“Sugar-Cube”: Pedestrian Hardware Platform that Fits in the Sole of a Shoe

We report on the design, implementation, and demonstration of a miniaturized Inertial Navigation platform. The platform, with a total volume of 7.1
$cm^{3}$
(excluding battery and case), includes the Inertial Measurement Unit (IMU), chip-scale barometer, magnetometer, as well as a powerful computational engine for signal processing and execution of the navigation algorithm. The sensors are integrated using separate PCBs with castellated edges forming the connections with the main board allowing some flexibility in sensor selection. The platform is small enough for integration in the sole of a shoe, which is an optimal location for implementation of Zero Velocity Update (ZUPT) algorithms for prolonged self-contained navigation. The navigation solution is performed using an Extended Kalman Filter (EKF) framework with an update rate of 500 Hz. A series of indoor walking experiments were conducted to verify the navigation accuracy of the platform which showed error 0.53% of the trajectory length for a 125 m, 2.75-minute duration walk including flat planes, stairs, and an elevator ride.