A Conceptual Framework and a Review of Conflict Sensing, Detection, Awareness and Escape Maneuvering Methods for UAVs (2011)

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 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 www.intechopen.com Aeronautics and Astronautics 550 adequate separation. Although large efforts have been done to address collision detection and avoidance problem to manned and unmanned aircraft, however there had been little survey and comparative discussion of the techniques and methods deployed to resolve conflicts. Some efforts towards describing and understanding the differences among proposed approaches have been introduced in the literature. The majority of conflict detection and resolution methods review tried to highlight the differences among different methods. Warren (Warren, October 1997) conducted an evaluation among three conflict detection methods. Zeghal (Zeghal, August 1998) provides a review of the differences among force field collision avoidance methods. In the last decade, Krozel et al. Current technology advances allow for innovative CAS systems to be more effective in reducing the number of collisions and utilizing airspace more efficiently. Those new systems need to be addressed and compared. Recently, Utt et al. That is to obtain routine access to airspace. Lacher et al. Albaker and Rahim (Albaker & Rahim, 2010b) proposed a generic collision avoidance system and presented a survey of some methods in the air traffic domain. A little explanation is given in the literature addressing the problem of how complete collision sensing and avoidance system is functioning to solve conflicts. Towards addressing these problems, this chapter has three main goals: (1) To explore the fundamental concept of operation and presents up-to-date literatures review of the collision sensing, detection, awareness and avoidance methods those deployed for aircraft, especially for unmanned aircraft. (2) To introduce a conceptual framework to assist in the design of context-aware application in collision avoidance domain. This is done by providing a better understanding of what context is and how it can be used in the conflict resolution domain. (3) To categorize methods into what type it is designed as well as point out its advantages and disadvantages. Furthermore, this work identifies common issues that should be considered in avoidance systems design process. The following sections are organized as follows: Firstly, the main functions carried by the collision avoidance system with an introduction on how to get knowledge of incoming threats are presented. Secondly, each function in CAS system is discussed in details, pointing out the significant researches done in each function. A context-awareness engine is explored as one of the functions in CAS system design. Next, the major design factors of collision avoidance systems are addressed. Finally, the developed trajectory escape maneuvering methods are classified.