LabSat 4 has been engineered to deliver ease of use, with saveable custom record settings and a web-based interface for effortless configuration. Its impressive file management capabilities, featuring 7.6TB internal storage and fast data transfer via Gigabit Ethernet and USB 3.0, meet high-volume data demands efficiently. Maintaining the compact size, portability, and cost efficiency of its predecessors, LabSat 4 is ideal for use both in the field and laboratory. Additionally, it integrates seamlessly with SatGen Simulation Software, enabling the creation of detailed GNSS RF I&Q scenario files based on custom trajectories, enhancing its utility for sophisticated GNSS signal testing.

Learn more.

This video is sponsored content by Racelogic.

<p>The post Introducing the LabSat 4 GNSS Simulator first appeared on GPS World.</p>

<p>The post ION GNSS+ 2023: Racelogic first appeared on GPS World.</p>

In which markets and/or applications do you specialize?

We originally designed our LabSat simulator for ourselves, because we supply GPS equipment to the automotive market. Then, we decided to sell it into that market, which is our primary market, for other people to use. That’s where we started, but it has moved on since then. We supply many of the automotive companies who use it for testing their in-car GPS-based navigation systems.

However, we’ve moved on to our second biggest market, which is the companies that make deployment systems for internet satellites, which use it for end-of-life testing. Several of our customers use it. That’s because we do space simulations, so we can simulate the orbits of satellites. That’s very useful when they’re developing their satellites.

We supply many of the major GPS board manufacturers — such as NovAtel, Garmin, and Trimble — when they’re developing their boards and testing their devices. We supply many of the phone companies — such as Apple and Samsung — and many of the GPS chip manufacturers — such as Qualcomm, Broadcom, and Unicom. More or less any company that’s into GNSS.

How has the need for simulation changed in the past five years, with the completion of the BeiDou and Galileo GNSS constellations, the rise in jamming and spoofing threats, the sharp increase in corrections services, and the advent of new LEO-based PNT services?

It all started off very simple, with just GPS, which was one signal and one frequency. We got that up and working very well and it helped us a lot. Then we got into this market. In the last few years, we’ve had to suddenly invent 15 new signals. We do two systems, really: one is a record-and-replay system. You put a box in a car, on a bike, in a backpack, or on a rocket, and you record the raw GPS signals; then you can replay those on the bench. That requires greater bandwidth, greater bit depth, smaller size, battery power, all of that.

The other is pure signal simulation. We simulate the signals coming from the satellites from pure principles. So, we’ve had to dive into how those signals are structured, reproduce them mathematically, and then incorporate that in into our software. That’s been 15 times the original work we thought it would be, but as we add each signal it tends to get a bit simpler until they add new ways to encode signals, and then it gets complex again. We’ve had to increase our bandwidth, increase our bit depth for the recording to cover all of these new signals.
Because our systems record and replay, they’re used a lot to record real-world jamming. In many scenarios, our customers will take one of our boxes into the field and record either deliberate jamming or jamming that’s been carried out by a third party. Then they can replay that in the comfort of their lab.

With regards to spoofing, we’ve just improved our signal simulation. So, we can completely synchronize it with real time. We can do seamless takeover of a GNSS signal in real time. We can reproduce the current ephemeris and almanac. If we transmit a sufficiently powerful signal, we can completely take over that device. Then we can insert a new trajectory into it. That’s a very recent update we’ve done.

If the complexity and amount of your work has gone up so much in the last few years but you cannot increase your prices at the same rate, what does that do to your business model?

It’s the same people that produce the signals in the first place, so they still have a job. However, as we add more signals and capabilities, we tend to get more customers as well.

Oh, so, you’re expanding your market!

Right, right.

Regarding some of the new PNT services being developed, how do you simulate them realistically without the benefit of recordings of live sky signals?

It is all pure signals simulation. You go through the ICD line-by-line and work out the new schemes. Here’s an interesting anecdote. Our developer who does a lot of the signal development is Polish and is also fluent in Russian. When we were developing the GLONASS signals, he was working from the English version of the GLONASS ICD. He said that it didn’t make any sense. So, he looked at the Russian version and discovered that the English one had a typo. When he used the Russian version, everything worked perfectly. He told this to his contacts at GLONASS and they thanked him and updated the English translation of their document. So, you are very, very much reliant on every single word in that ICD.

Are there typically differences between the published ICD and the actual signal?

No, no. Apart from the Russian one, which had a typo, they’re very good. For example, we’ve recently implemented the latest GPS L1C signal. My developer spent six months recreating it and getting all the maths right and the only way you could test it was to connect it to a receiver and hit “go.” It just worked the first time. He almost fell off his chair. The ICD in that case was very, very accurate.

Hope that Xona’s ICD is just as good.

Yeah.

Are accuracy requirements for simulation increasing, to enable emerging applications?

