Collision avoidance

About: Collision avoidance is a research topic. Over the lifetime, 8014 publications have been published within this topic receiving 111414 citations.

Carrier sense collision avoidance with auto abort

Abstract: A Carrier Sense Multiple Access with Automatic Abort collision avoidance (CSMA/AA) controller for application in a wireless local area network (LAN). The CSMA/AA controller reduces the number of invalid states arising from collision conditions on the communication channel. The controller features hardware logic control for time critical functions. The hardware logic circuit detects events and fault conditions under the CSMA reservation protocol which may otherwise be missed by the Medium Access Control software layer and aborts the transmit procedure. The off-loading of time critical functions also improves the performance of the system and reduces the variability arising from overhead execution times associated with the system CPU.

UAV Collision Avoidance Based on Varying Cells Strategy

Abstract: This paper presents a trajectory planning strategy for collision avoidance in unmanned aerial vehicles. First, a varying cell strategy is proposed to integrate aerodynamic constraints into trajectory planning. Basic avoidance actions in the varying cell strategy are adapted accordingly to go through different cells, enabling more flexible avoidance maneuvers. Second, given the limited decision-making time involved, offline and online path planning methods are developed to increase the convergence rate. Finally, Monte Carlo simulations demonstrate that the proposed method satisfies aerodynamic constraints, while both the convergence and collision avoidance rates are better than that achieved by fixed cell-based methods.

Autonomous collision avoidance: the technical requirements

Abstract: Autonomous collision avoidance is necessary if Unmanned Aerial Vehicles (UAVs) are to "blacken the sky" in massed attacks, accompany manned fighters on combat missions, and transition civil airspace. These vehicles will, in some manner, have to "see and avoid" other aircraft. An automated air collision avoidance system will fulfill a part of this need. It will automatically maneuver an aircraft, at the last instant, to avoid an air-to-air collision. It will function in a manner similar to a pilot avoiding a collision. It is a system that must be reliable, verifiable, and partially redundant, forming the last line of defense against collisions. It must provide nuisance free operation and allow safe interoperability. The requirements for such a system will be discussed in detail. Of particular interest are criteria to enable a safe, nuisance free system that will have embedded rules of the road for all encounters. Autonomous control of unmanned aerial vehicles is a goal for the US Air Force in the future. However, flying multiple unmanned vehicles in the same tactical airspace with manned fighters presents very challenging problems. Autonomous collision avoidance is a necessary step in moving toward this goal.

Real-time decentralized search with inter-agent collision avoidance

Abstract: This paper addresses the problem of coordinating a team of mobile autonomous sensor agents performing a cooperative mission while explicitly avoiding inter-agent collisions in a team negotiation process. Many multi-agent cooperative approaches disregard the potential hazards between agents, which are an important aspect to many systems and especially for airborne systems. In this work, team negotiation is performed using a decentralized gradient-based optimization approach whereas safety distance constraints are specifically designed and handled using Lagrangian multiplier methods. The novelty of our work is the demonstration of a decentralized form of inter-agent collision avoidance in the loop of the agents' real-time group mission optimization process, where the algorithm inherits the properties of performing its original mission while minimizing the probability of inter-agent collisions. Explicit constraint gradient formulation is derived and used to enhance computational advantage and solution accuracy. The effectiveness and robustness of our algorithm has been verified in a simulated environment by coordinating a team of UAVs searching for targets in a large-scale environment.

A Passive Approach to Autonomous Collision Detection and Avoidance in Uninhabited Aerial Systems.

Abstract: A new approach to passive detection and avoidance of collision and near-collision with moving obstacles by Uninhabited Aerial Systems (UAS) is proposed in this paper. It takes as inputs the bearings between the ownship and the moving obstacles (intruders) only. Bearings can be measured by passive sensors such as millimetre-wave (mmW) or infra-red (IR) imaging thus adding an important aspect of covertness. The first stage of the approach deals with the detection of the moving obstacle (intruder) and is called collision risk estimator (CRE). The proposed novel approach estimates the risk of collision based on the density of consecutive bearings (constant bearings correspond to high risk and variation in bearings corresponds to low risk). The approach is recursive and thus makes possible to take as many past values of the bearings as practically needed without memorising them. Once a collision is detected, in the second stage of the approach, a decision is taken whether an emergency collision avoidance manoeuvre is necessary or a smoother and optimal (in terms of minimum time) rerouting can take place (de-confliction). The decision which of the two possible alternative avoidance actions is going to be taken can be based on the estimated ‘time-to-collision’ or on the degree of risk and is outside of the scope of the current paper. Emergency collision avoidance manoeuvres are taken in accordance to the Rules of the Air (RoA) and are limited by the ownship kinematic and aerodynamic characteristics only. Optimal re-routing provides a trajectory and the sequence of control actions that are necessary to be taken to ensure this trajectory of the ownship. As a whole, the above stages provide a new approach to passive detection and avoidance (in an optimal fashion) of moving obstacles (intruders) based on bearings only provided by passive sensors.