Question: In an FDD (Frequency Division Duplex) UE (User Equipment), what event marks the end of the measurement period for determining the active set update delay during a soft handover?
Option 1: Receipt of the last TTI (Transmission Time Interval) containing an RRC (Radio Resource Control) message implying soft handover
Option 2: Successful establishment of a new downlink DPCH (Dedicated Physical Channel)
Option 3: Switch off of the old downlink DPCH
Option 4: Completion of the first TTI on the new cell's downlink DPCH
Explanation: The active set update delay is a critical metric in evaluating how quickly a UE can adapt to changes in its active set during soft handover. This delay is specifically measured from the point when the UE receives the last TTI with an RRC message indicating the need for a soft handover update, marking the initiation of the handover process at the UE's protocol layer. This event signifies the UE's awareness of the impending change, after which it must complete the necessary adjustments.