While most people think GPS is the be-all and end-all for navigation, it doesn't work if the satellite signal is unavailable.

Enter Dr. Dan Stancil, head of North Carolina State's Department of Electrical and Computer Engineering. He and a team of researchers decided to put GPS-like capabilities in a practical device. The answer Stancil came up with was shoes. 

The shoes use a combination of sensors, called inertial measurement units, and radar. The inertial measurement units are similar to those in a Wii controller, and measure acceleration and deceleration to determine how quickly someone has moved. The radar checks the speed and determines if the person is really taking a step. The technology works with the GPS by tracking the movement of a person after they have lost satellite signal.

The easiest way to navigate on foot is GPS. But if you don't have access to the satellites, whether you are in an urban area with satellites that block out the satellites or maybe you're in a cave or a tunnel,  finding your way back to where there is GPS availability can become a problem, Stancil said. You wouldn't do this instead of GPS, he added. You would do it to trace your steps and figure out how far you have moved since you lost GPS. This would allow you find the GPS.

Traditional IMU devices often go astray when minor errors in measuring acceleration snowball. Stancil says even if someone is standing still, but the IMU might think they are moving 0.1 meters per second, the problem will get worse.

 To address this problem of accumulating acceleration error, we've developed a prototype portable radar sensor that attaches to a shoe, Stancil said. The radar is attached to a small navigation computer that tracks the distance between your heel and the ground. If that distance doesn't change within a given period of time, the navigation computer knows that your foot is stationary.

The concept is still in prototype phase, says Stancil, and will need significant development before it becomes commercially viable. He says ideally it could be used for military situations where a team goes out into unfamiliar territory.

Stancil, who worked with researchers from NC State and Carnegie Mellon University on the project, co-authored a paper on the concept called, A Low-Power Shoe-Embedded Radar for Aiding Pedestrian Inertial Navigation. It was published in the October issue of IEEE Transactions On Microwave Theory And Techniques.