L1/L2 Triggered Mobility Execution for 5G Handover Latency
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Solution Overview
Problem
Current 5G/NR wireless communication systems face challenges in reducing latency and signaling overhead during handover procedures, particularly in scenarios with frequent handovers and high-speed vehicular movements, due to network-controlled mobility mechanisms that rely on higher layer signaling.
Innovation Solution
Implementing Layer 1/Layer 2 (L1/L2) triggered mobility (LTM) that allows handovers to be triggered by L1/L2 signaling based on L1 measurements, enabling beam switching between cells and reducing latency and overhead through L1 measurement-driven decisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If network-controlled mobility mechanisms relying on higher layer signaling are used, then connection reliability is maintained, but handover latency and signaling overhead increase
Solution Approach 1:
The patent segments the mobility control function into two parts: L1/L2 layer triggers and executes handovers autonomously based on measurements, while RRC layer provides configuration and recovery mechanisms. This segmentation allows fast handover execution at L1/L2 without waiting for RRC signaling, reducing latency while maintaining reliability through RRC-configured fallback options.
Solution Approach 2:
The patent implements preliminary action by pre-configuring LTM candidate cells and recovery parameters through RRC signaling before handover is needed. The UE prepares L1/L2 measurement configurations and candidate cell lists in advance, so when handover is triggered, the execution can proceed immediately without delay for configuration setup.
2Reliability
If network-controlled mobility mechanisms relying on higher layer signaling are used, then connection reliability is maintained, but signaling overhead increases
Solution Approach 1:
The patent segments signaling functions to minimize overhead: RRC layer sends only essential configuration information (LTM candidate cells, recovery parameters) while L1/L2 layer handles execution without additional RRC signaling. This reduces the volume of RRC messages compared to traditional network-controlled handover where each step requires RRC confirmation.
Solution Approach 2:
The UE performs self-service by autonomously executing handovers based on L1/L2 measurements and pre-configured parameters without continuous network signaling. The UE independently evaluates candidate cells, triggers handover when conditions are met, and manages the process, eliminating the need for network-confirmed signaling at each handover step.
3Loss of time
If L1/L2 triggered mobility is implemented, then handover latency and signaling overhead are reduced, but complexity of mobility management increases
Solution Approach 1:
The patent introduces an intermediary mechanism where pre-configured LTM parameters and candidate cell lists act as a bridge between RRC layer and L1/L2 layer. This intermediary structure simplifies the autonomous decision-making at L1/L2 by providing ready-made configuration data, reducing the complexity of real-time processing while enabling fast handover execution.
4Productivity
If L1/L2 triggered mobility is implemented, then mobility execution efficiency is improved, but reliability during frequent handovers deteriorates
Solution Approach 1:
The patent implements beforehand cushioning by pre-configuring multiple LTM candidate cells and recovery parameters before frequent handovers occur. When handovers become frequent or failures occur, the UE has pre-prepared alternative candidates and recovery mechanisms ready, preventing connection loss without requiring complex real-time decision-making during high-stress scenarios.
Data Source
AI summary
Methods and apparatuses for a L1/L2 triggered mobility execution in a wireless communication system are provided. The method of UE comprises: receiving information related to (i) an LTM configuration and (ii) an applicability of the LTM configuration to recover from a failure of an LTM execution; determining whether the applicability of the LTM configuration to recover from the failure of the LTM execution is enabled; determining whether the LTM execution fails; performing a cell selection operation based on a determination that the LTM execution fails; determining whether a cell that is selected in the cell selection operation is an LTM candidate cell; performing the LTM execution based on a determination that the cell is an LTM candidate cell and the applicability of the LTM configuration to recover from the failure of the LTM execution is enabled; applying the LTM configuration and transmitting a random access preamble.