While the GPS can locate anything on Earth as long as the receiver is in the line of sight of multiple satellites, the location of the same device when indoors can be difficult. A team of researchers at the University of Utah have found a solution for this problem. The team has developed a suite of sensors and circuits that can be mounted to a boot (shoe) to determine its position with an accuracy of about 5 meters both indoors and outdoors, without using GPS.
The navigation system, installed in a very hefty prototype boot, could help rescue workers navigate inside buildings, and show firefighters where their team members are. It might also be integrated with virtual or augmented reality games. The Utah researchers presented their GPS-free navigation system at the International Solid-State Circuits Conference in San Francisco, earlier this year.
The Utah group’s navigation system is built on an inertial measurement unit or IMU—a little black box containing a gyroscope, magnetometer, and accelerometer. High-end systems of this kind help airplane pilots navigate the skys. Darrin Young, an electrical engineer at the University of Utah, wanted to make it possible to use an IMU in portable electronics. However readings from cheap versions of these sensors drift over time, and errors can accumulate rapidly. Young asked graduate student Qingbo Guo to figure out a way to keep these sensors calibrated. Guo found the solution in biomechanics. During each step, the heel is anchored to the ground for about 100 milliseconds. Guo figured out how to measure this instant of stillness, and use that to correct for the false motion in drifting data from the IMU.
Guo designed a flexible MEMS pressure sensor to place under the insole of a boot with an IMU. He calculated that the system needed about 1000 sensors to get accurate readings (and provide redundancy in case some sensors broke underfoot), and built a custom circuit to combine data from the IMU and the pressure sensors, and designed the necessary algorithms. In the prototype, the custom circuit is on a printed circuit board mounted to the side of the boot. They put the sensor outside the boot for easy access and debugging, but it could be inside the sole, and use Bluetooth.
Then he connected it all up with cables to a laptop in his backpack, and started walking. To test the navigation system, Guo walked in Salt Lake City for about three kilometers with the navigational boot tracker, and then compared data from the prototype with GPS data. After ten walks around campus, the maximum error was about 5.5 meters. He also tested the system during a longer walk in San Francisco’s Golden Gate Park. It doesn’t matter what kind of terrain, the system works. The performance is comparable to GPS, but it works inside, says the teamed duo.
