Time-Based Triggered Handover in Non-Terrestrial Networks

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Solution Overview

Problem

In Non-Terrestrial Networks (NTNs), especially in quasi-earth-fixed cell scenarios, frequent handovers due to satellite movements and long propagation delays lead to significant control plane overheads and service interruptions, with challenges in managing handovers efficiently across overlapping cell beams.

Innovation Solution

The introduction of time-based and location-based trigger conditions for Conditional Handover (CHO) in NTNs, allowing the UE to perform handovers based on predefined time windows and distance thresholds, thereby reducing unnecessary handovers and signaling overheads.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If frequent handovers are performed due to satellite movements in NTNs, then connectivity is maintained, but control plane overheads increase significantly

Engineering Contradiction:

ImproveconnectivityVSAvoidcontrol plane overheads

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The network configures the UE with multiple candidate target cells and their corresponding handover conditions in advance, before the actual handover is needed. This allows the UE to have handover instructions ready, reducing the signaling overhead during frequent handovers caused by satellite movements.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The UE autonomously evaluates the configured handover conditions (such as signal quality thresholds and time-based criteria) and independently decides when to execute handover to the appropriate candidate cell, without requiring continuous network intervention and signaling for each handover decision.

Inventive Principle:

Principle #25Self-service

2Reliability

If frequent handovers are performed due to satellite movements, then connectivity is maintained, but service interruptions increase

Engineering Contradiction:

ImproveconnectivityVSAvoidservice interruptions

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The network provides the UE with pre-configured handover instructions including multiple candidate target cells and execution conditions before handover is triggered. This preparation eliminates delays during actual handover execution, maintaining connectivity while minimizing service interruptions.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The UE continuously monitors signal quality and other handover conditions, providing feedback to evaluate whether configured handover conditions are met. This enables timely and accurate handover execution, maintaining connectivity while reducing unnecessary handovers that would cause service interruptions.

Inventive Principle:

Principle #23Feedback

3Ease of operation

If traditional handover mechanisms are used in NTNs, then handover capability is provided, but ping-pong effects occur reducing handover robustness

Engineering Contradiction:

Improvehandover capabilityVSAvoidhandover robustness

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The network configures the UE with multiple candidate target cells and specific execution conditions in advance. This allows the UE to make informed handover decisions based on pre-evaluated conditions, reducing random or unnecessary handovers that cause ping-pong effects and improving handover robustness.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The UE continuously evaluates handover conditions including signal quality measurements and compares them against configured thresholds. This feedback mechanism ensures handovers are triggered only when genuinely beneficial, preventing ping-pong effects between cells and enhancing handover reliability.

Inventive Principle:

Principle #23Feedback

4Productivity

If conditional handover with time-based trigger conditions is implemented, then unnecessary handovers are reduced, but configuration complexity increases

Engineering Contradiction:

Improvehandover efficiencyVSAvoidconfiguration complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The handover configuration mechanism is designed to be universal, supporting both traditional signal-quality-based handovers and new time-based trigger conditions through a unified configuration framework. This allows the same infrastructure to handle multiple handover scenarios without requiring separate complex configuration systems.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS20250184854A1Systems and methods for time-based triggered handover in non-terrestrial networks

Publication Date: 2025.06.05 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A method by a wireless device, configured for conditional handover to at least one candidate target cell, includes determining at least one of: a plurality of conditions associated with the conditional handover of the wireless device to the at least one candidate target cell has been fulfilled, at least one condition associated with the conditional handover of the wireless device to the at least one candidate target cell has not been fulfilled, an execution of the conditional handover to the at least one candidate target cell has failed within at least one time window associated with the at least one candidate target cell, and an execution of the conditional handover to the at least one candidate target cell succeeded within at least one time window associated with the at least one candidate target cell. Based on an outcome of the determining step and a configuration of the wireless device, the wireless device performs at least one action.