Radio Link Monitoring in NR-U via Dynamic Evaluation Period Extension
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Solution Overview
Problem
In 5G new radio unlicensed bands (NR-U), the absence of periodic reference signals due to listen-before-talk (LBT) impacts normal radio resource management (RRM) and radio link monitoring (RLM) operations at user equipment (UE), leading to mis-detection of interference signals and inaccurate RLM measurements.
Innovation Solution
The method involves selecting available radio link monitoring reference signal (RLM-RS) samples based on signal quality and extending the evaluation period using an extension factor to ensure sufficient samples are received, allowing for accurate RLM procedures in unlicensed bands by distinguishing between in-synchronization and out-of-synchronization conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If listen-before-talk (LBT) is performed before transmission, then collision avoidance is improved, but periodic reference signal transmission may be blocked leading to insufficient RLM samples
Solution Approach 1:
The evaluation period is dynamically extended from a fixed duration to a variable duration based on the extension factor K. When RLM samples are insufficient during the initial evaluation period, the period is extended to T_eval × K, allowing the UE to collect adequate samples while respecting LBT constraints on reference signal transmission opportunities.
Solution Approach 2:
The patent changes the parameter of evaluation period duration from a static value to a scalable value using extension factor K. This parameter adjustment allows the system to adapt the sampling window to actual transmission opportunities created by LBT, ensuring sufficient samples are collected without violating collision avoidance requirements.
2Measurement precision
If evaluation period is extended to collect more RLM samples, then measurement accuracy is improved, but time consumption increases
Solution Approach 1:
The evaluation period is made dynamic rather than fixed. The base period T_eval is extended by a factor K only when necessary to achieve sufficient sample collection. This dynamic adjustment balances measurement accuracy requirements with time efficiency, extending the period only to the extent needed to overcome LBT-induced sample shortages.
3Reliability
If RLM-RS samples are selected based on signal quality thresholds, then measurement reliability is improved, but number of available samples decreases
Solution Approach 1:
The patent segments the sample selection process into two stages: first filtering samples by signal quality threshold to ensure reliability, then compensating for the reduced sample count by extending the evaluation period. This segmentation allows the system to maintain high measurement reliability while obtaining sufficient samples through the extended time window.
Data Source
AI summary
Aspects of the disclosure provide apparatuses and methods for wireless communications. One apparatus includes processing circuitry that selects one or more first available radio link monitoring reference signal (RLM-RS) samples from a plurality of received RLM-RS samples based on signal qualities of the one or more first available RLM-RS samples. The one or more first available RLM-RS samples are received within a first evaluation period. The processing circuitry determines whether a total number of the one or more first available RLM-RS samples is less than a target number. When the total number of the one or more first available RLM-RS samples is determined to be less than the target number, the processing circuitry determines a second evaluation period that is greater than the first evaluation period, and performs an RLM procedure in an unlicensed band within the second evaluation period.