Radio Link Monitoring LBT Failure Detection

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Solution Overview

Problem

In NR unlicensed (NR-U) cellular communication systems, it is challenging to distinguish between out-of-sync indications due to poor link quality and those caused by listen before talk (LBT) failures, leading to incorrect declarations of radio link failures (RLF).

Innovation Solution

The proposed solution involves calculating a hypothetical Physical Downlink Control Channel (PDCCH) block error rate to differentiate between in-sync and out-of-sync indications, weighing reference signal (RS) samples, and using a weighting factor to suppress invalid out-of-sync indications, thereby reducing false RLF declarations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the UE monitors downlink radio link quality to detect out-of-sync status, then the radio link monitoring function is achieved, but false RLF declarations occur due to inability to distinguish LBT failure from poor link quality

Engineering Contradiction:

Improveradio link monitoring reliabilityVSAvoidout-of-sync detection accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent segments the out-of-sync detection process by introducing separate detection mechanisms: one for link quality assessment (using RLM-RS) and another for LBT failure detection (using LBT failure indicators). This segmentation allows the system to distinguish between the two causes of out-of-sync status, preventing false RLF declarations while maintaining reliable radio link monitoring.

Inventive Principle:

Principle #1Segmentation

2Reliability

If the UE declares RLF based on consecutive out-of-sync indications, then the radio link failure detection function is achieved, but false RLF declarations occur due to LBT failure being misinterpreted as poor link quality

Engineering Contradiction:

ImproveRLF detection reliabilityVSAvoidfalse RLF declaration

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an intermediary mechanism - the LBT failure indicator - that acts as a mediator between the physical layer monitoring and the RLF declaration process. When an LBT failure indicator is detected, it intermediates the out-of-sync indication, preventing it from being counted toward RLF declaration. This resolves the harmful effect of false RLF declarations caused by misinterpreting LBT failures as link quality issues.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If the UE uses standard RLM procedure to monitor link quality, then the monitoring process is simple, but the system cannot differentiate between OOS due to poor link quality and OOS due to LBT failure

Engineering Contradiction:

Improvemonitoring process complexityVSAvoidcause differentiation accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent enhances the RLM procedure by giving it multi-functionality: the same monitoring framework is used to simultaneously assess both link quality (via RLM-RS measurements) and detect LBT failures (via LBT failure indicators). This universal approach allows the system to perform multiple detection functions without significantly increasing complexity, while achieving accurate differentiation between poor link quality and LBT failure causes.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS11979904B2Detection of listen before talk failure during radio link monitoring

Publication Date: 2024.05.07 INTEL CORP

AI summary

Disclosed embodiments are related to distinguishing between listen-before talk (LBT) failure and LBT success, reducing the effect of invalid out-of-sync (OOS) indications and preventing false declaration of radio link failures (RLFs). Other embodiments may be described and/or claimed.