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

CAST Navigation
CAST-SGX GPS Satellite Simulator

CAST Navigation

CAST-SGX GPS Satellite Simulator

The SGX GPS satellite signal simulator from CAST Navigation provides the user with dynamic, repeatable GPS RF signals for use in the laboratory or in the field for a wide range of GPS applications. The SGX simulator is housed in a portable, lightweight handheld enclosure measuring 7 × 11× 3 inches and weighing just over 4 pounds.

The SGX replaces the CAST-SIMCOM simulator, a 17-inch, 50-pound simulator. The SGX is lightweight, portable, operates on AC or battery power, features 16 channels of L1 C/A- and P-codes, and is extremely accurate and repeatable. It is based on CAST technology that has been developed for use in the company’s larger military products.

The SGX is controlled via an intuitive touchscreen interface that allows the user to select start and stop scenarios, change screen views, and change satellite RF power levels while a scenario is running. Three test scenarios are delivered with the simulator.

XGen Scenario Generation Software. This optional software gives the user the ability to generate custom scenarios for use with the SGX. The software allows for complete control over GPS almanac, ephemeris, and all satellite error sources, including multipath. The user can select from a variety of vehicle types and simulate static or dynamic motion for land, sea, air, and space-based vehicles. The user may also employ antenna gain patterns and vehicle silhouettes.

www.castnav.com
phone: 978 858-0130
email: sales@castnav.com

IFEN Inc.
NavX-NCS Professional / Essential

IFEN Inc.

NavX-NCS Professional / Essential

IFEN Inc., located in California, offers the IFEN NavX-NCS (Navigation Constellation Simulator), a premium-grade RF GNSS simulator. It is available in either the Essential or Professional version, tailored to the customer’s individual test and research needs.
The NavX-NCS Essential simulates dynamic and static GNSS scenarios with up to 42 channels in the upper L-band (such as GPS / SBAS L1, GLONASS G1, Galileo E1, BeiDou B1, and QZSS / IMES L1) and is designed mainly for product testing and system integration.

The NavX-NCS Professional offers up to 108 signal channels in virtually all frequencies and signals. Superior simulation options such as various feared events can be performed by the NavX-NCS Professional.
Both versions of NavX-NCS offer high precision and numerous simulation options. Intuitive, user-friendly software makes test scenarios easy, fast, and clear, whether pre-defined or set up individually.

These IFEN simulators have a unique modular hardware and software architecture, which offers great flexibility when it comes to changes in a company’s strategic test requirements. Every NavX-NCS is fully upgradeable, not only in the number of RF signal channels or available frequencies, but in a possible subsequent supplement of up to four RF outputs.

www.ifen.com, Mark Wilson, VP Sales
phone: 951-739-7331
email: M.Wilson@ifen.com

Aeroflex
GPSG-1000: Portable GPS/Galileo/SBAS Positional Simulator

AeroFlex

GPSG-1000: Portable GPS/Galileo/SBAS Positional Simulator

Designed to be a versatile yet affordable satellite simulator, the GPSG-1000 is used by those validating and testing GNSS receivers in a variety of applications in the transportation, consumer electronics, aerospace, and military industry segments, to name a few. The GPSG-1000 is a single carrier, multi-channel GPS/Galileo simulator. Portable and ruggedized, it can be safely and confidently deployed in a variety of outdoor and indoor environments. The unit is available in a 6- or 12-channel configuration, and supports L1, L1C, L2C, L5, E1, E5, E5a, E5b, and SBAS (WAAS and EGNOS) signals.

The GPSG-1000 can be directly connected to a GNSS receiver under test. It can also simulate actual “open sky” situations, whereby the unit can generate its signals through the included antenna coupler system that isolates and transmits to the UUT’s antenna(s). Utilizing an integrated GPS receiver, the GPSG-1000 simulates actual time of day and date as well as the real constellation that would be available for navigation at that specific time. Multiple almanacs and route files can be saved to memory, enabling current and past history dynamic motion, constellation environment creation/recreation, and other troubleshooting capabilities. During any given static or dynamic simulation, space vehicle parametrics and health can be user controlled.

