Question: In UTRA TDD/FDD networks, what event 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: Completion of the Random Access Channel (RACH) procedure on the new cell
Option 3: End of the last downlink DPCH transmission containing a transport block on the old cell
Option 4: Start of the UE's transmission of the new uplink DPCCH on the new cell
Explanation: The handover interruption time is specifically defined as ending when the UE begins transmitting on the new cell, which is marked by the start of the new uplink DPCCH (Dedicated Physical Control Channel) transmission. This event signifies the UE's successful transition to the new cell for uplink communications, concluding the handover interruption period.