Yes, absolutely. No one can have too much accuracy. Everyone’s chasing the goal of getting smaller, faster, and more accurate systems. They want greater precision and better accuracy from their simulators, as well as a faster response. We do real-time simulators and they want a smaller and smaller delay from when you input the trajectory to when you get the output. Luckily for us, Moore’s law is still in effect, so, as the complexity of the signals and the accuracy requirements increase, computers can churn through more data. Luckily, we’re able to keep up on the hardware side as well, because much of our processing is done using software. Some companies do it in hardware and some companies do it in software. We concentrate on the software side of things.

Here’s another interesting anecdote from my Polish guy. He noticed that the latest Intel chips contain an instruction that multiplies and divides at the same time but that it wasn’t available in Windows. So, he put in a request with Microsoft for that operational code and they incorporated it into the very latest version of dotnet, which has improved our simulation time by 7%. I see little improvements like that all the time.

Are all your simulators for use in the lab or are some for use in the field? If the latter, for what applications and how do they differ from the ones in the lab? (Well, for starters, I assume that they are smaller, lighter, and less power-hungry…)

All our systems are designed to be used inside and outside the lab. They can all be carried in a backpack, on a push bike, in a car. We do that deliberately, because we come from the automotive side of things, so we have to keep everything very small and compact.

Besides automotive, what are some field uses?

Some of our customers have put them in rockets, recording the signal as it goes up, or in boats. We have people walking around with an antenna on their wrist connected to one of our systems, so that they can simulate smartwatches. There are many portable applications. We have a very small battery-powered version, which makes it very independent.

Are there any recent success stories that you are at liberty to discuss?

Our most exciting one is a seamless transition for simulation that we developed to replace or augment GPS in tunnels. We’ve been talking to many cities around the world that are building new tunnels. Because modern cars automatically call emergency services when they crash or deploy their airbags, they need to know where they are, of course. Cities need to take this into account when they are building new tunnels, which can pass over each other or match the routes of surface streets. Therefore, accurate 3D positioning in the tunnels has become essential. It requires installing repeaters every 30 meters along each tunnel and software that runs on a server and seamlessly updates your position every 30 meters. As you enter a tunnel, your phone or car navigation system instantly switches to this system. It’s been received very well because it’s mainly software and the hardware is pretty simple. We’ve brought the cost down to a fifth of the cost of standard GPS simulators for tunnels. So, we’re talking to several cities about some very long tunnels, which is very exciting.

<p>The post Faux signals for real results: Racelogic first appeared on GPS World.</p>

Image: Safran Federal Systems (formerly Orolia Defense & Security)

As the number of constellations, satellites, and signals has grown in recent years — especially in the past few years, with the completion of the BeiDou and Galileo constellations — simulator manufacturers have been challenged to keep up. Threats of jamming and spoofing also increased. Then, a few companies began to develop new positioning, navigation and timing (PNT) constellations in low-Earth orbit (LEO).

For the August 2023 cover story, I discussed these challenges and the prospect for the simulation industry with representatives of six companies: Safran Federal Systems (formerly Orolia Defense & Security), Racelogic, CAST Navigation, IFEN, Spirent Communications and Spirent Federal Systems.

Due to the limited space available in print, I was able to use only used a small portion of the interviews I conducted for our August cover story. For full transcripts of them see below:

• Full interview with Tim Erbes, Technical Director, Safran Federal Systems (formerly Orolia Defense & Security).
• Full interview with Julian Thomas, Managing Director, Racelogic.
• Full interview with Jürgen Pielmeier, Managing Director, IFEN.
• Full interview with Mark Holbrow, VP of Product Development, Spirent Communications and Roger Hart, Sr. Director of Engineering, Spirent Federal Systems.

<p>The post Online Exclusive: Faux Signals for Real Results first appeared on GPS World.</p>

Spirent’s GSS6450 record and playback system (RPS) used to record live-sky signals in an urban environment for testing in the lab.(Image: Spirent Federal Systems)

These are interesting and challenging times for the makers of GNSS signal simulators.

For decades, developers and manufacturers of GNSS receivers have needed to simulate the satellites’ signals to test receivers in their labs and in the field. Meanwhile, users of GNSS receivers for critical missions — such as military operations and rocket launches — have needed to simulate the exact conditions (the number of satellites in line of sight, the positional dilution of precision, etc.) at specific points in time and space.

As the number of constellations, satellites and signals grew — especially in the past few years, with the completion of the BeiDou and Galileo constellations — simulator manufacturers were challenged to keep up. Threats of jamming and spoofing also increased. Then, a few companies began to develop new positioning, navigation and timing (PNT) constellations in low-Earth orbit (LEO). Now, it is common for simulators to require several hundred channels.

I discussed these challenges and the prospect for the simulation industry with representatives of five companies:

• Tim Erbes, Technical Director, Safran Federal Systems (formerly Orolia Defense & Security
• Julian Thomas, Managing Director, Racelogic
• John Clark, VP of Engineering, CAST Navigation
• Jürgen Pielmeier, Managing Director, IFEN
• Mark Holbrow, VP of Product Development, Spirent Communications
• Roger Hart, Director of Engineering, Spirent Federal Systems

For the full transcripts of my interviews, click here. If you like this article, you will love the interview transcripts, which cover much more than I had room for here.

