CMX500 for non-terrestrial networks (NTN)

Our solution for NR-NTN testing

NR-NTN testing presents challenges that go beyond those encountered in traditional terrestrial networks. These challenges arise primarily from the vastly different operating environment and the dynamic nature of satellite-based communication.

Challenge #1: Dynamic channel conditions and realistic emulation

One of the major challenges is emulating the radio channel as it would appear via satellite. NR-NTN satellites operate primarily in the lower earth orbit (LEO) because it offers lower latency and higher data transmission rates. LEO satellites move at very high speeds relative to user equipment (UE). This causes rapidly changing Doppler shifts in the signal frequency. In addition, the distance from the satellite to the UE introduces propagation delays that also change with satellite movement. The long distance also causes signals to experience free-space path loss, which results in a lower signal-to-interference-plus-noise ratio (SINR) on the UE side.

The CMX500 features advanced channel emulation to provide realistic test scenarios:

• Multiorbit support, covering LEO, MEO, GEO and GSO, as well as both inter- and intra-orbit handovers
• Multiband support to ensure reliable access to satellite spectrum bands – especially important because the frequency specifications of a satellite cannot be changed once it is in orbit, and spectrum efficiency must be improved within the allocated spectrum
• Internal 3GPP RF fading and channel emulation that simplify testing under realistic conditions and allows for a smaller device footprint
• Dynamic Doppler shift emulation for both uplink and downlink signals
• Variable propagation delay and round-trip time (RTT) emulation, with the ability to assess the impacts of timing advance, HARQ retransmission process and overall latency
• NTN-specific fading profiles that incorporate effects such as atmospheric attenuation, rain fading and combined atmospheric/terrestrial fading
• High path loss and low SINR emulation

Challenge #3: Network architecture and integration complexity

NTN is designed to complement terrestrial networks, providing service in unserved areas. Ensuring seamless interplay, synchronization and handover between NTN and terrestrial infrastructure is a major challenge that demands sophisticated conformance testing.

The CMX500 has advanced network emulation functionalities and support for interoperability testing:

• Base station (gNB) and core network emulation to enable comprehensive end-to-end testing
• Support for 3GPP NR-NTN specifications for testing protocol stack compliance for both the UE and the network infrastructure
• Testing for integration and interoperability between NTN and terrestrial network components, ensuring service continuity
• Simulation of both transparent (bent-pipe) and regenerative (on-board processing) satellite payload architectures to optimize network flexibility, resilience and readiness for future demands, allowing operators to choose the right solution based on specific use cases
• Ground station network simulation to assess the impact of ground stations and gateways on overall system performance

Challenge #4: Measurement and analysis

NR-NTN testing presents challenges for measurement and analysis. The high velocities of satellites, especially in LEO, introduce quickly changing Doppler shifts and propagation delays. This dynamic environment hinders reliable measurements of key performance indicators (KPI), such as throughput, latency and signal-to-interference-plus-noise ratio (SINR). In addition, the diverse orbital paths and varied terrestrial conditions lead to unpredictable fading profiles. Consequently, identifying the root cause of performance degradation is a complex task and requires robust, real-time data acquisition and sophisticated analysis tools to accurately correlate network impairments with specific satellite positions or UE movements.

The CMX500 features advanced measurement analysis capabilities:

• RF measurement support on both transmitter (TX) and receiver (RX) sides, allowing for a wide variety of measurements, such as RX BLER and TX Multi Eval
• Configuration of certain frequency bands for communication with a SAT gateway, according to factors like signal quality, bandwidth requirements, regulatory constraints or specific application needs
• Support for connection to an IP-based backend service, such as the internet or a company network, to enable testing of IP-based applications, such as video streaming, video calls, XR and gaming

Challenge #5: User-friendliness and scalability

Simulating dynamic elements requires intuitive tools that can visualize and manage these intricate parameters without overwhelming the user. Furthermore, the need to define, modify and integrate diverse satellite constellations, along with simulating numerous UE locations, requires highly adaptable and automated test environments.

The CMX500 has many features for an intuitive user experience:

• Intuitive, web-based user interface that visualizes the deployed network and relevant parameters, such as the delay, elevation and Doppler effect
• Integrated TLE editor that allows you to define and add your own constellations via WebGUI
• Constellation Insight Tool that combines UE location information with the constellation configuration information to deploy a simulated network
• Protocol testing with XLAPI, the Python interface of the CMX500, verifies that a protocol can “talk” to the 5G core network