



A centimeter-accurate GPS-based positioning system that could revolutionize geolocation on virtual reality headsets, cellphones, and other devices has been developed by researchers in the Cockrell School of Engineering at The University of Texas at Austin.

Applications could include drones that can deliver packages to a specific spot on a consumer’s porch, precise collision-avoidance systems on cars (via vehicle-to-vehicle communications), and a globally referenced 3-D map of one’s surroundings that would place a VR game in the real world instead of being limited to indoors in about a three-feet radius.

“Imagine games where, rather than sit in front of a monitor and play, you are in your backyard actually running around with other players,” said Todd Humphreys, assistant professor in the Department of Aerospace Engineering and Engineering Mechanics and lead researcher. “To be able to do this type of outdoor, multiplayer virtual reality game, you need highly accurate position and orientation that is tied to a global reference frame.”

Humphreys and his team in the Radionavigation Lab have built a low-cost system that reduces location errors from the size of a large car to the size of a nickel — a more than 100 times increase in accuracy.

A positioning breakthrough in mobile technology

“Under good multipath conditions, 2-to-3-meter-accurate positioning is typical with current smartphones and tablets,” the researchers note in a GPS World article. “Under adverse multipath, accuracy degrades to 10 meters or worse.”

That’s not an inherent GPS limitation. Centimeter-accurate positioning systems are already used in geology, surveying and mapping, but the survey-grade antennas these systems employ are too large and costly for use in mobile devices. The breakthrough by Humphreys and his team is the creation of a powerful, sensitive software-defined GPS receiver that can extract centimeter accuracies from the inexpensive antennas found in mobile devices and at low cost.

Humphreys and his team have spent six years building a specialized receiver, called GRID, to extract “carrier phase” measurements from low-cost antennas. GRID currently operates outside the phone, but it will eventually run on the phone’s internal processor, the researchers say. Humphreys and his team are now working with Samsung to develop a snap-on accessory that will tell smartphones, tablets, and virtual reality headsets their precise position and orientation.

The researchers designed their system to deliver precise position and orientation information — how one’s head rotates or tilts — to less than one degree of measurement accuracy. This level of accuracy could enhance VR environments that are based on real-world settings, as well as improve other applications, including visualization and 3-D mapping.

Humphreys collaborated with Professor Robert W. Heath from the Department of Electrical and Computer Engineering and graduate students on the new technology, which they describe in an open-access article in a recent issue of GPS World. The research was funded by Samsung.

Abstract of Accuracy in the palm of your hand

The smartphone antenna’s poor multipath suppression and irregular gain pattern result in large time-correlated phase errors that significantly increase the time to integer ambiguity resolution as compared to even a low-quality stand-alone patch antenna. The time to integer resolution — and to a centimeter-accurate fix — is significantly reduced when more GNSS signals are tracked or when the smartphone experiences gentle wavelength-scale random motion.