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(c) 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.Abstract-This paper proposes a taxonomy of Conflict Detection and Resolution (CD&R) approaches for Unmanned Aerial Vehicles (UAV) operation in an integrated airspace. Possible approaches for UAVs are surveyed and broken down based on their types of surveillance, coordination, maneuver, and autonomy. The factors are combined back selectively, with regard to their feasibility for operation in an integrated airspace, into several 'generic approaches' that form the CD&R taxonomy. These generic approaches are then attributed to a number of available method in the literature to determined their position in the overall CD&R scheme. The attribution shows that many proposed methods are actually unsuitable for operation in an integrated airspace. Furthermore, some part of the taxonomy does not have an adequate representative in the literature, suggesting the need to concentrate UAV CD&R research more in those particular parts. Finally, a multi-layered CD&R architecture is built from the taxonomy, implementing the concept of defense-in-depth to ensure UAVs safe operation in an integrated civil airspace.

This paper proposes a novel avoidance method called the Three-Dimensional Velocity Obstacle (3DVO) method. The method is designed for Unmanned Aerial Vehicle (UAV) applications, in particular to autonomously handle uncoordinated multiple encounters in an integrated airspace, by exploiting the limited space in a three-dimensional manner. The method is a three-dimensional extension of the Velocity Obstacle method that can reactively generate an avoidance maneuver by changing the vehicle velocity vector based on the encounter geometry. Adverse maneuvers of the obstacle are anticipated by introducing the concept of a buffer velocity set, which ensures that the ownship will diverge with sufficient space in case of sudden imminence. A three-dimensional resolution is generated by choosing the right plane for avoidance, in which the UAV conducts a pure turning maneuver. Implementation of the 3DVO method is tested in several simulations that demonstrate its capability to resolve various three-dimensional conflicts. A validation using Monte Carlo simulations is also conducted in stressful super-conflict scenarios, which results in zero collisions occurrences for the entire 25,000 samples. Nomenclature BV Buffer Velocity set CC Collision Cone set P φ Avoidance Plane at the angle φ RV i Obstacle Reachable Velocity set S pz Protected Zone VO P φ Velocity Obstacle section on Avoidance Plane-φ VO Velocity Obstacle set α vo Opening angle of the Velocity Obstacle Cone, [-] ∆t Time-step of the VO set generation, [s] δ P Dihedral angle of the avoidance-plane from the XY-plane, [-] ω a.cr Critical avoidance turning rate, [-/s] ω avo Avoidance turning rate, [-/s] φ P Angle of Avoidance Plane around X-axis ψ oi Azimuth angle of the obstacle-i from the ownship, [-] σ col Standard Distribution of Collision Probability, [-] θ oi Elevation angle of the obstacle-i from the ownship, [-] A vo Apex position of the Velocity Obstacle cone, [m] D vo Velocity Obstacle cone symmetric axis vector, [m] E φ vo Escaping point of a VO set, [m/s]

A novel architecture for a general Unmanned Aerial Vehicle (UAV) Conflict Detection and Resolution (CD&R) system, in the context of their integration into the civilian airspace, is proposed in this paper. The architecture consists of layers of safety approaches, each representing a combination of different methods for surveillance, coordination, action, and decision. These are collected from a survey of various CD&R methods existing in both manned and unmanned domains. The combination process shows that some approaches are suitable, while others are not, for the context of UAV integration. The suitable approaches are then arranged using the 'defense in depth' concept, where each layer filters a specific type of intruder. The final arrangement is set as the proposed architecture, and implemented in an assumed UAV operation within the civil airspace. System and infrastructure considerations are discussed for several examples of prospective types of operation in the airspace.

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Autonomous systems are required in order to enable UAVs to conduct self-separation and collision avoidance, especially for flights within the civil airspace system. A method called the Velocity Obstacle Method can provide the necessary situational awareness for UAVs in a dynamic environment, and can help to generate a deconflicting maneuver. This paper focuses on the assessment of the Velocity Obstacle Method application and its ability to resolve various conflict situations in three dimensional space. This assessment results in a redefinition of the criteria of avoidance. A novel technique is introduced to support the avoidance decision, by representing the conflict situation in various avoidanceplanes. Several new definitions to support the method are introduced. This method is then implemented in three-dimensional simulations for UAVs in cases of conflict, in which more than one option of resolution is provided.

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