Hovering information is a mobile computing paradigm where pieces of self-organizing information are responsible to find their own storage on top of a dynamic set of mobile devices. Once deployed, the hovering information service acts as a location-based service for disseminating Geo-localized information generated by and aimed at mobile users. It supports a wide range of pervasive applications, from urban security to stigmergy-based systems. A piece of hovering information is attached to a geographical point, called the anchor location, and to its vicinity area, called the anchor area. A piece of hovering information is responsible for keeping itself alive, available and accessible to other devices within its anchor area. It does not rely on any central server.
User generated content is taking a large part of the Internet with social networking web sites such as YouTube or MySpace. The equivalent of these sites for mobile users, now combine both user-generated content and location-based services (LBS). Among other, they allow groups of mobile users to share dynamic real-time content or retrieve themselves on a map. Location-based services usually rely on base stations and from there possibly to the whole Internet to provide some requested information to a mobile user. This solution has clear advantages such as providing access to large computing capabilities and broadband network access that go beyond those of mobile phones or PDAs.
However, it is not always possible or desired to rely on a central server in particular for user-generated content: extra-terrestrial systems need local communication infrastructures, they cannot communicate with an Earth-based server, or if in a hostile environment cannot rely entirely on a single server; after a natural disaster, when no more infrastructure is available, local communications among available devices help coordination among emergency services; finally, for reliability reasons, it is not always possible to rely on a centralized server representing a single point of failure. Hovering Information is a concept characterizing self-organizing information responsible to find its own storage on top of a highly dynamic set of mobile devices. This is a location-aware service for mobile users (people, cars, robots, etc.) that supports dissemination of user-generated Geo-localized data among a highly mobile set of devices. This service exploits the mobile devices themselves as a physical support and do not make use of a server.
The illustration below shows a piece of hovering information (blue hexagon) and two mobile nodes (yellow circles). One of them hosts the hovering information whose anchor location, radius and area are also represented (blue circle). The communication range of the second mobile node is also showed.
The main requirement of a single piece of hovering information is to keep itself stored in the vicinity of some specified location, which we call the anchor location, despite the unreliability of the device n which it is stored. Whenever the mobile device, on which the hovering information s currently stored, leaves the area around the specified anchor location, the information has to hop - "hover" - to another device. Current services supporting Geo-localized data, are deployed using one of the following approaches: centralized servers, virtual structured overlay network offering a stable virtual infrastructure, or direct communication among the mobile nodes themselves. In all these approaches, the mobile nodes decide when and to whom the information is to be sent. Here we take the opposite view; it is the information that decides upon its own storage and dissemination. This opens up other possibilities, not available for traditional MANET services, such as different pieces of hovering information all moving towards the same location and (re-)constructing there a coherent larger information for a user, e.g. TV or video streaming on mobile phones. A piece of hovering information is a self-organizing user-defined piece of data which does not need a central server to exist. Individual pieces of hovering information each use local information, such as direction, position, power and storage capabilities of nearby mobile devices, in order to select the next appropriate location. Hovering information benefits from the storage space and communication capacities of the underlying mobile devices. Main dependability requirements of hovering information are survivability, availability and accessibility. Survivability means that the information is alive somewhere in the environment (i.e. it is stored in some device) but not necessarily close to its anchor location. Availability means that the information has found storage in the vicinity of the anchor location. Accessibility combines both availability and communication range of wireless mobile devices, and represents the possibility for a user located in the anchor location to access hovering information stored on nearby devices. The hovering information service requires the following: mobile nodes with computing capacity; direct wireless communications among mobile node such as Bluetooth or Wi-Fi; and a location tracking capability such as a GPS (mobile PDAs), relative distances calculations or light-color tracking (robots).
