L1/L2-Triggered Mobility Configuration for Low-Latency Cell Switching
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Solution Overview
Problem
Existing methods for serving cell change in wireless communication, such as RRC reconfiguration signaling, result in longer latency, larger overhead, and longer interruption time, which are addressed by enabling L1/L2-triggered mobility (LTM) to reduce these issues.
Innovation Solution
A central unit (CU) determines and transmits candidate cell configurations and indexes to a UE, source DU, and candidate DU, allowing for LTM cell switches without RRC reconfiguration, maintaining candidate cell configurations post-switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If RRC reconfiguration signaling is used for serving cell change, then the cell switch can be performed, but the latency, overhead, and interruption time increase
Solution Approach 1:
The patent segments the cell switch process into two distinct phases: preparation phase (RRC reconfiguration with candidate cell configurations) and execution phase (L1/L2-triggered switch using MAC CE). This segmentation allows the time-consuming RRC signaling to be performed in advance, while the actual switch uses fast lower-layer signaling, thereby reducing overall latency and interruption time while maintaining reliability.
Solution Approach 2:
The patent performs preliminary action by configuring multiple candidate cell configurations and their corresponding indexes through RRC reconfiguration before the actual cell switch is needed. The UE stores these configurations and their indexes, so when a cell switch is required, the execution can immediately reference the pre-configured data, eliminating the need for real-time RRC signaling during the switch and reducing latency.
2Reliability
If RRC reconfiguration signaling is used for serving cell change, then the cell switch can be performed, but the signaling overhead increases
Solution Approach 1:
The patent extracts the essential cell configuration data and indexes during the preparation phase through RRC signaling, and then removes the need for extensive RRC signaling during the actual cell switch execution. The MAC CE only carries a compact index reference to pre-configured candidate cells, significantly reducing signaling overhead while maintaining the reliability of the cell switch capability.
3Loss of time
If L1/L2-triggered mobility is used for serving cell change, then the latency and overhead are reduced, but the candidate cell configuration management becomes more complex
Solution Approach 1:
The patent introduces an intermediary mechanism where the network configures and manages candidate cell configurations and their indexes through RRC signaling in advance. The UE stores these configurations locally and uses them as intermediaries during L1/L2-triggered switches. This intermediary approach allows fast switching without real-time network intervention, reducing latency while the network retains control over configuration management.
Solution Approach 2:
The patent creates copies of candidate cell configurations and their indexes during the preparation phase. The UE stores multiple copies of these configurations locally, allowing immediate reference during cell switch execution without needing to retrieve or process full configuration data in real-time. This copying mechanism simplifies the execution phase while maintaining configuration integrity.
Data Source
AI summary
The present application relates to methods and apparatuses of supporting subsequent L1/L2-triggered mobility (LTM). An embodiment of the present disclosure provides a central unit (CU), comprising: a transceiver; and a processor coupled with the transceiver and configured to: determine a candidate cell configuration and an index of the candidate cell configuration for each candidate cell of one or more candidate cells, wherein the index of the candidate cell configuration for each candidate cell is generated by the CU, or received from a source distributed unit (DU), or from a candidate DU; transmit, to a user equipment (UE) via the source DU, a first message indicating the candidate cell configuration and the index of the candidate cell configuration for each candidate cell; transmit, to a source DU, a second message indicating the index of the candidate cell configuration for each candidate cell; and transmit, to a candidate DU, a third message indicating the index of the candidate cell configuration for each candidate cell.