You have to know where you are to tell where you’re going. And if you want to rendezvous with someone at a precise point in time or share data faster with them, you’d better know when you are as well.
Those realities and the need to be better at position, navigation and timing (PNT) are the reasons behind a new program of record, Assured PNT, which falls within the U.S. Army’s Program Executive Office for Intelligence, Electronic Warfare & Sensors. Kevin Coggins, Assured PNT product manager, detailed its overall goals.
“It’s meant to assure our access to PNT information for our systems and our soldiers. And not just assure access to that PNT information but ensure the integrity of that PNT information. We need to make sure that we’ve got trusted PNT when we get it,” he said.
Those simple-sounding aims entail numerous challenges. To understand them, it helps to go over a bit of history and technology. Twenty or so years ago, the Army and other branches of the military digitized and put GPS technology to work. The result was improved PNT with orbiting GPS satellites providing signals from which pinpoint positioning information is derived. Although several factors can impact the results, position information is frequently better than within a meter accuracy. Just as important in an increasingly interconnected world, the signals provide time information accurate to 100 nanoseconds or better. That allows distant locations to synchronize clocks more tightly. In turn, that ups the rate at which data can be transmitted.
With better PNT, the U.S. military improved its capabilities. Data flowed faster, units coordinated better and targeting was more precise. Another consequence was that the number of GPS receivers soared. Today, the number is huge, as can be seen by how many receivers are found on each soldier and an armored fighting vehicle found in the thousands in the Army.
“We have soldiers that carry five GPS receivers,” Coggins said. “I may have eight to 12 GPS receivers on different variants of the Stryker.”
Not all of these are DAGRs—Defense Advanced GPS Receivers. A fraction will be civilian-grade GPS receivers that do not use the encrypted military signal. Individual soldiers may, for instance, carry one of these receivers, preferring them due to familiarity, ease of use or the presence of additional capabilities not found on their military counterpart. Even given that, the number of Defense Department-specific GPS receivers represents a logistics burden and makes it costly to update the technology.
What’s more, a significant change to that technology is on the way. Starting in fiscal year 2018, in compliance with Public Law 111-383, the Department of Defense must buy receivers that work with M-Code, a new GPS signal that offers improved anti-jamming and other enhancements. Use of the new signal means that every GPS receiver in the entire military will eventually need to be upgraded, which requires touching every piece of gear and every soldier potentially multiple times with a technology refresh.
There’s another challenge associated with the widespread use of GPS. Loss of the signal can cause a hiccup that ripples through communications, weapons, sensors and other systems. That signal loss could be due to tall buildings in an urban area or signal jamming, something that is easier to accomplish because the transmission arises from orbit. Given that signal strength falls with the square of the distance from transmitter to receiver, it will always be the case that a ground-based jammer will be in a good position to swamp a GPS signal.
In considering this situation, Coggins invoked Carl von Clausewitz, the 19th century military theorist. Although he lived at a time when the steam engine was the latest innovation, the German general had something to say about today’s technology.
“He talked about identifying an enemy’s critical dependencies and then turning those into critical vulnerabilities. If you take away the things that we’re critically dependent on, you take away our ability to conduct our mission. We view PNT as a critical dependency,” Coggins said.
The military is responding to these interlocking challenges with Assured PNT, a solution set formed after studying the landscape. Broadly speaking, the solutions involve the addition of capability vectors and the use of a systems-of-systems architecture. The first entails adding ways to ensure position, navigation and timing information are maintained in the event of a loss of the GPS signal. As for the second, in implementation this means that one assured PNT device will be on a soldier or piece of equipment. Everything else will get information from this master.
The Army is shifting focus from GPS receivers to PNT user equipment, Coggins indicated. This will allow the Army to attain a resilient PNT capability.
To see how this will work and explore the benefits, consider how PNT information can be maintained after a loss of the GPS signal. There are ways to keep highly accurate time other than by using a satellite signal. Atomic clocks, which mark time by measuring the emissions of atoms, are the world standard for timekeeping, with the best so accurate they only lose one second every five billion years. Achieving that kind of performance requires cooling the atoms and conducting the measurements in a well-controlled setting, neither of which is easy to do with objects carried by a dismounted soldier.
