  Unmanned aerial vehicles (UAVs) are widely applied in civil applications,
such as disaster relief, agriculture and cargo transportation, etc. With the
massive number of UAV flight activities, the anti-collision technologies aiming
to avoid the collisions between UAVs and other objects have attracted much
attention. The anti-collision technologies are of vital importance to guarantee
the survivability and safety of UAVs. In this article, a comprehensive survey
on UAV anti-collision technologies is presented. We firstly introduce laws and
regulations on UAV safety which prevent collision at the policy level. Then,
the process of anti-collision technologies are reviewed from three aspects,
i.e., obstacle sensing, collision prediction, and collision avoidance. We
provide detailed survey and comparison of the methods of each aspect and
analyze their pros and cons. Besides, the future trends on UAV anti-collision
technologies are presented from the perspective of fast obstacle sensing and
fast wireless networking. Finally, we summarize this article.
