Despite its marvelous success over the last three decades, the Global Positioning System (GPS) has two Achilles heels: its signals are weak and in the case of civil GPS - it is unauthenticated. At UT Austin's new Radionavigation Laboratory, directed by Assistant Professor Todd Humphreys, we are working to address both these vulnerabilities.

Weak GPS Signals: Just how weak are the signals transmitted by GPS satellites? Consider this comparison: a hand-held GPS device recovers less power from a GPS satellite than it would from a 30-Watt light bulb held 4000 km away. For typical GPS users this means that, unlike cell-phone and television signals, GPS signals do not penetrate well indoors. Weak signals also make GPS an easy target for jamming: A single well-placed handheld 1-Watt jammer built with off-the-shelf parts could knock out GPS across the entire Manhattan borough of New York City. The deepening dependence of the civil infrastructure on GPS - especially for timing synchronization and the potential for finnancial gain or high-profile mischief makes civil GPS jamming a gathering threat. Finally, weak signals make GPS vulnerable to natural interference events like solar radio bursts and ionosphere-induced power fuctuations called scintillation.

At the Radionavigation Laboratory, we are developing techniques to harden GPS against man-made and natural interference and to push GPS use deeper inside buildings. This work involves innovative signal tracking techniques, re-purposing signals of opportunity for navigation (e.g., from cell phone towers, Iridium satellites, etc.), and collaborative navigation.

Unauthenticated GPS Signals: GPS signals come in two flavors: military and civil. Military GPS signals are strongly encrypted to prevent counterfeiting, but civil GPS signals support no such authentication; they are broadcast "in the clear," which means they are vulnerable to spoofing. To better assess and defend against the spoofing threat, the Radionavigation Lab, in colloboration with Cornell University and Coherent Navigation, Inc., has developed a fully functional portable civil GPS spoofer. We have demonstrated that a malefactor in possession of such a device could dupe any off-the-shelf civil GPS receiver into reporting erroneous position and time data, and we have warned that such spoofing could threaten cell telephone systems, power grids, and financial transactions, which all depend on GPS-based synchronization, as well as location-based regulatory practices such as fishing regulation and road-user charging schemes. To address this threat, we are busy developing effective and practical defenses against civil GPS spoofing.