Legacy Constellations and New Ones

Simulator manufacturers cite a variety of challenges. According to Erbes, a big one is determining users’ requirements. “Often,” he said, “they can’t determine what the specs need to be. All they know is that they need it to work.” This is particularly true when mixing and matching receivers, IMUs, and components from different manufacturers, he pointed out.

For decades, there were only two GNSS constellations (GPS and GLONASS). A couple of years ago, two more came online (BeiDou and Galileo). Meanwhile, several regional augmentation systems were developed (SBAS, EGNOS, NavIC, QZSS and KASS), some of which may later grow into global systems. Now, new LEO-based systems are being developed. For simulator manufacturers, what was once clear “began to get fuzzy,” Erbes said. “If you ask members of our team right now how many constellations we support, you will not get a quick answer. We’re trying to be forward-looking and add everything that might be up there so lab users can develop and test.”

Multi-constellation simulation is a particularly challenging problem for groups that don’t have simulators, Erbes pointed out. “We have the advantage of having a software-defined architecture. We designed the software so that it is easy to add new constellations to it. Basically, once we’re given a proper interface control document (ICD), we’re only a couple of months away from a first draft implementation of that new signal. Then we iterate.”

LabSat 3 Wideband compact GNSS simulator. (Image: Racelogic)

In the past few years, said Thomas, Racelogic “had to suddenly invent 15 new signals.” It makes a record-and-replay system — “You put a box in a car, on a bike, in a backpack, or on a rocket, and you record the raw GPS signals,” Thomas said — and another system in which it simulates the satellites’ signals “from pure principles.” The latter, he noted, has been “15 times the original work we thought it would be. However, as we add each signal it tends to get a bit simpler until they add new ways to encode signals, and then it gets complex again.”

Spirent Communications’ technology, Holbrow said, focuses around “its dedicated SDR hardware platform and software simulation engine, which provide performance, scalability and flexibility, within an open accessible architecture. Close collaboration with our selected partners ensures the opportunity to support and integrate new and emerging PNT technologies through their tools, applications and hardware.” Two other aspects that have continued to grow in importance have been “increased realism and test automation,” Holbrow said. “Both are areas in which Spirent continues to prioritize and invest R&D dollars.”

Spirent “can enable the user with effectively an arbitrary waveform simulator or ‘sandbox’ to experiment with different modulation schemes, different chipping rates, codes, bandwidths and navigation data content,” Holbrow said. “The increasing number of signals that we can support multiplies the permutations and combinations of test cases that users can do,” Hart added.

Not every simulator user is equally interested in simulating all the existing and emerging constellations. Those in the U.S. military market do not use foreign signals, pointed out Clark. However, they may want to understand how those signals could impact their vehicle, platform, or individual receiver.

LEO-based constellations “have become a buzzword in the last year or so,” Clark said. Because CAST Navigation’s simulators are modular and use an FPGA-based design, “we can add different satellite constellations or satellite protocols to our system,” he said. “However, we don’t offer anything commercially yet due to a lack of an official ICD, or any kind of documentation that defines any of these new LEO-based signals.”

Today, said Pielmeier, all high-end RF simulators must support “all existing GNSS systems with all related signal components on all frequencies.” Additionally, to remain competitive, they must be kept “up-to-date with the new and continuously evolving GNSS signals.” He added: “Beyond the L-band signals, we are also fully supporting the S-band signals of the NavIC constellation.”

The increased request for precise point positioning (PPP) corrections service, Pielmeier pointed out, was the driver for IFEN to add the High Accuracy Service (HAS) PPP-correction capability on Galileo’s E6-B signal to its next release. “We expect further improvements here during the next few years, especially to cover the emerging needs of the PPP-RTK market.” The advent of LEO-based PNT services, he said, makes this “the most important driver for the next five years, extending the signal frequencies beyond the current L- and S-band signals, seeing new modulations, two-way transfer and many more topics.”

Jamming and Spoofing

Concern about jamming and spoofing has increased significantly over the past several years. These, however, are not new concepts for simulator manufacturers. “In a way, simulation is ahead of this state of the world,” said Erbes. “Spoofing is similar to simulation. So, we already know how to do that.” That could change, however. “If new requirements come up, such as higher data rates or wider bandwidth waveforms or different types of waveforms, then we would have to adapt and add support for that kind of stuff.”

“Because our systems record and replay, they’re used a lot to record real-world jamming,” said Thomas. Regarding spoofing, Racelogic has just improved its signal simulation. “We can do seamless takeover of a GNSS signal in real time. We can reproduce the current ephemeris and almanac. If we transmit a sufficiently powerful signal, we can completely take over that device.”

Over the past five years, most of CAST Navigation’s customers have become much more interested in being able to simulate jamming and spoofing, Clark said. “If you’re doing anything of any importance in a contested environment, you’re going to come up against some type of spoofing and/or jamming interference.”

