Uplink LBT Failure Handling in Wireless Handover
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Solution Overview
Problem
Current wireless communication networks face challenges in performing seamless handovers in unlicensed spectrum, particularly due to inconsistent behavior in listen-before-talk (LBT) failures, which can lead to radio link failure (RLF) and disrupt service.
Innovation Solution
The proposed solution involves a method where a user equipment (UE) performs a first random-access procedure in initial RA resources of a target cell and, upon failure, refrains from declaring RLF and instead performs a second random-access procedure in different RA resources. This approach allows for more robust handover operations by mitigating the impact of initial LBT failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a UE performs a first random-access procedure in initial RA resources of a target cell and experiences LBT failure, then the UE would traditionally declare radio link failure (RLF), but this leads to disrupted service and reduced handover reliability. The invention allows the UE to perform a second random-access procedure in different RA resources instead of declaring RLF immediately.
Solution Approach 1:
The network configures multiple RA resources (first RA resources and second RA resources) in advance before the handover occurs. When the UE experiences LBT failure on the first RA resources, it can immediately switch to the pre-configured second RA resources without declaring RLF, thereby maintaining handover reliability while minimizing additional latency.
Solution Approach 2:
The patent prepares alternative RA resources as a cushion against LBT failures. By having backup RA resources configured beforehand, the system cushions against the harmful effect of LBT failures, allowing the UE to recover from failures without declaring RLF and ensuring continuous service during handover.
2Reliability
If the UE declares RLF upon first RA procedure failure, then the procedure is simple and fast, but the handover reliability deteriorates due to inconsistent behavior in LBT failures. The invention introduces multiple RA procedures with different resources to mitigate LBT failure impact.
Solution Approach 1:
The patent segments the RA resources into multiple distinct sets (first RA resources and second RA resources) with different time-frequency characteristics. This segmentation allows the UE to attempt RA on alternative resources when LBT fails on the initial resources, improving reliability without requiring complex dynamic resource selection algorithms.
Solution Approach 2:
The UE dynamically selects which RA resources to use based on LBT outcomes. If LBT succeeds on the first RA resources, the UE proceeds with the first RA procedure; if LBT fails, the UE switches to the second RA resources. This dynamic adaptation improves reliability while keeping the procedure manageable through clear conditional logic.
Data Source
AI summary
The invention relates to a method in a user equipment, UE, for performing handover to a target cell in a wireless network, the method comprising performing (1340) a first random-access, RA, procedure in first RA resources of the target cell, in response to failure of the first RA procedure, refraining (1350) from declaring a radio link failure, RLF, for the target cell and performing a second RA procedure in second RA resources of the target cell that are different from the first RA resources; and declaring (1370) a RLF for the target cell based on failure of the first RA procedure and a failure of the second RA procedure, or an expiration of a timer before successful completion of the second RA procedure; the invention further relates to a UE implementing the method, to a corresponding method in a network node and a network node implementing the method.