Question: In UTRA TDD, what is the primary event that marks the end of the handover interruption time for a User Equipment (UE) during a handover process?
Option 1: Receipt of the first downlink DPCH on the new cell
Option 2: UE starts transmission of the new uplink Dedicated Physical Channel (DPCH)
Option 3: Completion of the last downlink data transmission on the old cell's Shared Channel
Option 4: Initiation of the Random Access Procedure on the new cell
Explanation: The handover interruption time in UTRA TDD is specifically defined as ending when the UE begins transmitting on the new uplink DPCH, marking the transition to the new cell for active communication. This highlights the importance of minimizing this interval to reduce service disruption during handovers.