Autonomous LTE Return via CSFB Cell Search
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Solution Overview
Problem
Current LTE network deployments experience sub-par voice calling user experiences due to longer call setup times, IRAT cell re-selection/handover failures, and inefficient return to E-UTRAN during CSFB procedures, particularly in scenarios where GERAN/UTRAN upgrades are not feasible.
Innovation Solution
Implementing autonomous cell search capabilities in UE devices during CSFB procedures, facilitated by RRC connection release and handover procedures, allowing UE to search for LTE cells after CSFB call release, and providing redirection information to speed up return to LTE without requiring enhancements to the A/Iu interface in GERAN/UTRAN.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If CSFB is implemented to provide voice calls over LTE, then voice service compatibility is improved, but call setup time increases
Solution Approach 1:
The network pre-configures cell reselection priorities and parameters before the UE needs to return to LTE. The MME stores and provides E-UTRAN cell information in advance, so when the CS call ends, the UE can immediately resume LTE data services without delay for network signaling or cell search.
Solution Approach 2:
The MME acts as an intermediary between the CS domain and E-UTRAN. It maintains a mapping between the UE's IMSI and E-UTRAN cell information, enabling fast redirection back to LTE by providing pre-stored cell priorities and parameters without requiring direct interaction between the CS network and E-UTRAN.
2Productivity
If autonomous cell search is implemented in UE during CSFB, then return to LTE efficiency is improved, but device complexity increases
Solution Approach 1:
The UE autonomously performs cell search and reselection to E-UTRAN based on pre-configured parameters received from the network. The device uses stored cell priorities, frequency information, and reselection thresholds to independently determine when and where to return to LTE without continuous network control, reducing signaling overhead while maintaining simplicity.
3Ease of operation
If fast return to E-UTRAN is implemented after CSFB call release, then user experience is improved, but network signaling overhead increases
Solution Approach 1:
Cell reselection priorities, frequency lists, and reselection parameters are pre-configured in the UE during initial LTE attachment or previous CSFB events. When the CS call ends, the UE immediately uses these pre-stored parameters to return to LTE without requiring additional network signaling for parameter acquisition.
Solution Approach 2:
The MME pre-stores the mapping between UE IMSI and E-UTRAN cell information in advance. During fast return, the MME provides this pre-configured cell information to the UE using existing signaling messages (e.g., RRC Connection Release), avoiding the need for additional dedicated signaling exchanges between network and UE.
Data Source
AI summary
Mobile devices, base stations, and/or relay stations may implement CSFB (circuit switched fallback) operations by using RRC (radio resource control) connection release and/or handover procedures. If the CSFB RAT (radio access technology) target is not well configured, the UE may be informed and provisioned by the NW during a CSFB procedure with the information to return to LTE. Having this information, the UE may perform an autonomous search of LTE cells after the CSFB call release, speeding up return to LTE. To minimize potential call failures during CSFB, the UE may autonomously perform an additional cell search, in particular a search for cells on a RAT different from the initial target RAT. This creates an opportunity to prevent call failure of CSFB calls that would otherwise fail. The UE may be provisioned during the CSFB procedure with information to perform the additional cell search, should such a search be necessary.