Exclusive Interview: PNT by Other Means

July 11, 2023

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Xona Space Systems demonstration satellite tests
Image:  Xona Space Systems

For the cover story of the July 2023 issue of GPS World magazine, Matteo Luccio, editor-in-chief, sat down with Jaime Jaramillo, Director of Commercial Services at Xona Space Systems, Paul Crampton, Senior Solutions Architect at Spirent Federal Systems, and Jan Ackermann, Director of Product Line Management at Spirent Communications, to discuss complementary PNT.

It has been said that “the only alternative to a GNSS is another GNSS”. Your website’s homepage claims that Xona will be “the next generation of GNSS.” Will it provide all the positioning navigation and timing services that the four existing GNSS provide?

Jaime Jaramillo: The answer at a high level is “Yes, it will provide all the services that legacy GNSS provides and more.” Xona is developing a dedicated constellation of PNT satellites in Low Earth Orbit — this allows us to provide PNT signals and service with significant improvements to precision, protection, and power compared to what’s available today. Xona’s service, called PULSAR, is designed to meet a variety of commercial and modern applications that have been seeking performance improvements.

So, the short answer to my question is, “Yes. All of that, and then some.”

Jaime Jaramillo: Yes, absolutely. Traditional GNSS constellations provide tremendous value to the world today, though we’ve seen market demand signals for even higher performance PNT and that we intend to deliver on.

How many satellites and orbital planes will the full constellation have?

Jaime Jaramillo: The target is approximately 300 satellites. That will include several spares. There will be a diverse set of orbital planes and a combination of polar and inclined orbits.

When all the satellites are up, their locations and broadcast frequencies will be public, right? They will have to be disclosed to various regulatory bodies.

Jaime Jaramillo: You hit it on the head. Because we’re in the process of going through regulatory approvals for the full constellation, we can’t talk a lot about our frequencies and a lot of the specifics publicly though this will change over time.

Roughly, when do you expect to achieve initial operational capability (IOC)? And when you expect to achieve full operational capability (FOC)?

Jaime Jaramillo: As you can imagine, it is expensive to put up all 300 satellites — we’ll have a three-phase roll-out approach. Our target is to launch our next satellites at the end of 2024. In our first phase, we’re going to offer services beginning in North America and Europe that only require one satellite in view — for timing services and GNSS enhancements. IOC will be achieved in 2025. Then, as we roll out to phase two with more satellites in view, we’ll be able to start to offer positioning services in mid-latitudes. As we move to phase three, the service will provide even higher-performance PNT globally, and the services’ ability to operate independently from GNSS. We also designed the constellation with polar orbits to provide much better coverage in the polar regions which will be an improvement over what GNSS provides today.

With climate change and more traffic through the Arctic, that’s going to become more important.

Jaime Jaramillo: Exactly. When we talk to potential customers today, that question comes up.

When do you expect to complete your constellation?

Jaime Jaramillo: Our target for full operational capability is 2027.

So, two or three years to fill out the constellation.

Jaime Jaramillo: We have basically locked down our signal and system architecture. Now, it’s a matter of building out the ground segment and launching satellites on schedule. There are several factors at play here, but those are the targets that we have today.

Speaking of launch, who will launch your satellites?

Jaime Jaramillo: That decision will depend on the satellite manufacturers with which we proceed. But the demo satellite that we have in space was launched last year in May on a SpaceX Falcon 9 rocket.

What is your business model? Will you have different tiers of service? Will your rate structure enable mass adoption?

Jaime Jaramillo: We are targeting both mass market applications and high-performance ones. LEO brings many benefits in comparison to MEO in just about every industry to which it can be applied. Our business model supports industries that prefer a lifetime fee, as well as ones that prefer recurring subscriptions. We’ve also designed PULSAR with different performance tiers to support a wide variety of customer needs.

What would be the differentiators between the different tiers?

Jaime Jaramillo: The PULSAR base service will include timing and positioning from Xona satellites. We have some in-band capabilities to broadcast additional services, such as GNSS enhancements, enhanced security features, and signal/service integrity. The integrity service will verify that the signal has a certain level of performance thresholds. Critical applications that need certain levels of performance will be able to receive the signal. If it drops below certain performance thresholds, we will flag that to the device so that it knows that, even though it is receiving a signal, it should not continue to use it due to signal degradation.

With legacy GNSS, satellites in MEO broadcast signals to receivers. There’s no need for two-way communication and, anyway, transmitting to the satellites would require too much power. With LEO satellites, however, you need a lot less power from the ground to talk to the satellites. Would two-way communication benefit certain applications?

Jaime Jaramillo: The initial service will not have two-way capabilities. However, we are leaving room in the signal and hardware designs to potentially offer that in the future.

Your business model is the exact opposite of the gift from U.S. taxpayers to the world that is GPS.

Jaime Jaramillo: Agreed that GPS is one of the greatest gifts US taxpayers have given to the world. While similar in function, GPS and Xona have different mission sets. As a commercial company, we have a mandate to listen to the commercial world’s needs and address them in a cost-effective manner. The world is evolving much faster than current GNSS can improve. This forces commercial industries to design around satnav limitations and use other navigation technologies that may not be as scalable or cost-effective.

