CSFB Frequency Selection and Timer Override

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Solution Overview

Problem

The existing Circuit Switched Fall Back (CSFB) procedure in LTE networks fails to effectively redirect users to better signal frequencies during Inter-Radio Access Technology (RAT) switching, leading to increased call failure rates due to restrictive timer settings and lack of frequency selection options.

Innovation Solution

The method allows User Equipment (UE) to collect neighbor frequency lists from the network, select the best frequency for camping based on signal conditions, and override timers to initiate multiple RRC connection requests, thereby improving the CSFB call success rate.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the UE camps to the serving frequency till the expiry of timer T300 during RRC connection establishment, then the existing procedure is simple to implement, but the CSFB call failure rate increases due to inability to switch to better frequencies

Engineering Contradiction:

ImproveCSFB call success rateVSAvoidfrequency selection and timer management complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent implements dynamic frequency selection by allowing the UE to transition from a static serving frequency to multiple neighbor frequencies based on signal quality measurements. The UE dynamically adjusts its camping frequency during the T300 timer period, switching to frequencies with better signal conditions to improve CSFB call success rate.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent applies preliminary action by having the UE collect and evaluate neighbor frequency information before the T300 timer expires. The UE proactively identifies suitable alternative frequencies in advance, preparing a list of candidate frequencies with their signal quality metrics, so that if the current frequency proves inadequate, the UE can quickly switch without waiting for timer expiry.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If the UE uses the redirected frequency from LTE network, then the redirection procedure is straightforward, but the call setup fails when the redirected frequency is in poor signal conditions

Engineering Contradiction:

Improvecall setup success rateVSAvoidfrequency selection process complexity

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent implements self-service by enabling the UE to autonomously evaluate signal conditions of redirected frequencies and independently select alternative frequencies from the neighbor list. The UE performs self-assessment of frequency quality using measurement criteria (S-criteria) and automatically switches to better frequencies without requiring network intervention, thereby improving call setup success rate while maintaining operational simplicity.

Inventive Principle:

Principle #25Self-service

3Adaptability or versatility

If the UE is restricted to a single redirected frequency, then the redirection procedure is simple, but the UE cannot utilize other available frequencies with better signal conditions

Engineering Contradiction:

Improvefrequency selection flexibilityVSAvoidneighbor frequency list management

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent applies segmentation by dividing the frequency selection process into distinct phases: (1) receiving the redirected frequency from the network, (2) collecting neighbor frequency lists, (3) evaluating signal conditions for each frequency, and (4) selecting the optimal frequency. This segmented approach allows the UE to systematically manage multiple frequencies while maintaining clear procedural structure, thereby improving adaptability without excessive complexity.

Inventive Principle:

Principle #1Segmentation

4Productivity

If the UE follows the existing T300 timer specification, then the timer management is standardized, but the UE cannot initiate maximum possible RRC connection requests during CSFB procedure

Engineering Contradiction:

ImproveRRC connection request rateVSAvoidtime utilization efficiency

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The patent implements continuity of useful action by allowing the UE to continuously attempt RRC connection requests throughout the entire T300 timer period across multiple frequencies. Instead of being restricted to a single frequency attempt, the UE continuously switches between candidate frequencies and initiates connection requests on each, maximizing the utilization of the T300 timer duration and increasing the probability of successful connection establishment.

Inventive Principle:

Principle #20Continuity of useful action

Data Source

PatentEP2962492B1Method and system for improving circuit switched fall back (CSFB) performance

Publication Date: 2021.06.09 SAMSUNG ELECTRONICS CO LTD

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AI summary

A method and system to improve CSFB performance specified in the 3GPP standard is disclosed. The method disclosed enables the UE to collect neighbor frequency list from the network along with the redirection frequency sent by the Long Term Evolution (LTE) network in response to Extended Service Request (ESR) initiated by the UE. UE selects best frequency on which the UE can camp for CS call by applying additional offset criteria over the existing S-criteria during selection of serving frequency that effectively increases CSFB call success rate. The method enables the UE to override timer T300 and parameter N300 in the RRC connection establishment process during CSFB call procedure and effectively utilize the ESR time to attempt maximum possible RRC connection requests. The method increases chances of the UE to establish successful RRC connection, reduce the CSFB call failure rate and enhance user experience.