While the invasion of GPS technology in everything - from cars to cell phones - has ensured that we never get lost, it is pertinent to ask what if your GPS stops working?
North Carolina State University and Carnegie Mellon University researchers have now developed a shoe-embedded radar system that may help you find your way.
"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," said Dr. Dan Stancil.
"So what do you do without satellites?"
One solution is to use inertial measurement units (IMUs), which are electronic devices that measure the forces created by acceleration (and deceleration) to determine how quickly you are moving and how far you have moved.
But minor errors an IMU makes in measuring acceleration lead to errors in estimating velocity and position - and those errors accumulate over time.
But, "if you had an independent way of knowing when your velocity is zero, you could significantly reduce this sort of accumulate error," Stancil said.
Enter the shoe radar.
"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," Stancil said.
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 said, "by resetting the velocity to zero during these pauses, or intervals, the accumulated error can be greatly reduced."
The paper is published in the October issue of IEEE Transactions On Microwave Theory And Techniques.