This paper introduces a positioning system for walking persons, called "Personal Dead-reckoning" (PDR) system. The
PDR system does not require GPS, beacons, or landmarks. The system is therefore useful in GPS-denied environments,
such as inside buildings, tunnels, or dense forests. Potential users of the system are military and security personnel as
well as emergency responders.
The PDR system uses a small 6-DOF inertial measurement unit (IMU) attached to the user's boot. The IMU provides
rate-of-rotation and acceleration measurements that are used in real-time to estimate the location of the user relative
to a known starting point. In order to reduce the most significant errors of this IMU-based system−caused by the
bias drift of the accelerometers−we implemented a technique known as "Zero Velocity Update" (ZUPT). With the
ZUPT technique and related signal processing algorithms, typical errors of our system are about 2% of distance traveled.
This typical PDR system error is largely independent of the gait or speed of the user. When walking continuously for
several minutes, the error increases gradually beyond 2%. The PDR system works in both 2-dimensional (2-D) and 3-D
environments, although errors in Z-direction are usually larger than 2% of distance traveled.
Earlier versions of our system used an impractically large IMU. In the most recent version we implemented a much
smaller IMU. This paper discussed specific problems of this small IMU, our measures for eliminating these problems,
and our first experimental results with the small IMU under different conditions.