Researchers from Sandia National Laboratories and Ohio State University are pioneering a backup system using cell signals to keep an airplane on course when it cannot rely on global positioning system satellites. The study is based on the Doppler Effect and how radio transmissions from a satellite moving toward a receiver become compressed as they travel, while radio signals from a satellite moving away become stretched out. With some advanced mathematics and enough signals, the scientists say they can determine the source of the signals and calculate the receiver’s position.
Sandia lead researcher Jennifer Sanderson and her team are studying these “signals-of-opportunity” navigation at high altitudes. If they can collect signal data from the stratosphere, they may be able to develop a way to guide vehicles, such as aircraft, using a network of atmospheric radio frequency waves.
“While we are still processing the flight data, we believe our preliminary findings indicate that we detected cell tower signal beacons at our peak altitude of about 82,000 feet,” Sanderson said. “If these signals are clean enough for navigation, it will significantly change what we thought was possible for alternative navigation,” Sanderson said.
Commercial GPS receivers are susceptible to a couple different threats, according to Sanderson, one being jamming. Jammers, devices that overwhelm receivers with meaningless signals on GPS frequencies, are illegal but commercially available.
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