July 9, 2024
Ricardo Verdeguer Moreno
The ever-growing reliance on PNT technologies, and the emergence of new threats, means we need more sources of PNT to keep receivers robust and resilient.
There are plenty of new sources to choose from, from PNT constellations in Low Earth Orbit (LEO) like Xona PULSAR, to Locata’s ground-based service, which offer independent backup to GNSS.
But the proliferation of new PNT sources can create challenges in lab testing. Scenarios involving different signals, sensors and threat sources can be difficult to define realistically, and sometimes require multiple simulators which have to be synchronized.
Hosted by Inside GNSS, Spirent recently hosted a webinar that explored:
Cathryn Mitchell, Professor at University of Bath (UK) and Royal Society Industry Fellow, kicked off the webinar by looking at the key drivers for alternative and complementary PNT. These could be summarized as:
Professor Mitchell then explored the options available to integrators, including established technologies like inertial sensors through to planned low Earth orbit (LEO) PNT constellations and ground-based networks.
Bryan Chan, Co-Founder, Strategy and Business Development, Xona Space Systems then introduces the Xona PULSAR constellation.
PULSAR is a LEO constellation that will deliver PNT services to enabled devices and systems. Currently under development, Bryan gives an update on the current status and the forecasts for availability and for precision levels and accessibility. Spirent recently announced the first certified provision of PULSAR production signals from its suite of high-performance PNT simulation systems.
With options available, new technologies forthcoming, and demands on PNT multiplying, developers are faced with a series of challenges.
These are exactly the challenges that Spirent is addressing with PNT X—the world’s most advanced simulator platform. If you’re looking to incorporate alternative and complementary signals into your test scenarios, here are some of the benefits that PNT X can deliver.
Many of today’s mission-critical scenarios involve complex RF environments that combine multiple GNSS signals, threat waveforms, sensor inputs and signals of opportunity.
To reflect this increasing complexity, PNT X is the first simulator to enable up to 640 independent signals to be generated simultaneously from the same unit, with no loss of performance. PNT X supports all GNSS constellations and frequencies as standard, additional PNT signals, and custom waveforms defined by users.
Additionally, our industry-leading 2 kHz hardware update rate means signal simulation can match the trajectories of very fast-moving vehicles, ensuring a realistic signal environment for high-dynamics scenarios. And an ultra-low 2ms latency and up to 10 Gbps Ethernet connection keep the simulator tightly synchronized with other units in a hardware-in-the-loop (HIL) test setup.
The potential for LEO-based PNT services is huge, and a lot of exciting developments are happening in this space. Companies like Xona Space Systems are showing the way, and PNT X is the first simulation platform to include native support for Xona PULSAR production signals. Developers can use the SimXona tool to generate high-fidelity PULSAR signals alongside GNSS in any scenario.
Spirent has closely considered the needs of LEO PNT users and constellation developers in the design of PNT X. As well as the out-of-the-box PULSAR support, there is also the capability to inject custom LEO signals as I/Q files and generate the RF coherently with other signals in the scenario.
PNT X also allows developers to modify a range of low-level RF signal parameters such as modulation type and navigation data.
For those developing new LEO constellations, PNT X also offers unrivalled LEO satellite orbit modeling capabilities, ensuring that the unique physics of LEO orbits, such as drag coefficients and enhanced Doppler effects, are realistically applied to the space vehicles (SVs) in the model.
One of the key capabilities of PNT X is its support for user-defined I/Q files. Future signals, custom signals, interference waveforms and other signals without published ICDs can all be injected into the simulator as pre-recorded I/Q files, ensuring they stay confidential or classified.
The major step forward here is in its handling of I/Q files. Previously, the simulator could only replay the signal as recorded. Now, with the new, patented SimIQ Spatial Awareness capability, PNT X automatically superimposes realistic effects onto the pre-recorded signals, relative to the motion and trajectory of the device under test (DUT). Power levels, Doppler offsets and signal delay effects are applied to all I/Q-defined transmitters, bringing new realism to test scenarios.
GNSS signals have traditionally operated in the 1–2 GHz (L-band) frequency range. However, a growing number of signals are transmitting in the 2–4 GHz S-band range, including India’s regional NavIC constellation and Locata’s ground-based GNSS augmentation service. S-band signals will also be an important component of NASA’s PNT architecture for planned lunar missions. PNT X introduces native S-band support for the first time, with internal upconverters to generate S-band signals at RF.
Inertial measurement units (IMUs) are an essential component of many robust PNT systems, enabling continued navigation in RF-denied environments. PNT X supports the emulation of inertial sensors, using the SimINERTIAL suite to model the sensors and generate their outputs coherently with the other signals in the scenario, as well as the trajectory that has been modeled.
Understanding how real-world obstacles will affect signals is a key consideration in PNT testing. Another ground-breaking feature of PNT X is 3D terrain modeling: the ability to import 3D maps into the simulator to evaluate the performance of signals or user equipment in real-world environments.
Both ground-based and space-based transmitters can be placed into the 3D environment to measure the impact of obscuration, diffraction and multipath on signal transmission and reception. This isn’t just possible for GNSS signals, but for any signal generated natively or from external I/Q files—from LEO PNT and interference transmitters to ground stations and spoofing equipment.
This represents a significant leap forward from statistical obscuration and multipath models, and is a particularly powerful capability for NAVWAR test scenarios, as it enables complex adversarial RF environments to be realistically created in the lab rather than having to book an outdoor test range.
As the PNT landscape gets more complex, developers need to be able to test with more signals and waveforms—and have high confidence in the test results. PNT X is designed for the world beyond GNSS, enabling the broadest-ever range of signals to be generated coherently from a single unit.
To learn more complementary and alternative PNT signals, and how PNT X supports them, watch the on-demand webinar: Beyond GNSS: An Introduction to Alternative PNT Solutions.
