Locata’s technology was enabled by a cheaper alternative to the atomic clock found inside every GPS satellite. Each satellite uses its clock to timestamp the signal it sends back to Earth. A receiver can use that timestamp to calculate its distance from a satellite, based on the time it took for the signal to travel. Repeating this trick with several satellites reveals a gadget’s position through triangulation.
Locata’s satellite mimics are built with timing chips much less accurate than an atomic clock. That’s possible because they only keep in sync with one another, not to an external standard, says Gambale. LocataLites do this by listening to each other’s signals. Each LocataLite adjusts the timing of its outgoing signal based on the timing of the signals it picks up from other LocataLites, creating a feedback loop that ensures all the signals are in sync. “All the clocks drift together,” says Gambale, and all the signals are synchronized to within two nanoseconds.
“Synchronizing this kind of device is a big research task,” says Per Enge, professor and leader of the GPS research lab at Stanford University. His group is working on similar devices known as pseudolites that will be deployed across the U.S. by the Federal Aviation Authority to boost the reliability of GPS and to protect signals against jamming or natural interference. The goal is to make it possible for civilian aircraft to rely on GPS more heavily so they can use more sophisticated autopilots that help cut fuel use.
Enge says it is likely that these pseudolites will rely on time signals sent over the Internet, using a new protocol that enables high accuracy. Some may tune in to time signals broadcast by Iridium communications satellites, which are in lower orbits than GPS satellites and so yield stronger signals back on Earth.
Locata’s approach of using feedback among its devices sounds “valid,” Enge says, although those at the edge of a network might be more likely to lose their timing if they cannot correlate with as many of their fellows as those nearer the center.
Gambale hopes Locata’s technology could also aid aviation, and he says he has conducted test flights in Australia using the technology. However, civil aviation adopts new technology very cautiously due to the need for absolute safety. “Locata will make their money from construction and agriculture,” says Enge.