Abstract — Advances in computing hardware, communications technologies, and novel multimedia applications are spurring the development of smart phones and personal digital assistants. There is world-wide accessibility to 2G, 3G, and Wi-Fi networks. Some examples of well-known wireless handheld devices are BlackBerry, iPhone, iPad, iPod, and Kindle. On the one hand, small size and light weight are their attractive features for high mobility and accessibility. On the other hand, the same features impose significant constraints on their processing, memory, and energy storage capabilities, thereby limiting the device’s general functionalities and availabilty. User expectations in terms of performance from handheld devices are ever increasing. In addition to performance expectations, the requirement of portability imposes severe constraints on size and weight of a handheld system. Consequently, batteries too are small and light, and, therefore, the system energy budget is severely limited. The amount of energy in a fully charged battery is one of the most important resources of a handheld system, and battery lifetime is one of the most important characteristics. Unfortunately, improvements in energy density of batteries have not kept pace with the advancements in microelectronics technology. Therefore, reserachers have proposed novel architectures, strategies, methodologies, and techniques to make handheld devices energy efficient. In this paper, we study the results published in about 200 reserach papers to have a comprehensive understanding of the various approaches to make handheld devices energy efficient. We present our study in the form of 12 cohesive sections that include the following topics: smart batteries, energy-efficient graphical user interface design, the concept of a sleep mode to save energy, power efficient communication, proxy assisted energy saving, source-level power control, transport control protocol based energy saving, upperlevel power management, virtual memory on the network, programming and compilation techniques, integrated power management, and energy estimation models. I
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