As new satellites launch and the non-terrestrial network (NTN) ecosystem matures, expectations for ubiquitous coverage and profitable new services grow. However, the road to achieving these goals is paved with significant technical challenges that extend far beyond the already-complex demands of terrestrial networks. There are unique and complex challenges in testing NTN systems as well as test solutions that revolutionize testing workflows to accelerate NTN development and deployment.

The ongoing evolution of 5G is paving the way for transformative connectivity solutions. NTNs are at the forefront of this innovation and gain relevance, especially in the context of future 6G systems. By leveraging satellites and high-altitude platforms, NTNs promise to extend connectivity to remote and underserved areas, enhance global IoT applications, and support emergency communication services. Flagship smartphones already incorporate basic NTN connectivity for emergency messaging, and fledgling NTN services have been deployed in disaster response scenarios, such as hurricane recovery efforts in the United States.

CMX500 one-box tester (Source: Rohde & Schwarz)

The complexities of NTN testing

Testing NTNs is a far more intricate endeavor than terrestrial network testing. The unique characteristics of satellite-based communication introduce a variety of challenges, all of which must be addressed to ensure reliable and standards-compliant operations.

Dynamic satellite channels

Unlike terrestrial networks, NTN systems must contend with a constantly changing radio environment. Low Earth orbit (LEO) satellites move at extreme velocities relative to user equipment (UE) on the ground. This introduces dynamic Doppler frequency shifts, variable propagation delays, and significant path loss. These factors make channel emulation far more complex, as they must accurately replicate real-world satellite conditions in a controlled test environment.

Multi-orbit and multi-band complexity

NTN services operate across various orbital configurations, including LEO, medium Earth orbit, and geostationary orbit. Each orbit type presents unique challenges in terms of handovers, latency, and coverage. Additionally, NTNs utilize multiple frequency bands, including both sub-6-GHz and higher frequency range 2 (FR2) bands, with bandwidths of up to 200 MHz. Unlike terrestrial networks, FR2 transmissions in NTNs must use frequency-division duplex rather than time-division duplex, which adds another layer of complexity.

Handover and mobility challenges

Maintaining seamless connectivity in NTNs requires frequent handovers between satellite beams and even between satellites in different orbits. This is especially critical for LEO constellations, where each satellite has a small coverage area and moves quickly across the sky. Effective handovers depend on precise real-time ephemeris data, which tracks the positions and velocities of satellites and UEs. The challenges of mobility management are further compounded by the need to ensure interoperability between NTN and terrestrial network segments.

Long-duration testing scenarios

Simulating real-world NTN operations over extended periods introduces additional challenges. Manual deployment and handover configurations can lead to errors, inefficiencies, and delays. Testing must also account for complex scenarios, such as conditional handovers based on power levels, distance, or other factors, to ensure robust service continuity.

Comprehensive solution for NTN testing

A very user-friendly way to address the full spectrum of challenges associated with NTN testing is using a 5G signaling tester equipped with the necessary test functionality. The CMX500 one-box tester from Rohde & Schwarz, for instance, integrates multiple functionalities into a single platform, providing a complete, end-to-end test environment for realistic simulation and in-depth analysis of NTN devices and infrastructures.

To address different stakeholders in the NTN ecosystem, this test platform supports two key testing configurations.

Full satellite access network emulation

For device manufacturers, the test platform emulates the entire NTN architecture, including the satellite payload, gateway, and terrestrial core network functions. This enables comprehensive device testing against a fully simulated, standards-compliant NTN environment (see Figure 1).

Figure 1: Satellite access network emulation (Source: Rohde & Schwarz)

gNB and 5G core network emulation

For satellite network operators, the test platform can emulate terrestrial gNB and 5G core networks to validate live or emulated satellite components. This setup ensures compatibility between proprietary satellite infrastructures and standards-compliant cellular technologies (see Figure 2).

