Adaptive 3D Position Estimation of Pedestrians by Wearing One Ankle Sensor

Without the assistance of Global Positioning System (GPS), estimating the 3D position of indoor and outdoor pedestrians using a single wearable device is a daunting if not impossible task, especially if micro-sensors are used. Here, we present a novel 3D position estimation method using one integrated ankle sensing device, which consists of an accelerometer, a gyroscope, a magnetometer, and a barometer. Pedestrians' vertical position is estimated by fusing the acceleration and angular velocity as well as the height derived from barometer data. To estimate pedestrians' horizontal position, we proposed an adaptive multimodal stride length model and a multi-sensor-fusion-based heading angle estimation method, using the Pedestrian Dead Reckoning (PDR) mechanism. By introducing a vertical variable into the stride length model, this new model greatly improved the applicability and accuracy of PDR in horizontal position estimation. Based on this new model, PDR can be used not only for estimating the horizontal position of the pedestrian walking on flat areas but also for those walking up and down stairs. The effectiveness and applicability of our method in 3D position estimation have been demonstrated in several different experiments of indoor and outdoor scenes. The first is when a pedestrian walks on an indoor flat ground, following a spiral trajectory. The estimation accuracy of pedestrians' height position is 1.5cm and the ratio of horizontal walking estimation error is 1.02m with a total walking distance of 53.1m. The second is when a pedestrian walks up staircases from Floor 4 to Floor 8 in a building. The cumulative error of the estimated height is 0.23m with a total height of 14.4m, and the root mean square error of the estimated horizontal 2D position is 15cm compared to a total horizontal walking distance of 38.4m. The third case involves a pedestrian walking on audience stands of an outdoor stadium and returns to the starting position for a total distance of 94.4m. The estimation error from the sensing device is 0.92m in this case, with mean error of the estimated height position of each step at 3.3cm. Having the capability to provide centimeter-level position estimation of pedestrians, this sensing device can be applied for 3D body tracking and indoor/outdoor pedestrian positioning and navigation.