Question: In a UTRAN TDD environment, 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 given RRC procedure performance value and no additional interruption time?
Option 1: Immediately after receiving the command
Option 2: Within 20 ms from the end of the last TTI containing the RRC command
Option 3: At the next available TTI after the RRC procedure delay seconds
Option 4: Within 50 ms from the end of the last TTI containing the RRC command
Explanation: According to the specifications, when the activation time is "now" or earlier than the RRC procedure delay seconds, the UE must be ready to transmit on the new channel within Dhandover seconds. Given that Dhandover equals the RRC procedure performance value plus interruption time, and assuming no additional interruption time for this scenario, Dhandover effectively equals the RRC procedure performance value, which is specified as 50 ms. Thus, the UE must be ready to transmit within 50 ms from the end of the last TTI containing the RRC command.