Terminal Cell Selection via CSFB Blacklist for Voice Setup
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Solution Overview
Problem
The existing LTE and 5G networks face high failure rates for voice calls due to inadequate support for circuit-switched fallback (CSFB) technology, particularly when core network entities do not support CSFB, leading to unsuccessful voice service setups in 2G/3G circuit domains.
Innovation Solution
A cell selection method that involves a terminal saving location identifiers of non-supporting and supporting networks to a blacklist, allowing it to avoid cells with previous failure records during subsequent CSFB attempts, thereby improving voice call success rates by prioritizing alternative cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the terminal camps on the LTE network and uses CSFB technology to fall back to 2G/3G circuit domain for voice service, then the voice service can be supported, but the voice call setup fails when the core network entity does not support CSFB or call information transmission is abnormal
Solution Approach 1:
The terminal performs preliminary actions by saving location identifiers of failed CSFB attempts to a blacklist before subsequent voice call attempts. This preliminary recording action enables the terminal to proactively avoid previously failed cells, preventing repeated failed setup attempts and improving overall voice call reliability without adding complex network compatibility handling.
Solution Approach 2:
The patent converts the harmful effect of repeated failed CSFB attempts into a beneficial outcome by using the failure information itself to create a blacklist. The previously harmful failed location identifiers are transformed into useful avoidance data, turning the harm of network incompatibility into a benefit that automatically steers the terminal away from problematic cells, thereby improving voice call setup success rate.
2Ease of operation
If the terminal repeatedly attempts to camp on the same cell that caused previous CSFB failures, then the terminal maintains simple cell selection logic, but the voice service setup continues to fail
Solution Approach 1:
The terminal performs self-service by autonomously managing its own cell selection process through the blacklist mechanism. The terminal independently records failed location identifiers, automatically checks against the blacklist before camping decisions, and self-corrects by avoiding previously failed cells. This self-service approach maintains ease of operation while significantly improving voice service establishment reliability without requiring external network intervention.
Solution Approach 2:
The patent implements a feedback mechanism where the terminal uses information from previous CSFB failure experiences to guide future cell selection decisions. The blacklist serves as a feedback storage that continuously learns from failed attempts and adjusts subsequent camping behavior accordingly. This feedback loop maintains simple cell selection logic while preventing repeated failures, thereby improving voice service establishment reliability.
3Reliability
If the terminal uses a blacklist to avoid previously failed cells during CSFB attempts, then the voice call success rate improves, but the terminal requires additional memory and processing to manage the blacklist
Solution Approach 1:
The patent applies segmentation by dividing the cell selection process into distinct phases: normal cell selection, blacklist checking phase, and blacklist update phase. The blacklist itself is segmented into individual location identifier entries, each representing a specific failed attempt. This segmentation allows the terminal to manage complexity by handling only one blacklist operation at a time while maintaining high CSFB voice call success rate.
4Adaptability or versatility
If the terminal falls back from 5G network to LTE network and then to 2G/3G circuit domain for voice service, then the voice service can be supported in 5G network, but the same CSFB setup failure problem occurs
Solution Approach 1:
The patent implements universality by creating a blacklist mechanism that functions across multiple network generations (4G LTE and 5G). The same blacklist structure and avoidance logic universally apply regardless of which network type initiates the CSFB process. This multi-functional approach enables the terminal to maintain adaptability for 5G voice service support while simultaneously improving CSFB setup reliability through consistent failure avoidance across different network contexts.
Data Source
AI summary
A cell selection method includes: when a terminal camps on a first network that does not support a voice service, and voice service needs to be initiated or received, falling back, by the terminal in a circuit switched fallback (CSFB) manner, to a second network that supports the voice service when the terminal fails to establish the voice service with the second network, saving, by the terminal, a location identifier of the first network and a location identifier of the second network to a blacklist. The blacklist is used by the terminal to choose to camp on a cell of the second network when performing CSFB subsequently.