Prof. Todd Humphreys's Research Team Forges Ahead with Opportunities in Radionavigation
By Tara Haelle(Reprinted from the Aerospace Engineering and Engineering Mechanics Web Site) Whether it's investigating ways to preserve the security of GPS signals or developing new types of receivers, the field of radionavigation is ripe with possibility and Dr. Todd Humphreys does not hesitate for a moment in defining how his research team fits into the mix. What's the next big thing in GPS he asks. That's what we're trying to pursue. In fact, that's what we're trying to create. In short, Humphreys said his goal is that his research team becomes THE go-to group for several exciting new research areas in GPS and radionavigation. His team's five main research thrusts encompass some of the most important issues and most compelling innovations developing in the field, and he makes it clear that he intends The University of Texas to lead the pack in all five areas. Each of them is pretty exciting, Humphreys said. And we have evidence that we're on the right path with them. The areas include radionavigation security and integrity, software receiver development, opportunistic navigation and ionospheric investigations. Radionavigation Security and Integrity Though they comprise two distinct research areas, security and integrity have related goals: it's vital that a user can get clear, accurate information from a GPS signal free from intentional or unintentional (natural or manmade) interference and from the false data that a malicious hacker could generate to replace a signal's real data.Security is related to an intelligent actor doing something like a hacking attack on your computer, Humphreys explained. Integrity relates to someone trying to increase the background noise in the signal or from Mother Nature having a bad day and increasing the background noise. Humphreys said radionavigation security is a relatively new field, thanks in part to one of his papers, Assessing the Spoofing Threat, published in 2008. Graduate students Kyle Wesson and Daniel Shepard are focused on this area. 'In the late 90s and early 2000s, civil GPS became more precise and useful, but few gave much thought to its security vulnerabilities,' he said. While the military uses encrypted signals, civilian signals are unauthenticated, opening the door for anyone to mimic the signal and insert their own information. Humphreys and his colleagues built a spoofer that reveals this Achilles heel of GPS, allowing them to 'hack' the signal and force a target receiver to display the time and location of their choosing. Imagine a person wearing an ankle bracelet while awaiting trial, for example, who could 'spoof' the signal received by the bracelet and show them as being in their home when they're actually halfway across the globe. 'As long as you understand the recipe for generating the signals, you can generate fictitious GPS signals carrying fake data that look indistinguishable from the authentic signals,' he said. They've tested their device on everything from iPhones to high end receivers. 'We've never met a civil receiver we couldn't spoof,' he said. Their work has gotten attention: the Department of Homeland Security visited in March, and Humphreys was asked to chair a panel session on Radionavigation Security for The Institute of Navigation at the GNSS Conference in September. Meanwhile, graduate student Jahshan Bhatti is helping with research in radionavigation integrity, which can be compromised by an intentional actor or simply by natural phenomena. 'When the sun has a bad day - sun spots, solar flares GPS receivers have to deal with an elevated noise level,' Humphreys said. 'Or, somebody could turn on a jammer and knock out your signal. Radionavigation integrity means not getting blindsided.' Software Receivers Another big area of research focuses on building receivers built with general-purpose chips that can run software to generate or gather GPS signals rather than receivers with special-purpose hardware chips. 'Software receivers are the best platform for GNSS innovation,' Humphreys said. 'They're power hungry right now, but that's getting better, and the reconfigurability is often attractive enough that it offsets the additional use of power.' In conjunction with Cornell University, where Humphreys did his graduate work, his team has built CASES, a dual-frequency software-defined receiver that the two schools have been able to commercialize and license to a small business. Along with graduate students Bhatti, Shepard, Andrew Higdon and Andrew Joplin, Humphreys has been collaborating with UT Aerospace Engineering's Dr. Glenn Lightsey to put the software package into another piece of hardware, called FOTON, that they hope will operate in space aboard one of the Lightsey group's microsatellites. 'This device will allow a cubesat to know its position and probe the atmosphere while it orbits, measuring temperature, water vapor and the thickness of the ionosphere,' Humphreys said. They hope their collaboration leads to a next-generation satellite sensor: the very first compact software-defined occultation GPS that can track GPS signals piercing through the atmosphere from satellites as they set behind the earth. Opportunistic Navigation and Ionospheric Investigations Graduate students Ken Pesyna and Zak Kassas are focused on opportunistic navigation, basically exploiting any possible signals already out there even if they were never intended for navigation. Such signals include the very stable CDMA cell phone signals, such as those broadcast by Verizon and Sprint towers, which can be used to track GPS better. 'Our motto is hungry navigation,' Humphreys said. 'Even though the signal may not be high quality, as long as we can characterize its quality, then we'll use it to the extent that it's warranted.' Though the field is crowded, it's also lucrative, and Humphreys is determined be at the head of the pack. The fifth research area his team is pursuing, ionospheric investigations, primarily deals with the interference caused by ionospheric storms. 'One man's signal is another man's noise and vice versa,' Humphreys said. 'Something that causes disruption to GPS is also informative, so if you want to know what the ionosphere is doing, you can use GPS to visualize what's happening.' Humphreys has big plans for his team's research. When the Iridium Constellation of satellites is replenished in 2015, for example, Humphreys wants to see several FOTON receivers hitching a ride, and he's been involved in lobbying the NSF to put these sensors on the satellites that will be going up. But all five areas are integral to his vision for UT's radionavigation research. 'We want to be known as the ones who jumpstarted radionavigation security as a field of research and are pushing the envelope in opportunistic navigation,' he said. 'And we want to be known as one of the foremost research institutions on software receivers.'