Question: Which of the following is NOT a primary issue that Mobility Robustness Optimisation (MRO) aims to detect and correct in Evolved Universal Terrestrial Radio Access Network (E-UTRAN)?
Option 1: Connection failure due to intra-LTE mobility
Option 2: Unnecessary Cell Updates while in idle mode
Option 3: Unnecessary HO to another RAT (too early IRAT HO with no radio link failure)
Option 4: Inter-system ping-pong
Explanation: Mobility Robustness Optimisation primarily focuses on issues related to handovers and mobility between different Radio Access Technologies (RATs) or within the same LTE network. Unnecessary Cell Updates while in idle mode relate more to location management and paging, rather than mobility robustness during active sessions, which is what MRO targets. The other options directly align with the described goals of MRO: correcting connection failures due to intra-LTE or inter-RAT mobility, preventing unnecessary handovers to another RAT without radio link failure, and mitigating inter-system ping-pong effects.