L1/L2 Triggered Mobility for Low Latency Handover
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Solution Overview
Problem
Current mobile communication systems face challenges in achieving low latency and minimizing interruption time during handover processes, especially in high-speed mobility scenarios, due to intricate and time-consuming procedures involving L3 signaling.
Innovation Solution
Implementing L1/L2 triggered mobility (LTM) by receiving an RRC reconfiguration message with LTM candidate cell configuration, transmitting a random access preamble, and performing cell switching based on a MAC control element, allowing for early synchronization and efficient handover operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If L3 signaling is used for handover, then handover procedure is completed with reliable signaling, but handover latency and interruption time increase
Solution Approach 1:
The patent performs early synchronization with the target cell before the actual handover execution. The UE transmits a random access preamble to the target cell in advance and obtains uplink timing advance information, so that when handover is triggered, the synchronization is already established, reducing the handover execution time while maintaining reliability through the pre-established connection.
Solution Approach 2:
The patent divides the handover process into distinct phases: early synchronization phase (performed in advance), handover preparation phase (RRC reconfiguration), and execution phase (MAC CE triggered). By segmenting the handover procedure, the time-consuming synchronization operation is separated from the critical handover execution path, reducing overall latency while maintaining reliability through structured signaling.
2Ease of operation
If L3 signaling is used for handover, then comprehensive control is achieved, but device complexity and procedure intricacy increase
Solution Approach 1:
The patent introduces a MAC Control Element as an intermediary mechanism to trigger handover execution. Instead of using complex L3 RRC signaling for the actual handover execution, a simplified MAC CE carries the handover command, reducing the signaling complexity while maintaining network control. The MAC CE acts as a lightweight mediator between the network's handover decision and the UE's execution.
3Loss of time
If early synchronization is performed, then handover latency is reduced, but additional signaling overhead is generated
Solution Approach 1:
The patent employs self-service mechanisms where the UE autonomously performs the random access procedure and obtains timing advance information without extensive network coordination during the early synchronization phase. The UE independently completes synchronization operations, reducing the need for additional signaling exchanges with the network while still achieving the latency reduction benefit of early synchronization.
Data Source
AI summary
Provided are method and apparatus for controlling the mobility of a UE in a mobile communication system. The method may include receiving an RRC reconfiguration message including an L1/L2 triggered mobility (LTM) candidate cell configuration from a network node, transmitting a random access preamble to the LTM candidate cell based on a PDCCH order of a serving cell to perform an early synchronization operation for obtaining an uplink timing advance of an LTM candidate cell, receiving a MAC control element (CE) including a cell switch command from the serving cell, and performing a cell switching operation to a target cell based on the MAC CE.