Question: In a Closed Subscriber Group (CSG) scenario for a Home NodeB (HNB), which function ensures that only authorized User Equipment (UE) can access a CSG cell, specifically in closed mode?
Option 1: Admission and Rate Control Function
Option 2: CSG Charging Function
Option 3: CSG Access Control Function
Option 4: Paging Optimization Function
Explanation: The CSG Access Control Function is specifically designed to verify that a UE has a valid subscription to access a particular CSG in closed mode. This function acts as a gatekeeper, ensuring only subscribed members can utilize the services of the specified CSG cell, thereby maintaining the integrity and exclusivity of the Closed Subscriber Group.