Pielmeier agreed that simulation of jamming and spoofing threats has been a major market driver in recent years. “Our latest RF simulator generation, NCS NOVA+,” he said, “fully supports all types of jamming and spoofing and is fully integrated into our RF simulators to enable coherent signal generation. With the coming safety-of-life and automated driving applications based on DFMC (SBAS/GBAS dual-frequency multi-constellation), the need to support advanced jamming and spoofing simulation solutions will remain a continuous driver.”

IFEN’s rf signal generator technology, based on a modular and highly flexible Software Defined Radio (SDR) platform. (Image: IFEN)

Simulating What Does Not Yet Exist

The current GNSS constellations broadcast signals that can be recorded, played back, and used to generate accurate simulations. For systems still being developed, however, simulator manufacturers must rely on each system’s ICD, if and when it is available. Even for established systems, the live sky signals may diverge from the ICD. “Is the simulator supposed to match live sky,” Erbes wondered, “or is it supposed to match the intended final state of the constellation, according to the ICD? This is a huge topic for M-code, which is ever changing, and has a very large ICD that is released incrementally. We’re constantly having to make changes to the simulator to match those releases.”

A big challenge for simulator manufacturers is to keep pace with new and evolving ICDs. “There are more constellations than ever, and the technology makes it easier to change signal architectures,” said Erbes. “We’re going to start talking about signals that can be reprogrammed on the fly. That’s going to make simulation more and more challenging.”

Simulating signals for new systems that are not yet deployed is a matter of “pure signals simulation,” said Thomas. “You go through the ICD line-by-line and work out the new schemes. You are very much reliant on every single word in that ICD.”

New LEO-based systems are not the only ones to present this challenge to simulator manufacturers. “L1C is another one of those problem child signals that we have developed,” said Clark. “All we can do is buy all the makes and models of L1C receivers available for sale and utilize our simulator, along with those receivers, to see whether things are good. We’ve asked the government for an L1C code sample, but it will not be available until the satellite manufacturers launch the satellites in their final configuration. Until then, we’ll develop to the ICD that’s been released and defined, then cross our fingers.”

Spirent’s core simulation engine and SDR “are agnostic of the constellation and signal type that’s being generated,” Holbrow said. “So, the underlying principles of accuracy, range rate, pseudo-range control, and delay, together with the RF fidelity from Spirent’s SDR+ Sim engine, can be readily manipulated to simulate the wealth of emerging signals, including LEO.” Additionally, when an ICD is not available, the company can enable its customers to use its tools “to readily populate elements of that ICD themselves.”

In the Lab vs. In the Field

“All our systems can be carried in a backpack, on a push bike, in a car,” said Thomas. “We do that deliberately, because we come from the automotive side of things, so we have to keep everything very small and compact. Some of our customers have put them in rockets, recording the signal as it goes up, or in boats. We have people walking around with an antenna on their wrist connected to one of our systems, so that they can simulate smartwatches.”

CAST Navigation has simulator packages that range “anywhere from shoebox size to nine-foot-tall racks,” said Clark. “They are all modular, so you can add options and capabilities over time. We have simulators that are used in the field. Some of the testing groups with the U.S. armed forces have used our simulators in the back of a Humvee along with other proprietary equipment to conduct their own field experiments.”

Spirent supports in-the-field use cases: its portable simulator can test PNT resilience while the DUT is receiving live-sky signals, and their record-and-playback system takes real-world soundings in a wideband RF environment for playback in the lab.

Currently, Pielmeier said, all IFEN simulators are designed for lab use. However, “we recognize an increased request for field-capable RF simulators, specifically to perform spoofing of real SIS to test deployed GNSS receivers in the field. Offering a portable in-field solution is in our mid-term planning, but not a current driver for our developments.”

Testing vs. Mission Planning

How do simulators used by receiver manufacturers in their labs and in the field to tweak existing receivers or develop new ones differ from those used for mission planning? “In most lab simulations, they can just run with a default constellation for a given day,” Erbes explained. “They’ll run that scenario hundreds or thousands of times and never need to change it because they’re testing parts of the receiver that don’t care a whole lot about the specifics of what’s happening.”

Missions, by contrast, are time- and location-specific. Planners need to know which satellites will be overhead at an exact time and place. “When you’re doing real day mission planning, the big problem isn’t so much how to generate a signal, it’s how to find out what’s happening today.”

Increasing Accuracy Requirements

Like those for receivers, accuracy requirements for simulators are increasing to match those of emerging applications. “Everyone’s chasing the goal of getting smaller, faster, and more accurate systems,” said Thomas. “We do real-time simulators, and they want a smaller and smaller delay from when you input the trajectory to when you get the output. Luckily, we’re able to keep up on the hardware side as well, because much of our processing is done using software.”

As accuracy requirements rise, “Real-world testing has an incredibly important role to play,” said Holbrow. Additionally, as resilience testing places increasing demands on test equipment, Spirent Communications now supports “a multitude of vulnerability and corresponding mitigation/prevention test cases” to deal with jamming, spoofing, cyber-attack and CRPA

CAST Navigation’s simulators meet or exceed accuracy requirements, Clark said. “We have pseudo-range accuracy down to a millimeter, our phase coherence doesn’t wander, and we’re able to achieve 2.5 ps to 3 ps synchronization coherence during multi-element, phased-array antenna simulations. We see our customers interested in a higher performing simulator, and that is our commitment.”

