Filling the PNT Hole—Why Non-Satellite-Based Technology is Urgently Needed

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Despite its impressive legacy of success driving many essential position, navigation and time (PNT) capabilities, GPS is not an infallible system and requires improvement to meet new threats, needs and PNT challenges, some of which go beyond GPS’s obvious vulnerability to interference and dependence on an aging satellite constellation. Make no mistake, GPS should be improved–taken to the limit to provide a growing user base the absolute best possible satellite-based PNT solution in terms of accuracy, integrity and affordability. Unfortunately, despite a number of improvements that can be made, GPS will always suffer from system limitations, many of which are inherent in all Global Navigation Satellite Systems (GNSS). Therefore, it is becoming clear to the industry that a complementary non-satellite-based technology to mitigate these limitations­—and fill the "PNT holes"­—is required.

One limitation is the technique upon which GPS is based: trilateration, the process of determining a location by measuring distances based on the geometry of spheres. Applied to GPS, trilateration requires adequate satellite visibility to yield an accurate solution, but adequate geometry is often impossible to achieve in the presence of natural or man-made obstructions. This is why GPS is really only useful outdoors and often does not perform well in forested areas, in deep canyons or near tall buildings. Even worse, attempting to navigate indoors via GNSS signals rather often results in "no geometry" because all signals are blocked by the building itself, which confounds the indoor navigation requirements of many industrial, construction, emergency services and indoor applications. Quite simply, the problem is that users in GPS-challenged or GPS-denied environments really have no control over what satellite signals will or will not be available, regardless of the number of satellites in a constellation.

Another limitation of satellite-based positioning systems is their technological complexity. GNSS is a technology which is cripplingly expensive to deploy and maintain. You literally need to be a superpower nation, capable of spending upwards of $20 billion to launch a full constellation and then maintain a commitment of more than $2 billion per annum to keep it flying. It is not trivial to build and launch a satellite constellation, and then sustaining it requires a vast support infrastructure. And to make a serious problem worse, unlike other GNSS systems where two satellites can be launched simultaneously, GPS satellite launch costs are currently exasperated by a single-launch capability. The USAF estimates it could save $50 million in launch costs per satellite with a dual launch option, savings that would add up to hundreds of millions of dollars over time. Unfortunately, despite these cost-savings advantages, a GPS dual launch capability will not likely be available before 2017, starting with the fifth and sixth GPS Block III satellites.

Even with this projected reduction in satellite launch costs, a target on-orbit GPS satellite cost on the order of $175 million is still immensely expensive by most measures. The consequence is that non-superpower countries, which also have a growing dependency on PNT in their own national infrastructures, must depend on these superpowers for what is a core national requirement. Put bluntly, the dependent nations have absolutely no sovereign control over the accuracy or availability of a critical national requirement. This critical dependency­—with no back-up available to a sovereign nation­—is becoming a major source of concern for many countries.

This sounds like a daunting problem to solve: a technically complex PNT service combined with a growing user base, interference problem, aging satellite constellation, questionable economic conditions and sovereignty concerns. Fortunately, techniques and technologies exist that augment GPS to mitigate these shortcomings. Some solutions are more effective than others, but each can be considered and employed according to a user’s requirements and budget to try to preserve PNT service during a GNSS outage or bring a PNT capability to an area that GNSS cannot reach.

To solve the GPS interference problem, one needs to either increase the GPS transmission power or develop a better anti-jam capability for GPS receivers. Work on both of these initiatives is underway. Anti-jam technology has been advancing for some time, and, starting with the recently deployed GPS Block IIF satellites, the constellation will include a more efficient signal structure to effectively provide more signal strength at the receiver. However, there are limits to how much improvement one will get. GPS satellites are still in a medium earth orbit at approximately 20,000 km high, and transmission loss over that range will always be significant. Unless satellites can begin to generate significantly more power and host equipment that can handle the power increase–and receivers are redesigned to safely accept the higher powered transmissions–GPS signals will always remain relatively low compared to what a ground-based system can transmit. Because of this, low power GPS jammers will continue to be effective, making them cheap to construct and often difficult to geolocate and remove. Remember also that it takes around 20 years to launch all the satellites that will allow these new functions in the entire constellation. "Modernization" of GPS is a slow, protracted exercise.

On the other hand, a terrestrial-based augmentation system can broadcast at whatever power level is required to assure consistent reception and frustrate low-powered jammers across a dedicated area. More importantly, an effective ground-based augmentation system ought to use a non-GNSS frequency band so that a single jammer is unlikely to affect both GNSS-satellite and ground-based transmissions.

One such ground-based augmentation system that is advocated by many PNT insiders is Enhanced Loran (eLoran), despite the fact that the system in the USA was decommissioned in 2010. Featuring an independent, dissimilar signal that can work indoors and outdoors, as well as delivering reasonably accurate UTC time, eLoran has been put forward as an effective complement to GPS. However, eLoran’s primary problem is its inaccuracy, as it cannot deliver the cm-level accuracy required for many modern applications. Then there is the cost, estimated by the Institute for Defense Analysis’ Independent Assessment Team that development costs could exceed $20 million/year for five to eight years, plus operational costs at $37 million/year–a hefty investment for something that can only deliver part of the back-up requirements. Additionally, without a firm commitment from the Department of Transportation, Department of Homeland Security, or some other government organization, electronics manufacturers will not make the capital investment required to bring combined GPS/eLoran receivers to the commercial market. If and when these investments are made, eLoran could eventually improve PNT availability, but at significant cost.

