# Development, Implementation and Evaluation of An Epidemic Communication System
## 1 Introduction  
With the development of the Internet of Things (IoT), objects that were previously not connected to the Internet have been connected. The IoT is used in various fields for communicating and sharing information between objects. The information that is shared includes the data acquired by various sensors. In systems utilizing IoT technology, ad hoc communication methods have long been considered, and protocols such as the ad hoc on-demand distance vector (AODV) and optimized link state routing (OLSR) have been established [1; 2; 3; 4; 5]. Ad hoc communication serves as a relay technology between wireless stations, allowing for flexible links to be established and information to be shared among wireless stations. Although the collected information is determined by humans, ad hoc communication is representative of the device-to-device communication technology of the IoT. As a special case in IoT, communication applications that involve extremely long delays, ranging from seconds to hours or more, are emerging. Examples include the interplanetary Internet (IPN) for communication between planets or space stations, underwater communication for environmental monitoring, and communication between sensors attached to animals. These applications face challenging conditions, including intermittent connections between planned and unplanned communication links. Traditionally, communication systems have not been designed to address these conditions. Therefore, the traditional framework of Internet communication does not consider scenarios where vehicles or individuals physically move to locations without an established wired or wireless infrastructure to transport information. Delay-tolerant networking (DTN) addresses the challenges posed by the constraints of traditional communication technologies in such scenarios [6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]. A communication method related to DTN is called epidemic communication. Epidemic communication is useful for constructing more complex ad hoc network environments than the conventional ad hoc construction methods. For instance, the conventional ad hoc wireless networks may not always form a multi-hop wireless route between the source and destination nodes. In scenarios where the nodes frequently move and the spatial relationships among the moving nodes performing as relays between source and destination nodes as well as the availability of wireless links between each node vary, routing paths may not always exist between the source and destination nodes. Moreover, in situations with a low node density, such occurrences are more likely and multi-hop wireless communication may not function effectively. The theoretical framework of epidemic communication, in which information is shared among nodes to propagate as an epidemic, has been recently applied for analyses, such as in predicting the spread of the novel coronavirus infection (COVID-19). However, to date, the practical utilization of this communication method in communication services has not resulted in many optimal deployment methods. Therefore, we propose a specific application of epidemic communication for mobile devices such as robots and drones. Robots and drones have been rapidly adopted in various practical applications, and the control technologies for these devices have been standardized. For example, a robot operating system is an open-source robotics framework middleware that facilitates various R&D activities and practical applications to satisfy specific goals and requirements [21, 22, 23]. Robots and drones intended for deployment in disaster-stricken areas are designed to perform activities remotely, replace human labor, and collaborate with other robots and drones via information sharing. For example, drones are used for pollination tasks in agriculture and for transmitting data concerning instructions and flight control information [14, 24, 25]. In systems in which multiple robots or drones collaborate, accurate sharing of information among them is essential.