Conditional Handover for Unlicensed Channel Access Failures
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Solution Overview
Problem
In wireless communication systems using unlicensed spectrum, channel access failures due to listen before talk (LBT) procedure failures lead to degraded system performance, data rate, capacity, and spectral efficiency, as base stations or user equipment may not gain access to unlicensed frequency channels.
Innovation Solution
The base station configures the user equipment (UE) to perform a conditional handover to another cell and deactivate or activate secondary cells to ensure access to unlicensed frequency channels, using counters and timers for LBT protocol failures and signal quality metrics to determine channel availability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the base station or user equipment performs listen before talk (LBT) procedure to access unlicensed frequency channels, then channel access is attempted, but channel access failures occur leading to degraded system performance
Solution Approach 1:
The system performs preliminary actions by configuring conditional handover and secondary cell activation/deactivation before channel access failures occur. When LBT failures are detected, the pre-configured handover and cell reconfiguration mechanisms are immediately triggered, enabling rapid response without waiting for traditional fallback procedures.
Solution Approach 2:
The system implements feedback mechanisms by monitoring LBT procedure outcomes and using this information to dynamically adjust channel access strategies. The base station receives feedback about channel access successes and failures, and uses this feedback to trigger conditional handover or secondary cell reconfiguration, creating a closed-loop system that continuously optimizes channel access reliability.
2Reliability
If conditional handover and secondary cell reconfiguration are implemented to mitigate channel access failures, then access to unlicensed frequency channels is improved, but device complexity increases
Solution Approach 1:
The base station pre-configures multiple secondary cells and conditional handover parameters in advance, so that when channel access failures occur, the user equipment can immediately switch to pre-prepared alternatives without complex real-time decision-making. This reduces the operational complexity during actual handover execution.
Solution Approach 2:
The user equipment is empowered to autonomously execute conditional handover and secondary cell activation/deactivation based on pre-configured conditions and triggers. This self-service capability reduces the signaling overhead and coordination complexity between base station and user equipment, as the decision execution is distributed to the user equipment itself.
3Speed
If rapid switching between cells and secondary cells is performed to access unlicensed frequency channels, then channel access speed is improved, but loss of time due to reconfiguration occurs
Solution Approach 1:
The base station performs preliminary configuration of multiple secondary cells with all necessary parameters and settings before handover is needed. This pre-configuration eliminates the need for time-consuming reconfiguration during actual channel access switching, as the user equipment can immediately activate pre-prepared cell configurations when triggers are met.
Solution Approach 2:
The system implements dynamic activation and deactivation of secondary cells based on real-time channel conditions and LBT success/failure patterns. Rather than permanent reconfiguration, the system dynamically adjusts which secondary cells are active, allowing rapid switching without the overhead of full reconfiguration procedures.
Data Source
Figure 1
Figure 2A~2D
Figure 3
AI summary
A configuration to enable a UE to obtain access to an unlicensed frequency channel of the unlicensed frequency spectrum in the event of channel access failures. The apparatus receives a configuration from a first base station to perform a conditional handover. The apparatus determines a first unlicensed frequency channel is unavailable for a transmission to the first base station or from the first base station. The apparatus switches from the first unlicensed frequency channel to a second cell for communication through the second cell in the conditional handover upon receiving the configuration and upon determining that the first unlicensed frequency channel is unavailable for the transmission.