At less than 10 pounds, the GPSG-1000 features a touch-screen user interface that can be remotely hosted via an integrated Ethernet port. The unit uses a rechargeable, lithium-ion battery, enabling hours of untethered use, or can be used while the battery is recharging.

www.aeroflex.com/gpsg-1000
phone: 316-522-4981 or 800-835-2352
email: info-sales@aeroflex.com

RaceLogic
LabSat Turntable

RaceLogic

LabSat, LabSat 2, SatGen v2

LabSat and LabSat 2 are record and replay multi-constellation GNSS simulators. Designed as lightweight, easy-to-use standalone systems, the LabSat range has the ability to provide and deliver solutions for a wide range of testing requirements. Equipped with pre-recorded test scenarios and the ability to record and replay the user’s specific scenarios, LabSat delivers precise and accurate test results — replicating real-world situations in the lab or testing facility.

The range also has the ability to record and replay data from a wide range of data sources, including vehicle CANbus, inertial sensors — such as gyrometers and wheel speed sensors — and reference receivers. A recent innovation is the LabSat Turntable Solution, which allows for the replay of dead-reckoning turn-rate signals to be played into a navigation device to simulate use through built-up areas and urban canyons. Both LabSat and LabSat 2 can observe all satellites in view; while LabSat observes GPS, Gallileo, and SBAS, LabSat 2 includes GLONASS and BeiDou-2.

Reliability of the gathered data can be assured when used together with SatGen v2, Racelogic’s simulation software. This scenario-generation software enables users to create scenario files based on user-defined trajectories, which can be replayed on LabSat. With SatGen v2, a scenario can be generated anywhere in the world, with position, route, speed, and time defined by the user. This high-performance software allows users to verify that their GNSS equipment performs as required in a variety of locations that maybe geographically remote or unavailable due to hostile environments.

www.labsat.co.uk
phone: +44 (0)1280 823803

Rohde & Schwarz
R&S SMBV100A: GNSS Simulator on Vector Signal Generator

Rohde & Schwarz

R&S SMBV100A: GNSS Simulator on Vector Signal Generator

The GNSS simulator in the vector signal generator R&S SMBV100A is designed for development, verification, and production of GNSS chipsets, modules and receivers. The simulator supports all possible scenarios, from simple setups with individual, static satellites all the way to flexible scenarios generated in real time with up to 24 dynamic GPS, GLONASS, and Galileo satellites.

• GNSS simulator with support of GPS L1/L2 (C/A- and P-code), GLONASS L1/L2, and Galileo E1, including hybrid constellations.
• Simulation of realistic constellations with up to 24 satellites in real time (no precalculated waveforms).
• Flexible scenario generation including moving scenarios (import of NMEA waypoints), multipath, dynamic power control, and atmospheric modeling without the need for additional software tools.
• Unlimited simulation time with automatic, on-the-fly exchange of satellites.
• User mode in the GNSS simulator for full flexibility to select the satellites and to define the navigation data (import of RINEX files).
• Full localization for static and moving receivers with up to eight satellites with GPS P-code plus commercial C/A-code for complete testing of military receivers.
• Support of predefined and user-defined A-GPS test scenarios, including generation of assistance data.
• Easy way for time synchronous setup with two instruments for L1 and L2 band simulation.
• Support of digital communications standards.

www.rohde-schwarz.com
email: customersupport@rohde-schwarz.com

Spectracom
GSG-6 Series GNSS Simulator

Spectracom

Advanced GNSS Simulators

Spectracom’s line of simulators provides fast, comprehensive navigational, position, and timing testing for devices with GPS receivers. Designed for manufacturers and development engineers, Spectracom’s simulators provide complete testing of multi-channel GPS signal performance with high throughput and ease of use without unnecessary complexity or expense. All GSG-5 and GSG-6 series models are portable and fully operational via front-panel, web-based remote control, or SCPI protocol, and they operate with StudioView for easy scenario creation and file management. Most models are software upgradeable so users can easily add features as requirements change.

GSG-5 Series. The GSG-5 series is a GLONASS and GPS constellation simulator that provides the basic set of features for testing GNSS systems. With a base of four channels, upgradable to 8, 16, or more, it provides navigational fix and position testing for in-line product testing or basic engineering and development testing.

• Versatile multi-channel GLONASS + GPS signal generator with pre-configured test scenarios.
• Includes advanced features such as SBAS (WAAS, EGNOS, MSAS, or GAGAN), white noise generation, and multipath simulation.

