Cell Change Configurations for CCA Failure Mitigation
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Solution Overview
Problem
In cellular communications, especially in unlicensed spectrum, Clear Channel Assessment (CCA) failures can lead to failed cell changes, as User Equipment (UE) struggles to distinguish between CCA failures and lack of reference signals, resulting in connection failures during cell changes between licensed and unlicensed bands.
Innovation Solution
The implementation of cell change configurations that include preventative parameters to mitigate CCA failures and fallback procedures, allowing the UE to attempt cell changes multiple times, adjust signal margins, and operate in a relaxed mode, ensuring successful cell changes even with CCA failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the UE performs Clear Channel Assessment (CCA) before cell change to unlicensed band, then the channel occupancy is protected and interference is reduced, but the cell change failure rate increases due to CCA failures being indistinguishable from reference signal loss
Solution Approach 1:
The network performs CCA before transmitting reference signals and data to the UE during cell change to unlicensed band. This preliminary channel assessment ensures the channel is clear before the UE attempts to receive signals, preventing both interference and false CCA failure detections by the UE. The network's advance CCA action resolves the contradiction by eliminating the need for the UE to perform its own CCA that would otherwise fail indistinguishably from reference signal loss.
Solution Approach 2:
The network acts as an intermediary by performing CCA on behalf of the UE before cell change to unlicensed band. Instead of the UE independently performing CCA (which leads to failures), the network assesses the channel and provides this information to the UE, enabling reliable cell change while maintaining channel occupancy protection. This intermediary action resolves the contradiction between protecting the channel and ensuring reliable cell change.
2Reliability
If the UE attempts cell change multiple times with extended duration, then the cell change success rate improves, but the time consumption and mobility delay increase
Solution Approach 1:
The network performs CCA and prepares the channel in advance before the UE initiates cell change to unlicensed band. This preliminary preparation includes assessing channel availability and notifying the UE, so that when the UE attempts cell change, the channel is already confirmed clear. This eliminates the need for multiple repeated attempts by the UE, reducing mobility delay while maintaining high success rate.
Solution Approach 2:
The network provides feedback to the UE about channel availability and CCA results before and during the cell change process. This feedback mechanism allows the UE to immediately know whether the channel is clear without performing its own time-consuming CCA attempts. If the channel is clear, the UE can proceed with cell change in a single attempt, significantly reducing mobility delay while ensuring high success rate through network-confirmed channel availability.
3Object-affected harmful factors
If the UE performs CCA before each transmission in unlicensed band, then the channel is assessed properly and interference is avoided, but the transmission latency and operational complexity increase
Solution Approach 1:
The network performs CCA for multiple purposes: protecting its own transmissions, preparing the channel for UE cell change, and providing channel availability information to the UE. This single CCA action by the network serves multiple functions, eliminating the need for the UE to perform separate CCA operations. The network's CCA mechanism becomes universal, handling both network transmission protection and UE mobility support, thereby reducing device complexity while maintaining interference avoidance.
Solution Approach 2:
The network acts as an intermediary that performs CCA and communicates the results to the UE, replacing the UE's own CCA operations. The UE receives channel availability information from the network and uses this to determine when to transmit or switch cells, rather than independently performing CCA. This intermediary approach simplifies the UE's operational complexity while the network maintains proper channel assessment to avoid interference with other systems.
Data Source
AI summary
Systems and methods are disclosed herein that relate to performing a cell change to a target cell that is subject to Clear Channel Assessment (CCA). In one embodiment, a method performed by a wireless device for cell change to a cell that is subject to CCA comprises obtaining one or more cell change configurations that are related to CCA failures when performing a cell change to a target cell subject to CCA and performing a cell change to a desired target cell subject to CCA. Performing the cell change comprises performing the cell change based on the one or more cell change configurations. Corresponding embodiments of a wireless device are also disclosed. Embodiments of a method performed by a network node and corresponding embodiments of a network node are also disclosed.