A simulation perspective on supporting GPS modernization

Q & A with Roger Hart, Director of Engineering, Spirent Federal Systems. Read more from this cover story here. 

Why do you see the need to modernize GPS?

For many lay users, global navigation satellite systems (GNSS) are simply there, reliably guiding them and their systems to do the right thing in the right place at the right time. But with its vulnerabilities, we cannot take GNSS — GPS specifically — for granted, and it cannot remain static. Its ubiquity in commercial and defense applications demands ongoing improvements to signal quality, diversity, availability, and assurance. The GNSS signal space is increasingly contested, navigation warfare is common, and the risk to civilians and warfighters increases. For those of us focused on defense, we see the growing array of threats steadily ticking upward in novelty and number.

We applaud the ongoing efforts by the U.S. Space Force and Air Force to modernize the GPS space segment, control segment, and user equipment. GPS-contested and -denied environments are here to stay, so we must hone GPS as a tool for both the military and civil user.

Spirent’s flexible SDR-based GSS9000 Simulator supports
GPS modernization efforts. (Image: Spirent Federal Systems)

How is Spirent Federal supporting modernization efforts?

In short, by providing deterministic simulation for future signals and capabilities not yet in theater. Regional Military Protection (RMP) is a recent example. RMP is a nascent anti-jamming capability that will be available on GPS III Follow On (GPS IIIF) satellites. RMP provides military users with a steerable, narrow-beam M-code signal that greatly amplifies the power over a defined geographical area. According to the GPS IIIF satellite manufacturer, Lockheed Martin, RMP can provide up to 60 times greater anti-jamming support. This allows U.S. and allied forces to operate with accuracy and resilience much closer to interfering sources than with legacy signals. GPSIIIF satellites with RMP are in production, and the latest publicly forecasted launch date is FY2027. With Spirent’s software-defined-radio-based simulator’s ability to support RMP simulation, modernized GPS user equipment (MGUE) can be tested and integrated with RMP early in the design phase before live-sky signals are available. Adaptive antennas, other constellations, encrypted signals, and non-RF sensors can also be tested with RMP. Coupled with this, the ability to simulate a wide range of edge cases during development enables superior performance in the real world.

Image: U.S. Space Force

And beyond RMP?

Low-Earth-orbit (LEO) constellations have been a focus for several years as we look to next-generation alternative positioning, navigation and timing (PNT) methods to complement GPS. We have developed LEO simulators for both the military and commercial sectors, including modeling tools that simplify the generation of large LEO constellations with high-fidelity orbital dynamics, delivering greater realism for applications that have no margin for error.

As GPS modernizes, there is a growing movement toward software-defined radio (SDR) architectures for both receivers and transmitters. Flexible SDR-based simulation encourages experimentation: on the same platform, applications can range from standard GNSS signals to entirely new constellations and RF modulations, including interference threats. Simulation of RF signals can be done in concert with inertial and other non-RF sensors, and deterministic architecture ensures that performance is maintained.

Another focus is on spoofing — creating tools to support defense in their efforts to harden GPS. One of the latest technological advancements in simulation is an “augmented reality” range capability: the device under test (DUT) on a moving aircraft or land vehicle is attached to a portable simulator. The DUT receives live-sky signals from the antenna on the vehicle but also receives additional spoofed signals injected by the live-sky-synced simulator.* The DUT’s resilience to the spoofed signals can then be analyzed and hardened against future spoofing attempts. Without the difficulties of setting up an open-air test, the real-world dynamics are employed in the test, heightening realism — and the simulated signals augment it.

*It is the sole responsibility of the user to obtain appropriate permits.