GSG-6 Series (pictured). The GSG-Series 6 family offers multiple frequency band operation, multiple GNSS constellation simulation, and expansion to many more channels. Incorporating all of the features of the popular Series 5 family, the Series 6 line expands the capability to simulate all the new, emerging GNSS signals. With a base of 32 channels, upgradable to 48, 64, or more, it provides navigational fix and position testing for engineering and development testing.

• GPS standard, new (L2C, L5) GLONASS, Galileo, and Beidou/Compass coming soon.
• Simultaneous multi-frequency P-code (unencrypted) and C/A code.
• Simultaneous GNSS Constellation P-code and C/A codes.

www.spectracomcorp.com
email: sales@spectracomcorp.com
phone: 585-321-5800

Spirent Federal Systems
GSS8000 Simulator

Spirent Federal Systems

GNSS Simulators

Spirent provides simulators that cover all applications, including research and development, integration/verification, and production testing.

GSS8000 (pictured). Spirent’s flagship simulator, the GSS8000, is fully approved for Y-code, SAASM, AES M-code, and SDS M-code testing. Spirent provides options and configurations for testing GNSS interference effects and interference mitigation techniques, such as integrated GPS/inertial testing, CRPA testing, and jamming/anti-jam simulation.

Spirent has delivered simulators that produce both legacy signals as well as modernized signals such as 2C, L5, and L1C. In addition to GPS, systems can include GLONASS L1/L2, Galileo, and Beidou-2, plus SBAS (WAAS, MSAS, and EGNOS) and Japan’s QZSS.
CRPA Test System. Spirent’s Controlled Reception Pattern Antenna (CRPA) Test System generates both GPS L1/L2 and interference signals; multiple GSS8000 chassis may be combined to coherently control up to seven antenna elements. Null-steering and space/time adaptive CRPA testing are both supported by this comprehensive approach.

GSS7790. Spirent’s GSS7790 Multi-Output Simulation System allows the signal from each satellite to be mapped to a separate RF output. These signals can then be fed to individual transmit antennas, which, when suitably deployed in an anechoic chamber, replicate the spatial diversity of satellite and jammer signals incident on the receiver antenna. Additional flexibility is offered as the signal is further split into its GPS L1 and L2 components, as appropriate.

www.spirentfederal.com
Jeff Martin, Director of Sales
Kalani Needham, Sales Manager
email: info@spirentfederal.com
phone: 801-785-1448

Mark Sampson

By Mark Sampson, Racelogic

GNSS is changing. The days of only American GPS satellites providing signals to the civilian population are gone as new constellations are launched. GLONASS was a slow starter, but is now well established, and its signal architecture is now commonly implemented in manufacturers’ chipsets. Galileo is still very much in test phase with global coverage planned for 2019, although position fix using only Galileo satellites has already been demonstrated. The Japanese QZSS system, designed to aid navigation in urban canyons, is partially operational with further launches announced for the near future.

The latest openly documented network to come online is BeiDou-2, or BDS. Formerly known as Compass, the Chinese constellation now provides signals to China and surrounding areas, but plans for global coverage should come to fruition by the end of the decade.

Full control over its own constellation gives a country military, socio-political, and commercial advantages, especially if additional functionality — such as search and rescue services — is introduced alongside the standard navigational broadcast. BDS is unique in its use of a combination of standard-orbit and geo-synchronous satellites, the latter giving it a wider range of signal designed to carry more information.

The populace stands to benefit from a wide variety of localized and global satellite coverage, but only if there are end-user products available that actually make use of the new signals. Any manufacturer wanting a share of the market in China, for instance, will need to get BeiDou-2 integrated into its chipsets quickly, especially if an import levy is placed upon devices that don’t support it (as nearly happened with GLONASS).

How do you go about implementing BDS support in your new GPS product if you’re based in Europe or America? The coverage isn’t global yet; you can’t just go out into the office car park to test, and how are you going to incorporate the signals from the three geostationary satellites without actually being underneath them? Moving to China isn’t very practical, so the solution is a GNSS record-and-replay device.

Manufacturers and other customers will want to seek out simulators from companies that have been highly proactive in ensuring their products provide full support for each constellation, even before they come fully online. The convenience in being able to test new designs, applications, and system integration with reliability and consistency can bring significant savings in development cost and time.

