Computing devices and applications are now used beyond the desktop, in diverse environments, and this trend toward ubiquitous computing is accelerating. One challenge that remains in this emerging research field is the ability to enhance the behavior of any application by informing it of the context of its use. By context, we refer to any information that characterizes a situation related to the interaction between humans, applications and the surrounding environment. Context-aware applications promise richer and easier interaction, but the current state of research in this field is still far removed from that vision. This is due to three main problems: (1) the notion of context is still ill defined; (2) there is a lack of conceptual models and methods to help drive the design of context-aware applications; and (3) no tools are available to jump-start the development of context-aware applications. In this paper, we address these three problems in turn. We first define context, identify categories of contextual information, and characterize context-aware application behavior. Though the full impact of context-aware computing requires understanding very subtle and high-level notions of context, we are focusing our efforts on the pieces of context that can be inferred automatically from sensors in a physical environment. We then present a conceptual framework that separates the acquisition and representation of context from the delivery and reaction to context by a contextaware application. We have built a toolkit, the Context Toolkit, that instantiates this conceptual framework and supports the rapid development of a rich space of context-aware applications. We illustrate the usefulness of the conceptual framework by describing a number of contextaware applications that h...

With the growing prevalence of sensor and wireless networks comes a new demand for location-based access control mechanisms. We introduce the concept of secure location verification, and we show how it can be used for location-based access control. Then, we present the Echo protocol, a simple method for secure location verification. The Echo protocol is extremely lightweight: it does not require time synchronization, cryptography, or very precise clocks. Hence, we believe that it is well suited for use in small, cheap, mobile devices.

this article, we examine today's ubiquitous systems, focusing on software infrastructure, and discuss the road that lies ahead

CoolTown offers a web model for supporting nomadic users, based on the convergence of web technology, wireless networks and portable devices. This paper describes how CoolTown ties web resources to physical objects and places, and how users interact with resources using the information appliances they carry, from laptops to smart watches. Enabling the automatic discovery of URLs from our physical surroundings, and using localized web servers for directories, we create location-aware but ubiquitous systems. On top of this infrastructure we leverage device connectivity to support communication services. Keywords Web presence; nomadic computing; location-aware computing; ubiquitous computing; resource discovery. 1.

Abstract. Location-based information systems allow the user to access information in relation to the user’s position in geographical space. This paper outlines navigational and social aspects of such systems. It is argued that location-based systems must allow users to participate as content providers in order to achieve a social and dynamic information space. Moreover, as these systems allow commercial and private users to annotate space with information on a mass-scale, information filtering techniques will become essential in order to prevent information overload and user disturbance. We present a number of content-based and social filtering techniques to support this. We discuss implications for implementation and we describe a system (GeoNotes), which takes some of these aspects into account. Keywords. Real-world annotations, position-based services, social awareness, context awareness.

Ubiquitous computing promotes physical spaces with hundreds of specialized embedded devices that increase our productivity, alleviate some specific everyday tasks and provide new ways of interacting with the computational environment. Personal computers lose the focus of attention due to the fact that the computational environment is spread across the physical space. Therefore, the users ’ view of the computational environment is finally extended beyond the physical limits of the computer. Physical spaces become computer systems, or in other terms, Active Spaces. However, these Active Spaces require novel system software capable of seamlessly coordinating their hidden complexity. Our goal is to extend the model provided by current computer systems to allow interaction with physical spaces and their contained entities (physical and virtual) by means of a single abstraction called Active Space. 1.

technology to broadcast the URLs primarily because many of today's handheld computing devices have built-in IR transceivers. To receive data on the client side, we use e-Squirt, a simple protocol that provides a stable platform for passing URLs between devices over the IrDA medium. The directional nature of IR beacons also enables users to explicitly select a physical object in an environment garnished with beacons. Mechanically, CoolTown beacons are similar to indoor-location technologies such as Active Badges, 4 but they have a different application space. Users wear Active Badges or attach them to objects to keep track of their presence at a location, but beacons connect mobile users with hyperlinks to services associated with physical objects. Deploying bridging devices like beacons and tags raises scalability issues. Beacons require periodic maintenance because their batteries run out. Also, when URLs pointing to Web content change, the beacons

The Cooltown vision is that people, places, and things have a Web representation and that many useful services can be offered by creating a tighter link between the real world entity and its virtual representation. We defined a horizontal and uniform software architecture for building a Web presence for people, places, and things. This architecture enables the dynamic generation of Web contents based on the user context (location, identity, device capabilities), security permissions, and the relationships with other Web presences. Our implementation of this architecture is portable enough to be embedded in the entity that the Web presence describe but also scalable enough to support multiple Web presence hosting. We focused on making the creation of a Web presence easy for non-programmers.

The basic idea behind location-based information systems is to connect information pieces to positions in outdoor or indoor space. Through position technologies such as Global Positioning System (GPS), GSM positioning, Wireless LAN positioning or

The convergence of Web technology, wireless networks and portable client devices provide new opportunities for infrastructure to support "web presence" for people, places and things. Our goal is a bridge between the World Wide Web and the physical world we inhabit. This bridge includes the ability to interact with devices such as printers from a browser using standard HTTP communication. It also includes the ability to provide people, places and things -- electronic or otherwise -- with a web resource that is used to store information about them and which is automatically correlated with their physical presence. We aim to provide users, particularly mobile users, with support for their everyday activities, which mostly concern physical objects other than PC's.