Conditional Cell Switching for Low-Latency Successive Handover
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Solution Overview
Problem
Existing 5G and 6G wireless communication systems face challenges in managing fast mobility scenarios, particularly in non-terrestrial networks and terrestrial networks with high-speed user equipment, due to signaling overhead and delay during successive cell switches, which affect handover reliability and latency.
Innovation Solution
A user equipment (UE) is configured with cell switch configurations for multiple candidate cells, including conditional events such as beam, location, and time events, allowing autonomous cell switching based on predefined criteria without continuous network intervention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If network-controlled mobility with conditional handover is used, then connection quality is maintained, but signaling overhead and latency increase during successive cell switches
Solution Approach 1:
The UE autonomously evaluates trigger conditions and executes cell switching without continuous network intervention. The UE monitors measurement quantities, compares them against threshold values, and independently decides when to switch cells, eliminating the need for network-controlled handover procedures that introduce latency.
Solution Approach 2:
The network pre-configures multiple candidate cells with their associated trigger conditions and measurement criteria before the UE needs to switch. This preparation allows the UE to immediately execute cell switching when conditions are met, without waiting for network instructions, thereby reducing handover latency.
2Adaptability or versatility
If successive cell switches are performed in fast mobility scenarios, then mobility tracking is maintained, but signaling overhead increases and handover reliability decreases
Solution Approach 1:
The UE independently monitors and evaluates trigger conditions for multiple candidate cells simultaneously. When a cell becomes the active serving cell, the UE continues to monitor other candidate cells and can autonomously switch to them if their trigger conditions are met, ensuring reliable mobility tracking without excessive signaling.
Solution Approach 2:
The UE continuously monitors measurement quantities of candidate cells and maintains readiness to switch cells as needed. This continuous monitoring without interruption ensures that mobility tracking remains accurate and reliable, even during fast movement scenarios, while avoiding the signaling overhead of repeated network instructions.
3Loss of time
If L1/L2 triggered mobility is used, then mobility latency is reduced, but signaling overhead cannot be sufficiently decreased for successive switches
Solution Approach 1:
The UE autonomously evaluates L1 measurement conditions and trigger criteria without requiring continuous L1/L2 signaling from the network. The UE independently determines when cell switching is needed based on pre-configured conditions, significantly reducing signaling overhead while maintaining low latency through local decision-making.
Solution Approach 2:
The network pre-provides trigger conditions and measurement criteria in higher layer signaling, allowing the UE to autonomously evaluate and execute cell switching based on L1 measurements without requiring continuous network instructions. This preparation reduces the signaling overhead associated with successive cell switches while maintaining fast response capability.
Data Source
AI summary
Disclosed is a cell switch mechanism that enables successive conditional handover without configuration release or reconfiguration between cell switch executions. A UE receives from a source base station a cell switch configuration for a plurality of candidate cells. The cell switch configuration includes conditional events associated with a respective one of the plurality of candidate cells. The UE determines whether the conditional events associated with at least one cell from the plurality of candidate cells are fulfilled when the UE is connected to the source base station. The UE triggers a cell switch to connect to a first target cell from the plurality of candidate cells when the conditional events associated with the first target cell are fulfilled. The UE determines whether to switch from the first target cell to a second target cell from the plurality of candidate cells based on the cell switch configuration for the candidate cells.