Question: Under what condition is UE autonomous search for reselection to a previously visited Closed Subscriber Group (CSG) cell valid, in terms of radio configuration parameters?
Option 1: When the carrier frequency of the CSG cell has changed since the last visit.
Option 2: When the physical cell identity of neighboring non-CSG cells has been modified.
Option 3: When the radio configuration parameters (including carrier frequency and physical cell identity) of the CSG cell, non-CSG cell, and neighbor cells remain unchanged from the most recent previous visit.
Option 4: When at least two CSG IDs are included in the UE’s CSG whitelist.
Explanation: This is because the validity of the UE autonomous search for reselecting a previously visited CSG cell hinges on the consistency of radio configuration parameters. If these parameters (such as carrier frequency and physical cell identity) for the CSG cell, the non-CSG cell, and neighboring cells have not changed since the last visit, the UE can reliably use stored information to facilitate the reselection process, ensuring seamless connectivity without requiring a new search for updated parameters.