PNT by Other Means: Spirent

An exclusive interview with Paul Crampton, Senior Solutions Architect, Spirent Federal and Jan Ackermann, Director, Product Line Management, Spirent Communications. For more exclusive interviews from this cover story, click here.

Jan, what is the role of simulation in building a new GNSS with a very different constellation and very different orbits than existing ones?

J.A.: Before the Xona constellation or any other emerging constellation has deployed any satellites, simulation is the only way for any potential end-user or receiver OEM to assess its benefits. Before you can do live sky testing, a key part of enabling investment decisions — both for the end users as well as the receiver manufacturers, and everybody else — is to establish the benefits of an additional signal through simulation. Once it’s all up there and running, there are still benefits to simulation, but then there’s an alternative. Right now, there really isn’t an alternative to simulation.

With existing GNSS, you can record the live sky signals and compare them with the simulated ones. It’s a different challenge when it’s all in the lab or on paper.

JA: Yes, but it is not an entirely novel one, at least to us at Spirent. We went through it with other constellations and signals -for example with the early days of Galileo. It’s often the case that ICDs or services are published before there is a live-sky signal with which to compare them. So, we do have mechanisms in terms of first generating it from first principle, putting out the RF, running tests with that RF, and then seeing that what we put out is actually what we expect based on our inputs and the ICD. Obviously, we always work off the ICD, which is essentially our master. Then, a lot of work needs to happen to turn what’s written in the ICD into an actual full RF signal, overlay motion, and all those things. So, we have a well-established qualification mechanism to make sure that whole chain works for signals when we don’t have a real-world constellation.

Another very important check is when you work with some of the leading receiver manufacturers who have done their own implementation and you bring the two things together and see if they marry up. Then there’s always a bit of interesting conversation happening when things don’t line up, but we have a lot of experience in resolving that. So, there’s the internal (mathematical) validation of things — which we do internally, before we bring something to market — and then there is validation with partners, be they the constellation developer or a receiver manufacturer – or both.

JJ: Then, one step further from the receiver manufacturers, what we call the OEMs, want to validate that the receiver is doing what it’s supposed to do. The best way to do that is with a simulator. You can try to get a live sky signal, but it can be difficult. You must get on a roof. It may not have an optimal environment for that. The best way to prove that in a controlled environment is with a simulator. Spirent works with two levels of customers: first, the receiver manufacturers, then all the application vendors or OEMs that use those receivers.

JA: What we’ve done with the SimXona product recently follows very closely along those lines. First, we did validation ourselves. Then, we worked in a close partnership with Xona for them to certify that against some of their own developments. So, we follow that same proven development approach. It’s just that, in this case, the signal comes out of a LEO.

What is the division of labor here between Spirent Communications and Spirent Federal? In particular, which device comes into play with Xona?

PC: Spirent Federal has provided support to Xona but the equipment is the COTS equipment provided from the UK by Spirent Communications.

JA: This Xona product does not currently implement any restricted technology only accessible through Spirent Federal. That is very much the case, especially for the aspects of secure GPS, for which we have the proxy company, Spirent Federal. However, the SimXona product is a development through Spirent Communications, albeit heavily aided by Spirent Federal, from a technical perspective and others, but there are no Spirent-Federal-specific restricted elements to SimXona or the current Xona offering.

PC: If we ever had to go into a U.S. government facility to demonstrate SimXona or to sell it to them, that would be Spirent Federal that would be involved.