Cumulative TA goes negative at longer ranges (e.g., ~200 m shows −11 to −25 TA units)

[ujjwalpawar]

Hi folk I’m seeing an odd Timing Advance behavior where the cumulative TA becomes negative, and it tends to happen when the UE is farther from the base station. For example, around 200 m distance I sometimes see cumulative TA ≈ −11, occasionally down to −25 TA units. My expectation is that farther UEs should need positive TA (arrive earlier), not negative.

I’d love to understand whether this is expected under some corner-case, a sign convention mismatch, or a configuration issue on my side.

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Setup

• srsRAN version: 25.10 (gNB)
• NR band / BW: n77, 100 MHz
• Numerology (μ): μ=1 (30 kHz SCS)
• RU: Benetel RAN650 (outdoor with external directional antenna)
• UEs: stationary for these tests (single UE while observing)
• Sync: gNB clock via PTP
• Traffic: light UL (periodic SRS/PUSCH present)

TA manager params (current)

# srsRAN TA manager
ta_measurement_slot_period = 80
ta_measurement_slot_prohibit_period = 0
ta_cmd_offset_threshold = 0          
ta_target = 1                      
ta_update_measurement_ul_sinr_threshold = 0