Institute for Software Research
School of Computer Science, Carnegie Mellon University


Designing Energy and User Efficient Interactions
with Mobile Systems

Lu Luo
April 2008

Ph.D. Thesis


Keywords: Mobile computing, energy efficiency, user interaction, user interface design, cognitive modeling, ubiquitous computing

Mobile computing has thrived to provide unprecedented user experiences beyond the boundary of desks and wires. The increasing demand for mobility faces two major challenges: reduced form factor and limited energy supply. Although each challenge has been addressed by significant research efforts, the correlation between them is underexplored.

Energy efficiency should be integrated as an important metric of user interaction design in mobile systems. By carefully considering the specific requirements of the user and the context of usage, energy efficiency can be achieved without sacrificing user performance and satisfaction,and interaction design that facilitates user efficiency can also promote energy efficiency.

This dissertation starts with a detailed study of typical workload and screen usage that shows that users seldom use the entire screen on most workloads. Hence, Dark Windows, an energy efficient display design is presented and implemented to optimize display power consumption by adjusting the color and illumination of different screen regions according to the user's workload.

This dissertation next presents AstroRDS, a mobile computing system and network infrastructure that displays documents and information from user's mobile devices on ambient ubiquitous display resources, thus facilitates much better viewing experience of the user with comparatively ease of use. The energy consumption and network usage of AstroRDS is several orders of magnitudes less than VNC remote desktop protocol on viewing and controlling tasks, and with similar initial loading overhead.

A common challenge in these two efforts is the high cost of measuring user experience and energy consumption. This dissertation further presents KLEM, a quantitative methodology based on cognitive modeling techniques that can predict both user performance and system energy consumption from story boards of an interactive task during early stages of design. KLEM can be used as a convenient tool to compare and make early decisions among different design options, as well to resolve potential design issues before investing in actual user testing and iterative development. While KLEM is presented with a focus on handheld devices, the methodology can be applied on any interactive mobile system.

119 pages

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