This paper presents the design, implementation, and evaluation of Cricket, a location-support system for in-building, mobile, locationdependent applications. It allows applications running on mobile and static nodes to learn their physical location by using listeners that hear and analyze information from beacons spread throughout the building. Cricket is the result of several design goals, including user privacy, decentralized administration, network heterogeneity, and low cost. Rather than explicitly tracking user location, Cricket helps devices learn where they are and lets them decide whom to advertise this information to; it does not rely on any centralized management or control and there is no explicit coordination between beacons; it provides information to devices regardless of their type of network connectivity; and each Cricket device is made from off-the-shelf components and costs less than U.S. $10. We describe the randomized algorithm used by beacons to transmit information, the use of concurrent radio and ultrasonic signals to infer distance, the listener inference algorithms to overcome multipath and interference, and practical beacon configuration and positioning techniques that improve accuracy. Our experience with Cricket shows that several location-dependent applications such as in-building active maps and device control can be developed with little effort or manual configuration. 1

The decreasing cost of computing technology is speeding the deployment of abundant ubiquitous computation and communication.

We describe a framework for redirecting data streams to devices best equipped to handle them as users move around in a building. This is a useful capability for emerging pervasive computing environments such as MIT's Project Oxygen, as it allows a mobile user with a handheld device to easily control and benefit from specialized devices (e.g., speakers, large displays, etc.) available at various locations. For instance, as a user moves around, this system makes it possible for a sound or video stream to "follow" her, with the stream being played at whichever best-equipped, available output device is nearest to her at any point in time. The key challenges in building this system involve discovering resources identified by their location and in developing an architecture that achieves seamless stream redirection. We describe how our design and implementation meets these challenges. Thesis Supervisor: Hari Balakrishnan Title: Assistant Professor Thesis Supervisor: Stephen J. Garland Title: Principal Research Scientist 2 Acknowledgements I would like to thank the following people who have helped me with my project and my thesis: Kalpak Kothari (for writing the Swing GUI for the prototype application and helping me with all things iPAQ), Bodhi Priyantha and Allen Miu (for taking the time to help me with Cricket), everyone in the Networks and Mobile Systems group, my family and friends (who have supported me in many ways), and of course my professors, Hari Balakrishan and Stephen Garland, for giving me their time, their expertise, and their keen eye for grammatical and typographical errors. May I make all of them proud. 3 Contents 1

This thesis describes the design and implementation of a location support system called Cricket, which provides mobile applications with indoor location information. The system has no central point of control, which enables easy, decentralized management. Unlike traditional indoor location tracking systems, Cricket preserves user privacy by not tracking the locations of its users. It uses a combination of radio frequency (RF) and ultrasound signals, providing spatial information about the region of space in a which a user or a device resides, rather than simply providing location information as a point within some coordinate system. Cricket enables context-aware location-dependent applications; this thesis describes a few such applications.

As intelligent environments (IEs) move from simple kiosks and meeting rooms into the everyday offices, kitchens, and living spaces we use, the need for these spaces to communicate not only with users, but also with each other, will become increasingly important. Users will want to be able to shift their work environment between localities easily, and will also need to communicate with others as they move about. These IEs will thus require two pieces of infrastructure: a knowledge representation (KR) which can keep track of people and their relationships to the world; and a communication mechanism so that the IE can mediate interactions. This thesis seeks to define, explore and evaluate one way of creating this infrastructure, by creating societies of agents that can act on behalf of real-world entities such as users, physical spaces, or informal groups of people. Just as users interact with each other and with objects in their physical location, the agent societies interact with each other along communication channels organized along these same