Researchers have developed an algorithm that can “eavesdrop” on any signal from a satellite and use it to locate any point on Earth, much like GPS. The study represents the first time an algorithm was able to exploit signals broadcast by multi-constellation low-Earth orbit (LEO) satellites, namely Starlink, OneWeb, Orbcomm, and Iridium.
Researchers found that by listening to the signals of eight LEO satellites for about 10 minutes, their algorithm could achieve unprecedented accuracy in locating a stationary receiver on the ground and was able to converge on it with an error of only about 5.8 meters.
The research was led by Zak Kassas, Professor of Electrical and Computer Engineering at The Ohio State University and Director of the Department of Transportation Center for Automated Vehicles Research with Multimodal AssurEd Navigation (CARMEN).
The researchers did not need assistance from the satellite operators to use the signals, and they emphasized that they had no access to the actual data being sent through the satellites — only to publicly available information related to the satellites’ downlink transmission frequency and a rough estimate of the satellites’ location.
From transportation to communication systems to the power grid and emergency services, nearly every aspect of modern society relies on positioning, navigation and timing data from global navigation satellite systems (GNSS), or GPS, that orbit the Earth. Despite this, because GPS system signals are weak and susceptible to interference, they can often become unreliable in certain places such as indoor environments or in deep urban canyons. In addition, GNSS signals are spoofable, which poses serious security risks in safety-critical applications, such as aviation.
In the long term, such complications could lead to a number of navigational and cybersecurity issues, especially as virtually all of our current systems rely heavily on GPS, Kassas said. Technologies on the rise, such as autonomous vehicles, he noted, are beginning to amplify the limitations of our current GNSS systems.
“It’s becoming more pressing to find civilian and military alternatives to GPS, whether as a backup or in the case when GPS isn’t there whatsoever,” said Kassas.
His work suggests utilizing signals from LEO satellites as an alternative for humans’ positioning, navigation, and timing needs, as they reside about 20 times closer to Earth compared to GNSS satellites, which reside in medium Earth orbit — a little more than 20,000 km above the planet. According to Kassas, the technology could potentially usher in a new era of positioning, navigation, and timing.
“We are witnessing a space renaissance. Tens of thousands of LEO satellites will be launched into space over the next decade, leading to what is referred to as mega-constellations,” he said. “Signals transmitted by these satellites will revolutionize numerous technologies and benefit scientific inquiry in fields such as remote sensing.”
What also makes the study so different from all other attempts at creating an alternative to GPS is, unlike previous studies, this algorithm doesn’t reverse engineer the signal, said Kassas.
“Our algorithm is agnostic to the LEO constellation,” said Kassas. “Our receiver can listen to virtually any satellite signal, trains on the data it’s receiving on-the-fly, then deciphers certain features of the signal in a way where we can reconstruct what they are transmitting into location data.”
To demonstrate the team’s new approach, the team applied the algorithm to four different LEO satellite constellations: Starlink, OneWeb, Orbcomm, and Iridium. The algorithm cracked all these signals, with virtually no prior knowledge about what is being transmitted.
Although a patent has been filed on the algorithm, the team does plan to continue evolving all of the algorithm’s technical abilities, said Kassas.
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