Channel Access Failure Detection in Unlicensed Band Wireless Systems
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Solution Overview
Problem
In wireless communication systems using unlicensed bands, it is challenging to differentiate between channel access failures due to Listen Before Talk (LBT) failures and radio link failures, leading to delayed detection of radio link failures and poor Quality of Service (QoS) in next-generation wireless communication technologies like NR-U.
Innovation Solution
A method where user equipment (UE) detects channel access failures by exceeding a threshold of consecutive LBT failures or timer expirations, and communicates this information to the base station to differentiate between LBT failures and radio link failures, enabling efficient resource allocation and reducing unnecessary reconfiguration operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LBT procedure is performed before each transmission in unlicensed band, then channel access collision is avoided, but channel access delay increases and control plane requirements cannot be met
Solution Approach 1:
The patent applies preliminary action by performing LBT procedure in advance before data transmission and using early termination detection to identify failed transmissions before completing the full retransmission sequence. This allows the system to abort unnecessary retransmissions and switch to RLF detection procedures earlier, reducing overall access delay while maintaining reliable channel access through proactive LBT execution.
2Device complexity
If channel access failure is not differentiated from radio link failure, then detection simplicity is maintained, but service disconnection time increases and QoS deteriorates
Solution Approach 1:
The patent segments the failure detection mechanism into distinct pathways: one for LBT failure detection (using counter-based mechanisms for consecutive LBT failures) and another for RLF detection (using out-of-sync indications from physical layer). This segmentation allows the system to differentiate between temporary channel access issues and actual radio link problems, enabling appropriate recovery actions and reducing unnecessary service disconnections.
Solution Approach 2:
The patent implements feedback mechanisms where the MAC layer receives LBT failure information from the physical layer and uses this feedback to make informed decisions about transmission abortion and RLF detection initiation. The feedback loop enables the system to adapt its detection and recovery strategies based on real-time channel access outcomes, improving QoS by preventing false RLF declarations.
3Loss of time
If LBT failure causes reduced transmission of reference signals, then channel access delay is reduced, but RLF detection accuracy deteriorates due to missing RLM-RS
Solution Approach 1:
The patent introduces an intermediary mechanism where the MAC layer counter for LBT failures acts as a mediator between the physical layer's reference signal transmission status and the RLF detection process. When the counter indicates consecutive LBT failures, the system uses this intermediate information to distinguish between missing RLM-RS due to LBT failures versus actual radio link degradation, maintaining RLF detection accuracy despite reduced reference signal transmission.
Data Source
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AI summary
Provided are methods and apparatus for performing communication in an unlicensed band. The method includes: detecting a channel occupation failure of an unlicensed band wireless resource for transmitting and receiving uplink data or downlink data; determining that channel access failsinthe unlicensed band wireless resource if the channel occupation failure satisfies certain criteria; and transmitting upper layer signaling to a base station if channel access fails.