Energy management has been a critical problem since the earliest days of mobile computing. Although a large research investment in low power circuit design and hardware power management has led to more energy efficient system. The O.S. uses additional information available during execution , such as resource supply and demand , to advise application which trade off are best. The dissertation first shows how one can measure the energy impact of higher levels of system. It describes design and implementation of power scope , an energy profiling tool that maps energy consuming to specific code components. Power scope helps developers increase the energy efficiency of their software by focusing attention on those processes and procedures that are responsible for the bulk of energy use. It focuses on two dimensions.
1.Reduction of data and computation quality.
2.Relocation of execution to remote machines.
Thus increases lifetime of the batteryAlso the energy saving can be achieved by placing the remote network device in power save mode and service network requests from the local hard drive catche .It is over the remote network for certain file sizes.Tis is called as effect of large storage on mobile computing.

FUll Paper Link