With 14 BDS satellites currently in operation, and the recent release of the Interface Specification, we find more and more companies in the marketplace have been asking for BeiDou functionality. An added benefit for existing users would be flexible hardware capable of taking a simple firmware upgrade in order to record and replay BeiDou as well as GPS and GLONASS.

Icing on the system-testing cake would be a hard drive containing pre-recorded scenarios from China and Europe, with good BDS visibility, so that bench testing can commence immediately. Given that such a device can record raw signals, live recordings can be taken in Asia and then transferred to test facilities around the world.

Mark Sampson is Racelogic’s LabSat product manager. He has more than 15 years of experience in the development of GNSS technology. Working closely with leading businesses such as Bosch, Intel, Samsung, and Telefonica, he provides knowledge and expertise in testing any GNSS device, application, or integration.

GNSS have been with us for more than 30 years, giving rise to a wealth of positioning and navigation technologies for military, civilian, and consumer use. Today, we’re entering a new era of experimentation and innovation in satellite and hybrid positioning. In turn, this drives new test challenges and introduces an ever wider group of engineers to the art and science of GNSS test.

Where Is the Testing Panacea? I am sometimes asked, “What is the best way of testing a GPS receiver?” — as if there existed some laboratory panacea to all GNSS test and characterization woes. Well, there is a saying, “There are horses for courses,” meaning what performs well in one situation may not deliver in another, and nowhere is this more true than in the field of GNSS test. Not only is there a wide range of different test equipment available, but there are no universally applicable test objectives, test methods, or parameter definitions, in exactly the same way as there is not one universally applicable GNSS receiver. Just as the rapid time-to-first-fix of an automotive receiver may be less relevant in a maritime environment, so different test approaches have their place.

A Systematic Approach. If there is one thing, it is this: be systematic in your test design. Consider the purpose of the test, the test conditions, and the measurements you plan to take, and be wary of generic tests that may not achieve your objectives.

Equipment. A wide range of GNSS testing equipment is available, ranging from basic single-constellation RF simulators to highly configurable, multi-GNSS constellation simulators. Single-channel, multi-channel, and record and playback systems all have their place, and to get the best results in the fastest time, it’s essential to choose the kit that’s right for the kind of testing you need to do.

Vulnerability, Fidelity, Integrity, and Time Travel. More and more, receivers need to be tested for their vulnerability to interference, jamming, and spoofing. As GNSS-derived position and time become more ubiquitous, so the motivation for confounding the system grows. This has a double impact on test.

First, performance requirements around vulnerability may be introduced, with tests to match. Second, and perhaps less obvious, is the way in which this concern is reflected in the receiver’s design and potential rejection of the laboratory test signal. Yes, I mean receivers getting more fussy about the signals they lock onto. Anyone who has tested a receiver with an out-of-date recording or simulation scenario will have experienced a receiver refusing to track a satellite showing a time and date prior to its firmware release date. The receiver, discounting time travel, knows there has to be something wrong with a satellite showing a date before it was born. With the risk of spoofing, receivers will only get more picky and likely to reject poorly simulated signals. To avoid such effects, it is important to have very high integrity and fidelity in any simulator system. Getting these details right is not esoteric, but is essential to allow the proper attribution of any problems observed and if test results are to have any meaning.

Conclusion. Be systematic in your approach to test; beware the universal and generic; “good enough,” it rarely is.

Steve Hickling is lead product manager for Spirent’s GNSS simulator business and is based at the factory in Paignton, England. Previously he held a variety of marketing, technical, and management roles in the telecoms and optical components industries. He holds a bachelor of science degree in physics and electronic engineering from Birmingham University, an MBA from Open University Business School, and a post-graduate diploma from the Chartered Institute of Marketing.

Today’s customers ask for high-accuracy positioning everywhere, even in the most demanding environments. The time is long gone that the only requirement for a receiver was to track GPS L1 and L2 signals in open-sky conditions. State-of-the-art receivers operate in increasingly difficult conditions, cope with local radio-frequency interference, survive non-nominal signal transmissions, decode differential corrections from potentially untrusted networks — and more!

Difficult real-life operating conditions are typically not addressed in textbooks or in the specialized literature, and yet they constitute the real challenge faced by receiver manufacturers. Most modern GNSS receivers will perform equally well in nominal conditions, or when subjected to nominally degraded conditions such as the ones that correspond to standard multipath models. However, the true quality of a GNSS receiver reveals itself in the environment in which it is intended to be used.

