UE Handover Uplink Grant Selection Without Random Access

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Solution Overview

Problem

During handover in wireless communication systems, latency occurs due to the need for a random access procedure, which can be mitigated by implementing RACH-less handover.

Innovation Solution

A method for UE to perform handover by receiving UL grant configuration information via an RRC reconfiguration message, selecting an SSB from multiple SSBs, determining a corresponding UL grant and HARQ process, and transmitting a reconfiguration complete message using the HARQ process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If random access procedure is performed during handover, then connection reliability is improved, but handover latency increases

Engineering Contradiction:

Improveconnection reliabilityVSAvoidhandover latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The network pre-configures multiple UL grants and associates them with different SSBs before handover execution. The UE selects the appropriate UL grant based on the detected SSB, eliminating the need for random access during handover. This preliminary configuration enables direct uplink transmission and reduces handover latency while maintaining connection reliability.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Multiple uplink grants are configured as copies or alternatives to each other, each associated with a specific SSB. Instead of performing random access to establish a single uplink connection, the UE can directly use the pre-configured UL grant corresponding to the detected SSB, effectively copying the random access functionality through pre-established resources.

Inventive Principle:

Principle #26Copying

2Productivity

If multiple UL grants are configured for different SSBs, then handover efficiency is improved, but device complexity increases

Engineering Contradiction:

Improvehandover efficiencyVSAvoiddevice complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

Each UL grant is locally optimized and associated with a specific SSB, allowing the UE to select the most appropriate grant based on the detected SSB quality. This local association simplifies the selection process compared to evaluating multiple unrelated grants, as the UE only needs to match the detected SSB with its corresponding pre-configured UL grant.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The network performs the complex configuration of multiple UL grants and their associations with SSBs in advance, before handover execution. This preliminary action transfers the complexity from the UE side to the network side, simplifying the UE's task during actual handover to merely selecting the appropriate grant based on SSB detection.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentEP3925296B1Method and apparatus for performing communication in wireless communication system

Publication Date: 2025.12.24 SAMSUNG ELECTRONICS CO LTD

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AI summary

A method, performed by a user equipment (UE), of performing communication in a handover process includes receiving uplink (UL) grant configuration information via an RRC reconfiguration message, selecting a SSB among a plurality of SSBs included in the UL grant information, determining a UL grant corresponding to the selected SSB and a HARQ process corresponding to the UL grant based on the UL grant information and transmitting a reconfiguration complete message in the determined UL grant corresponding to the selected SSB using a HARQ process.