Pielmeier had a different perspective on this: “We saw no increase in the required accuracy, as the typical requested accuracies are far beyond the real accuracy of the signals anyway.”

Recent Success Stories

Racelogic has developed a system to replace or augment GPS in tunnels, which often pass over each other or match the routes of surface streets. “We’ve been talking to many cities around the world that are building new tunnels,” said Thomas. “It requires installing repeaters every 30 meters along each tunnel and software that runs on a server and seamlessly updates your position every 30 meters.”

Clark pointed out that CAST Navigation’s “bread-and-butter” for the past few years has been “larger systems that can drive phased array antennas, along with inertial units, and full high-dynamic aircraft, in real-time environments.” He added that “the smaller systems, which used to be popular, have mostly gone by the wayside.”

As a recent success, Holbrow cited Spirent Communications’ release of a Xona simulator, in partnership with Xona Space Systems, as well as the addition of “many realism-related capabilities, including simulating the vibration and temperature effects of inertial systems;” a cloud-based software application called Foresight that enables users to understand the GNSS coverage they would expect at a particular time, location and trajectory based upon accurate 3D scenes; and a simulation test solution for the Galileo Open Service Navigation Message Authentication (OSNMA) mechanism. Finally, he stressed Spirent’s increasing support for automation.

Pielmeier cited the Galileo second generation Test User Receiver contract that IFEN received from the European Space Agency as its most important recent success. “Within this contract, the NCS NOVA+ simulator as RF test tool will be upgraded to full G2G signal generation capability. The new already implemented G2G signals enable shorter time to first fix (TTFF) and improved acquisition performance but also higher updates rates (e.g., for PPP-RTK). Through the end of the year, the G2G signal will be fully implemented in our RF simulator, including the next generation of advanced authentication solutions.”

<p>The post Faux signals for real results: GNSS simulators keep up with a panoply of new signals first appeared on GPS World.</p>

An off-the-shelf PC provides the computing power for complex GNSS driving simulations. (Photo: Racelogic)

By Julian Thomas
Managing Director, Racelogic

Driving simulators are commonly used by vehicle manufacturers to expedite the test and development process of their many electronic systems. This not only saves the considerable time and expense of using a real car on a test track, but it is, of course, significantly more environmentally friendly.

LabSat simulators are used by many leading technology companies and car manufacturers to develop and verify the performance of their new products containing GNSS receivers. These tests are performed using either a pre-recorded or an artificially generated RF signal. This RF signal contains the combination of multiple satellite signals, which are decoded by the GNSS engine, tracking the artificial satellites as though they were real. Static or moving scenarios can be generated, and the user can select parameters to suit their own application, such as time, date and available constellations.

Julian Thomas
Managing Director
Racelogic

Recently, an automotive LabSat customer had a specific requirement to synchronize a GNSS receiver with the real-time trajectory data generated by one of their driving simulators. This was for a hardware-in-the-loop test rig where a human driver would navigate a route around a virtual test track, while the normal electronic systems reacted as if the vehicle were being driven around a real environment.

The challenge in this customer’s application was that the time delay between the trajectory coming from the simulator and the generation of the corresponding GNSS signals had to be less than 100 ms. This low latency was necessary to achieve realistic synchronization between the driver’s inputs and the resulting output from the GNSS-based device under test.

Traditionally, low-latency real-time simulators use bulky expensive hardware that relies on power-hungry field programmable gate arrays (FPGAs) to create the necessary satellite signals. However, due to the inevitable tick of Moore’s Law, and with some clever optimizations, your entry-level desktop PC now packs more than enough punch to simulate multiple constellations and signals with very low latency.

Using a standard PC to do the heavy lifting means that the hardware required to output the simulated signal is much easier to obtain, can be a lot simpler, and is considerably more cost effective. For example, an 8-core, 3-Ghz Intel i7 processor can generate the signals from 20 satellites in real-time, which normally is sufficient to simulate all but the most complex scenarios.

Our LabSat SatGen software has been continuously developed and optimized during the past 15 years, so it did not take us long to enable the reception of an NMEA trajectory stream with a latency of less than 100 ms. We then streamed this simulated data via USB to our LabSat Real-Time, which generated a corresponding RF signal that can be connected directly to the RF input of any modern GNSS engine.

Using a PC to generate the signals does not mean a loss of fidelity, with the resulting output achieving a repeatable position of less than 10 cm, while the trajectory data can be received at up to 100 Hz.

The resulting solution can take trajectory data from any kind of simulator that has an API to obtain real-time data, such as many popular off-the-shelf driving and flight software simulators, and use this to provide a real-time signal that can be utilized by the GNSS device under test.

Our future development roadmap includes synthesizing external signals, such as CAN-based sensors or inertial measurement units, and then synchronizing these signals with the incoming trajectory. With the amazing power of a modern PC, we are finding that this kind of complex simulation is now much more cost effective and easier to achieve.

