UE-Triggered L1/L2 Mobility with Preconfigured Target Cells
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Solution Overview
Problem
Legacy handover processes in mobile communications, such as those in 3GPP Release 17, involve long latency and large signaling overhead due to L3-based cell switching, while L1/L2 triggered mobility (LTM) is prone to radio link failures and inaccurate target cell decisions by the network.
Innovation Solution
UEs are equipped with a conditional LTM decision module to autonomously determine target cells based on measurements, allowing for earlier preparation and execution of handovers, reducing latency and improving accuracy by leveraging UE-specific radio environment insights.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If L3-based handover is used, then handover reliability is improved, but handover latency and signaling overhead increase
Solution Approach 1:
The patent applies preliminary action by having the network pre-configure multiple candidate target cells and their associated parameters (such as PDCCH configuration, PDSCH configuration, and TCI states) before the actual handover is needed. When handover is triggered, the UE can immediately switch to a pre-configured target cell without waiting for new configuration messages, thus reducing handover latency while maintaining reliability through pre-validated target cell selections.
Solution Approach 2:
The patent segments the handover process into distinct phases: configuration phase (where multiple candidate target cells are pre-configured with different parameter sets), measurement phase (where the UE evaluates these candidates), and execution phase (where handover to a selected candidate occurs). This segmentation allows the time-consuming configuration activities to happen in advance, separating them from the critical handover execution path and thereby reducing overall handover latency.
2Loss of time
If L1/L2 triggered mobility is used, then handover latency is reduced, but target cell decision accuracy deteriorates
Solution Approach 1:
The patent implements feedback mechanisms where the network receives measurement reports from the UE about candidate target cells and uses this feedback to make informed decisions about which target cell to select. The network can adjust the measurement configurations, thresholds, and candidate cell selections based on historical performance data and current radio conditions, ensuring accurate target cell decisions while maintaining fast L1/L2 triggered mobility execution.
Solution Approach 2:
The patent introduces an intermediary measurement and evaluation layer between the UE's raw measurements and the final handover decision. The UE performs detailed measurements on pre-configured candidate cells and provides structured measurement reports to the network. This intermediary layer processes and validates the measurements, ensuring that the final target cell selection is both accurate and appropriate for the current radio conditions, while still enabling fast L1/L2 triggered execution.
3Ease of operation
If network decides target cell, then handover control is improved, but radio link failure risk increases due to channel quality degradation
Solution Approach 1:
The patent applies dynamics by making the target cell selection process adaptive and flexible. The network configures multiple candidate target cells with different parameter sets, and the actual target cell is dynamically selected based on real-time measurement results and radio conditions. This dynamic approach allows the system to respond to changing channel quality, selecting the most appropriate target cell at the moment of handover execution, thereby reducing radio link failure risk while maintaining network control over the overall handover process.
Data Source
AI summary
Various solutions for conditional layer 1/layer 2 triggered mobility (LTM) in mobile communications are described. A user equipment (UE) may receive a configuration from a network node and may perform a measurement based on the configuration. Also, the UE may trigger a conditional LTM decision in an event that a triggering event is determined to have occurred based on the measurement, then the UE may perform an LTM execution procedure according to the conditional LTM decision. UE-triggered LTM decisions enhance UE autonomy and flexibility. Furthermore, the LTM decisions made by UE may be more accurate and reasonable due to the UE's more detailed measurement context of its radio environment.