UE RLM Procedure for 5G NR-U False Failure Reduction

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Current 5G NR-U networks face challenges in radio link monitoring (RLM) due to listen-before-talk (LBT) requirements, which can lead to unpredictable transmission of periodic signals and increased risk of false radio link failure (RLF) triggers, especially in unlicensed spectra.

Innovation Solution

Implementing a UE-based RLM procedure that differentiates between transmission failure and out-of-sync conditions using specific evaluation windows and SINR thresholds, allowing for accurate reporting of transmission failure occasions to the gNB, thereby reducing false RLF triggers and enhancing network reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If listen-before-talk (LBT) requirements are implemented in 5G NR-U networks, then spectrum sharing and coexistence with other systems is improved, but transmission of periodic signals becomes unpredictable and false radio link failure triggers increase

Engineering Contradiction:

Improvespectrum sharing capabilityVSAvoidradio link monitoring reliability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent implements dynamic RLM evaluation windows that adapt to LBT transmission patterns. The evaluation window size and position are adjusted based on actual signal detection outcomes, allowing the system to dynamically respond to the unpredictable nature of LBT-based transmissions while maintaining reliable RLF detection

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes key RLM parameters including evaluation window duration, number of evaluations required, and SINR thresholds based on transmission conditions. By adjusting these parameters dynamically, the system maintains reliability in both licensed and unlicensed spectra while accommodating LBT requirements

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If traditional RLM procedures are used in unlicensed spectrum, then implementation simplicity is maintained, but false radio link failure triggers increase due to inability to distinguish transmission failure from poor link quality

Engineering Contradiction:

ImproveRLM procedure complexityVSAvoidradio link failure detection accuracy

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent segments the RLM evaluation process into distinct phases: signal detection phase, quality evaluation phase, and failure determination phase. By dividing the procedure into manageable segments with specific evaluation criteria for each, the system achieves high detection accuracy without excessive complexity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces an intermediary evaluation mechanism that acts as a buffer between signal reception and RLF declaration. This intermediary layer performs additional checks including multiple evaluation opportunities and alternative reference signal usage, preventing false RLF triggers while maintaining procedural simplicity

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If periodic reference signals are transmitted in unlicensed spectrum with LBT, then spectrum utilization efficiency is improved, but transmission occasions become unpredictable leading to RLM challenges

Engineering Contradiction:

Improvespectrum utilization efficiencyVSAvoidlink quality measurement accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent implements preliminary actions including transmitting multiple reference signals before a potential RLF event, pre-configuring alternative reference signal resources, and establishing evaluation windows in advance. These preliminary measures ensure that when LBT prevents expected transmissions, the UE has alternative measurements available, maintaining measurement precision

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent employs partial evaluation approaches where not all reference signals need to be received to make a valid RLM determination. By requiring only a subset of expected signals or allowing evaluation based on alternative signals, the system maintains measurement accuracy even when LBT causes some transmissions to be missed

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS11477676B2RLM enhancements for 5G networks

Publication Date: 2022.10.18 APPLE INC

AI summary

An apparatus of user equipment (UE) includes processing circuitry coup led to a memory, where to configure the UE for radio link monitoring (RLM) in a New Radio-Unlicensed (NR-U) network, the processing circuitry is to decode radio resource control (RRC) signaling from a base station. The RRC signaling includes configuration information to configure transmission occasions for a plurality of RLM reference signals (RLM-RSs). A primary synchronization signal (PSS) or a secondary synchronization signal (SSS) detection is performed to determine a number of RLM-RSs of the plurality of RLM-RSs that are successfully transmitted during the transmission occasions. Signal measurements are performed on the RLM-RSs that are successfully transmitted within an evaluation duration to determine a block error rate (BLER). The signal measurements are performed when the number is higher than a threshold number. An in-sync (IS) indicator or an out-of-sync (OOS) indicator are generated based on the signal measurements.