Non-Terrestrial Networks for 5G and Global Connectivity

In 1901, Guglielmo Marconi sent the first transatlantic wireless signal from Poldhu in Cornwall, England, to Newfoundland, Canada. Ironically, the signal was digital and not analog. Marconi sent the letter `S’ and transmitted it using Morse code. Since that stunning achievement, wireless technology has continued to connect people who are far apart.

What Is Different about NTNs?

Consider your mobile device. Although it operates wirelessly, the 5G base station (gNB), that provides the connection is a terrestrial infrastructure. Leaving a coverage area means that you have no service. This is all about to change with the advent of non-terrestrial networks (NTNs).

What Role Does the 3GPP Have in NTN?

The 3rd Generation Partnership Project (3GPP) Release 17 provides the standard for 5G operators to expand their service beyond terrestrial networks. This means your mobile devices will always have service, regardless of whether you are in a remote desert village or sailing the high seas. This is a transformative technology that will extend the reach of digital communication to remote communities and increase personal freedom and security.

How Do NTNs Work?

NTNs refer to a constellation of satellites or high-altitude platforms (HAPs) that function as relays, extending the coverage and capacity of terrestrial 5G networks. These networks have the potential to do the following:

How Do NTNs Use 5G NR?

3GPP Release 17 specifies how operators can use 5G NR for NTN using the bent pipe architecture. In this configuration, the encoded signal from gNB is unaltered in the feeder link and service link. The signals may, however, be up-converted or down-converted in frequency. Because the signal is not regenerated, we refer to it as a transparent payload.

What Satellite Payloads Are Used in NTNs?

By contrast, non-transparent payloads require the satellite to demodulate and modulate the signal. Transparent payloads have the benefit of leveraging many of the mature NR technologies and simplifying the satellite design. Figure 1 shows a comparison of the two architectures.

Figure 1. Transparent versus non-transparent NTN payload architectures

What Benefits Do NTNs Provide?

The primary benefit of NTNs is extended coverage. Remote and underserved regions such as rural areas, islands, and isolated communities can benefit from the technology. NTNs can also provide service to ships at sea and aircraft in flight. NTNs provide an opportunity for network service providers to operate in an otherwise untapped market and can offer premium services to customers who require services beyond the capabilities of traditional terrestrial networks. Machine-to-machine (M2M) applications, including agriculture, transportation, environmental monitoring, and asset tracking, can tap into NTNs for ubiquitous and reliable connectivity to the Internet.

NTNs adds an additional layer of resilience and redundancy to the existing 5G network. In the event of natural disasters, regional conflicts, or network outages, NTNs can provide backup connectivity to ensure continued service for mission-critical communications.

What Are the Challenges of Deploying NTNs?

There are numerous technical and regulatory challenges to consider when deploying NTN networks. For example, unlike terrestrial networks where the base station is stationary, NTNs have satellites in low Earth orbit (LEO) moving at several kilometers per second, which introduces the Doppler shift in frequency and varies depending on the satellite's trajectory. The user equipment needs to compensate for the varying shift in the frequency, so it also needs to know about the satellite orbit. The distance through the atmosphere that the signal must travel to reach the user is much greater, leading to a higher path loss.

The network's performance, as measured by latency and capacity, is also affected by distance and path loss. A combination of these factors and a greater susceptibility to interference presents a challenge for design engineers. Using simulation software and digital twins can help mitigate many of these challenges.

Spectrum allocation, location of the ground stations, compliance with national and international regulations, and complex licensing approvals also create hurdles to deploying NTNs across multiple jurisdictions.

A successful deployment of NTNs will require cooperation among satellite operators, network service providers, government agencies, and standards bodies to overcome regulatory barriers.

How Does Simulation Software Help NTN Design?

Simulation software is useful for any electronic design, but its importance in NTN design cannot be overstated. Simulation software enables designers to mitigate the risk of costly mistakes before the operator launches the satellites. System performance can be validated by modeling and simulating the signal integrity of the uplink and the downlink under varying atmospheric and orbital conditions.

Simulation enables designers to mimic real-world scenarios, such as satellite position, atmospheric conditions, Doppler effect, and interference. Figure 2 shows the 3D trajectory of a satellite with the parameters, distance, path delay, doppler, and elevation angle plotted. Features found in simulation software include trajectory generation, satellite link model, terrestrial link model, and antenna array.

Beyond the deployment phase, simulation software is useful in monitoring, provisioning, and troubleshooting. As networks evolve, simulation software can answer what-if scenarios.

Figure 2. Simulation software showing satellite trajectory

How to Emulate NTNs Using Digital Twins

At Mobile World Congress Barcelona 2023, Keysight demonstrated an end-to-end test solution for NTNs, which included video streaming over a live 5G NTN connection. Figure 3 shows the setup of the demonstration.

Integrating hardware emulators replicates the real-world signal along the communication path and becomes the digital twin of the NTN. Designers can use the digital twin to test any equipment in the system quickly and reliably, with the flexibility to alter the testing parameters. A critical part of NTN testing is emulating the effects of the moving satellite, signal interference, and path loss. Keysight PROPSIM channel emulator can emulate these and other distortions.

Figure 3. Digital Twin of a NTN using Keysight’s UXM 5G wireless test platform, the PROPSIM channel emulator, and UESim simulator

What’s Next for NTN?

NTNs hold the potential to bridge the digital divide by providing ubiquitous communication services to remote and rural areas and enabling previously impossible applications. Beyond the technical achievements of NTNs, greater inclusivity will help foster economic development and empower individuals. Businesses will find new applications to manage their operations more efficiently and reliably. NTN is a catalyzing technology that will accelerate innovation and growth in many industries.

To learn more about Keysight’s NTN solutions, please visit the links below:

S8825A Satellite and Aerospace Channel Emulation Toolset

E7515B UXM 5G Wireless Test Platform

Channel Emulation Solutions

W4516E PathWave 5G NR NTN Channel Model Kit

W4812B PathWave System Design, 5G and Cellular

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