Non-terrestrial Networks for 5G and Beyond

- Overview

Non-terrestrial network (NTN) is a terminal-satellite direct communication technology that supplements terrestrial cellular communications. NTNs are important for 5G networks because they:

• Provide backup connectivity in the event of natural disasters, regional conflicts or network outages
• Offer advantages over urban and rural areas in 5G target performance (i.e. experienced data rates and reliability)
• Provide connectivity to users and mMTC devices in unserved/underserved areas
• Deliver high-speed wireless access to remote areas
• Wide area coverage ensures service availability and meets connection needs anytime and anywhere.

NTN is based on the new air interface defined by 3GPP standard Release 17. They use satellites on the access side of mobile networks to provide mobile services to ground users.

Looking beyond 5G/6G, NTN will consist of multi-layer networks including GEO satellites, LEO satellites and HAPS (multi-layer NTN). These satellites and HAPS will be connected to each other via inter-satellite links.

- The Role of Satellites in 5G Networks

To fully realize the promise of fifth-generation mobile networks (5G)—nearly ubiquitous, instant connectivity to vast numbers of devices around the world—terrestrial telecommunications systems that rely heavily on buried fiber optic cables will not be enough.

Instead, we will need to move from (a) primarily addressing "last mile" problems (areas where laying fiber is a physical or economic challenge) or for discrete use cases (such as processing credit card payments at gas stations) to (b) integrated 5G "a network of networks", in which satellites play an increasing role alongside terrestrial networks.

- 5G from Space: 3GPP Non-Terrestrial Networks (NTNs)

The basic idea of Non-terrestrial Network (NTN) is obvious. It is to provide 5G/NR services through space (satellite) or air (airborne platform). Therefore, realizing wireless communication in an integrated network has attracted the attention of the industry and research community.

Future wireless networks will need to provide more wireless services at higher data rates and global coverage. However, existing wireless networks of the same kind, such as cellular and satellite networks, may not be able to meet such requirements alone, especially in remote areas, including oceans and mountains. One possible solution is to use a diverse wireless network that can utilize the interconnection of satellites, air base stations (BSs) and terrestrial BSs on interconnected space, ground and air networks. 

- Non-Terrestrial Networks 5G Integration

Satellites maximize the inherent value of 5G networks by solving coverage problems and difficult use-cases that ground-based infrastructure alone cannot address. 5G standards make Non-Terrestrial Networks (NTN) -including satellite segments – a recognized part of 5G connectivity infrastructure.

Non-Terrestrial Networking (NTN) is a relatively new term in the world of communications. NTN refers to networks that provide connectivity via spaceborne vehicles (satellites), airborne platforms such as airships and balloons, and UAS (Unmanned Aircraft System) platforms (including unmanned aerial vehicles such as drones) . 

Air-to-ground networks can provide onboard connectivity to aircraft with base stations placed in specific geographic areas. Before the term was introduced, the more common term was a network of satellites, or Geostationary Earth Orbit (GEO) satellites. 

The priorities and use cases will be driven by satellite operators needs while working with the terrestrial providers to ensure that mobile network operators and others can seamlessly and cost-effectively integrate with satellite systems.

- Terrestrial Networks

A terrestrial network (or broadcast network in the US) is a group of radio stations, television stations, or other electronic media outlets that form an agreement to broadcast or broadcast content from a centralized source. For example, ABC (USA), CBC/Radio-Canada (Canada), BBC (UK), ABC (Australia), DW (Germany), KBS (Korea) and NHK (Japan) are examples of local terrestrial TV affiliates offering access to local audiences A program that is broadcast on a signal that your home TV can receive. Networks usually, but not always, operate nationwide; that is, they cover the entire country.

Streaming, webcasting, and webcasting are sometimes considered forms of broadcasting, although there are no terrestrial stations; its practitioners may also be referred to as "broadcasters" or even "broadcast networks."

- Non-Terrestrial Networks (NTNs) and 3GPP

For the integration of NTN, 3GPP initiated Study Release 15 on channel models and deployment scenarios. After completing this study, 3GPP followed up Study Release 16 on solutions for adapting 5G NR to support NTN.

3GPP Release 17 supports New Radio (NR) based satellite access deployed in the FR1 frequency band, serving handsets for global service continuity. 3GPP Release 17 supports satellite access based on NB-IoT and eMTC to address numerous Internet of Things (IoT) use cases in agriculture, transportation, logistics, and more. 

This joint effort between the mobile and satellite industries will enable full integration of satellite into the 3GPP ecosystem and define a global standard for future satellite networks. This will address accessibility and service continuity challenges in unserved/underserved areas, enhance reliability through connectivity across various access technologies, and improve network resilience and reliability in response to natural and man-made disasters. 

[5G NTN Use Cases - IEEE Xplore]

-  Satellite-based NTN in 5G

5G is being deployed more widely around the world, but the technology could also end up in the skies. 3GPP has established and continues to establish standards to enable 5G services to be delivered over satellite infrastructure, also known as 5G New Radio on Non-Terrestrial Networks (NTN).

Why do we need satellite-based non-terrestrial networks (NTN) in 5G? A: Meet the ubiquitous connectivity needs around the world.

Terrestrial networks using 5G technology are primarily focused on providing coverage and services to users in specific geographic areas. However, mobile broadband services are limited in locations and environments such as rural and remote areas, deserts, deep forests, mountains, oceans, and emergencies involving public safety. NTNs address these issues by providing long-range coverage on the order of tens to hundreds of kilometers.

In 5G, NTNs represent a plethora of connectivity scenarios for satellite-based communications via airborne stations, considering situations such as air-to-ground or drone flight control. These include various satellite-based connectivity scenarios, where the satellites fly at different altitudes and cover areas.

- The Path to 5G-Advanced and 6G NTN Systems

Today, 5G networks are rolling out across the globe, bringing enormous benefits to our economy and society.

However, 5G systems alone are not expected to be sufficient to meet the challenges that networks will face in 2030, including always-on networks, 1 Tbps peak data rates, <10 cm positioning, etc. 

Therefore, for 5G-Advanced (5G-A) and 6G, science and industry are already addressing the evolution of 5G systems and the definition of (r)evolution.

In this framework, Non-Terrestrial Networks (NTNs) have been successfully integrated into 3GPP Rel. 17 and they are expected to play an even more critical role in 5G-A (up to Rel.20) and 6G systems (beyond Rel.20).

We need to explore the path to 5G-A and 6G NTN communications, providing a clear perspective in terms of system architecture, services, technologies and standardization roadmaps.