L1/L2 Mobility Cell Switching With Partial MAC Reset Control
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Solution Overview
Problem
The determination of a set of LTM candidate cells for partial MAC reset, the handling of initial source cell configuration for subsequent LTMs, UE behavior during radio link failure, and signaling between gNB-CU-CP and gNB-CU-UP for LTM are unclear in existing L1/L2 mobility enhancements.
Innovation Solution
The gNB-DU and gNB-CU communicate through messages to determine whether a full or partial MAC reset is required for LTM cell switches, and the RRC message includes identifiers for initial source and candidate cells to manage configurations, with explicit control over MAC resets and cell switch procedures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If L3 measurement and RRC signaling are used for serving cell change, then reliability is improved, but latency and interruption time increase
Solution Approach 1:
The patent segments the mobility management into L1/L2 fast mobility (for frequent cell changes) and L3 mobility (for less frequent changes). L1/L2 handles beam-level and cell-level switching with minimal reset, while L3 provides full reconfiguration when needed. This segmentation allows the system to use the faster L1/L2 path for most transitions, reducing latency while maintaining reliability through the more robust L3 path when necessary.
Solution Approach 2:
The patent applies partial MAC reset instead of full reset during L1/L2 mobility. Only the necessary MAC layer functions are reset (partial action) rather than performing a complete reset of all MAC entities. This reduces the interruption time and latency while maintaining sufficient reliability for the cell change operation.
2Reliability
If full MAC reset is performed during serving cell change, then reliability is improved, but productivity decreases
Solution Approach 1:
The patent performs partial MAC reset instead of full MAC reset during L1/L2 mobility operations. Only the specific MAC entities that need reconfiguration are reset, while other MAC functions continue operating. This maintains sufficient reliability for the cell switch while significantly improving productivity by reducing the time and resources required for the mobility operation.
Solution Approach 2:
The patent applies different reset strategies to different MAC entities based on their specific requirements. Only the MAC entities directly involved in the cell change are reset (local quality), while other MAC functions maintain their state. This selective approach ensures reliability for the critical cell switch function while preserving productivity by avoiding unnecessary resets of other MAC entities.
3Loss of time
If L1/L2 signaling is used for inter-cell mobility, then latency is reduced, but device complexity increases
Solution Approach 1:
The patent segments the signaling complexity across different layers: L1 handles fast beam indications with minimal signaling, L2 handles MAC-level cell switching with partial reset, and L3 handles full reconfiguration when needed. This segmentation reduces the latency by distributing functions across layers while managing device complexity through clear layer boundaries and standardized interfaces.
Solution Approach 2:
The patent performs preliminary configuration of candidate cells and beams at L3 before L1/L2 mobility operations. This preliminary action prepares the necessary configurations in advance, reducing the complexity of L1/L2 signaling during actual mobility events. The L1/L2 layer then only needs to trigger pre-prepared actions, reducing latency while keeping signaling complexity manageable.
4Adaptability or versatility
If multiple candidate cells are configured for LTM, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent segments the candidate cell configurations into different categories (intra-DU, inter-DU, intra-gNB-CU, inter-gNB-CU) with specific reset rules for each segment. This segmentation allows the UE to apply appropriate reset strategies based on the mobility scenario, improving adaptability while reducing configuration management complexity through structured categorization.
Solution Approach 2:
The patent creates a universal L1/L2 mobility framework that handles multiple mobility scenarios (intra-DU, inter-DU, intra-gNB-CU, inter-gNB-CU) through a common mechanism. The same basic L1/L2 signaling and partial MAC reset approach is applied across different scenarios, improving adaptability while reducing device complexity by avoiding scenario-specific complex configurations.
Data Source
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AI summary
A distributed unit (DU) receives one or more first messages from a central unit (CU) regarding preparation of one or more candidate cells for Layer-1/Layer-2 triggered mobility (LTM) of a radio terminal. In response to receiving the one or more first messages, the DU sends one or more second messages to the CU. The one or more second messages indicate whether a full Medium Access Control (MAC) reset or a partial MAC reset is to be applied to an LTM cell switch between an initial source cell and any cell included in the one or more candidate cells, or between any two cells included in the one or more candidate cells. For example, this enables the DU to inform the CU whether a full MAC reset or a partial MAC reset is to be applied to the LTM candidate cells provided by the DU.