Question: In a TDD (Time Division Duplexing) network, what event triggers the start of the cell re-selection delay timer in a User Equipment (UE)?
Option 1: Receipt of a paging message from the current serving cell.
Option 2: Completion of a voice call, returning to idle mode.
Option 3: Initiation of a handover procedure by the network.
Option 4: Change in cell quality levels indicating a better ranked cell is available.
Explanation: The cell re-selection delay timer begins when the UE detects a change in cell quality levels that indicates another cell is now ranked higher (i.e., considered 'better' based on predefined criteria). This detection prompts the UE to initiate cell re-selection, culminating in updating its location to the new, preferred cell. This scenario relates to managing mobility and radio resource utilization in wireless communications, highlighting the UE's autonomous decision-making process based on observed network conditions.