<p>The post Using modern PCs to carry the load first appeared on GPS World.</p>

If your use of RTK corrections is localized, then you can still gain the benefits of increased range and signal reliability offered by utilizing internet-based correction messages. Simply connect your base station to a computer with internet access and cast the correction messages from your base station directly to the VBOX NTRIP Modem.

Learn more.

This video is sponsored content by Racelogic.

<p>The post Receive RTK correction data with a VBOX NTRIP Modem first appeared on GPS World.</p>

GNSS receivers — which were never as simple as FM radio receivers or garage door remote controls — are becoming increasingly complex. The causes for this include continuing efforts to:

• reduce their size, weight, and power (SWAP)
• utilize new signals from up to four GNSS constellations
• integrate them with other sensors, such as inertial measurement units (IMUs), cameras, and lidars
• take advantage of a growing number of public and private, global, regional, and local correction services
• meet the requirements of booming new markets, such as autonomous vehicles
• mitigate the threats posed by the proliferation of unintentional and intentional RF interference, the latter better known as jamming, and by spoofing.

In short, receiver manufacturers must constantly adapt to a GNSS/PNT landscape that is, as one of the respondents to this Q&A put it, “ever evolving.”

In turn, the growing complexity of GNSS receivers requires increasingly sophisticated simulators to test receivers and their integrations in controlled conditions before field testing and deployment. Increasingly, this is achieved by replacing with software what was once done in hardware. Simulation remains a vital, though often underappreciated, segment of our industry.

On the following pages, five simulator vendors briefly explain their evolution in response to changes in GNSS/PNT, comment on the principal technical challenges they face, and outline their principal markets.

Spirent Federal Systems’ GSS6450 RF record and playback GNSS simulator is portable, for testing automotive applications in the field. (Photo: Spirent Federal)

Lisa Perdue
Product Line Director, Simulation
Orolia

OROLIA

How has your approach to simulation changed over the years and in response to what changes in GNSS/PNT?

We have transitioned away from the GNSS simulator approach of using fixed, allocated hardware that we used in our early simulators to the more modern software-defined approach we use today. Given the ever-evolving PNT landscape, it is difficult to design hardware that will support all future GNSS and PNT simulation needs. Instead, we focus on the development of the Skydel software platform, which can then be used with the supported COTS hardware or turnkey system to generate the necessary signals. This gives us the benefit of maximum scalability and flexibility while being truly future proof.

The software-defined approach also allows us to offer Skydel in new and exciting ways. We aim to make PNT simulation accessible to everyone and we can do that through subscription and cloud-based simulation services.

What are currently the greatest technical challenges to GNSS/PNT simulation?

Today GNSS is only a part of the PNT picture. GNSS receivers are often tightly integrated with other sensors and many times the GNSS receiver cannot be isolated to test it on its own. Other sensors must also be stimulated or simulated and included as part of testing. Correction services are becoming more common, but many are proprietary with no public specification. With no common standards available, it can be technically challenging to create a one-size-fits-all test solution.

We tackle these challenges through our plug-in feature. The plug-in architecture allows you to expand the capabilities of Skydel by adding your own features or complex integration with other systems. It allows you to exchange information with the Skydel Engine and even integrates it into the Skydel UI. With our open-source SDK, which includes example plug-ins, you can create your data outputs synchronized to the GNSS simulation, such as IMU or correction services data.

In what markets and applications are your simulators used? Are they used only in labs or also in the field?

At Orolia, we say ‘Skydel Everywhere.’ Skydel is used in applications ranging from military encrypted receiver testing (SAASM, M-Code, PRS) to commercial applications supporting any of the GNSS signals available.

Skydel is used in systems that are found in labs, but you can also find Skydel at an individual engineer’s desk, or even home offices. In the field, Skydel has provided simulation and threat generation capability to authorized test ranges and field test events.

The broadsim software-defined GNSS is powered by Orolia’s Skydel GNSS simulator engine. (Photo: Orolia)

RACELOGIC

Julian Thomas
Managing Director
Racelogic

How has your approach to simulation changed over the years and in response to what changes in GNSS/PNT?

Over the years, GNSS technology has changed significantly but our approach of identifying a need and creating a solution hasn’t changed since we launched our first LabSat GNSS simulator. We created LabSat because we needed a cost-effective, accurate and easy to use record and replay simulator that we could use for product development and production line testing for our VBOX Automotive and VBOX Motorsport technologies. This need could not be met by any other simulator manufacturer, so we developed our own solution, which in turn became LabSat. Although our approach has not changed, the needs of users, including our own engineers, have, so we continue to develop and improve LabSat to meet these needs.

Racelogic’s LabSat GNSS simulators offer multi-constellation and multi-frequency capabilities. (Photo: Racelogic)

With the increasing number of satellite launches in market segments such as communication and navigation, the number of requests for testing space-qualified receivers has increased dramatically. To test these kinds of scenarios, we have been making some major upgrades to simulate rocket launches and Earth orbit trajectories that require very different characteristics from land-based simulation.

