUE_params()->ntn_ta_common;
 
   // initialize all signal buffers
   init_nr_ue_signal(ue, nb_connected_gNB);