What’s New in GNSS Simulation?

It used to be that if you were going to build an RF navigation receiver, you had to also build your own simulation system to test it. I remember working with a couple of “home-built” RF simulation systems myself, way back when. We experience a lot of maintenance and support issues. And, of course, if you build something and also build something to test it, its likely that incorrect assumptions will end up in both systems. Today, there are a number of excellent sources for GNSS simulation equipment and support you can buy on the open market.

The spectrum of today’s providers seems to range from highly sophisticated scientific systems used for development by precision receiver manufacturers, through systems with GNSS and aiding solutions, to specialized systems for both general and specific application developers and also for production test. So this month I’d like to try to summarize (in no particular order) what some of the suppliers of GNSS simulation systems are up to, how they may be positioned in the market and, wherever possible, what we might expect to see from them in the future.

GSG Series 6 GNSS simulator.

Spectracom is a more recent entrant to the GNSS simulation market, though the company has been providing frequency and time synchronization test equipment for about 40 years. Spectracom has integrated GPS into these products for more than ten years, and decided three years ago to use the knowledge it had gained to get into the GNSS simulation business.

The GSG family of simulators is positioned at the “affordable” end of the simulation equipment scale, and is targeted at users and integrators of GNSS, rather than developers of receivers. Spectracom claims to have about 80 percent of the features of the top-end simulations systems, but its more capable (Series 6) systems sell in the $20-30k range. While new to the business, the Spectracom team feels that this allows them to bring the newest technology and innovation to the market.

The Spectracom system is derived from its well-known frequency/time synthesizer equipment — in fact, it has the same look front panel and chassis — and also makes use of the same “easy-to-use” concepts. “It doesn’t take a navigation scientist to operate these simulators,” said John Fischer, chief technology officer at Spectracom. The accompanying Studio View software is reportedly relatively easy to use to generate trajectories and other test scenarios by connecting to Google Maps and uploading them to the simulator.

But with all new firmware and FPGA implementation, 64 channels, and four frequency bands covering both GPS and GLONASS, the GSG family appears to be very well positioned for application developers integrating GNSS. Galileo and Beidou/Compass are in the works and expected this year, and will be supplied as upgrades to existing equipment.

Spectracom anticipates significant growth in its target market for application developers in “anything that moves,” including automotive and airborne, video matching, radar/lidar, and handheld nav devices, including mobile phones. Spectracom has a number of product lines and around 100 people working for them, but the GNSS simulation group is around 12 strong.

Rohde & Schwarz is another relatively recent GNSS simulation entrant with new products for the market.

SMBV100A vector signal generator.

Its current offering — the SMBV100A Vector Signal Generator – can simulate 24 dynamic GPS, GLONASS and Galileo satellites.  The SMBV 100A has wide bandwidth and high output power levels. Real-time test scenarios can be customized by the user — including a neat facility that allows modeling of satellite masking by downtown buildings, along with anticipated multipath for the same urban scenario.

While somewhat new to GNSS simulation, R&S has been around since the 1930s, and its experience with frequency synthesizers and similar equipment is being carried forward into what the company terms its “cost-effective” GNSS simulation offerings. R&S anticipates significant growth in automotive, aerospace, UAV, and cellular assisted-GNSS application markets.

R&S has had success in the aerospace market for UAVs, and has developed the capability to model antenna patterns and UAV body mask as the vehicle rotates and attitude changes towards visible satellites. Along the same lines, R&S has hooked up its system to flight simulators and provided hardware-in-the-loop testing for clients. R&S also has the ability to run simulation scenarios for long periods of time, and for “very long” periods if the receiver is stationary — this feature makes use of large internal memory storage within the SMBV100A; of course, almanac validity limits just how long this is possible. P-code capability is provided as an option, and there is a roadmap for adding SBAS and Beidou capability later.

IFEN NavX-NCS Professional

In the meantime, IFEN in Germany is focusing on its NavX-NCS Navigation Constellation Simulator range of multi-GNSS signal simulators.

