CSG Cell Access Check Update Mechanism for PLMN Handover
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Solution Overview
Problem
User equipment (UE) experiences inaccuracies in identifying allowed Closed Subscriber Group (CSG) cells during handovers between cells in different Public Land Mobile Networks (PLMNs) due to outdated PLMN and equivalent PLMN lists, leading to false matches and missed matches, which affect handover decisions and signaling efficiency.
Innovation Solution
Implementing a system that detects changes in PLMN and equivalent PLMN lists between serving and target cells during handovers and sends indications to the UE, allowing for updated PLMN checks to determine CSG cell accessibility, thereby preventing false and missed matches by ensuring accurate CSG cell reporting and handover decisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the UE uses the registered PLMN and stored EPLMN list for CSG cell access checks during handover, then the access check can be performed without network signaling, but the PLMN information may be outdated leading to false matches or missed matches
Solution Approach 1:
The network performs preliminary detection of PLMN and EPLMN list changes between source and target cells before handover execution. The target cell determines whether the UE's stored PLMN information will be outdated by comparing with its own PLMN configuration, and prepares change indication information in advance to be sent to the UE during handover.
Solution Approach 2:
The system introduces feedback by sending PLMN/EPLMN list change indication from the network to the UE during handover. This feedback mechanism allows the UE to update its stored PLMN information based on network-provided changes, ensuring accurate CSG cell access checks without requiring full location area updates.
2Measurement precision
If the UE performs location area update procedures to refresh PLMN information, then the PLMN and EPLMN lists remain accurate, but signaling overhead and handover time increase
Solution Approach 1:
The invention extracts only the essential PLMN and EPLMN list change indication information from the full location area update procedure. Instead of requiring the UE to perform complete location area updates with extensive signaling, the network sends only the necessary PLMN change information to the UE during handover, reducing signaling overhead while maintaining accuracy.
3Measurement precision
If the network sends detailed PLMN update information during handover, then the UE can accurately identify CSG cells, but signaling overhead increases
Solution Approach 1:
The PLMN/EPLMN list change indication is designed as a lightweight, temporary information element used specifically during handover procedures. This disposable indication mechanism provides necessary PLMN update information without the overhead of permanent or recurring update procedures, reducing overall signaling load while maintaining accuracy when needed.
Data Source
AI summary
Various combinations of these teachings solve dual errors for a user equipment UE checking whether a private cell is allowed when handing over between serving and target cells, where the PLMN and/or list of EPLMNs of the serving and target cells may differ. The serving cell may send a one-bit indication that there is a change in a handover command or a system information SI6 message after which the UE may or may not refrain from reporting new cells until it performs a registration/location area update in the target cell. The target cell may trigger in the UE a registration update then provide the UE with the PLMN of the target cell. The serving cell can provide the PLMN of the target cell in a SI6 message or handover command, which the UE may use in place of or in addition to the PLMN/EPLMN of the serving cell when checking whether a private/closed subscriber group cell is allowed.