UE Random Access Timing Alignment for Fast 5G Cell Handover

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Solution Overview

Problem

The existing 5G system experiences long delays and service interruptions during cell handover due to the need for L2 and L1 resetting during PCell or PSCell changes, which can be improved by configuring multiple candidate cells for handover and achieving uplink timing alignment before the handover.

Innovation Solution

User equipment sends a PRACH preamble on a target cell based on downlink control information (DCI) to receive uplink timing synchronization information, using MAC-CE or MAC RAR commands to determine the success of the random access procedure and achieve uplink timing alignment with candidate cells.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If PCell or PSCell change is performed by reconfiguration with sync triggered by RRC, then serving cell change is achieved, but L2 and L1 resetting causes long delay and long service interruption time

Engineering Contradiction:

Improveserving cell change completionVSAvoidhandover delay and service interruption time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent performs uplink timing alignment with candidate cells before the actual handover occurs. The terminal sends random access preambles to candidate cells in advance and receives timing advance commands, so that when handover is triggered, the timing alignment is already established, eliminating the need for L2/L1 resetting and reducing service interruption time.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent divides the handover process into separate stages: (1) uplink timing alignment with candidate cells using random access procedure, and (2) actual serving cell switching via RRC reconfiguration. This segmentation allows timing synchronization to be established independently before the critical handover moment, avoiding the need to reset all layers simultaneously.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If multiple candidate cells are configured for handover, then handover options increase, but service procedures need to be triggered and completed for each cell

Engineering Contradiction:

Improvehandover candidate cell selectionVSAvoidservice procedure triggering and completion

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent uses a universal random access procedure that can be applied to multiple candidate cells simultaneously. The terminal sends random access preambles to all configured candidate cells using the same mechanism, and receives timing advance commands for each cell, eliminating the need to execute separate service procedures for each candidate cell.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS20260052577A1Method performed by user equipment, and user equipment

Publication Date: 2026.02.19 SHARP KK

AI summary

The present invention provides a method performed by a user equipment (UE), and a user equipment. The method performed by a user equipment includes: a user equipment sending a random access preamble PRACH preamble on bandwidth of a target cell, according to downlink control information (DCI) on a primary cell, the target cell being a serving cell or a non-serving cell of the user equipment; and the user equipment receiving, on the primary cell, information of uplink timing synchronization with the target cell.