Alternatively, PNT industry experts have also suggested that navigationgrade inertial units could be employed to complement GPS. Unjammable because they do not rely on signal transmissions to operate, low-cost inertial navigation aids have already proven effective to carry a user through a short GPS outage. However, their solutions will unfortunately drift during an extended absence of GPS, and they provide no capability for providing accurate time transfer. Thus, inertial navigation aids could improve PNT availability, but without time-transfer and at the expe
nse of accuracy in prolonged GPS outages. High accuracy units are also very expensive.

A very new back-up technology which is not yet well known to the public is Locata­a terrestrial positioning system that remains accurate in the absence of GPS, is vastly more accurate and operationally robust than eLoran, and which can be flexibly modified to meet specific application requirements. Full disclosure: I work for Locata Corporation, but I would be remiss not to include Locata technology in this discussion, as it does not rely on GPS signals to deliver extremely accurate PNT solutions and has been proven to provide a reliable and high-accuracy solution when GPS is jammed or otherwise unavailable. Locata uses a network of small, ground-based transmitters that blanket a chosen area with strong GPS-like radio-positioning signals. Because it is terrestrially based and transmits powerful signals, Locata can deliver positioning information in indoor or outdoor environments. Additionally, Locata’s innovative TimeLoc technology is capable of synchronizing Locata signal transmitters to within a nanosecond without GPS or atomic clocks. This is the "secret sauce" invention which allows a Locata network to independently replicate the full satellite constellation on the ground. There is no other technology which can do this.

TimeLoc synchronization makes it possible to use Locata not only for accurate autonomous positioning and navigation solutions, but also costeffective time transfer to help preserve critical timing applications during a GPS outage. In fact, the importance of using Locata technology for national infrastructure has already been acknowledged in Australia by the State of New South Wales and the city of Sydney. The Surveyor General for New South Wales recently set up a "Sydney Satellites" project which was the first urban deployment of a LocataNet. This test bed became operational on October 10, 2012. A NSW government report on Locata performance has been delivered to the Australian government to consider Locata incorporation as a core part of critical national infrastructure. (An educational conference video of Paul Harcombe, NSW Chief Surveyor, presenting Sydney Satellites can be seen here:

It is important to understand that a Locata network can easily be scaled­ from the size of a room to thousands of square miles­using the same transmitters. Case in point, Locata has just been granted a contract to deploy a nonGPS-based positioning system to deliver cm-accurate positioning and nanosecond time transfer across 2,500 square miles of White Sands Missile Range in the United States. This is a completely new capability for the U.S. military.

Locata’s new capabilities also ensure a reliability which is impossible to guarantee using satellites­and the efficiency gains in commercial systems is extremely impressive. For instance, Leica Geosystems of Switzerland–one of the world’s best professional-grade GPS companies–has developed the world’s first GPS+Locata systems to seamlessly transition between satellitebased and Locata-based solutions as required. They launched their first "Powered by Locata" system at the international MINExpo Conference during the last week of September, and the acceptance by the industry has been overwhelming and immediate. The efficiency gains in the first Leica installation at the Newmont Boddington Gold Mine in Western Australia are simply spectacular. At the time of writing, Boddington has installed Locata in only 10 drill rigs, yet the mine is already reporting about $1,000,000 per month in increased efficiency in the operation of those drills. With this kind of measureable efficiency, the return on investment for Locata technology is merely a period of months. Boddington has now mandated that every highprecision machine in the pits must be Locata-enabled.

And perhaps most importantly for the nearly 200 non-superpower countries seeking a sovereign PNT solution, a Locata network allows them, in some measure, to remove the GNSS dependency on foreign superpowers from around their local and significantly vulnerable areas. Locata installations can be designed to ensure PNT availability in areas where satellite-based systems will not reliably work (even indoors). End users can therefore literally guarantee signal availability wherever it is needed, so nations can now provide and control PNT for critical applications in their infrastructure.

GPS has become so deeply integrated into critical applications that it is prudent to improve the technology by whatever means possible, but in the end, satellite-based positioning systems will still have shortcomings. The fact is, with all due respect to the fantastic success of GPS technology and the multitude of applications it has supported and inspired, those GPS signals were never designed to do what today’s applications need. Today, the public and business demands accurate PNT everywhere, and that’s something that was not even imagined when GPS was being developed. It is no wonder that satellite systems alone cannot deliver the world’s increasing expectations for positioning, navigation and time-transfer. Consequently, there must be a non-GPS-based augmentation technology to fill an essential technological hole that GNSS cannot deliver on its own. Marrying GNSS with a terrestrial equivalent will inevitably be embraced by the PNT community because it is such a sensible, elegant and seamless extension of what is today’s gold standard. Locata is the invention which finally allows the GPS-style positioning required for the future. MC

Paul Benshoof began his 22 years in GPS as the Project Manager responsible for the development and procurement of the PLGR ­ the DoD’s first secure handheld GPS receiver, manufactured by Rockwell Collins. He then devoted his technical prowess to developing navigation warfare (NAVWAR) test assets to support advanced technology demonstrations in GPS-denied environments, as well as supervising international test programs for NATO and allied forces. As GPS testing became increasingly important, he formed and directed the GPS Test Center of Expertise, a consortium of U.S. test agencies dedicated to GPS test and evaluation, while also chairing an international working group that helped standardize GPS test practices among 11 participating countries. Ultimately, he was selected to implement and lead the 746th Test Squadron’s Strategic Development activity that worked with commercial and military GPS industry to project guidance, navigation and NAVWAR testing shortfalls, and then managed developmental programs to fill technical capability gaps.

Nunzio Gambale is CEO of Locata Corporation, a privately owned Australian company that has invented terrestrial positioning networks which function as local ground-based replicas of GPS. The company’s LocataNets work alongside satellite-based GPS systems to improve reliability and expand coverage for modern industrial, commercial, government and consumer applications where GPS is erratic, jammed or unavailable.

A 1.154Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE