The radar is connected to a small navigation computer that measures the distance between the heel and the ground at regular intervals. If it doesn't change, then the system knows that the user isn't actually moving and resets the IMU's inertial velocity reading to zero.
Nancy Sinatra once mused that her boots were made for walking. In these days of global positioning, going walkabout is not as random an event as it might once have been, but there are still occasions when the all-seeing GPS device can't pick up a satellite. In such cases, having a back-up could mean the difference between getting out of the deep, dark underground cave in one piece or being lost in its tunnels forever. Researchers from North Carolina State University and Carnegie Mellon University have combined technology that is used to measure speed and distance with portable radar equipment to help keep track of a user's location.