UE Cell Selection and Reselection Under CCA-Limited DRS Access
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing UE operation in NR-U systems faces challenges with LBT failures in RRC_IDLE and RRC_INACTIVE states, particularly in unlicensed spectrum, leading to inefficiencies in cell selection and reselection procedures due to LBT-based procedures not being fully configured.
Innovation Solution
The UE adapts its measurement periods and filtering strategies based on LBT failures, allowing it to combine measurement samples within certain time constraints and adjust measurement times to account for unavailable DRS occasions, thereby enhancing cell selection and reselection processes in low RRC activity states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the UE performs measurements on DRS occasions in unlicensed spectrum, then cell selection and reselection accuracy is improved, but LBT failures cause measurement occasions to be unavailable, worsening measurement reliability
Solution Approach 1:
The network configures the UE with multiple DRS measurement occasions in advance, allowing the UE to attempt measurements at multiple pre-specified times. This preliminary configuration enables the UE to recover from LBT failures by having backup measurement opportunities already scheduled, thus maintaining measurement reliability despite channel access uncertainties in unlicensed spectrum.
Solution Approach 2:
The patent modifies measurement parameters by introducing flexibility in measurement period determination. The UE determines measurement periods based on DRX cycle configurations and adjusts measurement timing to account for LBT failures. This parameter adaptation allows the system to balance measurement accuracy requirements with the unreliable nature of LBT-based channel access in unlicensed bands.
2Reliability
If the UE frequently monitors for DRS to ensure timely cell reselection, then connectivity reliability is improved, but power consumption increases in RRC_IDLE and RRC_INACTIVE states
Solution Approach 1:
The patent implements periodic measurement opportunities aligned with DRX cycles, where the UE performs DRS measurements at predetermined intervals rather than continuously. This periodic approach allows the UE to maintain connectivity reliability by regularly monitoring for cell reselection while consuming less power by remaining in low-power states between measurement occasions, particularly in RRC_IDLE and RRC_INACTIVE states.
3Measurement precision
If the UE waits for LBT success before performing measurements, then measurement accuracy is improved, but measurement delay increases, affecting cell selection timeliness
Solution Approach 1:
The network pre-configures multiple DRS measurement occasions and corresponding LBT opportunities in advance. The UE attempts LBT and measurements at these pre-scheduled times without waiting for dynamic LBT success notifications. This preliminary action approach eliminates measurement delays by having the UE proactively attempt measurements at configured opportunities rather than passively waiting for channel availability confirmation.
Data Source
AI summary
Systems and methods for User Equipment (UE) operation in presence of Clear Channel Assessment (CCA) are provided. In some embodiments, a method performed by a wireless device for cell selection accounting for requirements includes: determining a measurement period in a serving cell for the cell selection or cell re-selection (T1), wherein the measurement period is determined based on a number of consecutive Discontinuous Reception (DRX) cycles; determining a number of measurement occasions configured with a Discovery Reference Signal (DRS) in the serving cell during T1; determining availability of the DRS at the measurement occasions; and performing measurement based on availability of the DRS at the measurement occasions during T1. In this way, a wireless device may operate in NR RRC_IDLE/RRC_INACTIVE in the presence of CCA, e.g., Listen-Before-Talk (LBT).