Technology enthusiasts know that getting lost has almost become a thing of the past thanks to global positioning systems (GPS). But if GPS fails you, what can you do? A shoe-embedded radar system could soon be a useable backup option that may help you find your way.
A team of researchers from North Carolina State University and Carnegie Mellon University (CMU) are responsible for the development of the secret agent-like shoe device.
“There are situations where GPS is unavailable, such as when you’re in a building, underground or in places where a satellite connection can be blocked by tall buildings or other objects,” says Dr. Dan Stancil, co-author of a paper describing the research and professor and head of NC State’s Department of Electrical and Computer Engineering. “So what do you do without satellites?”
One solution would be to use inertial measurement units (IMUs), which are electronic devices that measure the force created by acceleration and deceleration to determine how rapidly you are traveling and how far you have moved.
The technology works together with GPS, with the IMU recording your movement after you lose a GPS signal; it ultimately provides you with location data that relates to your last known location via GPS. For example if you went into a cave and your GPS signal was lost, you should utilize the IMU to retrace your steps to the last known GPS location and you could find your way back out.
IMUs however, have traditionally come with a significant challenge. Any slight errors an IMU makes in recording acceleration lead to errors in estimations of velocity and position, and those errors add up over time. If an IMU thinks you are traveling, even as little as 0.1 meters per second, when you are actually being still, the IMU will have moved you about 18 meters away from your real position.
But wait, “if you had an independent way of knowing when your velocity is zero, you could significantly reduce this sort of accumulate error,” Stancil says.
This where the shoe radar enters the picture.
“To address this problem of accumulating acceleration error, we’ve developed a prototype portable radar sensor that attaches to a shoe,” Stancil says. “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.” That could mean that you are standing still, or it could signal the natural pause that occurs between steps when someone is walking. Either way, Stancil says, “By resetting the velocity to zero during these pauses, or intervals, the accumulated error can be greatly reduced.”
A different way to say it would be that the navigation computer gathers data from the shoe radar and the IMU and by including the most recent location data from GPS; it can do a much better job of monitoring your present location.
The academic research paper, “A Low-Power Shoe-Embedded Radar for Aiding Pedestrian Inertial Navigation,” is published in the October issue of IEEE Transactions On Microwave Theory And Techniques.