RAT Information Table for CSFB Delay Reduction

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Solution Overview

Problem

In wireless communication systems, particularly in LTE networks, Circuit Switched FallBack (CSFB) voice calls experience significant delays due to the lack of Radio Access Technology (RAT) information, leading to incorrect RAT selection and prolonged scanning processes when switching from LTE to 2G or 3G networks during call failures.

Innovation Solution

A method and apparatus that maintain and update a RAT information table on the User Equipment (UE) with Location Area Identification (LAI) and RAT information, enabling local selection of the best suitable network for CSFB calls, thereby reducing delays by selecting the appropriate RAT for voice call connections.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the UE performs random RAT selection and PLMN scanning when ESR fails, then the UE can eventually find a suitable network, but the call setup time is significantly delayed

Engineering Contradiction:

Improvecall connection reliabilityVSAvoidcall setup time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The UE performs RAT selection and network identification in advance by maintaining a stored list of suitable GERAN/UTRAN RATs and PLMN information obtained during initial LTE attach. When ESR fails, the UE immediately uses this pre-stored information to camp on a suitable network without performing time-consuming random selection and full PLMN scanning, thus reducing call setup time while ensuring reliable connection

Inventive Principle:

Principle #10Preliminary action

2Speed

If the UE selects a High Priority RAT based on SIM HPLMN files, then the UE can quickly establish connection, but the selected RAT may be incorrect or unavailable causing call failure

Engineering Contradiction:

Improveconnection establishment speedVSAvoidcall connection success rate

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

During the initial LTE attach procedure, the UE proactively obtains and stores the correct GERAN/UTRAN RAT information and PLMN details provided by the network in the Attach Accept message. This preliminary action ensures that when CSFB is triggered, the UE has verified, network-approved RAT information to use, combining fast connection establishment with high reliability by avoiding selection of incorrect or unavailable RATs

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9565598B2Method and system to reduce delay in circuit switch fallback (CSFB) procedures while operating with multi/dual SIMs

Publication Date: 2017.02.07 SAMSUNG ELECTRONICS CO LTD

AI summary

A method of reducing delay in Circuit Switched FallBack (CSFB) in a Radio Access Technology (RAT) communications network. The method includes initiating, by a terminal, a combined attach procedure by sending an attach request message to the RAT communications network, receiving, by the terminal, an attach accept message along with Location Area Identification (LAI) information from the network in response to the attach request message, checking, by the terminal, network identifier information in a RAT information table based on the received LAI, and selecting a mobile network based on the network identifier information to trigger establishment of a circuit-switched call.