For cases where the network knows in advance that a particular UE will perform a Random Access Procedure to acquire uplink synchronization, a dedicated preamble is reserved and assigned to the UE under consideration.
Dedicated preamble assignment for handover (HO) is handled by RRC, whereas preamble assignment for DL data arrival is handled by MAC. When the UE transmits the dedicated preamble in Phase 1, the network knows to which UE this preamble was assigned, and at the time of detection of this preamble can already determine the identity of the UE. Thus, no contention resolution is needed, and the delay before data transmission can be resumed is reduced. The application of Contention Free Random Access is applicable in handover scenarios.
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