Unpublished work

Abstract - In this article presents the design, implementation, and verification of a cooperative collision avoidance algorithms for unmanned aerial vehicles (UAVs) in multi-aircraft conflict scenarios. Two types of collision avoidance algorithms are developed and verified in simulation: a rules-based algorithm and a cooperative path planning based algorithm. The rules-based collision avoidance algorithm is modelled after the tactical Traffic Collision Avoidance System (TCAS) that is used on commercial passenger airliners. TCAS system issues complementary altitude rates for conflict resolution directions which are climb or descend to an aircraft pilot. To enable multi-aircraft collision avoidance, two methods for combining the pairwise rules-based collision avoidance actions are proposed, namely Resolution Action Superposition (RAS) and pairwise Closest-Intruder-First (CIF). A set-piece conflict avoidance simulation of Three UAVs for the two multi-aircraft approaches were analysed for decision making from of rules and equation of motions of aircraft. The CIF pairwise approach seeks to maximize separation distance per pair UAVs’ closest distance. The pairwise of conflict resolutions were simulated from a single intruder under below altitude level of 1000 feet which a single UAV had to manoeuvre with maximum effort

Abstract—his article presents the design, implementation, and verification of a strategic path planning which nominally simulates aircraft from states received through a communication network. The states of intruder aircraft are nominally propagated sixty seconds ahead of time for conflict prediction with conflict detection at each ten seconds time step. After a conflict is detected within a trajectory from path plan inputs, an iterative path-planning-based collision avoidance algorithm grows a search tree of admissible conflict resolution paths, and searches the tree to find the conflict-free path with the lowest cost. To enable cooperative collision avoidance, all aircraft communicate their current positions and intended flight paths to all other aircraft. Therefore, a token allocation strategy is used so that the individual aircraft plan their new collision avoidance paths sequentially according to a predetermined priority order. The conflict resolution search-tree re-plans trajectories which are divided into six time steps of vertical climb and descend rates commands. The vertical rates used for states sampling are benchmark from TCAS. Furthermore, the search-tree is a UAV navigation structure from an initial conflict-free position, where vertical rates command are motion primitives which deviate a UAV from its nominal altitude. The search algorithm was able to use a cost function for optimization of altitude deviation of a UAV from its nominal flight through minimization of the climb and descend inputs which deviates a UAV.

Abstract - In this paper we show a review few of the existing sampling-based path planning algorithms in literature, our interest is to use success cases of these algorithms to computes collision-free paths to resolve collisions for UAVs with other multiple aircraft in real-time. In particular we survey different algorithms to use in real-time collision avoidance in airspace for UAVs, the intruder aircraft we consider are the semi-cooperative; multiple number aircraft in airspace where some are cooperative, and others are non-cooperative due to some communication uncertainty. Because time is limited for these problem and UAVs are constrained by dynamic variables e.g fixed-wing aircraft, we looked at the probabilistic sampling-based roadmap, RRT then the kinodynamics planning to avoid collision in high dimensional space constrained by dynamic obstacles; because in a conflict all aircraft are obstacles to each other. Sampling-based algorithms are recommended for time-bounded problems because an aircraft configuration connectivity can be obtained faster in PRM and multiple queries can be processed faster. Path generated by kinodynamic planning algorithms respect the Dubin kinematics equation of each aircraft, therefore the path planner has to generate safe flyable path for UAVs. We make references on how RRT and PRM features when it comes to convergence rate, connectivity and query processing after a short sampling time when handling problems of these nature in future research for aircraft. We must remember that both PRM and RRT makes an assumption that the workspace obstacles are static, its a challenge for for UAVs which has to avoid each other during path planning.

Abstract - Wireless communication technologies with short range are used as communication media for some UAVs. One of the most commonly used is the IEEE Wifi. UAVs which use Wifi and other related wireless technologies remains not completely autonomous for long range navigation. We present the 3G wireless cellular communication network as a solution to extend communication range for the AR.Drone 2.0 quadcopter. This allow AR.Drones and other similar UAVs to communicate with base stations over the Internet on a distance coverage limited by the 3G network service provider. However the service provides impose bandwidth limit and latency on the 3G network. We investigate and analyse the impact of these limitations imposed by the service provider.