NG Handover Rejection Signaling for Unsupported UE Capabilities

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Solution Overview

Problem

Next Generation (NG) handover failures occur due to unsupported user equipment (UE) capabilities, particularly when target cells do not support the UE's subcarrier spacing (SCS) and/or bandwidth configurations, leading to undefined cause values in signaling, which prevents the source node from avoiding incompatible handovers.

Innovation Solution

Implementing a method at the target network node to reject handover requests with a specific cause value indicating unsupported UE capabilities, such as SCS and bandwidth, allowing the source node to avoid future handovers to incompatible target cells by maintaining a neighbor relation table with supported capabilities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the target cell performs admission control based on UE capabilities, then handover failure rate is reduced, but signaling overhead increases due to capability checking and reject message transmission

Engineering Contradiction:

Improvehandover success rateVSAvoidsignaling overhead

Core Design Contradiction:

ReliabilityVSLoss of information

Solution Approach 1:

The target cell performs capability checking and capability mismatch detection before admitting the handover request. By proactively checking whether the target cell supports the UE's SCS and bandwidth configurations before committing resources, the system prevents incompatible handovers from being established, thereby reducing handover failures while minimizing unnecessary signaling exchanges.

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If the source node attempts handover to all neighboring cells, then handover options are maximized, but incompatible handovers increase causing failures

Engineering Contradiction:

Improvehandover optionsVSAvoidhandover success rate

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The target cell provides feedback to the source node about capability compatibility through the handover response message. This feedback mechanism allows the source node to identify which target cells are compatible with the UE's capabilities and prioritize or select those cells for handover, thereby maintaining adaptability while improving success rate by avoiding incompatible targets.

Inventive Principle:

Principle #23Feedback

3Reliability

If capability checking is performed at target cell, then incompatible handovers are prevented, but handover latency increases due to additional processing

Engineering Contradiction:

Improvehandover compatibilityVSAvoidhandover latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The capability checking is performed as a preliminary step during the handover preparation phase, before the actual handover execution. By checking UE capability compatibility early in the process when the target cell receives the handover request, the system prevents incompatible handovers from proceeding to later stages, thereby ensuring compatibility without significantly impacting overall handover latency.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS12445918B2Next generation handover failure due to unsupported user equipment capabilities

Publication Date: 2025.10.14 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A method performed by a target network node includes receiving, from a source network node, a handover request associated with a wireless device. The target network node transmits, via a core network node, a handover reject message to the source network node. The handover reject message comprises a cause value for rejecting the handover request.