UE Circuit-Switched Fallback Latency Reduction
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Solution Overview
Problem
The LTE system's circuit-switched fallback (CSFB) process experiences increased call setup time and incoming call failures due to location updates when a user equipment (UE) is handed over to a 2G/3G base station with a different location area, leading to degraded user experience.
Innovation Solution
A UE establishes a learning database to prioritize redirection frequencies based on the current registered local area identity (LAI) and signal reference information, allowing it to select a target base station with the same LAI, thereby avoiding unnecessary location updates and reducing CSFB latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE is handed over to a 2G/3G base station with a different location area, then the CSFB procedure can be completed, but the call setup time increases due to location update procedures
Solution Approach 1:
The UE performs location update procedures in advance before the CSFB procedure. The device proactively updates its location information to the target location area while still connected to the LTE network, so that when handover to 2G/3G occurs, the location update is already complete and no additional delay occurs during the fallback process.
2Ease of operation
If the UE selects a target base station with a different LAI, then the CSFB procedure can proceed, but the probability of incoming call failure increases
Solution Approach 1:
The UE monitors and compares the LAI of the current registered location area with the LAI of the target base station. This feedback mechanism allows the device to identify when a location mismatch exists and trigger the preliminary location update action to prevent call failures.
3Reliability
If the UE performs location update procedures during CSFB, then the CSFB procedure can be completed successfully, but the user experience deteriorates due to increased latency
Solution Approach 1:
The UE performs location update procedures in advance before the CSFB procedure. The device proactively updates its location information to the target location area while still connected to the LTE network, so that when handover to 2G/3G occurs, the location update is already complete and no additional delay occurs during the fallback process.
Data Source
AI summary
A user equipment and a circuit-switched fallback method thereof are provided. An initial base station sends a radio resource control connection release message containing the redirection frequency list to the UE. The redirection frequency list includes at least one redirection frequency. The UE determines a priority of the at least one redirection frequency according to a current registered LAI, a learning database and a piece of signal reference information of the redirection frequency list. Accordingly, the UE executes a circuit switch fallback procedure according to the priority of the at least one redirection frequency.