In view of this, a GNSS manufacturer’s testing revolves around three main pillars:
◾    identifying the conditions and difficulties encountered in the environment of the intended use,
◾    defining the relevant test cases, and
◾    maintaining the test-case database for regression testing.

In developing new receiver functionality, it is important to involve key stakeholders to comprehend the applications in which the feature will be used and the distinctive environment in which the receiver will function. For example, before releasing the precise-point-positioning (PPP) engine for the AsteRx2eL, we conducted a field-test campaign lasting a full month on a ship used for dredging work on the River Thames and in the English Channel. This enabled engineers to capture different types of sea-wave frequency and amplitude, assess multipath and signal artifacts, and characterize PPP correction data-link quality.

Most importantly, we immersed the team in the end-user environment, on a work boat and not simply in a test setup for that purpose. As another example, in testing our integrated INS/GNSS AsteRxi receiver for locating straddle carriers in a container terminal, we spent months collecting data with the terminal operator. This was necessary to understand the specificities of a port environment, where large metal structures (shore cranes, container reach-stackers, docked ships) significantly impair signal reception.

Furthermore, the close collaboration between the GNSS specialist, the system integrator, and the terminal owner was essential to confirm everything worked properly as a system. In both examples, in situ testing provide invaluable insight into the operating conditions the receivers have to deal with, much surpassing the possibilities of a standard test on a simulator or during an occasional field trip.

Once an anomaly or an unusual condition has been identified in the field, the next step is to reproduce it in the lab. This involves a thorough understanding of the root cause of the issue and leveraging the lab environment to reproduce it in the most efficient way. Abnormalities may be purely data-centric or algorithmic, and the best approach to investigate and test them would be software-based. For example, issues with non-compliance to the satellite interface control document or irregularities in the differential correction stream are typically addressed at software level, the input being a log file containing GNSS observables, navigation bits, and differential corrections.

Other issues are preferably reproduced by simulators, for example those linked to receiver motion, or those associated to a specific constellation status or location-dependent problems. Finally, certain complicated conditions do not lend themselves to being treated by simulation. For example, the diffraction pattern that appears at the entrance of a tunnel is hard to represent using standard simulator scenarios. For these circumstances, being able to record and play back the complete RF environment is fundamental.

Over the years, GNSS receiver manufacturers inventoried numerous cases they encountered in the field with customers or during their own testing. For each case, once it has been modeled and can be reproduced in the lab, it is essential to keep it current. As software evolves and the development team changes, the danger exists that over time, the modifications addressing a dysfunctional situation get lost, and the same problem is reintroduced. This is especially the case for conditions that do not occur frequently, or do not happen in a systematic way. Good examples are the GLONASS frequency changes, which arise in an unpredictable way, making it very difficult for the receiver designer to properly anticipate. This stresses the importance of regression testing. It is not enough to model all intricate circumstances for simulation, or to store field-recorded RF samples to replay later. It is essential that the conditions of all previously encountered incidents be recreated and regularly tested in an automated way, to maintain and guarantee product integrity.

The coverage of an automated regression test system must range from the simplest sanity check of the reply-to-user commands to the complete characterization of the positioning performance, tracking noise, acquisition sensitivity, or interference rejection. Every night in our test system, positioning algorithms including all recent changes are fed with thousands of hours of GNSS data, and their output compared to expected results to flag any degradation. Next to the algorithmic tests, hardware-in-the-loop tests are executed on a continuous basis using live signals, constellation simulators, and RF replay systems, with the signals being split and injected in parallel into all our receiver models. Such a fully automated test system ensures that any regression is found in a timely manner, while the developer is concentrated on new designs, and that a recurring problem can be spotted immediately. The test-case database is a valuable asset and an essential piece of a GNSS company’s intellectual property. It evolves continuously as new challenges get detected or come to the attention of a caring customer-support team. Developing and maintaining this database and all the associated automated tests is a cornerstone of GNSS testing.

Adapted from a Mercedes Benz Sprinter van, this unique measurement vehicle has been delivered to ESTEC by Austria’s Joanneum Research institute. “This is a dual-purpose vehicle, suitable for both telecommunications and navigation system testing,” explained Simon Johns of ESA’s Radionavigation Systems and Techniques Section.

