UE MICO Mode Registration Area Handling
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Solution Overview
Problem
When a UE in Mobile Initiated Connection Only (MICO) mode is assigned an 'all PLMN' registration area, there is a risk that control plane messages may not be routed to the serving AMF, leading to message rejections and increased latency and power consumption, especially for low-energy devices.
Innovation Solution
The UE is configured to receive a Within Serving AMF (WSA) area indication from the network, allowing it to determine if it is within the covered area and adjust its registration and service request procedures accordingly, using a mobility registration update when outside the WSA and periodic updates or service requests when within it.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the UE uses periodic registration update or Service Request procedures, then the signaling overhead is reduced, but the messages may not be routed to the serving AMF when the UE is outside the serving AMF coverage area
Solution Approach 1:
The UE performs preliminary determination of its location relative to the serving AMF coverage area before transmitting control plane messages. The UE checks whether it is within the serving AMF coverage area using available information (such as tracking area information and stored coverage area data) and only uses periodic registration update or Service Request procedures when confirmed to be within the coverage area, thereby preventing routing failures before they occur
Solution Approach 2:
The system implements a feedback mechanism where the UE continuously monitors its location information and compares it with the serving AMF coverage area boundaries. When the UE detects that it has moved outside the coverage area, it switches to using mobility registration update procedures instead, ensuring that control plane messages are always routed correctly based on real-time location feedback
2Reliability
If the UE performs mobility registration update whenever outside serving AMF area, then message routing reliability is improved, but latency and power consumption increase
Solution Approach 1:
The solution applies different registration procedures based on the UE's local situation - when the UE is within the serving AMF coverage area, it uses the lightweight periodic registration update or Service Request procedures; when outside the coverage area, it uses mobility registration update. This localized adaptation of procedures based on geographic position optimizes both reliability and latency for each specific scenario
Solution Approach 2:
The UE dynamically changes the type of registration procedure used based on the parameter of its location relative to the serving AMF coverage area. By changing the procedural parameter (from periodic registration update to mobility registration update) based on location conditions, the system achieves reliable routing without unnecessarily increasing latency in cases where the UE remains within the coverage area
3Reliability
If the UE performs frequent registration updates to ensure proper routing, then message delivery reliability is improved, but power consumption increases which is troublesome for low energy devices
Solution Approach 1:
The UE performs preliminary verification of its location relative to the serving AMF coverage area before initiating any registration update procedure. By checking location conditions in advance and only performing mobility registration update when actually outside the coverage area, the UE avoids unnecessary signaling and power consumption while still ensuring reliable message delivery when needed
Solution Approach 2:
Instead of always performing the more robust mobility registration update procedure, the UE applies partial action by using the lighter periodic registration update or Service Request procedures when within the serving AMF coverage area. This partial application of the more intensive procedure only when necessary reduces overall power consumption while maintaining sufficient reliability for the given conditions
Data Source
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AI summary
A UE is configured such that, when in MICO mode, the UE does not transmit certain messages (e.g., Service Request, periodic registration update message) whenever there is a risk that the certain message will not be routed to the UE's serving AMF. In some embodiments, the network (e.g., serving AMF) indicates to the UE in MICO mode an area (parts of, or the entire PLMN) that is covered by the serving AMF, the Within Serving AMF (WSA) area. While the UE is within the indicated WSA area, the UE in MICO mode may continue to use periodic registration area update or Service Requests (instead of the more extensive mobility registration update procedure) as there is no risk of addressing a new AMF in that area.