  In this paper we propose a method to achieve relative positioning and
tracking of a target by a quadcopter using Ultra-wideband (UWB) ranging
sensors, which are strategically installed to help retrieve both relative
position and bearing between the quadcopter and target. To achieve robust
localization for autonomous flight even with uncertainty in the speed of the
target, two main features are developed. First, an estimator based on Extended
Kalman Filter (EKF) is developed to fuse UWB ranging measurements with data
from onboard sensors including inertial measurement unit (IMU), altimeters and
optical flow. Second, to properly handle the coupling of the target's
orientation with the range measurements, UWB based communication capability is
utilized to transfer the target's orientation to the quadcopter. Experiment
results demonstrate the ability of the quadcopter to control its position
relative to the target autonomously in both cases when the target is static and
moving.
