PUB - Publikationen an der Universität Bielefeld

Mobile ad-hoc networks (MANETs) are communication networks that do not rely on fixed, preinstalled communication devices like base stations or predefined communication cells. MANETs are wireless networks consisting of mobile nodes which are characterized by their decentralized organization and the potentially high dynamics of the network structure. Therefore, MANETs are ideally suitable for applications with multi-robot systems. One of the most promising applications of a multi-robot system is to assist humans in urban search and rescue (USAR) scenarios in the aftermath of natural or man-made disasters. We are focusing on an ad-hoc network communication system with the mobile robots being communication nodes offering a robust communication infrastructure. Main disaster scenario covered by our system is a large industrial warehouse in fire, described in the GUARDIANS project funded by the European Union. In this scenario, black smoke may fill large space of the warehouse that makes it very difficult for the firefighters to orientate themselves in the building which in turn will usually limit the action space of the firefighters. In order to increase the coverage area of the fire fighters the ad-hoc network has to provide position data to support localization of the mobile robots and humans, which might be of great importance to guide the humans and robots to specific targets and locations or to quickly exit the search area. In our proposed approach a cell-based network with master nodes in each cell forms the basic structure of the network. Some nodes formed by speciallyequipped robots act as beacons to uniformly span the network. These robots have a role as reference points when positioning other mobile robots or humans and at the same time form the infrastructure to support communication all over the search area. A combination of distance and radio signal quality measurements as well as dedicated swarming behaviors of the robots are capable of maintaining suitable distribution of the robots even in the presence of walls that obstruct the radio signals. Communications standards considered for the ad-hoc network are Wireless LAN, Bluetooth and QigBee. All are integrated on a miniature robot for real experiments. The features of the network are studied analytically, in simulations as well as in experiments to verify the results. Furthermore, frequency and power managements are also taken into consideration to ensure robustness of communication in the network.