NR_UE: Perform autonomous timing advance to compensate for fast time drift...

NR_UE: Perform autonomous timing advance to compensate for fast time drift with relatively large RTT

As we don't have SIB19 with continuously updated ta-Common and ta-CommonDrift values yet, the UE can only adapt it's UL timing according to it's DL drift.
This is required for the UE to keep UL sync with fast time drift and relatively long RTT (e.g. LEO satellite).
We should replace this with the standard compliant way as soon as we have SIB19 with continuously updated contents.

executables/nr-softmodem-common.h

@@ -98,7 +98,6 @@
 #define CONFIG_HLP_TELN          "Start embedded telnet server \n"
 #define CONFIG_HLP_SNR           "Set average SNR in dB (for --siml1 option)\n"
 #define CONFIG_HLP_NOS1          "Disable s1 interface\n"
-#define CONFIG_HLP_AGC "Rx Gain control used for UE"
 
 /*--------------------------------------------------------------------------------------------------------------------------------*/
 /*                                            command line parameters for LOG utility                                             */

executables/nr-ue.c

@@ -889,6 +889,9 @@ void *UE_thread(void *arg)
       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);
+      // TODO: remove this autonomous TA and use up-to-date values of ta-Common, ta-CommonDrift and ta-CommonDriftVariant from received SIB19 instead
+      if (get_nrUE_params()->autonomous_ta)
+        UE->timing_advance -= 2 * shiftForNextFrame;
       // read in first symbol
       AssertFatal(fp->ofdm_symbol_size + fp->nb_prefix_samples0
                       == UE->rfdevice.trx_read_func(&UE->rfdevice,
@@ -949,6 +952,9 @@ 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;
+      // TODO: remove this autonomous TA and use up-to-date values of ta-Common, ta-CommonDrift and ta-CommonDriftVariant from received SIB19 instead
+      if (get_nrUE_params()->autonomous_ta)
+        UE->timing_advance -= 2 * shiftForNextFrame;
       shiftForNextFrame = -round(UE->max_pos_acc * get_nrUE_params()->time_sync_I);
     }
 

executables/nr-uesoftmodem.h

@@ -14,6 +14,8 @@
 #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"
+#define  CONFIG_HLP_AUTONOMOUS_TA          "Autonomously update TA based on DL drift (useful if main contribution to DL drift is movement, e.g. LEO satellite)\n"
+#define  CONFIG_HLP_AGC                    "Rx Gain control used for UE\n"
 
 /***************************************************************************************************************************************/
 /* command line options definitions, CMDLINE_XXXX_DESC macros are used to initialize paramdef_t arrays which are then used as argument
@@ -67,7 +69,8 @@
   {"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}, \
+  {"autonomous-ta",                CONFIG_HLP_AUTONOMOUS_TA,   PARAMFLAG_BOOL,  .iptr=&(nrUE_params.autonomous_ta),          .defintval=0,      TYPE_INT,      0}, \
+  {"agc",                          CONFIG_HLP_AGC,             PARAMFLAG_BOOL,  .iptr=&(nrUE_params.agc),                    .defintval=0,      TYPE_INT,      0}, \
 }
 // clang-format on
 
@@ -93,6 +96,7 @@ typedef struct {
   unsigned int ntn_koffset;
   double ntn_ta_common;
   double ntn_ta_commondrift;
+  int autonomous_ta;
   int agc;
   char *usrp_args;
   char *tx_subdev;