NR-U Channel Failure Reporting for UL LBT and Beam Recovery
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Solution Overview
Problem
Existing NR-based operations in unlicensed spectrum face challenges with hidden nodes causing asymmetric channel conditions for UL and DL directions, leading to delayed detection of persistent UL LBT failures, which are not timely reported due to periodic RSSI measurements, and require improved mechanisms for beam failure recovery.
Innovation Solution
Implementing a method for wireless transmit/receive units (WTRUs) to detect UL Listen-Before-Talk (UL-LBT) failures and beam failures, transmitting failure recovery requests on secondary cells, and conditionally canceling these requests to manage channel access effectively, along with separate RLF mechanisms for UL and DL, and employing Beam Failure Recovery (BFR) procedures to re-establish beam pairs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If periodic RSSI measurements are used to detect UL LBT failures, then the detection mechanism is simple, but the detection timing is delayed and not timely
Solution Approach 1:
The patent introduces a new failure detection mechanism that performs preliminary checks before periodic RSSI measurements are due. The WTRU monitors channel access attempts and detects UL LBT failures as they occur, rather than waiting for the next periodic measurement interval. This preliminary detection action eliminates the timing delay inherent in periodic measurement approaches.
2Measurement precision
If separate RLF mechanisms are implemented for UL and DL, then failure detection accuracy is improved, but system complexity increases
Solution Approach 1:
The patent segments the failure detection mechanism into separate UL-specific and DL-specific components. The UL LBT failure detection operates independently from DL beam failure detection, with separate counters, thresholds, and reporting mechanisms. This segmentation improves detection accuracy by addressing the asymmetric nature of UL-DL channel conditions in unlicensed spectrum, while the modular design keeps complexity manageable.
Solution Approach 2:
The patent introduces an intermediary failure recovery SR (Scheduling Request) mechanism that mediates between UL LBT failure detection and the network. When UL LBT failures are detected, the WTRU sends a failure recovery SR on a DL channel to notify the network, which then coordinates the recovery process. This intermediary approach enables accurate separate UL/DL failure detection while managing system complexity through coordinated control.
3Reliability
If beam failure recovery procedures are implemented, then beam pair re-establishment capability is improved, but processing time increases
Solution Approach 1:
The patent prepares beam failure recovery resources and configurations in advance through semi-static RRC configuration. The WTRU is pre-configured with candidate beam information, recovery SR resources, and associated parameters before actual beam failure occurs. When beam failure is detected, the WTRU can immediately execute the pre-prepared recovery procedure, significantly reducing processing time compared to ad-hoc recovery approaches.
Solution Approach 2:
The patent implements dynamic beam failure recovery where the WTRU can adaptively select from multiple pre-configured candidate beams based on current channel conditions. The recovery process is dynamic and flexible, allowing the WTRU to switch between different recovery paths (e.g., different candidate beams, different SR resources) depending on real-time measurements, thereby optimizing the balance between reliability and processing time.
Data Source
AI summary
Methods and apparatuses are described herein for reporting channel failure, and may be used, among others, for New Radio (NR) operation in unlicensed spectrum (NR-U). Upon detecting a consistent uplink (UL) listen-before-talk (LBT) failure or upon detecting a beam failure on a cell, a Scheduling Request (SR) may be triggered to have a UL resource granted for transmission of the failure to another cell, or to a subset of other cells, using, for example, a failure recovery Medium Access Control-Control Element (MAC-CE). If no grant of an available UL resource can be obtained for transmission of the MAC-CE, or the grant is not suitable for the failure reporting, a failure recovery SR may be transmitted repeatedly to obtain an UL grant suitable for transmitting the failure report. In some cases, a WTRU may initiate a random-access procedure for transmitting the MAC-CE, for example when resources for failure reporting are not configured.