“…In the first step, Automatic Dependent Surveillance-Broadcast (ADS-B) system, in which the UAV periodically transmits information about its altitude, speed and location through GPS to a ground control station [111,112]. Other sensing methods include radar [113,114] and infrared sensors [115]. Collision estimation techniques include distance-based, act-as-seen [116], probabilistic estimation [117] and worst case estimation [118].…”