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NR_UE: add PI controller to time sync

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this allows to compensate larger continuous time drift in DL (e.g. large Doppler from LEO satellite)
This commit is contained in:
Thomas Schlichter
2024-08-01 13:16:20 +02:00
parent 8ab7f1dd68
commit 4039473a70
5 changed files with 31 additions and 25 deletions
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2
executables/nr-ue.c
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@@ -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;

6
executables/nr-uesoftmodem.h
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@@ -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;

42
openair1/PHY/NR_UE_ESTIMATION/nr_adjust_synch_ue.c
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@@ -24,7 +24,7 @@
#include "PHY/NR_UE_ESTIMATION/nr_estimation.h"
#include "PHY/impl_defs_top.h"
#include "executables/softmodem-common.h"
#include "executables/nr-uesoftmodem.h"
#include "common/utils/LOG/vcd_signal_dumper.h"
//#define DEBUG_PHY
@@ -43,12 +43,9 @@ int nr_adjust_synch_ue(NR_DL_FRAME_PARMS *frame_parms,
short coef)
{
int max_val = 0, max_pos = 0;
uint8_t sync_offset = 0;
VCD_SIGNAL_DUMPER_DUMP_FUNCTION_BY_NAME(VCD_SIGNAL_DUMPER_FUNCTIONS_UE_ADJUST_SYNCH, VCD_FUNCTION_IN);
short ncoef = 32767 - coef;
// search for maximum position within the cyclic prefix
for (int i = -frame_parms->nb_prefix_samples/2; i < frame_parms->nb_prefix_samples/2; i++) {
int temp = 0;
@@ -67,32 +64,37 @@ int nr_adjust_synch_ue(NR_DL_FRAME_PARMS *frame_parms,
}
// filter position to reduce jitter
ue->max_pos_avg = ((ue->max_pos_avg * coef) >> 15) + (max_pos * ncoef);
int diff = ue->max_pos_avg >> 15;
const int ncoef = 32767 - coef;
ue->max_pos_iir = ((ue->max_pos_iir * coef) >> 15) + (max_pos * ncoef);
const int diff = (ue->max_pos_iir + 16384) >> 15;
// FIXME: Do we really need this hysteresis for FR2?
int sampleShift = diff;
if (frame_parms->freq_range == FR2)
sync_offset = 2;
else
sync_offset = 0;
if (abs(diff) <= 2)
sampleShift = 0;
int sampleShift = 0;
if (abs(diff) > (NR_SYNCH_HYST + sync_offset))
sampleShift = diff;
const int sample_shift = -(sampleShift / 2);
// reset IIR filter for next offset calculation
ue->max_pos_avg += sample_shift * 32768;
// PI controller
const double PID_P = get_nrUE_params()->time_sync_P;
const double PID_I = get_nrUE_params()->time_sync_I;
int sample_shift = -round(sampleShift * PID_P + ue->max_pos_acc * PID_I);
LOG_D(PHY,
"Slot %d: diff = %i, rx_offset (final) = %i : max_pos = %d, max_pos filtered = %ld, max_power = %d\n",
"Frame %d, Slot %d: max_pos = %d, max_pos filtered = %f, diff = %i, sampleShift = %i, max_pos_acc = %d, sample_shift (final) = %d, max_power = %d\n",
frame,
slot,
max_pos,
ue->max_pos_iir / 32768.0,
diff,
sampleShift,
max_pos,
ue->max_pos_avg,
ue->max_pos_acc,
sample_shift,
max_val);
// reset IIR filter for next offset calculation
ue->max_pos_iir += -round(sampleShift * PID_P) * 32768;
ue->max_pos_acc += max_pos;
VCD_SIGNAL_DUMPER_DUMP_FUNCTION_BY_NAME(VCD_SIGNAL_DUMPER_FUNCTIONS_UE_ADJUST_SYNCH, VCD_FUNCTION_OUT);
return sample_shift;
}

3
openair1/PHY/NR_UE_ESTIMATION/nr_estimation.h
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@@ -29,9 +29,6 @@
* @{
*/
/*!\brief Timing drift hysterisis in samples*/
#define NR_SYNCH_HYST 1
/* A function to perform the channel estimation of DL PRS signal */
int nr_prs_channel_estimation(uint8_t gNB_id,
uint8_t rsc_id,

3
openair1/PHY/defs_nr_UE.h
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@@ -456,7 +456,8 @@ typedef struct PHY_VARS_NR_UE_s {
/// temporary offset during cell search prior to MIB decoding
int ssb_offset;
uint16_t symbol_offset; /// offset in terms of symbols for detected ssb in sync
int64_t max_pos_avg; /// Timing offset IIR filter
int64_t max_pos_iir; /// Timing offset IIR filter
int max_pos_acc; /// Timing offset accumuluated error for PI filter
/// Timing Advance updates variables
/// Timing advance update computed from the TA command signalled from gNB