  Accurate relative localization is an important requirement for a swarm of
robots, especially when performing a cooperative task. This paper presents an
autonomous multi-robot relative positioning technique. An Extended Kalman
filter (EKF) uses onboard sensing of velocity, yaw rate, and height as inputs,
and then estimates the relative position of other robots by fusing these
quantities with ranging measurements obtained from onboard ultra wide-band
(UWB). Specifically, innovations involve fast-ranging communication (333Hz for
2 robots), an automatic initialization procedure, proofs and demonstrations of
consistent estimation convergence under control commands such as formation
flight. Simulations concisely show the high precision, efficiency, and
stability of the proposed localization method. Real-world experiments are
conducted on a team of 5 Crazyflie2 quadrotors, demonstrating autonomous
formation flight and coordinated flight through a window. All results indicate
the effectiveness of the proposed relative positioning method for multi-robot
systems. Video and code can be found at
\textnormal{\url{https://shushuai3.github.io/autonomous-swarm/}}
