The proliferation of mobile devices such as the Apple iPhone entails ubiquitous availability of a variety of multimedia information to users on the move; ready at our fingertips, virtually anywhere and anytime. However, these devices have strong limitations: small screen real estate and restricted input capabilities. Moreover, with the ever increasing number of multimedia data and services, the navigation complexity rises and in turn decreases both user experience and usability. This thesis explores how the affordances of mobile devices can be leveraged to design novel interfaces for the mobile interaction with large multimedia information spaces, toward a more usable and enjoyable user experience. The contributions are placed alongside three main research directions:

The first, device-centric interaction, investigates how mobile devices can be used efficiently in spite of the small screen leveraging input modalities such as touch or tilt. It focuses on mobile video browsing as a guiding scenario and contributes an exploration of the design space of mobile video browsers. It further contributes a set of novel interfaces, which are analyzed in an extensive controlled experiment. To state only one example, our analysis shows that the video player included in the iPhone has significant drawbacks; it also points out how future versions can be designed to be more usable.

The second research direction, space-centric interaction, pushes the boundaries of the virtual information space beyond the small screen toward the physical environment. It particularly looks at how mobile devices can be used as see-through displays when mapping the virtual information to the physical space. It also contributes an empirically grounded theory thereof and a novel movement time model for the embodied navigation with spatially-aware displays.

The third axis of research is devoted to the questions of how virtual and physical space can be tightly integrated, allowing for both device- and space-centric interaction with real-world objects--not just one particular mobile device. Pico projectors are used to project virtual information into physical space, turning objects into dedicated projection surfaces and tangible interaction devices. The thesis investigates this in an exploratory field study. Based upon this study, it advances the field of pico projector interaction by deriving novel interaction techniques. Results from a user study indicate the potential to fundamentally change how we ubiquitously interact with augmented real-world objects.