As the number of constellations and signals has expanded very rapidly, the number of simultaneous signals that need to be simulated has put a far greater requirement on the computing power needed to render them. We have been working very hard on optimizing our routines to make the most of the new breed of high-performance multi-core processors. The result has been a big decrease in the time taken to create a scenario, and an increase in the number of signals that can be simulated in real-time.

What are currently the greatest technical challenges to GNSS/PNT simulation?

The biggest challenge is in simulating a large number of constellations and signals in real-time without using dedicated, expensive hardware to create them. The good news is that with the latest Intel Xeon processors boasting up to 40 cores and 80 threads, a much larger number of signals can now be created in real-time using off-the-shelf PC components.

In what markets and applications are your simulators used? Are they used only in labs or also in the field?

With the global pandemic causing national lockdowns, many engineers switched to working from home. Our largest growth in the simulator market has therefore been due to providing these engineers with a small, low cost, easy to use simulator that they can have on their desks at home, allowing them to continue to develop GNSS applications without having to go into the office. The markets these engineers work within are as varied as the markets that use GNSS technology.

We have also seen a big increase in the use of our simulators to test mass produced satellites used in providing global internet coverage. These satellites are being produced in large volumes, and the need for a low cost, reliable testing method on the production line has driven strong growth in this area.

Our simulators are often used in the field to gather data for in-lab testing, as small size and battery life are very important factors in this environment.

SPIRENT FEDERAL SYSTEMS

Phillip Bonilla
Senior Systems Engineer

How has your approach to simulation changed over the years and in response to what changes in GNSS/PNT?

Spirent has provided highly accurate simulation solutions since the early phases of GPS availability, starting with defined hardware for each signal type. As the GNSS landscape has grown, Spirent has worked closely with leading developers, adding key flexibility and functionality to adapt and provide a growing product portfolio. By adopting a robustly defined system architecture, and employing signal-agnostic hardware, Spirent simulators can generate any of the available constellations and frequencies, with no more than a few clicks of a mouse.

While broadening the support for the increasing number of constellations has been a focus, so too has the necessity to provide users with high numbers of available channels and auxiliary simulation needs. To complement GNSS simulation, significant effort is being devoted to resilient application testing, providing users with flexible solutions for introducing jamming and spoofing to the test environment. Our agnostic hardware supports signal generation using software defined radio (SDR), including interference sources and user-defined IQ signal data. As customer demands have grown, alternative RF and PNT sensors have been—and continue to be—incorporated, allowing users an expanded and comprehensive test environment.

The new spirent simulator generates alternative RF navigation signals concurrently with GNSS signals. (Photo: Spirent Federal)

What are currently the greatest technical challenges to GNSS/PNT simulation?

Today, nearly all industries rely on GNSS or other PNT sources to some extent. With such varied and widespread use, laboratory testing is critical, and maintaining the highest levels of accuracy, reliability and robustness remains one of the greatest challenges. For modern hardware-in-the-loop configurations, simulation systems must be able to keep latency consistent to enable powerful post-processing of results. With this challenge in mind, we at Spirent design and manufacture our own hardware, ensuring precision and ultra-low latency.

Another significant test challenge posed by modern applications is the growth in vehicle speed and maneuverability. Creating a truly realistic test environment for supersonic and even hypersonic vehicles with high rates of spin and jerk places huge demands on a simulator. Spirent recently has introduced the industry’s first 2 kHz update rate, enabling the most accurate trajectories for the most mobile technologies.

Lastly, positioning engines are becoming more complex. In addition to GNSS and inertial, vision systems and a range of other sensors and signals-of-opportunity are providing developers greater opportunity for precision and robustness. Therefore, a core part of Spirent’s mission statement is delivering test equipment that is designed to be integrated into wider test benches and ensuring that equipment is always orders of magnitude more accurate than any device under test.

In what markets and applications are your simulators used? Are they used only in labs or also in the field?

Spirent simulators are used in all phases of the product life cycle across nearly all applications. Receiver manufacturers use our solutions beginning with initial research and development, throughout product development, and well into production and field testing. Along with the ability to use Spirent’s simulators for live range testing, Spirent’s GSS6450 record and playback system enables users to record the real world in high dynamic detail for repeatable lab testing.

JACKSON LABS

Gregor Said Jackson
President and CTO

How has your approach to simulation changed over the years and in response to what changes in GNSS/PNT?

Initially, we saw a large demand for GPS-only solutions. We are shipping units into this market and it is growing more than 30% year over year for us. Recently, customers are looking to also supporting other constellations. There is an emerging market for LEO simulation capability. Many LEO constellations are becoming reality, such as OneWeb, Kuiper, Starlink, Iridium, Xona, and others, and customers are more frequently asking if we can support these types of signals in our simulators. Demand also is arising for additional base-band signals to accommodate the RF signals, such as synchronized raw IMU data and other observables. Jamming and spoofing signals also are being requested and reproducing these as faithfully as possible is a big challenge for synthesized simulation. Lastly, we see demand rising for mil-type secure applications, such as M-Code, PRS (Galileo) and P(Y) code SAASM of course. The complexity of future simulators will rise in lockstep with the complexity of the RF spectrum coming to us from space.

