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;

executables/nr-uesoftmodem.h

@@ -9,6 +9,8 @@
 #define  CONFIG_HLP_DLSCH_PARA             "number of threads for dlsch processing 0 for no parallelization\n"
 #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_TIME_SYNC_P            "coefficient for Proportional part of time sync PI controller\n"
+#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"
 
@@ -59,6 +61,8 @@
   {"ue-timing-correction-disable", CONFIG_HLP_DISABLETIMECORR, PARAMFLAG_BOOL,  .iptr=&(nrUE_params.no_timing_correction),   .defintval=0,      TYPE_INT,      0}, \
   {"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}, \
+  {"time-sync-P",                  CONFIG_HLP_TIME_SYNC_P,     0,               .dblptr=&(nrUE_params.time_sync_P),          .defdblval=0.5,    TYPE_DOUBLE,   0}, \
+  {"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}, \
   {"agc",                          CONFIG_HLP_AGC,             PARAMFLAG_BOOL,  .iptr=&(nrUE_params.agc),                   .defintval=0,       TYPE_INT,   0}, \
@@ -82,6 +86,8 @@ typedef struct {
   int N_RB_DL;
   int ssb_start_subcarrier;
   int ldpc_offload_flag;
+  double time_sync_P;
+  double time_sync_I;
   unsigned int ntn_koffset;
   double ntn_ta_common;
   int agc;