  Decentralized state estimation is one of the most fundamental components of
autonomous aerial swarm systems in GPS-denied areas yet it still remains a
highly challenging research topic. Omni-swarm, a decentralized omnidirectional
visual-inertial-UWB state estimation system for aerial swarms, is proposed in
this paper to address this research niche. To solve the issues of
observability, complicated initialization, insufficient accuracy, and lack of
global consistency, we introduce an omnidirectional perception front-end in
Omni-swarm. It consists of stereo wide-FoV cameras and ultra-wideband sensors,
visual-inertial odometry, multi-drone map-based localization, and visual drone
tracking algorithms. The measurements from the front-end are fused with
graph-based optimization in the back-end. The proposed method achieves
centimeter-level relative state estimation accuracy while guaranteeing global
consistency in the aerial swarm, as evidenced by the experimental results.
Moreover, supported by Omni-swarm, inter-drone collision avoidance can be
accomplished without any external devices, demonstrating the potential of
Omni-swarm as the foundation of autonomous aerial swarms.
