Question: In a TDD UTRAN handover scenario, if a UE receives an RRC HANDOVER FROM UTRAN COMMAND with an activation time set to "now", how soon must the UE be ready to transmit on the new channel of the new RAT, considering the interruption time is already accounted for in Dhandover?
Option 1: Immediately after receiving the command
Option 2: Within the RRC procedure delay seconds from the end of the last TTI containing the RRC command
Option 3: Within 50 ms (RRC procedure performance value) from the end of the last TTI containing the RRC command
Option 4: At the next available TTI after the interruption time has elapsed
Explanation: According to the specifications, when the activation time is "now" or earlier than the RRC procedure delay seconds from the end of the last TTI containing the RRC command, the UE must be ready to transmit on the new channel within Dhandover seconds. Since Dhandover equals the RRC procedure performance value (50 ms) plus the interruption time, and the question states that the interruption time is already accounted for in Dhandover, the key factor here is the 50 ms RRC procedure performance value. Thus, the UE must be ready within this timeframe from the end of the last TTI containing the RRC command.