LEO-NTN TAC Lists for Lower Tracking Area Update Signaling

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Solution Overview

Problem

In Low Earth Orbit (LEO) Non-Terrestrial Networks (NTN), the high speed of satellites leads to frequent cell reselection, causing excessive tracking area update (TAU) signaling due to mismatched tracking area codes, increasing network load.

Innovation Solution

Each cell broadcasts a dynamic list of multiple tracking area codes (TAC List) corresponding to its coverage area, allowing UEs to perform TAU only when the current TA does not match any code in the list of the reselected cell.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If LEO satellites move at high speed, then coverage speed is improved, but TAU signaling load increases

Engineering Contradiction:

Improvesatellite speedVSAvoidTAU signaling load

Core Design Contradiction:

SpeedVSProductivity

Solution Approach 1:

The network performs preliminary action by pre-configuring the UE with a list of valid TACs (tracking area codes) before the UE actually needs to perform TAU. The network sends this TAC list to the UE in advance, so when the UE moves to a new cell, it can immediately check whether TAU is needed without waiting for network instruction. This preliminary preparation eliminates unnecessary TAU signaling while maintaining proper tracking area management.

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If cell reselection occurs frequently, then mobility tracking is improved, but TAU frequency increases

Engineering Contradiction:

Improvemobility trackingVSAvoidTAU frequency

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The system implements feedback by having the UE continuously monitor the TAC list broadcast by the current cell and compare it with the previously provided TAC list. When the UE detects that the current cell's TAC list contains the same TACs as before, it feedback this information to the network by not initiating TAU, thereby reducing unnecessary signaling. This feedback mechanism allows the system to maintain mobility tracking while reducing TAU frequency.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The network performs preliminary action by pre-configuring the UE with a list of valid TACs before the UE actually needs to perform TAU. The network sends this TAC list to the UE in advance, so when the UE moves to a new cell, it can immediately check whether TAU is needed without waiting for network instruction. This preliminary preparation eliminates unnecessary TAU signaling while maintaining proper tracking area management.

Inventive Principle:

Principle #10Preliminary action

3Device complexity

If single TAC is broadcast per cell, then system simplicity is improved, but TAU signaling overhead increases

Engineering Contradiction:

Improvesystem simplicityVSAvoidsignaling overhead

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The system segments the TAC information by separating the TAC list broadcast by the cell from the actual TAU decision logic. The cell broadcasts only the TAC list (simple information), while the UE performs the complex comparison and decision-making process locally. This segmentation allows the broadcast message to remain simple while the signaling overhead is reduced through intelligent UE-side processing.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS12381619B2Efficient tracking area update in LEO-NTN

Publication Date: 2025.08.05 MEDIATEK SINGAPORE PTE LTD

AI summary

Low Earth Orbit (LEO) satellites orbit around the earth at a high speed (mobility), but over a predictable or deterministic orbit. In this invention, an efficient mechanism to include a list of multiple Tracking Area Codes (TAC List) in LEO-NTN is proposed for efficient tracking area update (TAU). Each cell broadcasts a TAC list corresponding to all the tracking areas it covers as it moves, dynamically. A UE selects a cell and is registered with a TA during initial registration and cell selection. As the satellite moves, the UE reselects another cell during cell reselection. The UE triggers a TAU only if its current TA does not match with any tracking area code of the TAC List broadcasted by the reselected cell. By using the concept of TAC list, it significantly reduces the TAU signaling overhead in LEO-NTN.