Matteo Luccio, editor in chief of GPS World magazine, interviewed Ricardo Verdeguer Moreno, lead product manager at Spirent Communications, for the July cover story on complementary PNT. This article first appeared in GPS World magazine and on GPSWorld.com.
Spirent Communications recently introduced a new GNSS and PNT simulation system, PNT X, which brings together L-band, S-band, and alternative navigation signals, as well as Regional Military Protection (RMP) support. I discussed the new product with Ricardo Verdeguer Moreno, lead product manager for the company’s positioning technologies business unit.
PNT X is the sixth generation of our PNT simulation platforms. It builds on the software-defined architecture that we have on the GSS9000, addressing all the changes in the industry in the decade since we launched it. The core focuses for our development remained system performance, signal fidelity, solution scalability and configuration flexibility. There are also different features that further enhance the realism of our solutions. Additionally, with the future in mind, we have tried to enable testing using as many of the available signals of opportunity as possible, alongside GNSS and emulated inertial outputs.
Some of the emerging use cases driving this need for change are demanding more signals and a wider variety of them. For instance, LEO-PNT in concert with GNSS — and particularly when you add in reflections for multipath — can demand a high density of independent signals.
In addition, many applications are beginning to look beyond L-band, not only for regional systems such as NavIC or KPS, but also for applications such as lunar PNT. That’s why we have made a seamless integration of S-band frequency upconverters into our system.
First and possibly foremost is NAVWAR. Jamming and spoofing threats have been growing in prevalence and variety in recent years. With conflict and tensions around the world, and with the greater reliance on PNT from both defense and civil applications, the ability of developers to validate systems against threats in the lab needed to be enhanced. Several of the advances of PNT X have been designed to achieve this.
One of them, and one of the main changes in our offering, is that we are introducing 3D terrain modelling within the GUI. Previously, simulations using just the GSS9000 were 2D and did not enable users to bring realistic multipath and obscuration signatures into the test. With 3D terrain modelling, users can define the environment in which their vehicle or device is, or is moving through, and this environment will interact realistically with all signals present in the scenario. This can include GNSS, LEO PNT, novel ground-based and space-based PNT signals, jammers, spoofers and I/Q-defined transmitters.
If you imagine your receiver somewhere in a landscape or a city, and there are jamming beacons somewhere in your vicinity, these could impact the performance of your system. However, the performance of your system will also be impacted by the obscuration of GNSS signals, and of the jamming signals. So, it enables you to convert a pure or ideal GNSS simulation, in which you are considering all the signals that are around you, into a realistic one that only considers the ones that you would see in the real world. We want our users to be able to bring as much of their testing into the lab as possible, and this enhanced realism helps to achieve that.
Some of the testing we’ve done on this, in partnership with our customers, has yielded some very interesting results.
In the past few years, some customers have been dealing with special interference waveforms against which they want to harden their systems. They are starting to use I/Q data to generate those signals in our system without us getting directly involved. The problem is that the content you have in the I/Q file is what gets used to generate RF. Imagine that you have a receiver that is moving around the transmitter. The relative movement will cause some Doppler offsets, signal delays, and power level offsets. By using pre-recorded data, you lose all that information because you cannot consider the dynamics of the scenario.
Our solution to that problem is SimIQ spatial awareness. PNT X takes the I/Q, analyzes the scenario and the relative movement between both entities and then automatically applies the right effects to the signal. So, the RF that you get when you are testing your PNT system fully matches scenario dynamics.
Because of features like this, it would be fair to think of PNT X as a platform or a tool for developers and testers. When users want to break new ground — test against new threats or utilize new sources of PNT — they do not have to wait for us to implement those signals. They can define the raw waveform and PNT X will apply all our years of expertise to add realism to that waveform.
This has obvious applications in the NAVWAR domain, but it also helps to future-proof both the PNT X and our customers’ labs. As we start to look beyond GNSS for added robustness and resilience, and the continuity needed for autonomous platforms, PNT X users can iterate, evaluate, and make informed decisions far of the additional PNT sources coming into operation!
Thinking about alternative and complementary PNT, and even about new communications technologies in general, LEO is a key focus area. PNT X offers a toolset to enable both the creation of high-performance LEO constellations and the downstream testing of devices utilizing new LEO PNT signals.
We have built in highly realistic LEO orbits for modelling the constellation and for testing the devices using it. We’ve incorporated factors such as drag coefficients, mass, and cross-section area to deliver the most realistic solution available. For testing applications that can’t feasibly be field-tested, lesser solutions just aren’t viable. For instance, utilizing MEO models for LEO testing just bakes error into the test scenario before you even start.
In addition to modelling the orbits of the constellations, we are enabling the generation of novel LEO PNT signals. This includes the first and only Xona-certified ICD implementation for generating Xona Space Systems’ PULSAR signals, meaning chipset, receiver, and device developers can utilize the full LEO constellation, using the most precise representation of the real thing, years before it is at FOC.
We have also sought to enable the development of other PNT systems. PNT X enables the generation of novel PNT signals using two different methodologies. Users can either inject new signals via I/Q data files, or they can use our FLEX software feature to modify existing L-band and S-band signals. In this respect, as in many others, the PNT X represents a platform or a toolkit for developers. We’re offering the opportunity to use our established expertise and precision to push boundaries, and to do so in the most simple and user-friendly fashion. It’s a blend of realism and control that hasn’t existed before in PNT testing, and it can deliver key advantages to the user — in terms of time saved in the field, of being able to iterate and test rapidly and reliably, and of assessing and implementing new technologies ahead of the market.
In addition to enhancing performance and realism, flexibility is a key goal for us. Take, for example, Locata. With the PNT X, if you have I/Q files of Locata signals, you could simply define ground transmitters in the scenario and assign the I/Q files to each of them. Then, we have the SimIQ spatial awareness feature, so that, no matter what the content of that I/Q is, even if it’s a “pure” waveform of Locata signals, you can start moving around and traveling with any sort of vehicle in our scenario and PNT X automatically applies the realism — all the different signal effects — that are happening because of that movement. It really simplifies testing.
Furthermore, Locata signals are in the S-band, so we can natively generate them with our upconverters. Locata is simply a good example because it mixes all these features and capabilities. Because it’s a ground-based system as well, you can use terrain modeling to locate your transmitters and to understand how performance would be impacted by realistic multipath and obscuration effects.