Fortunately, soldier- and vehicle-borne PNT doesn’t need that degree of extreme time accuracy. DARPA, the Department of Defense agency engaged in advanced research, is working on making atomic clocks as small and portable as a computer chip. DARPA also has programs that seek to create chip-sized gyroscopes and inertial measurement systems, which would provide portable and highly accurate position information. Assured PNT is partnering with DARPA in these efforts, according to Coggins.
As for the systems-of-systems concept, consider a Stryker. One new-generation device could acquire a PNT signal and could then distribute it throughout the armored vehicle. It would be able to do this because there are standard interfaces that GPS receivers use. Thus, a carefully designed master unit can stand in for the GPS receiver that a host of other devices expect to see.
“By having the ability to have this one box support those standard interfaces, we’ve found that it’s as easy as taking the old one off and plugging the new one in. We’ve found that it just works because we do a lot of work to verify interface compliance,” Coggins said.
The creation of a single point of failure in new devices is mitigated in two ways. One is through carrying the proper inventory so that a working device is available to be swapped in as needed. The second is by having a very low rate of failure. The current DAGR devices have that low rate; Coggins indicated that the successor, which is a DAGR Distributed Device (D3), is also proving to be as robust.
There’s a fiscal bonus to this distributed approach. Currently, a fleet of 3,500 Strykers carries some 11,500 or more GPS receivers. With this new approach, there will be 3,500 GPS receivers, as the ratio of vehicles to receivers will be 1:1. As Coggins noted, the result of the distributed approach is a reduction in maintenance and operational expenses by more than 67 percent. He added that this belt-tightening will be happening at the same time as an increase in capability.
For soldiers, a distributed approach will pay dividends in other ways. For instance, the Defense Department mandate is that soldiers must use keyed, and therefore secure, GPS receivers. This means that they must carry keys and batteries for multiple devices. That burden will be reduced when there is only one PNT device, not many.
On top of that, soldiers may not have to give up their beloved commercial units. Assured PNT is working with the science and technology communities to develop a prototype device that will interface with smartphones and other GPS-enabled commercial devices. Working behind the scenes, the device, which resembles a hockey puck, will supply a low-power wireless connection to these commercial devices. The hidden technology will assure any device being used has access to trusted PNT data without the soldier having to think about it or do anything differently.
According to Coggins, Assured PNT has four sub-programs. Two are focused on PNT user equipment, one for mounted and the other for dismounted situations. The remaining two sub-programs involve developing anti-jamming technology and what are called pseudolites, a contraction of the phrase “pseudo satellites.” The idea is to augment the orbiting constellation of satellites with transmission sources that are much closer to the user. Because the resulting signals will originate nearer to the receiver, they will be much harder to jam.
There already are commercial implementations of pseudolites, such as those from Locata Corp. of Canberra, Australia. Assured PNT has put out an RFP for its own pseudolite prototypes, with a contract due to be awarded in the fourth quarter of 2014.
As part of the implementation of the systems-of-systems concept and the rollout of the new technology, forces will be at the best PNT assurance level. That is, forces may be in a situation where they don’t need as much protection, referred to as PNT Assurance Level 0, all the way up to those circumstances in which the need is for the highest degree of protection, or PNT Assurance Level 3. The use of different levels of assurance will help smooth the transition and also help make it more cost-effective, a critical need given tight budget constraints. This means the Army will have the capability to scale units to the level of protection they require, resulting in significantly less cost for the taxpayer, according to Coggins.
In speaking of the future of Assured PNT and the rollout of solutions to the challenges of positioning, navigation and timing, he said, “There’s a window of time over the next several years, stretching all the way out to the 2020 timeframe, that cover how these technologies are going to start with some high-visibility demonstrations and field deployments.”
As Coggins said, “We’re not going to move slowly.” ♦
- Issue: 5
- Volume: 5