Non-Terrestrial Networks (NTN): Definition, Platforms and 3GPP Perspective

Introduction Non-Terrestrial Networks (NTN)

Non-Terrestrial Networks (NTN) Wireless communication networks have traditionally relied on terrestrial infrastructure such as cellular towers, base stations, fiber networks, and microwave links. However, as the demand for ubiquitous connectivity continues to increase, wireless networks are expanding beyond traditional terrestrial infrastructure.Non-Terrestrial Networks (NTN)

This is where Non-Terrestrial Networks (NTNs) become important.

A Non-Terrestrial Network (NTN) is a wireless communication network that utilizes radio network equipment placed on an airborne or spaceborne vehicle. This broad definition means that communication networks using airborne platforms can also be considered part of the NTN ecosystem.

For example, if radio network equipment is deployed on an Uncrewed Aerial Vehicle (UAV) or drone, a network involving UAVs can qualify as an NTN from this general perspective.

However, the NTN specifications developed by the Third Generation Partnership Project (3GPP) specifically focus on particular types of non-terrestrial platforms, including satellites and High-Altitude Platform Stations (HAPS).Non-Terrestrial Networks (NTN)

Non-Terrestrial Networks (NTN)

What is a Non-Terrestrial Network?

At its most basic level, an NTN is a wireless communication network where some of the radio network equipment is deployed on a platform that operates above the Earth's surface, rather than being located on traditional terrestrial infrastructure.

These platforms can be:

• Airborne vehicles

• High-altitude platforms

• Satellites

• Other spaceborne platforms

The purpose is to provide wireless communication coverage from platforms that are not fixed terrestrial network infrastructure.

This approach can help extend connectivity into areas where conventional terrestrial networks may be difficult to deploy.

Examples include:

• Remote geographical areas

• Rural regions

• Oceans and offshore locations

• Mountainous regions

• Areas with limited terrestrial infrastructure

  
  

UAVs and NTN

From a general perspective, Uncrewed Aerial Vehicles (UAVs) or drones can also be considered part of the NTN concept when they carry radio network equipment.

A UAV can operate as an airborne communication platform, potentially providing radio coverage to users on the ground.

This means that a network architecture involving UAV-based radio equipment can fall under the broader definition of a non-terrestrial network.

Indeed, some technical literature considers UAV-based communication systems as part of the NTN ecosystem.

However, it is important to distinguish this broad industry definition from the specific scope of 3GPP NTN specifications.

3GPP NTN Platforms

The 3GPP NTN specifications focus on specific types of non-terrestrial platforms.

These include:

1. Satellites

3GPP NTN specifications consider different satellite platforms, including:

• Low Earth Orbit (LEO) satellites

• Medium Earth Orbit (MEO) satellites

• Geosynchronous/Geostationary Earth Orbit (GEO) satellites

Each satellite category operates at a different altitude and therefore has different characteristics in terms of coverage, propagation delay, and network operation.

2. High-Altitude Platform Stations (HAPS)

Another important platform considered in 3GPP NTN specifications is the High-Altitude Platform Station (HAPS).

A HAPS is an airborne vehicle that operates at an altitude between approximately 8 km and 50 km.

HAPS therefore occupies a position between conventional terrestrial infrastructure and satellite-based communication systems.

Uncrewed Aerial Systems (UAS)

The broader NTN ecosystem also includes Uncrewed/Unmanned Aerial Systems (UASs).

According to the terminology used in 3GPP-related work, examples of UAS include:

• Lighter-than-Air (LTA) UAS

• Heavier-than-Air (HTA) UAS

These systems represent different approaches to airborne platforms and can potentially be used for communication-related applications.

The classification is important because different airborne platforms have different operating characteristics, deployment models, and technical requirements.

Understanding Satellite Orbits in NTN

One of the most important aspects of satellite-based NTN is the orbital altitude of the satellite.

Different satellite orbits provide different network characteristics.

Low Earth Orbit (LEO)

LEO satellites generally operate at altitudes between approximately:

300 km – 1,500 km

Because LEO satellites operate relatively close to Earth, they can provide characteristics that are different from higher-orbit satellite systems.

LEO satellite systems are often deployed as constellations consisting of multiple satellites.

Their movement relative to users on Earth also makes satellite mobility and handover important considerations for NTN network design.

Medium Earth Orbit (MEO)

MEO satellites generally operate at altitudes between approximately:

7,000 km – 25,000 km

MEO satellites operate significantly higher than LEO satellites and can provide broader coverage per satellite.

