Energy Consumption in Mobile Devices: Why Future Systems Need Requirements–Aware Energy Scale-Down

Abstract

The current proliferation of mobile devices has resulted in a large diversity of designs, each optimized for a specific application, form-factor, battery life, and functionality (e.g., cell phone, pager, MP3 player, PDA, laptop). Recent trends, motivated by user preferences towards carrying less, have focused on integrating these different applications in a single general-purpose device, often resulting in much higher energy consumption and consequently much reduced battery life. This paper argues that in order to achieve longer battery life, such systems should be designed to include requirements-aware energy scale-down techniques. Such techniques would allow a general-purpose device to use hardware mechanisms and software policies to adapt energy use to the user’s requirements for the task at hand, potentially approaching the low energy use of a special-purpose device. We make two main contributions. We first provide a model for energy scale-down. We argue that one approach to design scale-down is to use special-purpose devices as examples of powerefficient design points, and structure adaptivity using insights from these design points. To understand the magnitude of the potential benefits, we present an energy comparison of a wide spectrum of mobile devices (to the best of our knowledge, the first study to do so). A comparison of these devices with general- purpose systems helps us identify scale-down opportunities. Based on these insights, we propose and evaluate three specific requirements-aware energy scale-down optimizations, in the context of the display, wireless, and CPU components of the system. Our optimizations reduce the energy consumption of their targeted subsystems by factors of 2 to 10 demonstrating the importance of energy scale-down in future designs.