NR_UE: make NTN parameter ta_CommonDrift_r17 configurable via command line parameter --ntn-ta-commondrift

While we don't have SIB19 support yet, UE gets this parameter from command line, just like --ntn-koffset and --ntn-ta-common.
We use this value to initialize the UE's time-tracking PI controller accumulator.
This allows to correctly track the time even if the delay is changing significantly (e.g. due to LEO satellite movement).
We also use it to compensate for the time drift that happenes while performing the initial sync.

executables/nr-ue.c

@@ -886,7 +886,9 @@ void *UE_thread(void *arg)
       stream_status = STREAM_STATUS_SYNCING;
       syncInFrame(UE, &sync_timestamp, intialSyncOffset);
       openair0_write_reorder_clear_context(&UE->rfdevice);
-      shiftForNextFrame = 0; // will be used to track clock drift
+      UE->max_pos_acc = get_nrUE_params()->ntn_ta_commondrift * 1e-6 * fp->samples_per_frame / get_nrUE_params()->time_sync_I; // ntn_ta_commondrift is in µs/s, max_pos_acc * time_sync_I is in samples/frame
+      shiftForNextFrame = -(UE->init_sync_frame + trashed_frames + 2) * UE->max_pos_acc * get_nrUE_params()->time_sync_I; // compensate for the time drift that happened during initial sync
+      LOG_D(PHY, "max_pos_acc = %d, shiftForNextFrame = %d\n", UE->max_pos_acc, shiftForNextFrame);
       // read in first symbol
       AssertFatal(fp->ofdm_symbol_size + fp->nb_prefix_samples0
                       == UE->rfdevice.trx_read_func(&UE->rfdevice,

executables/nr-uesoftmodem.h

@@ -13,6 +13,7 @@
 #define  CONFIG_HLP_TIME_SYNC_I            "coefficient for Integrating part of time sync PI controller\n"
 #define  CONFIG_HLP_NTN_KOFFSET            "NTN cellSpecificKoffset-r17 (number of slots for a given subcarrier spacing of 15 kHz)\n"
 #define  CONFIG_HLP_NTN_TA_COMMON          "NTN ta-Common, but given in ms\n"
+#define  CONFIG_HLP_NTN_TA_COMMONDRIFT     "NTN ta-CommonDrift, but given in µs/s\n"
 
 /***************************************************************************************************************************************/
 /* command line options definitions, CMDLINE_XXXX_DESC macros are used to initialize paramdef_t arrays which are then used as argument
@@ -65,6 +66,7 @@
   {"time-sync-I",                  CONFIG_HLP_TIME_SYNC_I,     0,               .dblptr=&(nrUE_params.time_sync_I),          .defdblval=0.2,    TYPE_DOUBLE,   0}, \
   {"ntn-koffset",                  CONFIG_HLP_NTN_KOFFSET,     0,               .uptr=&(nrUE_params.ntn_koffset),            .defuintval=0,     TYPE_UINT,     0}, \
   {"ntn-ta-common",                CONFIG_HLP_NTN_TA_COMMON,   0,               .dblptr=&(nrUE_params.ntn_ta_common),        .defdblval=0.0,    TYPE_DOUBLE,   0}, \
+  {"ntn-ta-commondrift",           CONFIG_HLP_NTN_TA_COMMONDRIFT, 0,            .dblptr=&(nrUE_params.ntn_ta_commondrift),   .defdblval=0.0,    TYPE_DOUBLE,   0}, \
   {"agc",                          CONFIG_HLP_AGC,             PARAMFLAG_BOOL,  .iptr=&(nrUE_params.agc),                   .defintval=0,       TYPE_INT,   0}, \
 }
 // clang-format on
@@ -90,6 +92,7 @@ typedef struct {
   double time_sync_I;
   unsigned int ntn_koffset;
   double ntn_ta_common;
+  double ntn_ta_commondrift;
   int agc;
   char *usrp_args;
   char *tx_subdev;

openair2/LAYER2/NR_MAC_UE/main_ue_nr.c

@@ -88,7 +88,7 @@ void nr_ue_init_mac(NR_UE_MAC_INST_t *mac)
 
   // Fake SIB19 reception for NTN
   // TODO: remove this and implement the actual SIB19 reception instead!
-  if (get_nrUE_params()->ntn_koffset || get_nrUE_params()->ntn_ta_common) {
+  if (get_nrUE_params()->ntn_koffset || get_nrUE_params()->ntn_ta_common || get_nrUE_params()->ntn_ta_commondrift) {
     NR_SIB19_r17_t *sib19_r17 = calloc(1, sizeof(*sib19_r17));
     sib19_r17->ntn_Config_r17 = calloc(1, sizeof(*sib19_r17->ntn_Config_r17));
 
@@ -98,9 +98,11 @@ void nr_ue_init_mac(NR_UE_MAC_INST_t *mac)
     }
 
     // NTN ta-Common-r17
-    if (get_nrUE_params()->ntn_ta_common) {
+    if (get_nrUE_params()->ntn_ta_common || get_nrUE_params()->ntn_ta_commondrift) {
       sib19_r17->ntn_Config_r17->ta_Info_r17 = calloc(1, sizeof(*sib19_r17->ntn_Config_r17->ta_Info_r17));
       sib19_r17->ntn_Config_r17->ta_Info_r17->ta_Common_r17 = get_nrUE_params()->ntn_ta_common / 4.072e-6; // ta-Common-r17 is in units of 4.072e-3 µs, ntn_ta_common is in ms
+      if (get_nrUE_params()->ntn_ta_commondrift)
+        asn1cCallocOne(sib19_r17->ntn_Config_r17->ta_Info_r17->ta_CommonDrift_r17, get_nrUE_params()->ntn_ta_commondrift / 0.2e-3); // is in units of 0.2e-3 µs/s, ntn_ta_commondrift is in µs/s
     }
 
     nr_rrc_mac_config_req_sib19_r17(mac->ue_id, sib19_r17);