Question: In a handover scenario from UTRAN to E-UTRAN, where the target cell is unknown but signal quality allows for successful detection on the first attempt, what is the maximum allowed interruption time (Tinterrupt) before the UE starts transmitting on the new PRACH channel?
Option 1: 60 ms (TIU of 10 ms + minimal Tsearch assumption)
Option 2: 100 ms (assuming a midpoint between specified Tsearch values)
Option 3: 140 ms (doubling the TIU for additional buffer, incorrectly assuming Tsearch as 0)
Option 4: 110 ms (Tsearch of 80 ms for unknown target cell + TIU of 10 ms + 20 ms as per specification)
Explanation: The correct calculation for the maximum allowed interruption time (Tinterrupt) when the target cell is unknown but detectable on the first attempt involves adding the time to search for the target cell (Tsearch = 80 ms), the interruption uncertainty in acquiring the first available PRACH occasion (TIU = 10 ms), and an additional 20 ms. Thus, Tinterrupt = Tsearch + TIU + 20 ms = 80 ms + 10 ms + 20 ms = 110 ms.