CSFB Cell Selection Prioritizing Registered Location Area
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Solution Overview
Problem
During the transition from second and third generation mobile communications systems to fourth generation systems, the Circuit Switched Fallback (CSFB) process often results in an extra call-setup delay due to Location Area Updates when the target cell's location area differs from the registered location area, affecting interoperability and user experience.
Innovation Solution
The user equipment (UE) employs a method to determine whether candidate cells belong to the registered location area by receiving redirection information from the LTE network, prioritizing cells within the registered location area, and adjusting measurement orders to minimize Location Area Updates, thereby reducing call-setup delays and ensuring smooth interoperability between different mobile communication standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE performs Location Area Update during CSFB procedure when the target cell's location area differs from the registered location area, then the UE can camp on the target cell, but an extra call-setup delay is generated
Solution Approach 1:
The network performs preliminary actions by providing redirection information that includes system information of candidate cells before the UE camps on them. This allows the UE to determine whether a location area update is needed in advance, avoiding the delay of performing LAU after cell selection. The network proactively supplies location area identification information so the UE can make informed cell selection decisions without subsequent reconfiguration delays.
2Speed
If the UE selects a candidate cell outside the registered location area, then the UE can establish connection quickly, but a Location Area Update is required causing call-setup delay
Solution Approach 1:
The network provides feedback to the UE by including system information and location area identification of candidate cells in the redirection information. This feedback mechanism enables the UE to determine in advance whether the selected cell belongs to the registered location area, allowing the UE to adjust its cell selection strategy to prioritize cells within the registered LA and avoid unnecessary location area updates that would cause call-setup delays.
Data Source
AI summary
The method and apparatus for CSFB are provided. The method includes transmitting a MO CS request to a LTE network or receiving a MT CS call notification from a LTE network; triggering or accepting a CSFB procedure by the UE; receiving redirection information from the LTE network; judging whether system information corresponding to candidate cells is provided in the redirection information; acquiring system information corresponding to candidate cells, wherein the system information includes location area identifications (LAI) corresponding to candidate cells in the redirection information to determine whether the candidate cells belong to a registered LA; setting the candidate cell belonging to the registered LA to a higher priority; selecting the candidate cell with the higher priority as a target cell; and connecting to the target cell first.