Serving Cell Configuration Preservation for Low-Latency Mobility
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Solution Overview
Problem
Current serving cell change in 3GPP LTE systems involves L3 measurements and RRC signaling, leading to longer latency, overhead, and interruption times due to complete L2 resets during mobility transitions.
Innovation Solution
Implementing Lower-layer Triggered Mobility (LTM) to preserve the cell configuration for the source cell and apply candidate cell configurations, enabling RACH-less mobility and maintaining TA and BFD/RLM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If L3 measurements and RRC signaling are used for serving cell change, then mobility management is achieved, but latency and interruption time increase due to complete L2 resets
Solution Approach 1:
The patent segments the mobility management process into two distinct approaches: L3-triggered mobility (complete L2 reset) and L1/L2-triggered mobility (partial reset). By dividing the mobility control into different triggering layers, the system can select the appropriate method based on service requirements, thereby reducing latency for time-sensitive applications while maintaining reliable mobility management.
Solution Approach 2:
The patent implements preliminary action by configuring candidate cell lists and maintaining source cell configurations in advance before mobility is needed. When L1/L2-triggered mobility is executed, the UE can quickly switch to a pre-configured candidate cell without performing complete L2 resets, as the necessary configurations are already prepared and stored.
2Adaptability or versatility
If complete L2 resets are performed during serving cell change, then mobility is achieved, but overhead and interruption time increase
Solution Approach 1:
The patent applies partial action by performing only necessary L2 resets instead of complete L2 resets during serving cell change. When L1/L2-triggered mobility is used, the UE resets only the MAC layer while maintaining RLC and PDCP configurations, thereby reducing overhead and interruption time while still achieving successful mobility to the target cell.
Solution Approach 2:
The patent implements local quality by applying different reset scopes to different L2 layers based on the mobility trigger type. L1-triggered mobility performs minimal resets (MAC only), while L3-triggered mobility performs complete L2 resets. This localized approach to resets reduces overall system overhead and complexity.
3Ease of manufacture
If source cell resources are released after mobility, then resource management is simplified, but TA maintenance and BFD/RLM capabilities are lost
Solution Approach 1:
The patent implements discarding and recovering by releasing source cell resources after successful mobility execution, but simultaneously recovering and maintaining the source cell configuration in the candidate cell list. This allows the UE to discard active source cell resources for simplification while recovering the configuration data for future TA maintenance and BFD/RLM operations.
Solution Approach 2:
The patent applies preliminary action by preserving source cell configurations in advance in the candidate cell list before mobility execution. This preliminary preservation ensures that TA maintenance and BFD/RLM capabilities are maintained without complicating active resource management during and after mobility.
Data Source
AI summary
A method and apparatus for handling previous serving cell is provided. A wireless device receives a cell configuration for a first cell, and receives a candidate cell configuration for a second cell. The second cell is added to a candidate cell list for mobility. Upon receiving a first mobility command, the wireless device applies the candidate cell configuration for the second cell, and the first cell is added to the candidate cell list for mobility. The wireless device preserves the cell configuration for the first cell, and upon receiving a second mobility command, applies the preserved cell configuration for the first cell.