Who will build the receivers? Do you expect that “if you build it, they will come”?

Jaime Jaramillo: Xona has established relationships with many of the receiver manufacturers out there. What’s publicly announced is that we have a strong relationship with Hexagon | NovAtel. They have been supportive of us for a long time now and are very advanced in their development and support for our signals. Some interesting announcements were made at JNC, with additional simulator and receiver manufacturer partners, with more to come. It’s going to be very exciting.

I assume that, at least for a transitional period of several years, we’re talking about adding Xona to the traditional GNSS on the receivers — just like, many years ago, we went from GPS-only to GPS and GLONASS, and then, more recently, to multifrequency receivers that use all the satellites in view. Would there be any reason, at some point, to have Xona-only receivers?

Jaime Jaramillo: We have designed our signals to make it as easy as possible for receiver manufacturers to support them. We designed the signal so that most receivers can support them with just with a firmware upgrade. Many receiver manufacturers ask the same question that you just asked. For certain applications, maybe Xona PULSAR-only makes sense or maybe it’s just GPS and Xona or GPS and some other constellation and Xona. There are initiatives looking at all these scenarios but most of them today are GNSS plus Xona as a complement.

It’s interesting what you said about firmware as opposed to needing new hardware.

Jaime Jaramillo: Correct. Given that we’re a startup we want to facilitate that as much as possible. For some of the advanced features — for example, enhanced signal security — the receiver needs more horsepower. So, it depends on the receiver. Some very optimized ASIC types of receivers may not have the horsepower for this.

Of course, that horsepower is increasing anyway…

Jaime Jaramillo: Exactly. And there are other techniques, right? For example, some IoT receiver manufacturers are offloading a lot of the processing power to the cloud. So, the device is designed to have some sort of network connection. Then, if it needs to do heavy processing, it can do that in the cloud. That can be done in different ways. For future applications, some receiver manufacturers are looking to potentially add this capability to next generation receivers.

Of course, the cloud introduces some lag…

Jaime Jaramillo: Right. It depends on the application. If it’s an IoT device or an asset tracker, maybe it’s not mission-critical. It just depends on the application.

What markets or applications are you targeting first?

Jaime Jaramillo: Timing is a big area of focus for us for initial applications. The precision agriculture, construction, and surveying markets are on the cutting edge of GNSS technology and are seeking improvements to their existing capabilities as well. We’re in discussions with players in high-volume markets that see a lot of potential even in the initial PULSAR phases as well.

Will the timing you provide be good enough for cell phone base stations? For television broadcasts? For financial transactions?

Jaime Jaramillo: Our patented system architecture will provide better timing accuracy than what GNSS provides today. One of its key pieces is that our satellites are designed to use GNSS signals, inputs from ground stations, and from other Xona satellites via cross-links for timing reference. Satellite clock and ephemeris will be updated very frequently which enables much higher accuracies.

That raises a critical question, especially in the context of complementary PNT: will your satellites have their own atomic clocks or will they rely entirely on GNSS? If the latter, any problem with GNSS would also affect your system.

Jaime Jaramillo: This was one of the key points that we kept in mind when we architected the constellation. Each Xona satellite uses timing inputs from a variety of sources (GNSS, ground, and other Xona satellites). If GNSS degrades or is removed entirely, the PULSAR service can continue to operate in this GNSS-independent mode indefinitely. In this scenario, the PULSAR service performance will degrade a bit since the number of quality timing inputs are reduced but can still meet about the same level of performance that GPS provides today.

The devil’s in the details. What kind of frequency standard will be on the satellites? How fast will their time degrade? How long will it remain sufficiently accurate for certain applications?

Jaime Jaramillo: I know where you’re going because I come from the timing industry. Since we’re a commercial company, one of the goals of the constellation design was to keep the cost of the satellites themselves as low as possible, so that we can deploy them at a low cost. We will leverage the very high-quality atomic clocks in GNSS satellites and ground stations in which governments have already invested. The type of clock that we use costs much less to keep the satellite cost down. The way to discipline these clocks properly is by updating them on a more frequent basis than traditional atomic clocks. This is done through the many inputs from GNSS, adjacent satellites, and the ground.

If GPS goes down entirely, we’ll have bigger problems. Your system would continue to work and, even if degraded, will be a lot better than nothing. Your architecture, however, leaves room for people to say that we also need ground-based systems.

Jaime Jaramillo: That’s a really good point. The idea of having another LEO-based constellation is to take advantage of what can be done in LEO for GNSS. It’s not intended to replace ground-based systems or alternative systems. If you want the most resilient time and position, you need to use a combination of everything. GNSS alone will not give you the best combination. We always like to say that we’re complementing GNSS.

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

Jan Ackermann: 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.

Jan Ackermann: 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.

Jaime Jaramillo: 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.

Jan Ackermann: 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?

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

Jan Ackermann: 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.

Paul Crampton: 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.

This article first appeared on

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