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Solution to blocked satellite signals: Shoe radar?

University researchers think they've come up with a fix for augmenting GPS systems when satellite signals are blocked: a shoe radar system.

shoe sensor system
Way more moving parts than a GPS app, but... James Downey
sensor in heel
The radar sensor attaches to the heel. North Carolina State University and Carnegie Mellon University

With GPS devices popping up in everything from cars to cell phones these days, getting lost is getting harder. But what are the GPS-dependent to do when a blocked satellite signal confuses their wanderings (besides panic and curl up in the fetal position)?

Researchers from North Carolina State University and Carnegie Mellon University think they've come up with a solution: a shoe radar system that likely will never make it onto the average Joe's sneaker but could have implications for the military and those who work in mines, tunnels, and other remote or high-risk environments.

The prototype system involves a portable radar sensor that attaches to a shoe's heel and also hooks up to a small navigation computer that tracks the distance between your heel and the ground. If that distance doesn't change over a set period of time, the computer figures your foot is stationary.

The low-power system works in conjunction with an inertial measurement unit, or IMU, an electronic device that measures acceleration and deceleration to determine speed and distance traveled. IMUs are frequently used to supplement GPS devices once a satellite signal drops (if you entered a remote canyon, you could use the IMU to retrace your steps to the last known GPS location and find your way back out).

But IMUs can be faulty, as minor errors can accumulate, leading to an increasing difference between where the system thinks it's located, and where it's actually positioned.

That's where the radar shoe system comes in, as it signals the natural pause between steps. "By resetting the velocity to zero during these pauses, or intervals, the accumulated error can be greatly reduced," said Dan Stancil, professor and head of North Carolina State's Department of Electrical and Computer Engineering and co-author of a paper describing the research and published in IEEE Transactions on Microwave Theory and Techniques.

We've seen GPS-fitted shoes before, including a pair specifically aimed at tracking Alzheimer's patients. But as any of us living underground or surrounded by tall buildings or mountains knows, GPS can't always tell you where you are. And in some situations you just got to know.