In a multi-agent system (MAS), the overall performance is greatly influenced by both the design and the control of the agents. The physical design determines the agent capabilities, and the control strategies drive the agents to pursue their objectives using the available capabilities. The objective of this thesis is to incorporate control strategies in the early conceptual design of an MAS. As such, this thesis proposes a methodology that mainly explores the interdependency between the design variables of the agents and the control strategies used by the agents. The output of the proposed methodology, i.e. the interdependency between the design variables and the control strategies, can be utilized in the requirement analysis as well as in the later design stages to optimize the overall system through some higher fidelity analyses. In this thesis, the proposed methodology is applied to a persistent multi-UAV surveillance problem, whose objective is to increase the situational awareness of a base that receives some instantaneous monitoring information from a group of UAVs. Each UAV has a limited energy capacity and a limited communication range. Accordingly, the connectivity of the communication network becomes essential for the information flow from the UAVs to the base. In long-run missions, the UAVs need to return to the base for refueling with certain frequencies depending on their endurance. Whenever a UAV leaves the surveillance area, the remaining UAVs may need relocation to mitigate the impact of its absence. In the control part of this thesis, a set of energy-aware control strategies are developed for efficient multi-UAV surveillance operations. To this end, this thesis first proposes a decentralized strategy to recover the connectivity of the communication network. Second, it presents two return policies for UAVs to achieve energy-aware persistent surveillance. In the design part of this thesis, a design space exploration is performed to investigate the overall performance by varying a set of design variables and the candidate control strategies. Overall, it is shown that a control strategy used by an MAS affects the influence of the design variables on the mission performance. Furthermore, the proposed methodology identifies the preferable pairs of design variables and control strategies through low fidelity analysis in the early design stages.

Η διπλωματική αυτή εργασία έχει ως αντικείμενο μελέτης εφαρμογές / διεργασίες στα ρομποτικά σμήνη. Οι εφαρμογές / διεργασίες που εξετάζονται είναι η καλυψιμότητα χώρου, η διατήρηση συνδεσιμότητας και τα παιχνίδια κυνηγού - κυνηγούμενου. Συγκεκριμένα, εξετάζονται δύο μέθοδοι καλυψιμότητας χώρου: κίνηση προς το κεντροειδές και κίνηση προς τη βάθμωση. Εισάγονται οι επικοινωνιακοί περιορισμοί και προτείνονται περιορισμοί κίνησης που εξασφαλίζουν διατήρηση N-hop συνδεσιμότητας, οι οποίοι έπειτα προσαρμόζονται στην καλυψιμότητα χώρου. Αναλύονται δύο τακτικές κυνηγού: οι έμμεσοι κυνηγοί και η τακτική περικύκλωσης, και προτείνονται δύο τακτικές για τους κυνηγούμενους. Η πρώτη αποτελεί μία παθητική αποφυγή των κυνηγών, ενώ η δεύτερη μια πιο δυναμική συνεργατική τακτική. Τέλος, προσομοιώσεις συνοδεύουν όλα τα παραπάνω μέρη, που επιβεβαιώνουν την αποτελεσματικότητά τους και προσφέρουν σύγκριση των διάφορων μεθόδων για την κάθε εφαρμογή. / This thesis addresses applications / tasks of robotic swarms. The applications / tasks presented are the area coverage, communication maintenance and pursuer - evasion games. Two methods for area coverage are examined; centroid and gradient movement. Communication constraints are considered and movement constraints are proposed, such that the swarm's N-hop connectivity is retained. Then the contraints are adapted for the area coverage problem. After that, two pursuing tactics are examined; the indirect pursuers and the blanket movement, and two evader tactics are proposed. The first is a passive pursuers avoidance, while the second is a more dynamic collaborative tactic. Finally, simulations accompanying the above sections, confirm the efficiency and offer a comparison between the different methods in each application.