IFEN emphasizes the flexibility of its design, with a platform scalable from a 12-channel GPS L1 system up to a full multi-GNSS system with 108 channels and 9 frequencies for GPS, GLONASS, Galileo, QZSS and SBAS. With this building-block approach, channels and capabilities can be added as and when additional testing complexity is required.

IFEN claims that the capability to generate all GNSS signals — by combining different modulations with up to nine L-band frequencies — is the only existing solution on the market providing GPS, Galileo, GLONASS, QZSS and SBAS in one chassis at the same time. And, since April 2013, all IFEN NavX-NCS GNSS RF signal simulators are to include BeiDou B1 signal capability in accordance with the official Chinese BeiDou B1 ICD, and are ready for the other B2 and B3 BeiDou signals.

IFEN also founded a subsidiary in the USA in January this year called IFEN, Inc., located in California and operational with Mark Wilson (formerly with Spirent) as VP Sales. In addition, IFEN has formed a partnership with WORK Microwave — a leading European manufacturer of advanced satellite communications and navigation equipment. WORK Microwave is responsible for RF and digital hardware design while IFEN develops the associated software and manages the distribution of the product range.

Little-known IP-Solutions in Tokyo, Japan, has been working to develop its ReGen GNSS DIF signal simulator, a software simulator that simulates ionospheric effects, generates digital IF (DIF) signals similar to those recorded by an RF recorder, and comes with an optional capability of simulating integrated inertial navigation.

IP-Solutions’ digital IF baseband signal simulator ReGen has been developed in close cooperation with the Japan Aerospace Exploration Agency (JAXA) to test and validate GNSS signal processing algorithms and methods for use on board aircraft using tight and ultra-tight integration with INS, including specific scintillation models and ionospheric bubble simulation.

Actual recorded flight data (left), ReGen replicated flight data (right).

Various configurations of ReGen can produce multichannel GPS and GLONASS L1 signals and single-channel GPS L1, L2, L5 and GLONASS L1 and L2 signals, as well as simulating noise and interference.

Meanwhile, Spirent, arguably the original market leader in GNSS simulation, has continued along its chosen path of supplying the industry with the greatest capability and most extensive simulation systems.

Spirent has recently released test systems with support for China’s BeiDou Navigation Satellite System in addition to GPS, GLONASS and Galileo.

Spirent started shipping BeiDou-ready systems to its customers in 2012. Now these may be upgraded to full BeiDou capability using the information available in the first full issue of the BeiDou-2 Signal In Space Interface Control Document (ICD).

Also aiming at mobile applications, Spirent’s Hybrid Location Technology Solution (HLTS) integrates Wi-Fi, Assisted Global Navigation Satellite System (A-GNSS), Micro Electro-Mechanical Systems (MEMS) sensor and cellular positioning technologies. HLTS integrates four very different and distinct location technologies and provides repeatable and reliable lab-based characterization of mobile devices supporting hybrid location technologies that will enable “accurate everywhere” location — including indoor user location determination.

Other notable players in the GNSS simulation business include Racelogic, CAST Navigation and Agilent who are each pursuing their chosen niches in this expanding market segment. Racelogic’s LabSat GPS simulator is gaining popularity with a number of leading companies, providing the ability to record and replay real GNSS RF data as well as user-generated scenarios. CAST has an extensive line-up of GPS and GPS/INS simulation systems and support software, and Agilent has added to its impressive electronic testing portfolio with a very capable looking GPS simulation product line.

Several other companies — some based in China and Russia — are also trying to figure out their development and marketing strategies to conquer their chosen GNSS simulation market niche. This is all a very healthy sign that there are many other companies with new embedded GNSS applications that they are bringing to market and who therefore need GNSS simulation/test capability. Overall, this means there is still significant growth underway and far wider applications of GNSS on their way to market. Great news for the GNSS industry!

Tony Murfin
GNSS Aerospace