Question: For a FDD UE supporting MIMO with single-stream restriction-STTD disabled, asymmetric CPICHs, what is the primary indicator for determining HS-SCCH detection performance?
Option 1: Probability of successful data transmission on HS-DPCCH (PDT)
Option 2: Probability of event Em (P(Em)), where UE is signalled on HS-SCCH-1 but DTX is observed in the corresponding HS-DPCCH/NACK field
Option 3: Signal-to-Noise Ratio (SNR) of the received CPICH
Option 4: Block Error Rate (BLER) of the HS-SCCH channel
Explanation: The correct answer directly relates to the provided context, where the detection performance of the HS-SCCH is determined by the probability of event Em (P(Em)), defined as the UE being signalled on HS-SCCH-1 but observing DTX in the corresponding HS-DPCCH/NACK field, making it the primary indicator for determining HS-SCCH detection performance under these conditions.