“For navigation, we have the Galileo constellation coming on stream, as well as the stepping up of ESA’s GNSS Evolution programme — designing what comes next after Galileo’s first generation.”

The four wheel-drive vehicle can host a three-person team, and is crammed with dedicated navigation and telecommunication monitoring equipment.

Testbed vehicle screen.

“One of the main goals driving the design was to have an ‘easy to adapt’ test platform suitable to set up test campaigns for different mobile satellite systems and standards that would require different types of antennas and specific receiver/transmit equipment,” explained Olivier Smeyers of ESA’s Communication-TT&C Systems and Techniques Section.

“On the telecommunications side, there is a continuous effort to enhance current and create new mobile satellite-based broadcast and interactive services via the evolution of current systems or developing new standards,” Smeyers said. “Testing in the field is an essential element for validating and eventually establishing evolved or new standards. The vehicle has built-in multimedia equipment, including storage and control computers, multimedia gateway, passenger LCD screens, cameras and microphones, to serve this purpose.”

The vehicle’s 8-meter-high telescopic mast.

The vehicle features include two removable roof plates to mount specialized antennas (one currently hosts the antenna of a Broadband Global Area Network satellite terminal for Internet connectivity and multimedia and data streaming), an 8-meter-high telescopic mast capable of carrying 25 kilograms, a rubidium atomic clock synchronized to GPS time with nanosecond accuracy, a high-end spectrum analyzer and oscilloscope for signal measurements, and mobile temperature sensors to monitor the rack equipment.

A fish-eye video camera incorporating onscreen GPS timing and positioning performs continuous recording of its surroundings — to throw light on high buildings, trees, or other factors that might affect results.

Internal and external generators yield up to 5 kilowatts to keep everything running — sufficient power to supply two typical European households.

“The challenge was to fit in all the equipment and provide the necessary power and air conditioning, while still weighing less than 3.5 tonnes,” said Thomas Prechtl of Joanneum Research. “Exceeding this weight would have meant drivers would have needed a special license, and potentially limited its operations in some European nations.”

Aeroflex has developed the capability of simulating WAAS LPV approaches to expedite and validate the installation of WAAS-enabled navigation systems in aircraft. The GPSG-1000 offers the following features to installers of these systems:

• Ability to perform structured, repeatable dynamic motion tests (actual flight) of a WAAS/LPV installation,
• Ability to check and validate the sensitivity and dynamic range of an airborne GPS receiver, either statically or while in motion,
• Reduce aircraft down time and flight demonstration time required by FAA,
• Additional support data for documenting proper FAA processes of WAAS/LPV system upgrades or installs without leaving the hangar.

New orders for the GPSG-1000 are ready for immediate delivery. For existing GPSG-1000 customers, a no-charge software upgrade will be available by mid-April 2013.

The FAA created the WAAS program in 1992 to provide the necessary integrity to utilize GPS signals for precision approach. The WAAS consists of a network of precisely surveyed wide area reference stations (WRS). These reference stations monitor GPS satellites to determine errors in the GPS satellite signal. Each reference station relays the information about the GPS satellites to the WAAS wide area master stations (WMS). The master station then develops corrections to the GPS position information and provides timely notification of unreliable GPS data. These corrections are sent to ground uplink stations (GUS) where they are transmitted in the form of a WAAS correction message to a Geostationary Earth Orbit (GEO) satellite. The WAAS signal is then broadcast to users on the same frequency as GPS. This WAAS corrected signal provides three-dimensional guidance to aircraft.

“IFEN Inc., located in Corona, California, will greatly facilitate order placement, delivery and support for U.S. customers,” said Günter Heinrichs, head of Customer Applications and Business Development, of IFEN GmbH. “We look forward to addressing the needs of this market.”

IFEN has appointed of Mark Wilson vice president of sales at IFEN Inc. Wilson has more than 20 years of experience in the GNSS market. “I am very excited to join the IFEN team. They have extensive experience in all aspects of GNSS and I am looking forward to offering this expertise and the excellent IFEN products to the American Market,” Wilson said. “Our exceptional products offer unrivaled flexibility and capability, at realistic prices providing huge advantages to our customers.”

IFEN has more than 15 years of experience in GNSS and offers a range of GNSS test equipment, including simulators capable of simulating all GNSS constellations and frequencies and a multi-GNSS software receiver.