Innovative Solution for Drones in GPS-Denied Environments

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Drones use GPS to find their way without a pilot. But GPS signals can be easily blocked by tall skyscrapers or trees — leaving drones lost. Now researchers have developed a new method that gives aircraft a backup system in case GPS fails: An antenna on the ground that can tell a drone where it is.

The University of Washington team’s unmanned drones carry transponders on board that send signals to operators and any surrounding aircraft about their whereabouts. The team used a large ground-based antenna array to pick up the signals and then triangulate the position of the aircraft.

“The ground station is smarter than the aircraft at that point,” said Christopher Lum, a UW research assistant professor of aeronautics and astronautics and the director of the Autonomous Flight Systems Laboratory. “We’re just modifying the autopilot onboard the aircraft. Instead of using GPS information to navigate, it’s listening to this message coming from the ground to figure out where it is.”

The team tested their system with the antenna array in June. The drone successfully completed its 1.25-mile flight path without using GPS. The only time it deviated from the designated path was due to wind.

The innovation in their method is the use of the transponder. The ground-based antenna system, on the other hand, makes this technique cumbersome. Right now it only works when the team is flying a drone at an airport with that antenna system. The researchers will partner with T-Mobile to try to use cellphone towers to perform the same function. Once the drones can fly larger distances without GPS, the team hopes to use them to help transport medical supplies to and from rural areas in the state of Washington.