Figure 2: gNB and 5G core network emulation (Source: Rohde & Schwarz)

The CMX500 creates a high-fidelity digital twin of the live-sky environment, simulating satellite orbits, frequency bands, and impairments such as Doppler shifts, fading profiles, and propagation delays. It supports both transparent and regenerative payloads, facilitating full-stack conformance testing. Additionally, the one-box tester is equipped for testing emerging direct-to-cell (DTC) technologies, such as LTE-DTC, ensuring readiness for the next wave of NTN services.

Key features include:

• Channel emulation: Dedicated internal FPGAs handle channel emulation and signaling, eliminating the need for multiple instruments.
• Over-the-air testing: For higher frequencies, users can pair the test platform with an anechoic chamber and, if necessary, a robotic arm to test larger antenna arrays.
• Comprehensive RF and QoS testing: Extensive RF measurements and application-level testing over external IP networks validate real-world performance.
• Automation: The system supports automated workflows through the XLAPI Python interface and includes an AI-based ScriptAssist tool for efficient script generation.

Enhancing testing with software

A software tool called Constellation Insights Tool complements and enhances the capabilities of the test platform, providing visualization and management features for NTN testing. It addresses some of the most complex aspects of NTN testing, such as mobility management, satellite constellation behavior, and long-duration scenario simulations.

Visualization and scenario modeling

The Constellation Insights Tool enables engineers to visualize satellite constellations in real time, analyze coverage gaps, and observe satellite trajectories. Users can define UE locations, select predefined constellations, or create custom ones. The tool displays key fading parameters, including path loss, Doppler shifts, and signal delays, offering a comprehensive view of the link conditions.

Figure 3 illustrates the Constellation Insights Tool. The left side shows the configuration, while the right side shows the visualization. The orange line at the top shows the coverage for the simulation period (in this case, 300 seconds) based on the selected satellites (box below “Satellite Selection”). This allows engineers to see if there are any coverage issues at any point in time. Additionally, the tool visualizes the corresponding fading data of the selected satellite, providing further insights into signal quality and reliability. Engineers can import the selected satellites, along with the UE location and all other necessary information, into the CMX500 to be used there for network emulation.

Figure 3: Screenshot of the Constellation Insights Tool, showing configuration (left) and visualization (right) of a simulation period (Source: Rohde & Schwarz)

Automated deployment and handover

Manual testing of long-duration scenarios is time-consuming and prone to errors. The Constellation Insights Tool automates the deployment of satellite constellations and manages handover processes, reducing manual intervention and ensuring consistent results. Engineers can simulate complex handover scenarios based on real-world conditions, such as power levels or satellite positions.

Realistic mobility simulations

By incorporating precise ephemeris data, the tool enables realistic simulations of satellite and UE mobility. This is especially critical for testing scenarios involving LEO satellites, in which frequent handovers and dynamic impairments are the norm. Engineers can simulate hours of travel, complete with automatic satellite connections, to evaluate battery life, detect software defects, and identify subtle anomalies in handover logic.

Using real-world TLE files

By using real-world two-line element (TLE) files from existing satellite constellations, engineers can create highly realistic scenarios for testing devices and networks. For example, they can set a GPS location, select a satellite constellation, and simulate how many satellites would cover the area, complete with the correct number of moving cells and propagation paths.

This capability allows for robust testing of conditional handovers, mobility scenarios, and application-level performance, ensuring that NTN systems can meet the rigorous demands of real-world deployment.

The future of 5G NTNs

As 5G NTN services continue to evolve, they hold the promise of transforming global connectivity and enabling groundbreaking use cases. However, the complexity of these networks demands cutting-edge testing solutions. State-of-the-art testers like the CMX500 equipped with the necessary software like the Constellation Insights Tool provide a unified, end-to-end platform that empowers engineers to tackle the challenges of NTN testing head-on.

By enabling realistic simulations, automated workflows, and comprehensive analysis, these tools accelerate development, enhance quality, and ensure the reliability of NTN services. The future of 5G NTNs isn’t just on the horizon; it’s already taking shape.

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