In this thesis the novel concept of Sycophant Wireless Sensors (SWS) is introduced. A SWS network is a static ectoparasitic clandestine sensor network mounted incognito on a mobile agent using only the agent&rsquo / s mobility without intervention. SWS networks not only communicate with each other through mobileWireless Sensor Networks (WSN) but also cooperate with them to form a global hybrid Wireless Sensor Network. Such a hybrid network has its own problems and opportunities, some of which have been studied in this thesis work. Assuming that direct position measurements are not always feasible tracking performance of the sycophant using range only measurements for various communication intervals is studied. Then this framework was used to create a hybrid 2D map of the environment utilizing the capabilities of the mobile network the sycophant. In order to show possible applications of a sycophant deployment, the sycophant sensor node was equipped with a laser ranger as its sensor, and it was let to create a 2D map of its environment. This 2D map, which corresponds to a height dierent than the follower network, was merged with the 2D map of the mobile network forming a novel rough 3D map. Then by giving up from the need to properly localize the sycophant even when it is disconnected to the rest of the network, a full 3D map of the environment is obtained by fusing 2D map and tracking capabilities of the mobile network with the 2D vertical scans of the environment by the sycophant. And finally connectivity problems that arise from the hybrid sensor/actuator network were solved. For this 2 new connectivity maintenance algorithms, one based on the helix structures of the proteins, and the other based on the acute triangulation of the space forming a Gabriel Graph, were introduced. In this new algorithms emphasis has been given to sparseness in order to increase fault tolerance to regional problems. To better asses sparseness a new measure, called Resistance was introduced, as well as another called updistance.

This thesis studies formation control for a class of general leader-follower multi-agent systems with Control Barrier Functions (CBFs) such that connectivity maintenance is fulfilled for all the neighboring agents. In leader-follower multi-agent systems, only the leader agents are controlled by the externally designed input, while the followers are guided through their dynamic couplings with the neighboring agents. The main problem is how to keep all adjacent agents maintain within the communication distance during the formation process. In this thesis, Control Barrier Functions (CBFs) are utilized in order to maintain connectivity among the neighboring agents. This thesis firstly introduces a general first-order leader-follower multi-agent systems with proper connectivity constrains. All edges in the system are divided into three categories: follower-follower edges, leader-follower edges and leader-leader edges. Three different kinds of edges are discussed individually. For each category, the relevant topological conditions and control barrier functions are defined and proved for both tree graphs and general graphs. Several simulation examples are implemented to verify the developed results. Both theory and simulation results show that the developed results are a strong support for the formation control of leader-follower system in order to achieve connectivity maintenance. / Denna avhandling studerar formationskontroll för en klass av generella ledare-följare multi-agent-system med kontrollbarriärfunktioner (CBFs) så att anslutningsunderhållet uppfylls för alla angränsande agenter. I ledar-följare multi-agent-system är det bara ledaragenterna som styrs av den externt utformade ingången, medan följaren guidas genom sina dynamiska kopplingar med grannagenterna. Huvudproblemet är hur man kan hålla alla intilliggande agenter inom kommunikationsavståndet under bildningsprocessen. I det här examensarbetet används kontrollbarriärfunktioner (CBF) för att upprätthålla förbindelser mellan angränsande agenter. Detta examensarbete introducerar först ett allmänt första ordningens ledare-följare multi-agentsystem med korrekta anslutningsbegränsningar. Alla kanter i systemet är indelade i tre kategorier: efterföljarkanter, ledare-följarkanter och ledare-ledarkanter. Tre olika sorters kanter diskuteras individuellt. För varje kategori definieras och bevisas de relevanta topologiska förhållandena och kontrollbarriärfunktionerna för både trädgrafer och allmänna grafer. Flera simuleringsexempel implementeras för att verifiera de framtagna resultaten. Både teori- och simuleringsresultat visar att de utvecklade resultaten är ett starkt stöd för bildandet av ledare-följare-system för att uppnå anslutningsunderhåll