Reachable sets analysis in the cooperative control of pursuer vehicles

This thesis is concerned with the Pursuit-and-Evasion (PE) problem where the pursuer aims to minimize the time to capture the evader while the evader tries to prevent capture. In the problem, the evader has two advantages: a higher manoeuvrability and that the pursuer is uncertain about the evader's state. Cooperation among multiple pursuer vehicles can thus be used to overcome the evader’s advantages. The focus here is on the formulation and development of frameworks and algorithms for cooperation amongst pursuers, aiming at feasible implementation on real and autonomous vehicles. The thesis is split into Parts I and II. Part I considers the problem of capturing an evader of higher manoeuvrability in a deterministic PE game. The approach is the employment of Forward Reachable Set (FRS) analysis in the pursuers’ control. The analysis considers the coverage of the evader’s FRS, which is the set of reachable states at a future time, with the pursuer’s FRS and assumes that the chance of capturing the evader is dependent on the degree of the coverage. Using the union of multiple pursuers’ FRSs intuitively leads to more evader FRS coverage and this forms the mechanism of cooperation. A framework for cooperative control based on the FRS coverage, or FRS-based control, is proposed. Two control algorithms were developed within this framework. Part II additionally introduces the problem of evader state uncertainty due to noise and limited field-of-view of the pursuers’ sensors. A search-and-capture (SAC) problem is the result and a hybrid architecture, which includes multi-sensor estimation using the Particle Filter as well as FRS-based control, is proposed to accomplish the SAC task. The two control algorithms in Part I were tested in simulations against an optimal guidance algorithm. The results show that both algorithms yield a better performance in terms of time and miss distance. The results in Part II demonstrate the effectiveness of the hybrid architecture for the SAC task. The proposed frameworks and algorithms provide insights for the development of effective and more efficient control of pursuer vehicles and can be useful in the practical applications such as defence systems and civil law enforcement

Distributed Simulation of Forward Reachable Set-Based Control for Multiple Pursuer UAVs

Abstract. A geometrical measure of a vehicle’s dynamics, called the Forward Reachable Set (FRS), serves as a useful tool in a Pursuit-Evasion (PE) game. By incorporating the FRS into the pursuer’s control strategy, it can determine if it can capture an evader of higher manoeuvrability as well as serve as a guidance mechanism for the pursuer’s trajectory. However, as most current applications of FRS-based pursuer control mainly deals with a single evader and centralized simulation, a distributed architecture for an existing FRS-based pursuit strategy for multiple pursuer Unmanned Aerial Vehicles (UAVs), is proposed, with an evader allocation extension to capture multiple evader UAVs. The advantages of such distribution are the relative feasibility and robustness. As the load of solving the central pursuer objective is divided amongst the pursuers, each of their individual control actions can be calculated faster. Also, performance degradation in one UAV will not have as major an adverse effect on the entire system, as compared to a centralized one. The distributed architecture allows for easier integration and implementation since most real UAVS systems and advanced simulation platforms are distributed. This paper presents the distributed FRS-based pursuer control strategy and architecture along its integration and simulation on the Real-time Multi UAV Simulator (RMUS). 1