Cell-Assisted Link Recovery for CHO and DAPS Handovers
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Solution Overview
Problem
Existing handover protocols in cellular and mobile communication systems, such as CHO and DAPS, face issues with radio link failures and incorrect UE behavior during handover execution, particularly when DAPS configurations are involved, leading to incomplete handover processes.
Innovation Solution
The proposed solutions include sending DAPS-activation-status to selected target cells, indicating CHO recovery actions, providing fallback configurations, and excluding cells with CHO and DAPS during recovery, along with sending DAPS indications outside target cell configurations to ensure proper handover execution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conditional handover and dual active protocol stack handover configurations are provided to UE, then mobility robustness is improved and interruption time is reduced, but radio link failures and handover failures occur due to incorrect UE behavior during handover execution
Solution Approach 1:
The network receives feedback from the UE indicating whether a target cell supports DAPS handover. Based on this feedback, the network determines the appropriate handover configuration to provide to the UE, ensuring the UE only receives configurations it can correctly execute, thereby preventing radio link failures and handover failures caused by incorrect UE behavior.
Solution Approach 2:
The network performs preliminary determination of target cell DAPS support status before providing handover configurations to the UE. This advance preparation ensures that the UE receives appropriate configurations matched to its capabilities, preventing execution errors during handover.
2Loss of time
If DAPS configuration is provided to UE for handover, then interruption time is reduced to close to 0 ms, but radio link failures occur due to incorrect UE behavior
Solution Approach 1:
The network receives feedback from the UE regarding its DAPS capability or support status. Based on this feedback, the network decides whether to provide DAPS configuration to the UE. This ensures that DAPS configuration is only provided when the UE can correctly handle it, preventing radio link failures while maintaining the fast handover benefit when applicable.
Solution Approach 2:
The system dynamically changes the handover configuration parameters based on UE feedback. When the UE indicates support for DAPS, the network provides DAPS configuration with near-zero interruption; when the UE indicates lack of support, the network provides alternative handover configurations, adapting the parameters to match UE capabilities.
3Adaptability or versatility
If multiple target cells are configured for conditional handover, then handover options are increased, but complexity of handover execution increases leading to failures
Solution Approach 1:
The network receives feedback from the UE about which target cells support DAPS handover. Based on this feedback, the network can selectively provide or prioritize configurations for specific target cells, simplifying the execution process by eliminating ambiguity about which cells the UE should attempt to handover to and in what order.
Solution Approach 2:
The network segments the set of target cells into different groups based on their DAPS support status, as indicated by UE feedback. This segmentation allows the UE to handle different target cells with appropriate configurations, reducing execution complexity by clearly distinguishing between cells that require DAPS handling and those that use traditional handover procedures.
Data Source
AI summary
A UE receives configuration from a source cell for conditional handover for target cell(s). At least one of the target cell(s) also supports DAPS handover. The UE determines that either a RLF or HOF has occurred. The UE selects one of the target cell(s) for a handover, and performs a process for handover to the selected target cell. A UE receives individual handover commands and corresponding configuration for conditional handover for target cell(s) and an indication to use DAPS handover if possible in response to a handover. The UE determined condition(s) for handover to one of the target cell(s) have triggered, wherein the one target cell supports DAPS handover. The UE performs, based on the indication to use DAPS handover if possible in response to a handover, handover by the user equipment to the one target cell without releasing the source cell while accessing the one target cell.