Question: In a UTRA FDD network, what is the primary condition for declaring the probability of event Em (P(Em)) related to HS-SCCH detection performance in a User Equipment (UE)?
Option 1: When the UE receives data on both HS-SCCH-1 and HS-DPCCH simultaneously.
Option 2: Upon observing an acknowledgement (ACK) in the HS-DPCCH/NACK field after being signalled on HS-SCCH-1.
Option 3: If the UE is idle while signalled on HS-SCCH-1, indicating no data transmission.
Option 4: When the UE is signalled on HS-SCCH-1 but observes Discontinuous Transmission (DTX) in the corresponding HS-DPCCH/NACK field.
Explanation: The correct answer, Option 4, aligns with the definition provided, where event Em's probability (P(Em)) is specifically tied to the scenario in which a UE, after being signalled on HS-SCCH-1, observes DTX (Discontinuous Transmission) in the corresponding HS-DPCCH/NACK field. This condition directly relates to assessing the detection performance of the High-Speed Shared Control Channel (HS-SCCH) in the context of High-Speed Downlink Packet Access (HSDPA) for UTRA FDD UEs.