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RA‑RNTI = 1 + t_id + 14 × f_id + 14 × 80 × ul_carrier_id
Per 5G NR spec, RA‑RNTI is derived from PRACH occasion indices: t_id (time), f_id (frequency), and uplink carrier index. Formula: 1 + t_id + 14×f_id + 14×80×ul_carrier_id.
RA‑RNTI (Random Access RNTI) — Short Description
RA‑RNTI is a temporary identifier used in 5G NR during the Random Access Procedure.
It uniquely represents a UE’s PRACH transmission occasion (defined by time index t_id and frequency index f_id), allowing the gNB to identify which UE sent the RA preamble.
Once calculated using the PRACH occasion, the gNB uses this RA‑RNTI to send the Random Access Response (RAR) to the correct UE.
February 16, 2026