  A decentralized swarm approach for the fast cooperative flight of Unmanned
Aerial Vehicles (UAVs) in feature-poor environments without any external
localization and communication is introduced in this paper.
  A novel model of a UAV neighborhood is proposed to achieve robust onboard
mutual perception and flocking state feedback control, which is designed to
decrease the inter-agent oscillations common in standard reactive swarm models
employed in fast collective motion.
  The novel swarming methodology is supplemented with an enhanced Multi-Robot
State Estimation (MRSE) strategy to increase the reliability of the purely
onboard localization, which may be unreliable in real environments.
  Although MRSE and the neighborhood model may rely on information exchange
between agents, we introduce a communication-less version of the swarming
framework based on estimating communicated states to decrease dependence on the
often unreliable communication networks of large swarms.
  The proposed solution has been verified by a set of complex real-world
experiments to demonstrate its overall capability in different conditions,
including a UAV interception-motivated task with a group velocity reaching the
physical limits of the individual hardware platforms.
