5G NTNs expand networks through satellite communications

Article By : Jessy Cavazos

5G NTNs will boost mobile broadband services, and bring challenges with latency and greater complexity.

Until now, all mobile networks were confined to the earth, but non-terrestrial platforms provide significant potential for network coverage expansion. Part of the 3rd Generation Partnership (3GPP) Release 17, non-terrestrial networks (NTNs) integrate 5G capabilities for a mix of unmanned aerial vehicles.

With NTNs, cellular networks will expand through satellite communications for the first time. Introducing satellite links in the 5G New Radio (5G NR) standard will bring many benefits. For example, NTNs enable the delivery of services in areas lacking network infrastructure or availability, such as during or following natural disasters.

Satellite links can also provide coverage for isolated or moving platforms such as aircraft, ships, oil platforms, and trains (Figure 1), and support machine-to-machine communications (M2M) for the IoT. Mobile operators can also use these links to cover their networks’ edges.

In addition, 5G NTNs can act as a fallback network to provide high network availability and enable multi-connectivity by connecting users through both terrestrial and satellite communication links.

illustration of how 5G NTNs reach isolated and moving platformsFigure 1 5G NTNs enable reaching isolated or moving platforms, among other use cases.

The 3GPP technical report (TR) 38.811 details the 5G use cases for NTNs. TR 38.811 aims to define the deployment scenarios and system parameters, adapt 3GPP channel models to NTNs, and identify any large impact on the 5G NR interface.

Table 1 3GPP TR 38.811 defines the 5G NTN use cases for satellite access networks. Source: 3GPP

table of 5G use cases

3GPP channel models enable the testing of 5G NR NTN satellite links. One of the key aspects to focus on when testing modern satellite communications (SATCOM) systems is latency. Latency is a major concern because 5G has much stricter latency requirements than 4G LTE.

In addition, SATCOM systems have increased in complexity. Modern systems use both terrestrial and satellite links and have more than one link active between the devices at a time, with signaling changing over time between the devices and the networks.

Test platforms need to address the greater complexity of these systems with the capability to simulate all orbital parameters, high-velocity satellites, and high-altitude solutions, and be able to test long-distance links with satellite interlinking.

Testing SATCOM systems with realistic environmental models is crucial to ensure performance. Testing a satellite link between two satellite modems, for example, requires modeling the ground-to-satellite links, satellite constellation, and satellite-to-ground links together. Using the correct multi-frequency transmission links and separating the uplink and downlink frequencies between the modems will be important. Also, the virtual environment needs to include all the signaling links and transmission paths between the two modems.

Onboard internet for aircraft passengers is a key use case for 5G NTNs. Aircraft passengers want the same level of connectivity in a flight as on the ground. Currently, satellite modems provide the internet link to a Wi-Fi router aboard the airplane for them to connect to the internet, but in the future, this router will be a cellular router, enabling passengers to stay connected the same way they are on the ground.

Simulating the aircraft-to-satellite use case requires modeling many environmental conditions to determine the implementation of the aircraft modem. In the example in Figure 2, a plane is flying at a certain speed and altitude. It has visibility into four satellites of the constellation it is connected to, each with a different power level. Path gain occurs between the modem, the satellite dish on board the aircraft, and the satellite, and there is delay between the satellite links due to the distance between the aircraft and the satellite. In addition, the plane’s orientation and direction vis-à-vis the four satellites change the Doppler shift in the frequency.

illustration of airplane connecting to 4 satellites mid-airFigure 2 An airplane is connected to four satellites to provide onboard internet service to passengers.

A channel emulator can simulate all the environmental conditions and interlinks of 5G NTN use cases, end to end. Simulating a whole network of devices enables the comparison of hardware variants and software versions during development (Figure 3). A channel emulation test setup also helps compare devices from different vendors objectively, while integrating full solutions during the development process.

Creating the scenario data is probably the most challenging part of the testing process for satellite networks and SATCOM links. Test platforms that provide tools for creating basic conditions and support third-party tools help reduce this challenge.

diagram of Keysight's PROPSIM channel emulatorFigure 3 Keysight’s PROPSIM channel emulator can simulate a network of devices and interlinking subsystems.

The focus on 5G NTNs is growing. These networks will improve existing applications and enable many new ones. 5G NTNs will boost mobile broadband services and enable massive machine-type communications (mMTC). Their impact will be far-ranging, spanning various industries, including transportation, public safety, energy, and agriculture. 5G NTNs will also bring challenges, though, with latency and greater complexity topping the list. Addressing these challenges will require test solutions that provide comprehensive simulation capabilities and facilitate scenario creation.

For more information on this topic, including live simulations, you can view Keysight’s webinar 5G Non Terrestrial Networks – Overview & Focus on Satellite Link Simulation, hosted on Keysight’s Assess 5G Real-World Performance page or visit Keysight’s space and satellite page.

This article was originally published on EDN.

Jessy Cavazos is part of Keysight’s Industry Solutions Marketing team.

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