LTM Cell Switching via MAC CE for Low-Latency 5G Handover

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Solution Overview

Problem

Existing wireless communication systems face high latency and overhead during cell handover due to L3 measurements and RRC signaling, leading to increased interruption times, which are not suitable for the stringent requirements of 5G systems.

Innovation Solution

Implementing L1/L2 Triggered Mobility (LTM) by using MAC CE for cell switch procedures, allowing early synchronization and synchronization with LTM candidate cells, reducing the need for complete L2 resets and minimizing latency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If L3 measurements and RRC signaling are used for cell handover, then the handover procedure is completed with proper synchronization, but the latency and service interruption time increase significantly

Engineering Contradiction:

Improvehandover synchronizationVSAvoidhandover latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent performs L2 synchronization and security update procedures in advance before the actual cell handover is triggered. The UE receives and processes RRC reconfiguration messages containing security parameters and synchronization information beforehand, so that when handover is needed, the UE is already prepared and can switch cells quickly without performing complete L2 resets

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent divides the handover procedure into separate stages: L1 beam switching for quick connection establishment, followed by L2 synchronization and security updates. This segmentation allows the critical path (beam switching) to be completed rapidly while non-critical operations (full L2 reset) are optimized or deferred

Inventive Principle:

Principle #1Segmentation

2Reliability

If complete L2 resets are performed during serving cell change, then synchronization is ensured, but overhead and interruption time increase

Engineering Contradiction:

ImprovesynchronizationVSAvoidprocedure overhead

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Instead of performing complete L2 resets, the patent applies partial L2 synchronization by updating only the necessary security parameters and synchronization information through MAC CE messages. This partial action is sufficient to maintain synchronization while avoiding the overhead of complete protocol stack resets

Inventive Principle:

Principle #16Partial or excessive action

3Reliability

If RRC signaling is used for cell handover, then proper security update is performed, but the number of messages and latency increase

Engineering Contradiction:

Improvesecurity updateVSAvoidsignaling latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent introduces MAC Control Elements (MAC CE) as an intermediary mechanism to convey security update information and synchronization parameters. MAC CE operates at layer 2 and can transmit this information more efficiently than L3 RRC signaling, reducing the number of messages required and decreasing signaling latency while maintaining security update integrity

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS20250351035A1Method and apparatus for performing security update in mobile wireless communication system

Publication Date: 2025.11.13 BLACKPIN INC

AI summary

A method to enable efficient data transfer for cell switch in conjunction with LTM operation is provided. The method of the terminal includes receiving from a base station a Radio Resource Control (RRC) reconfiguration message, receiving from the base station a specific Medium Access Control (MAC) Control Element (CE) wherein the MAC CE instructs the terminal to perform LTM cell switch procedure, performing a cell selection to a specific cell if reconfiguration with sync failure is detected and triggering either a first procedure for the specific cell or a second procedure in the specific cell depending on the selected cell.