Inter-gNB-CU LTM Signaling for Faster, Reliable Handover
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Solution Overview
Problem
Existing 5G wireless communication systems face challenges in managing increased communication traffic and require efficient inter-gNB-CU mobility solutions to minimize interruption times during cell changes, as traditional LTM methods are limited to intra-gNB-CU mobility.
Innovation Solution
A signaling method and apparatus are introduced to support inter-gNB-CU LTM, involving handover request and acknowledge messages between base stations, with LTM information requests and cancellations, and the use of LTM configuration updates, including channel state information and CSI-RS configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional LTM methods are used, then intra-gNB-CU mobility is supported, but inter-gNB-CU mobility cannot be achieved
Solution Approach 1:
The handover process is segmented into multiple phases: LTM configuration phase (where target gNB-CU prepares LTM information), execution phase (where UE performs handover), and cancellation phase (where prepared LTM can be cancelled if needed). This segmentation allows inter-gNB-CU mobility to be supported while maintaining reliability through structured control
Solution Approach 2:
The target gNB-CU performs preliminary actions by preparing LTM information and configuration before the actual handover execution. The source gNB-CU receives and stores this LTM information in advance, allowing the UE to execute handover quickly when conditions are met, thus achieving both extended mobility scope and reliable execution
2Adaptability or versatility
If inter-gNB-CU LTM is implemented, then mobility between different base stations is enabled, but signaling complexity increases
Solution Approach 1:
The LTM information structure is designed to be universal and multi-functional, serving both intra-gNB-CU and inter-gNB-CU mobility scenarios. The same LTM information elements and signaling procedures are used regardless of whether the handover is within or between gNB-CUs, reducing the need for separate complex signaling mechanisms
Solution Approach 2:
The source gNB-CU acts as an intermediary that manages the LTM information from the target gNB-CU. It stores the LTM information, determines when to trigger handover, and controls the execution timing. This intermediary role simplifies the overall signaling by centralizing the decision-making logic at the source side
3Speed
If LTM configuration is prepared in advance, then handover execution speed is improved, but network resources are consumed
Solution Approach 1:
The network prepares LTM information and configuration in advance for potential handover scenarios, but this preparation is done selectively based on measurement reports and handover conditions. Not all possible handovers are pre-configured, only those that are likely based on UE movement patterns and network conditions, thus balancing resource consumption with handover speed
Solution Approach 2:
The LTM configuration is dynamic and adaptable. The source gNB-CU can update or refresh the LTM information received from the target gNB-CU based on changing network conditions and UE status. This dynamic management allows the system to optimize resource usage by maintaining only relevant LTM configurations while enabling fast handover when needed
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
Disclosed are a L1/L2 Triggered Mobility (LTM) signaling method and apparatus in a wireless communication system. A source base station transmits a handover request message including a layer 1 (L1)/layer 2 (L2) triggered mobility (LTM) information request to a target base station and receives a handover acknowledge message including an LTM information response from the target base station. Further, the target base station transmits a first message for cancelling already prepared LTM to the source base station, and the source base station receives the first message.