Helping wireless devices find their location without GPS 

We expect our phones, cars and other connected technologies to know where they are and to communicate wherever we go. The Global Positioning System, or GPS, helps make that possible, but the satellite signals GPS uses can’t reach everywhere. Inside buildings, underground and among tall buildings, those signals can be blocked or disrupted. Now, Michigan State University researchers have demonstrated how wireless systems can work together without relying on GPS.

Jeffrey Nanzer, MSU Research Foundation Distinguished Professor in the College of Engineering, leads the team developing the technology, which uses what engineers call a “distributed array” to bring multiple wireless systems together so they can act like one larger system.

This technology also could help wireless systems pinpoint the location of objects with remarkable precision. Nanzer’s team has demonstrated positioning accuracy of an item within 0.82 millimeters, or roughly a grain of sand.

“One of the biggest challenges is synchronizing multiple wireless systems to work together to improve location accuracy,” said Nanzer. “It’s one thing to say that your phone is in Spartan Stadium and it’s another to say your phone is in section 21, row 61, seat 62."

In research published in IEEE Transactions on Microwave Theory and Techniques, Nanzer and his collaborators demonstrated a way for separate wireless systems to coordinate with one another in real time.

The approach uses commercially available wireless equipment and doesn't require cables connecting the systems or an outside timing reference such as GPS. Instead, the systems “talk” to each other by exchanging signals. By comparing those signals, the wireless systems can continuously adjust to stay in sync.

The researchers demonstrated this in environments where wireless signals bounce and reflect off of surrounding objects and were able to coordinate the wireless systems in less than one ten-billionth of a second.

“The ability to coordinate without relying on an external GPS reference could be particularly useful in environments where satellite signals are unavailable, unreliable or obstructed,” said Nanzer. “This technology could improve the performance of radar, wireless communications, satellite remote sensing and navigation systems.”