Their orbital characteristics result in different propagation and network requirements compared with LEO systems.

Geosynchronous/Geostationary Earth Orbit (GEO)

GEO satellites operate at an altitude of approximately:

35,786 km

A geostationary satellite appears fixed relative to a point on Earth's surface because it orbits Earth at the same rotational rate as Earth.

This characteristic makes GEO satellites particularly useful for applications requiring broad and relatively stable coverage.

However, the much greater distance between the satellite and the user introduces significant propagation delay compared with lower-altitude satellite systems.

Comparison of NTN Satellite Platforms

Satellite Type	Approximate Altitude
LEO	300 – 1,500 km
MEO	7,000 – 25,000 km
GEO	35,786 km

These orbital differences are extremely important when designing NTN systems because altitude affects factors such as coverage, propagation delay, satellite visibility, mobility, and network architecture.

The 3GPP Definition of NR NTN

While NTN can be described broadly as a wireless network using airborne or spaceborne platforms, 3GPP provides a more specific definition for NR NTN.

3GPP formally defines NR NTN as:

“An NG-RAN consisting of gNBs, which provide non-terrestrial NR access to user equipments (UEs) by means of an NTN payload embarked on an airborne or spaceborne NTN vehicle and an NTN Gateway.”

This definition is important because it connects NTN directly with the 5G New Radio (NR) architecture.

In simple terms, an NR NTN system involves:

UE → NTN Payload → NTN Gateway → NG-RAN / 5G Network

The NTN payload is carried by an airborne or spaceborne vehicle, while the NTN Gateway provides the necessary connection toward the terrestrial network infrastructure.

Key Components of NR NTN

Based on the 3GPP definition, several important components can be identified.

User Equipment (UE)

The User Equipment (UE) is the device used by the end user to access the network.

Depending on the deployment scenario, the UE communicates with the NTN radio access network through the NTN platform.

gNB

The gNB (Next Generation NodeB) is the 5G NR base station component responsible for providing NR radio access.

In an NTN architecture, the gNB functionality is associated with the NG-RAN and works with the NTN payload and gateway to provide non-terrestrial NR connectivity.

NTN Payload

The NTN Payload is the radio-related equipment carried by the airborne or spaceborne NTN vehicle.

This payload plays a central role in extending NR access from the non-terrestrial platform toward users on Earth.

Depending on the architecture, the implementation and location of network functions can vary.

NTN Gateway

The NTN Gateway provides connectivity between the non-terrestrial portion of the network and the terrestrial network infrastructure.

It is an important element for connecting the NTN system with the broader 5G network.

Why the 3GPP Definition Matters

The 3GPP definition provides a clear framework for understanding NTN within the 5G ecosystem.

It distinguishes the general concept of a non-terrestrial network from the specific 3GPP NR NTN architecture.

This distinction is important because the term NTN can be used broadly in research and industry discussions, while 3GPP NTN specifications focus on defined platforms and network architectures.

Therefore, when discussing 5G NR NTN, it is important to consider the specific terminology and architecture defined by 3GPP.

NTN: Connecting Airborne and Spaceborne Platforms with 5G

The evolution of NTN represents an important step toward expanding the reach of cellular networks.

Traditional terrestrial networks depend on infrastructure located on the ground. NTN introduces additional communication platforms operating in the air and in space.

The overall ecosystem can therefore include:

Terrestrial Networks + HAPS + UAV/UAS Platforms + LEO + MEO + GEO

This creates opportunities for communication services across geographical areas that are challenging to cover using terrestrial infrastructure alone.

NTN is therefore becoming an important part of the evolution of 5G, 5G-Advanced, and future 6G networks.

Conclusion

A Non-Terrestrial Network (NTN) is a wireless communication network that utilizes radio network equipment placed on an airborne or spaceborne vehicle.

From the broad definition, networks involving UAVs or drones can also be considered NTN systems. However, the 3GPP NTN specifications specifically address platforms such as satellites and High-Altitude Platform Stations (HAPS).

The major satellite categories include:

• LEO: 300–1,500 km

• MEO: 7,000–25,000 km

• GEO: 35,786 km

3GPP further defines NR NTN in the context of an NG-RAN consisting of gNBs that provide non-terrestrial NR access to UEs through an NTN payload carried by an airborne or spaceborne vehicle and an NTN Gateway.

Understanding these definitions and platforms is fundamental for anyone working with 5G NR, NTN, 5G-Advanced, satellite communications, and future 6G networks.

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