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Energy-efficient mobile system design: the user's perspective

Mobile systems, such as smart-phones and Pocket PCs, are likely to become personal servers for future pervasive computing. This dissertation highlights the energy efficiency bottleneck such systems face in achieving this goal: the slow-user problem, i.e., an increasingly powerful computer spends most of its energy waiting for a constantly slow user. To tackle this bottleneck, it proposes to evaluate and improve the energy efficiency of a mobile system from the user's perspective. 
The dissertation first highlights the slow-user problem and the importance of user interfaces and human factors. It offers a theoretical analysis for interface power and energy requirements, and a comprehensive energy characterization of state-of-the-art user interfaces. Based on this characterization, it presents a comparative study of their energy efficiency. It then tackles the slow-user problem in three different ways. First, it proposes to increase user productivity without much power overhead with a Bluetooth-based personal-area network of low-power interfacing devices. The network consists of a wrist-watch, single-hand single-tap multi-finger keypad, smart speech portal, and information-capturing devices. They synergistically provide a user with natural and power-efficient access to a mobile system. Second, it proposes to reduce the interfacing power requirement without decreasing user productivity much. Motivated by the memory-cache theory, the dissertation shows how a low-power interface cache device can be used to host simple interactive tasks outsourced from a mobile system, and thus improve the overall energy efficiency. Third, the dissertation proposes to aggressively power-manage a mobile system in its idle periods during human-computer interaction. It uses user interface information to predict user delays based on history and theories from the field of psychology. It shows that such a delay prediction can be combined with power management to significantly reduce idle power consumption.