Browsing by Author "Lin, Pochun"

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Energy Efficient Intra-Task Dynamic Voltage Scaling for Realistic CPUs of Mobile Devices
(2009-01-01)
Yang, Chien-Chung
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Wang, Kuochen
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Lin, Ming-Ham
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Lin, Pochun
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資訊工程學系
It is not energy efficient to run a CPU at full speed all the time for all kinds of tasks in mobile devices. This paper proposes two energy efficient intra-task dynamic voltage scaling (DVS) algorithms for CPUs. There are three main contributions in this paper. Firstly, unlike the tedious derivation in PACE [2], we have derived the same optimal speed schedule with minimal energy consumption in a discrete and elegant way by using the Lagrange multiplier procedure. Secondly, the CPU model assumed in PACE is ideal, meaning that such a CPU supports all possible frequencies/voltage levels. We call such CPUs as ideal CPUs. In reality, CPUs only support a limited set of frequency/voltage levels, and we call this kind of CPUs as realistic CPUs. Thirdly, since energy consumption is not a simple function of frequency, it is more reasonable to transform the original nonlinear programming problem to the Multiple-Choice Knapsack Problem (MCKP). Since the problem can be described by a multistage graph, we used dynamic programming to derive an Optimal Schedule for Realistic CPUs (OSRC) with minimal energy consumption for realistic CPUs by using actual power consumption specifications of realistic CPUs. Considering potential computation and transition overheads, we have also proposed a low overhead OSRC (LO-OSRC), which restricts the change of CPU frequency/voltage to only once in the speed schedule. By using actual data from the power consumption specifications of two classical CPUs for evaluation, experimental results have shown that the energy saving of the proposed OSRC (LO-OSRC) is up to 10.3% (9.4%) better than that of PACE for realistic CPUs.
Enhanced sleep mode operations for energy saving in IEEE 802.16e
(2007)
Zheng, Sixian
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Wang, Kuochen
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Tsao, Shiao-Li
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Lin, Pochun
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資訊工程學系
The broadband wireless access (BWA) network, such as IEEE 802.16e, becomes more and more popular in recent years. According to the IEEE 802.16e specifications, mobile subscriber stations (MSSs) with energy constraints are allowed to switch to the sleep mode to reduce their power consumption. Considering a number of service connections on the MSS with different traffic characteristics and requesting different power saving classes, the MSS may not be able to sleep and save energy due to improper schedules of sleep operations for service connections. In this paper, an enhanced longer common sleep time (E-LCST) scheme is proposed and it first schedules real-time packets together in less number of frames without violating their delay constraints. After the listen and sleep frames are determined for transmitting real-time packets, the proposed scheme then considers non-real-time packets and schedules them into the existing listen frames if the resources are available. Therefore, MSSs can have more sleep frames and save the energy. Simulation results have shown that the proposed E-LCST performs 33% to 68% better than the conventional IEEE 802.16e Standard in terms of percentage of sleep periods, which reflects power consumption. Although, the proposed E-LCST introduces a little bit more delay, the QoS requirements of real-time connections are still met.