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gNB: improve TA accuracy

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The TA calculation takes the CIR peak position error and scales it according to 38.213 section 4.2.
Till now it was simply an integer division "timing_advance_update = sync_pos / bw_scaling".

E.g. in case of bandwidth_scaling == 16, the timing_advance_update was 0 for sync_pos between -15 and +15.
With this change, this range (and thus the UL timing error) will be reduced to -8 and +8.
This commit is contained in:
Thomas Schlichter
2021-04-26 18:05:17 +02:00
parent 5c6865fbc6
commit b073ca48c3
1 changed files with 5 additions and 0 deletions
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openair1/SCHED_NR/phy_procedures_nr_gNB.c
+5
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@@ -369,6 +369,11 @@ void nr_fill_indication(PHY_VARS_gNB *gNB, int frame, int slot_rx, int ULSCH_id,
// scale the 16 factor in N_TA calculation in 38.213 section 4.2 according to the used FFT size
uint16_t bw_scaling = 16 * gNB->frame_parms.ofdm_symbol_size / 2048;
// do some integer rounding to improve TA accuracy
if (sync_pos > 0)
sync_pos += bw_scaling / 2 - 1;
else if(sync_pos < 0)
sync_pos -= bw_scaling / 2 - 1;
timing_advance_update = sync_pos / bw_scaling;
// put timing advance command in 0..63 range