5G • RAN
Timing Advance Timer
timeAlignmentTimer
RRC timer supervising uplink synchronization; upon expiry, the UE considers uplink timing lost and clears PUCCH.
Technical Explanation
Whenever a UE receives a Timing Advance Command (TAC) MAC CE, it restarts the timeAlignmentTimer. If the timer expires (due to prolonged lack of uplink updates), the UE assumes it has lost uplink synchronization, releases all PUCCH and SRS resources, and must perform PRACH random access before transmitting data again.
Key Functions
- Restarts upon reception of any Timing Advance Command MAC CE
- Prevents unsynchronized UEs from transmitting on PUCCH and causing interference
- Forces random access procedure (PRACH) to recover lost timing
Specifications
3GPP TS 38.321, TS 38.331
Interfaces
Uu
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