Next-generation global positioning technology is goal of new Stanford center

By David Orenstein

Finding and safely clearing buried landmines and ordnance is a humanitarian task of mammoth scale around the world. A metal detector that can sense position down to a few centimeters could determine whether a buried piece of metal has the shape of an unexploded shell or is merely the small, irregular fragment of one that has already exploded.

That is one of the many applications of giving people position information with centimeter accuracy, anywhere, anytime. Faculty from five Stanford departments have formed the Stanford Center for Position, Navigation and Time (SCPNT) to advance the Global Positioning System (GPS) to enable that resolution and reliability in location information. Currently, GPS tells civilians where they are within a few meters, but the signal can be lost when radio interference or overhead cover intervenes.

"Research at the SCPNT is aimed at vastly extending and expanding the already revolutionary benefits of GPS in society," said Per Enge, the center's research director and a professor of aeronautics and astronautics. Enge announced the center's launch at an Institute of Navigation research conference in Long Beach, Calif., on Sept. 13.

Added James Spilker, a consulting professor in electrical engineering and aeronautics and astronautics: "Society has still only begun to tap the potential of GPS, much less the enhancements we are working on at the center. Stanford has both the track record and the expertise to help develop this potential for a wide variety of applications."

Two of the center's founding members, Spilker and Bradford Parkinson, the Edward C. Wells Professor in the School of Engineering, Emeritus, were prominent architects of the original GPS. Parkinson, Spilker and Enge join faculty from several departments with expertise in the new technologies that will be required to build on GPS: aeronautics and astronautics, applied physics, electrical engineering, mechanical engineering and physics.

The future of position information

Stanford led the development and deployment of the Wide Area Augmentation System (WAAS) in 2003, which sharpened the resolution of GPS down to one meter by correcting errors caused by distortions of the signals coming from satellites as the signals traveled through the atmosphere. Since then, the main limitation to GPS has been loss of signal for either of two reasons: an obstructed line of sight to the satellites or radio interference (malevolent interference is known as "jamming"). Research at the SCPNT will address both problems.

The center's researchers already are looking at techniques to get the maximum benefit from the new signals that will be available from GPS satellites. To date, civilians have only had total access to signals at one frequency. In the next decade, GPS will begin to broadcast signals at three frequencies for civilians. In addition, the center's researchers will leverage the signals from the Russian satellite navigation system, called GLONASS; the upcoming system from Japan, called QZSS; and the signals from Galileo, a satellite navigation system under development by the European Union.

Researchers will concentrate particularly on signal structure and design of methods to simultaneously use both Galileo and GPS. Using both systems increases the number of signals a receiver could detect, thereby increasing the accuracy and availability of position and time information, said Enge, who is the Kleiner Perkins, Mayfield, Sequoia Capital Professor in the School of Engineering. In addition, researchers are working to develop "smart" antennas that can weaken a jamming signal relative to a legitimate signal from any of these satellites. Researchers at the Stanford center also are already working with the U.S. Navy on a precision automated airplane landing technology that takes advantage of advanced antennas as well as the frequencies already available to military users of GPS.

SCPNT researchers also are developing several technologies to compensate for temporary signal losses, such as ones due to interference or overhead cover. Among the solutions are new micro-electromechanical systems (MEMS) and atom-based sensors, including accelerometers and gyroscopes (to measure movement) and oscillators (to measure time) that can be embedded in GPS receivers, such as those in vehicle navigation systems. When a GPS satellite signal is lost, the sensors can continue providing position and time information by recording the vehicle's movement since the last signal was received. These receivers also will leverage signals from other radio sources like television stations and existing radio navigation systems such as LORAN (for LOng RAnge Navigation).

To ensure that these robust receivers are also inexpensive, researchers at the new Stanford center are working to develop GPS integrated circuits that use less power than today's devices.

New applications

Whereas Stanford researchers helped develop the accurate-to-a-meter WAAS for the Federal Aviation Administration and the Navy system, they also are working with the FAA to deploy a complementary Local Area Augmentation System (LAAS) that will be used at major airports. Providing decimeter accuracy, the LAAS will allow jetliners to land fully automatically in zero visibility.

Enge said many future projects at the new center will have direct applications for private industries, including defense, transportation and even entertainment. For example, location-based encryption, a method of securing data based on its geographic position, has applications for digital rights management of sensitive media content such as movies. If a studio distributes a digital movie directly to theaters, it could encrypt the movie such that it will only play on a system located inside a theater's projection booth.

"Indubitably the most exciting applications will be the ones we have not yet thought of," Enge said.

David Orenstein is the communications and public relations manager at the Stanford School of Engineering.