NR UE: add NTN specific parameter ta-Common and use it for initial timing...

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);

executables/nr-uesoftmodem.h

@@ -13,6 +13,7 @@
 #define  CONFIG_HLP_OFFSET_DIV             "Divisor for computing OFDM symbol offset in Rx chain (num samples in CP/<the value>). Default value is 8. To set the sample offset to 0, set this value ~ 10e6\n"
 #define  CONFIG_HLP_MAX_LDPC_ITERATIONS    "Maximum LDPC decoder iterations\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"
 
 /***************************************************************************************************************************************/
 /* command line options definitions, CMDLINE_XXXX_DESC macros are used to initialize paramdef_t arrays which are then used as argument
@@ -66,6 +67,7 @@
   {"SLC",                          CONFIG_HLP_SLF,             0,               .u64ptr=&(sidelink_frequency[0][0]),         .defuintval=2600000000,TYPE_UINT64,0}, \
   {"num-ues",                      NULL,                       0,               .iptr=&(NB_UE_INST),                         .defuintval=1,     TYPE_INT,      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}, \
 }
 // clang-format on
 
@@ -87,6 +89,7 @@ typedef struct {
   int            ssb_start_subcarrier;
   int ldpc_offload_flag;
   unsigned int   ntn_koffset;
+  double         ntn_ta_common;
 } nrUE_params_t;
 extern uint64_t get_nrUE_optmask(void);
 extern uint64_t set_nrUE_optmask(uint64_t bitmask);

openair1/SCHED_NR_UE/fapi_nr_ue_l1.c

@@ -373,7 +373,6 @@ static void configure_ta_command(PHY_VARS_NR_UE *ue, fapi_nr_ta_command_pdu *ta_
   if (ta_command_pdu->is_rar) {
     ue->ta_slot = ta_command_pdu->ta_slot;
     ue->ta_frame = ta_command_pdu->ta_frame;
-    ue->timing_advance = 0;
     ue->ta_command = ta_command_pdu->ta_command + 31; // To use TA adjustment algo in ue_ta_procedures()
   } else {
     ue->ta_slot = (ta_command_pdu->ta_slot + ul_tx_timing_adjustment) % slots_per_frame;

openair2/LAYER2/NR_MAC_UE/main_ue_nr.c

@@ -87,7 +87,7 @@ 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) {
+  if (get_nrUE_params()->ntn_koffset || get_nrUE_params()->ntn_ta_common) {
     NR_SIB19_r17_t *sib19_r17 = calloc(1, sizeof(*sib19_r17));
     sib19_r17->ntn_Config_r17 = calloc(1, sizeof(*sib19_r17->ntn_Config_r17));
 
@@ -96,6 +96,12 @@ void nr_ue_init_mac(NR_UE_MAC_INST_t *mac)
       asn1cCallocOne(sib19_r17->ntn_Config_r17->cellSpecificKoffset_r17, get_nrUE_params()->ntn_koffset);
     }
 
+    // NTN ta-Common-r17
+    if (get_nrUE_params()->ntn_ta_common) {
+      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
+    }
+
     nr_rrc_mac_config_req_sib19_r17(mac->ue_id, sib19_r17);
     asn1cFreeStruc(asn_DEF_NR_SIB19_r17, sib19_r17);
   }

openair2/LAYER2/NR_MAC_UE/nr_ra_procedures.c

@@ -41,6 +41,13 @@
 #include <executables/softmodem-common.h>
 #include "openair2/LAYER2/RLC/rlc.h"
 
+static double get_ta_Common_ms(NR_NTN_Config_r17_t *ntn_Config_r17)
+{
+  if (ntn_Config_r17 && ntn_Config_r17->ta_Info_r17)
+    return ntn_Config_r17->ta_Info_r17->ta_Common_r17 * 4.072e-6; // ta_Common_r17 is in units of 4.072e-3 µs
+  return 0.0;
+}
+
 int16_t get_prach_tx_power(NR_UE_MAC_INST_t *mac)
 {
   RA_config_t *ra = &mac->ra;
@@ -580,13 +587,17 @@ void nr_Msg3_transmitted(NR_UE_MAC_INST_t *mac, uint8_t CC_id, frame_t frameP, s
 {
   RA_config_t *ra = &mac->ra;
   NR_RACH_ConfigCommon_t *nr_rach_ConfigCommon = mac->current_UL_BWP->rach_ConfigCommon;
-  long mu = mac->current_UL_BWP->scs;
-  int subframes_per_slot = nr_slots_per_frame[mu] / 10;
+  const double ta_Common_ms = get_ta_Common_ms(mac->sc_info.ntn_Config_r17);
+  const int mu = mac->current_UL_BWP->scs;
+  const int slots_per_ms = nr_slots_per_frame[mu] / 10;
 
   // start contention resolution timer
-  int RA_contention_resolution_timer_subframes = (nr_rach_ConfigCommon->ra_ContentionResolutionTimer + 1) << 3;
-  // timer step 1 slot and timer target given by ra_ContentionResolutionTimer
-  nr_timer_setup(&ra->contention_resolution_timer, RA_contention_resolution_timer_subframes * subframes_per_slot, 1);
+  const int RA_contention_resolution_timer_ms = (nr_rach_ConfigCommon->ra_ContentionResolutionTimer + 1) << 3;
+  const int RA_contention_resolution_timer_slots = RA_contention_resolution_timer_ms * slots_per_ms;
+  const int ta_Common_slots = (int)ceil(ta_Common_ms * slots_per_ms);
+
+  // timer step 1 slot and timer target given by ra_ContentionResolutionTimer + ta-Common-r17
+  nr_timer_setup(&ra->contention_resolution_timer, RA_contention_resolution_timer_slots + ta_Common_slots, 1);
   nr_timer_start(&ra->contention_resolution_timer);
 
   ra->ra_state = nrRA_WAIT_CONTENTION_RESOLUTION;
@@ -788,11 +799,16 @@ void nr_get_RA_window(NR_UE_MAC_INST_t *mac)
   NR_RACH_ConfigCommon_t *setup = mac->current_UL_BWP->rach_ConfigCommon;
   AssertFatal(&setup->rach_ConfigGeneric != NULL, "In %s: FATAL! rach_ConfigGeneric is NULL...\n", __FUNCTION__);
   NR_RACH_ConfigGeneric_t *rach_ConfigGeneric = &setup->rach_ConfigGeneric;
+  const double ta_Common_ms = get_ta_Common_ms(mac->sc_info.ntn_Config_r17);
+  const int mu = mac->current_DL_BWP->scs;
+  const int slots_per_ms = nr_slots_per_frame[mu] / 10;
  
-  int ra_ResponseWindow = rach_ConfigGeneric->ra_ResponseWindow;
-  int mu = mac->current_DL_BWP->scs;
+  const int ra_Offset_slots = ra->RA_offset * nr_slots_per_frame[mu];
+  const int ta_Common_slots = (int)ceil(ta_Common_ms * slots_per_ms);
+
+  ra->RA_window_cnt = ra_Offset_slots + ta_Common_slots; // taking into account the 2 frames gap introduced by OAI gNB
 
-  ra->RA_window_cnt = ra->RA_offset * nr_slots_per_frame[mu]; // taking into account the 2 frames gap introduced by OAI gNB
+  int ra_ResponseWindow = rach_ConfigGeneric->ra_ResponseWindow;
 
   switch (ra_ResponseWindow) {
     case NR_RACH_ConfigGeneric__ra_ResponseWindow_sl1: