When opportunity proceeds from autonomy: A tour-based architecture for disconnected mobile sensors

Abstract

We consider the case of sparse mobile sensors deployed to implement missions in challenging environments. This paper explores a notion of tour networks that is well suited to circumstances in which autonomous sensing agents cannot rely on standard networking abstractions and must create their own opportunities for communication and interaction. Tours are high-level building blocks that combine motion, communication and sensing and can be assembled to implement a broad class of autonomous sensing missions. They are supported by an architecture designed to deliver performance and robustness without compromising design abstraction. Background and paper overviewMobility has the potential to dramatically broaden the range of sensing applications, but it also presents an array of unfamiliar obstacles to the networking task. Moreover, sensor mobility often coexists with environmental challenges that make it even more difficult to implement standard networking abstractions reliably and efficiently. We have started to explore strategies that forgo all-purpose networking in favor of mission-aware designs that can better use communication links opportunistically. We refer to such systems, in which mission-driven agent interaction is not expressed in terms of standard general-purpose networking abstractions, as disconnected mobile sensors.Much work has been done to implement standard networking functions and protocols as efficiently and comprehensively as possible in mobile networks with the goal of attaining a general purpose networking abstraction that can support a broad range of missions. Mobility, sparseness of * This research was supported in part by grant N00014-05-1-0666 from the U.S. Office of Naval Research. the network, and environmental challenges must be circumvented in order to provide users with the functionality found in more structured networks. Major progress has been made in the recent past towards this goal, for instance through elaborate routing algorithms that perform satisfactorily in spite of network disruptions, including in topologies that are possibly never fully connected [10, 4, 9].Nevertheless, there remains circumstances in which a general purpose network is undesirable, if at all possible. Reasons that prevent the establishment of a general purpose network vary and may result from design, the sensitivity of the mission to delays, limited resources or characteristics of the environment. An illustrative example is the case of Autonomous Underwater Vehicles (AUV) deployed in vast areas and limited to comparatively short-range acoustic communication [7,8]. Other cases include stealth missions, in which short-range communication is used to avoid enemy detection, or the use of energy efficient point-to-point directional communication devices, which make it difficult to maintain a connected network when nodes are mobile. In situations like these, agents are able to (or choose to) communicate in particular configurations of the agents only, for instance by having AUVs move underwater to withi...