Inter-PLMN Handover Control via MME CSG List Validation
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Solution Overview
Problem
In networks with Closed Subscriber Group (CSG) cells, inter-PLMN handovers are often incorrectly decided or blocked due to unsynchronized CSG lists between User Equipment (UE) and Home Subscriber Servers (HSS), leading to network connection losses or suboptimal handovers.
Innovation Solution
The proposed solution involves an access control method where the Mobility Management Entity (MME) and Home Subscriber Server (HSS) synchronize and transmit only the necessary CSG lists during Attach/Tracking Area Update procedures, ensuring accurate handover decisions by verifying the target PLMN's allowed CSG lists before initiating handovers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE uses the old allowed CSG list for measurement report before OMA-DM updates the CSG list, then the handover decision may be made based on outdated access rights information, but this leads to handover failures when the UE attempts to access the target CSG cell
Solution Approach 1:
The patent applies preliminary action by having the MME proactively update the UE's CSG list during the Tracking Area Update procedure before the OMA-DM synchronization occurs. This ensures the UE has current access rights information available before attempting handover, preventing handover failures due to outdated CSG list information.
Solution Approach 2:
The patent implements feedback by having the MME verify whether the target PLMN's CSG ID exists in the UE's allowed CSG list during handover decision-making. This feedback mechanism allows the MME to make informed handover decisions based on current access rights, preventing invalid handovers to CSG cells where the UE lacks permission.
2Reliability
If the MME checks the target PLMN's CSG list during handover decision, then accurate handover decisions can be made, but this increases the complexity of the handover control procedure
Solution Approach 1:
The patent applies universality by utilizing the existing MME's allowed CSG list information, which is already maintained for other purposes such as access control and subscription management. This existing data structure is repurposed to support handover decision-making, avoiding the need for separate CSG list management systems and reducing overall complexity.
Solution Approach 2:
The patent uses the MME as an intermediary that mediates between the UE's handover request and the target CSG cell's access rights. The MME leverages its existing subscription information and CSG list data to verify handover validity, simplifying the process compared to direct UE-to-target-cell verification while ensuring accurate handover decisions.
3Loss of information
If all CSG lists of all PLMNs are transmitted during Attach procedure, then the UE has complete CSG information, but this increases the signaling overhead and update frequency requirements
Solution Approach 1:
The patent applies extraction by having the HSS transmit only the specific CSG list information relevant to the target PLMN to the MME during handover, rather than transmitting all CSG lists of all PLMNs. This selective transmission reduces signaling overhead while providing the UE with the necessary access rights information for the specific handover scenario.
Solution Approach 2:
The patent segments the CSG list information by PLMN, allowing the MME to retrieve and transmit only the relevant CSG list for the target PLMN during handover procedures. This segmentation approach enables efficient information management and reduces the amount of data that needs to be transmitted and synchronized.
Data Source
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AI summary
The invention is directed to a terminal in a communication system, the terminal comprising: a transceiver configured to transmit and receive at least one signal; and a controller coupled with the transceiver and configured to: transmit, to a base station of a first public land mobile network, PLMN, a measurement report, and receive, from the base station, a handover command related to a target cell of a second PLMN, wherein a closed subscriber group, CSG, identity, ID, related to the target cell is transmitted from the base station to a mobility management entity, MME, wherein CSG subscription information for an equivalent PLMN list is transmitted from a home subscriber server, HSS, to the MME, and wherein a CSG membership of the terminal in the target cell is validated by the MME based on the CSG ID related to the target cell and the CSG subscription information for the equivalent PLMN list related to the terminal.