What are currently the greatest technical challenges to GNSS/PNT simulation?

The STL-1400 positioning and timing receiver is designed for battery-operated low SWaP-C applications. (Photo: Jackson Labs)

A faithful reproduction of the real live-sky RF signals would rank high on this list. There are almost an unlimited number of out-of-band and in-band benign and adversary RF signals on a typical GNSS antenna these days, and more recently the sun has been acting up with solar flare activity that can disrupt GNSS signals. As GNSS receivers mature and become capable of tracking four, five or more carrier frequencies and constellations at once it becomes increasingly challenging to supply these types of signals from a simulator, and at a reasonable price-point. Sometimes, a wideband recording and playback system can do a better job at reproducing live-sky signals, however these systems are limited to playing back the same exact mission over and over again of course, and thus are not very flexible.

In what markets and applications are your simulators used? Are they used only in labs or also in the field?

Our simulators are built for two different applications: the first is a traditional type of GPS signal simulation where a Windows application allows a user to set up static or dynamic scenarios, allows them to upload NMEA playback files, create jamming or spoofing signals, and generally tweak the RF signal in many ways, such as modifying power levels and antenna patterns and even creating space vehicle failures in real time. Our customers range from car, aircraft, and avionics manufacturers, to R&D labs, to the government and academia.

Our simulators also are used for a hardware-in-the-loop application that we call transcoding. It allows glueless retrofitting of existing GPS equipment with any and all the emerging PNT solutions such as LEO positioning and timing, celestial navigation, INS/IMU, CSAC holdover, and concurrent/multi-frequency GNSS using a 1×1-in. transcoder module. Our transcoders fly on Air Force aircraft, are used to retrofit telecom equipment, and allow deep-indoors and underground GPS reception. Transcoders created an entirely new market for simulators.

SYNTONY GNSS

Sylvain Daubas
GNSS Simulators R&D Teams

How has your approach to simulation changed over the years and in response to what changes in GNSS/PNT?

Manufacturers of GNSS receivers are targeting more precision and availability, especially in urban areas, which require acquiring more signals from more constellations and greater effort to minimize multipath errors. This confirms that an SDR design for signal generation is decisive to keep systems cost-efficient, as it directly benefits from Moore’s law. For instance, our new RTGS4-12 configuration is about four times more powerful (240 channels) than our previous standard configuration, for a similar budget level.

Regarding precision and RF quality, our simulators benefit from the same RF cards as Echo, our high-fidelity record and playback equipment, with a state-of-the-art RF front end: three channels at a 100 MHz sampling rate and a 16 bit IQ. The capacity to simulate protected signals is also crucial: with PRN Link, Constellator is ready for any present or future signal with encrypted spreading codes.

What are currently the greatest technical challenges to GNSS/PNT simulation?

Building a CRPA simulator is not an easy task, as this requires extreme levels of phase and time synchronization between several RF outputs, typically four, seven or more. This can be done in two ways: with a dedicated new RF board running with a single synthesizer for all channels or using the classical one, to which one should add a complex calibration mechanism. SYNTONY has made the tough choice, investing more at first in a mono-synthesizer version. However, this will benefit our customers, for which the usage will be simplified and it will save them a lot of time by shortening the calibration phase. This version already is available for sale.

Syntony’s Constellator simulator. (Photo: Syntony)

On another note, it is a significant challenge to keep our product and its interfaces user friendly while also enabling our clients to configure each of the more than 500 parameters available (at the last count). We also keep in mind that new signals may appear, from LEO constellations for instance, answering to new needs such as autonomous driving. Constellator is HW ready for them, only requiring a software update.

In what markets and applications are your simulators used? Are they used only in labs or also in the field?

Constellator currently is mainly used in laboratories, in many market segments. Because it was initially built in partnership with spacecraft manufacturers, it benefits from the high standards of performance of space industries and includes several advanced space-dedicated features.

On top of the typical usage inside the labs, two other SYNTONY simulator products that are directly derived from Constellator are used in the field:

• ECHO Recorder & Playback is used to record the GNSS environment with ultra-high fidelity: today @ 100Mhz, and before the end of 2021 even up to @ 200Mhz. ECHO has been used by our customers in cars, trains and often in aircraft test flights. Another usage of ECHO is to detect and record scintillation phenomena, as we will soon do in Brazil.
• SubWAVE (GNSS coverage extension for underground places) allows indoor positioning with precision, directly compatible with standard GPS receivers, which can be crucial for safety or operational reasons. We have installed SubWAVE inside subways stations and tunnels (for example, in Stockholm, Paris and New York), in road tunnels (soon in France, in the “Tunnel du Mont Blanc”), in an underground bus terminal (also in Stockholm), in underground train stations (in Switzerland), and before the end of 2021 also in an underground mine (in Finland).

<p>The post Simulating complexity: Testing GNSS receivers requires increasingly sophisticated simulators first appeared on GPS World.</p>