Question: In an inter-system environment, what is a key condition for detecting 'ping-pongs' as part of Mobility Robustness Optimization when a UE (User Equipment) is handed over between different systems (e.g., from E-UTRAN to NG-RAN and back to E-UTRAN)?
Option 1: The UE's service requires high-speed data transmission, triggering frequent handovers.
Option 2: The coverage of the source system (e.g., E-UTRAN) was insufficient for the UE's ongoing service during the handover cycle.
Option 3: Within a predefined limited time, the UE is handed back to a cell in the source system while the source system’s coverage was sufficient for the UE’s service.
Option 4: The handovers occur only at the edge of the cell boundaries between the two systems.
Explanation: This option correctly identifies the crucial condition for detecting inter-system 'ping-pongs' as part of Mobility Robustness Optimization. Specifically, it highlights the scenario where a UE is handed over from one system to another and then back again within a short timeframe, despite the initial source system having sufficient coverage for the UE’s service. This sequence of events, particularly with sufficient coverage in the source system upon return, is indicative of a potential 'ping-pong' issue that needs optimization.