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Radar in Shoes Can Step In When GPS Fails

GPS satellite (


A global positioning system (GPS) is handy if you’re in a location where the device can access the positioning satellite, but at other times, such as in a building or underground, it doesn’t do much good. An engineering team at North Carolina State University (NCSU) in Raleigh and Carnegie Mellon University (CMU) in Pittsburgh, Pennsylvania has developed a prototype solution for those times when the satellite and GPS device are not in contact.

That solution is a form of radar built into a person’s shoe. The radar has a sensor that tracks the distance between the heel of the shoe and the ground. It indicates if the individual is moving or standing still.

By itself, the shoe sensor would not tell much about a person’s location, but it fills a gap encountered by inertial measurement units (IMUs) that aim to step in when a GPS loses contact with satellites. IMUs are electronic devices that measure the forces created by acceleration and deceleration to determine how quickly people move and how far. IMU technology tracks a person’s movement after losing a GPS signal and provides location data based on someone’s last known position from the GPS.

IMUs often have problems, however, determining when someone is moving or standing still, and getting that part wrong throws off the IMU’s entire calculations. The trick is determining independently when a person is stationary. That’s the function of the shoe sensor: it tells when someone is standing still for a period of time, taking a brief pause between steps, or continuously moving.

The shoe radar uses the stationary/moving indicator in the sensor to adjust the IMU data showing movement — acceleration or deceleration — and combines that calculation with the last known position given by the GPS to determine an individual’s location. The team reports promising early results with the device.

The NCSU/CMU team published its findings in the October 2010 issue of IEEE Transactions On Microwave Theory And Techniques. The research was funded by grants from Air Force Research Laboratory and the Defense Advanced Research Projects Agency.

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