UE-Initiated Lower-Layer Mobility with Early TA Acquisition
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Solution Overview
Problem
Existing 5G wireless communication systems face challenges in efficiently managing UE-initiated lower layer triggered mobility due to limitations in early timing advance acquisition and candidate cell selection during handover processes, leading to increased latency and inefficiencies.
Innovation Solution
The system enables UE-initiated lower layer triggered mobility by allowing the user equipment (UE) to receive timing advance (TA) information and candidate cell configurations from the network, facilitating early TA acquisition and enabling RACH-less handovers through PDCCH orders and MAC CEs, thereby reducing latency and improving mobility management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If traditional handover procedures are used, then mobility management is achieved, but latency is increased due to multiple signaling exchanges
Solution Approach 1:
The network configures the UE with LTM candidate cell information and TA values in advance before handover is needed. When handover is triggered, the UE can immediately use the pre-configured TA value to access the target cell without waiting for TA acquisition during the handover process, thereby reducing latency while maintaining reliability
Solution Approach 2:
The patent extracts the TA acquisition step from the critical handover path by providing TA values through pre-configuration. This separates the TA acquisition process from the actual handover execution, allowing the handover to proceed faster while the TA value is already available
2Loss of time
If early TA acquisition is implemented, then handover latency is reduced, but system complexity increases due to additional configuration management
Solution Approach 1:
The patent uses existing MAC CE mechanisms for multiple purposes: both for delivering TA values during pre-configuration and for maintaining TA synchronization. This multi-functional use of existing protocols reduces the need for new complex signaling structures
Solution Approach 2:
The network acts as an intermediary by providing the TA value through MAC CE from the source cell. This intermediary approach allows the UE to obtain TA without directly interacting with the target cell during the pre-configuration phase, simplifying the overall system architecture
3Productivity
If RACH-less handover is enabled, then latency is reduced and efficiency is improved, but adaptability to different mobility scenarios is limited
Solution Approach 1:
The patent implements a dynamic approach where the UE can switch between conventional handover and RACH-less handover based on the availability of pre-configured TA values and the specific mobility scenario. This dynamic adaptability allows the system to optimize for speed when conditions permit while maintaining reliability when conditions require more robust procedures
Data Source
AI summary
A user equipment (UE) includes a transceiver configured to receive, from a source cell, a physical downlink control channel (PDCCH) order for a first UE initiated lower layer triggered mobility (LTM) candidate cell, and transmit, to the first LTM candidate cell, during a random access procedure initiated by the PDCCH order, a random access preamble. The transceiver is also configured to receive, from the source cell, after completion of the random access procedure, a medium access control (MAC) control element (CE) including timing advance (TA) information of the first LTM candidate cell. The UE also includes a processor operatively coupled to the transceiver. The processor is configured to store the TA information of the first LTM candidate cell, and start a candidate timing alignment timer (TAT) for the first LTM candidate cell.