Because of the key characteristics of Unmanned Aerial Vehicles (UAVs), removal of pilot, UAVs will be highly suited for repetitive, dirty, and dangerous operations. A wide range of civil and military applications are being explored in the community (Clapper et al., 2007). As a result, UAVs are given serious considerations in worldwide, making them the next step in evolution of aviation. Whatever missions are chosen for UAVs, their number and use will significantly increase in future. Currently, UAVs do not have convenient access to civil and military operation theatres due to their inability to provide an equivalent level-of-safety comparable to see-and-avoid requirements for manned aircraft. The current procedure requires a certificate of authorization be applied for every mission. Obtaining such an authorization may take more than a month. This lengthy process is not in line with increasing number of UAVs development. Therefore, an autonomous collision sensing, detection, awareness and avoidance system will be a key enabler for the integration of unmanned with manned aircraft in a shared airspace. The main objective of the Collision Avoidance System (CAS) is to allow UAVs to operate safely within non segregated civil and military airspace on a routinely basis. For this purpose, the UAV must be able to identify and be identified by the surrounding traffic. The diversity of UAVs and their missions involve a wide-range of system operating concept. Current unmanned aircraft range in size from small hand launch vehicles to large fixed-wing UAV with a wing span similar to Boeing 737. In addition, some UAV autonomously, semiautonomous or completely guided by ground pilot. Furthermore, unmanned vehicles cruise speed, climb/dive rate, turn rate and operating altitudes are similarly varied. Therefore, many CAS methods were proposed to account for that variation and to ensure that the unmanned aircraft efficiently avoids other cooperative traffic while also avoids fixed and moving obstructions such as terrain, obstacles and no flying zones. Numerous technologies are being explored in the community addressing CAS systems. Much of the research in collision avoidance methods for UAVs had been imparted from the air traffic management, maritime and mobile ground robot research communities. However, aircraft complicates the avoidance problem by added dynamic constraints that must be fulfilled for
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