Investigating the use of rotating foot mounted inertial sensors for positioning

Foot mounted inertial sensors have been used in recent literature to provide high accuracy positioning through the use of zero velocity updates (ZUPT) every time the user takes a step. When only ZUPTs are used, the remaining positioning errors are primarily a result of heading drift due to poor observability. This paper demonstrates that a single axis rotation of an Inertial Measurement Unit (IMU) provides improved observability of IMU accelerometer and gyro biases. In particular, all gyro biases become observable when the IMU is rotated about a single horizontal axis. This results in a significant reduction of heading errors and hence also improves positioning accuracy. This paper first presents results using simulated data from a static environment to verify observability of bias states. The paper then describes the results from a physical implementation of a rotating IMU platform that is attached to a user's shoe. It is demonstrated that maximum position errors are significantly reduced to less than 1.3m over three trials for the rotating IMU compared to 12.4m for the non-rotating IMU.