• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.7
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• pp.1704-1712
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• 2014

The unused Worst-Case Execution Time (WCET) allocated to a real-time task occurs when the actual execution time of the task can be far less than the WCET preassigned to the task for a schedulability test. Any unused WCET allocated to the task can be exploited to reduce the power consumption of battery-powered sensor nodes through real-time power-aware scheduling techniques. From the distribution perspective of the unused WCET, the unused WCET distribution policy is classified into three types: Conservative Unused WCET (CU-WCET), Moderate Unused WCET (MU-WCET), and Aggressive Unused WCET (AU-WCET) distribution policies. We evaluated the performance of real-time power-aware scheduling techniques incorporating each of three unused WCET distribution policies in terms of low power consumption.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.9
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• pp.4429-4445
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• 2019

As low-power and low-rate WSNs are being widely used for industrial applications, the scheduling of such applications becomes a critical issue to guarantee meeting the stringent requirements of determinism and tight latencies. This paper studies the link scheduling problem for real-time industrial applications in time-slotted channel hopping (TSCH) networks. We propose a heuristic algorithm for centralized link scheduling referred to as path-collision aware least laxity first (PC-LLF) algorithm, which dynamically prioritizes the packets based on the laxity time to the end-to-end deadlines and the amount of collisions that messages might deal with along their designated paths to the destination device. We propose schedulability analysis of real-time applications scheduled under our prioritization approach over TSCH networks, based on the literature on real-time schedulability analysis of multiprocessors and distributed systems. We show that our methodology provides an improved schedulability condition with respect to the existing approaches. Performance evaluation studies quantify to quantify the performance of our proposed approach under a variety of scenarios.

• KIPS Transactions on Computer and Communication Systems
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• v.2 no.8
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• pp.343-348
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• 2013

We proposes a power-aware fixed-priority real-time scheduling algorithm for multimedia service, called static voltage scaling algorithm with multi-granularity resource reservation (STATIC-MULTIRSV). The multi-granularity resource reservation was introduced to deliver higher system utilization and better temporal isolation than the traditional approaches in [2]. Based on this, our STATIC-MULTIRSV is designed to reduce the power consumptions while guaranteeing that all I-frames of each video stream meet their deadlines. We implemented the proposed algorithm on top of ChronOS Real-time Linux [6]. We experimentally compared STATIC-MULTIRSV with other existing methods which showed that STATIC-MULTIRSV reduce power consumption by maximum 15% compared to its experimental counterparts.

• Journal of Computing Science and Engineering
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• v.7 no.1
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• pp.30-43
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• 2013

Multicore and multiprocessor systems with dynamic voltage scaling architectures are being used as one of the solutions to satisfy the growing needs of high performance applications with low power constraints. An important aspect that has propelled this solution is effective task/application scheduling and mapping algorithms for multiprocessor systems. This work proposes an energy aware, offline, probability-based unified scheduling and mapping algorithm for multiprocessor systems, to minimize the number of processors used, maximize the utilization of the processors, and optimize the energy consumption of the multiprocessor system. The proposed algorithm is implemented, simulated and evaluated with synthetic task graphs, and compared with classical scheduling algorithms for the number of processors required, utilization of processors, and energy consumed by the processors for execution of the application task graphs.

• IEMEK Journal of Embedded Systems and Applications
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• v.3 no.1
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• pp.25-29
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• 2008

In this paper, we provide an adaptive power-aware checkpointing scheme for fixed priority-based DVS scheduling in dependable real-time systems. In the provided scheme, we analyze the minimum number of tolerable faults of a task and the optimal checkpointing interval in order to meet the deadline and guarantee its specified reliability. The energy-efficient voltage level at a fault arrival is also analyzed and used in the recovery of the faulty task.

• The Journal of the Korea Contents Association
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• v.7 no.1
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• pp.83-93
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• 2007

In this paper, we address a power-aware scheduling algorithm for a mixed real-time system which consists of periodic and sporadic tasks, each of which is characterized by its minimum period, worst-case execution requirement and deadline. We propose a dynamic voltage scaling algorithm called DVSMT(DVS for mixed tasks), which dynamically scales down the supplying voltage(and thus the frequency) using on-line distribution of the borrowed resources when jobs complete while still meeting their deadlines. With this scheme, we could reduce more energy consumption. As the proposed algorithm can be easily incorporated with RTOS(Real-Time Operating System), it is applicable for handhold devices and sensor network nodes that use a limited battery power. Simulation results show that DVSMT saves up 60% more than the existing algorithms both in the periodic-task and mixed-task systems.

• Journal of Korea Multimedia Society
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• v.11 no.5
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• pp.641-650
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• 2008

As portable devices are used widely, power management algorithm is essential to extend battery use time on small-sized battery power. Although many methods have been proposed, they assumed the voltage transition overhead was negligible or was considered partially. However, the voltage transition overhead might not guarantee to schedule real-time tasks in portable multimedia systems. This paper proposes the adaptive power-aware algorithm to minimize the power consumption by considering the voltage transition overhead. It selects only a few discrete frequencies from the whole frequencies of a system and adjusts the interval between two consecutive frequencies based on the system utilization to reduce the number of frequency change. This algorithm saves the power consumption about 10 to 25 percent compared to a CC RT-DVS method and a frequency-smoothing method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4A
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• pp.393-401
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• 2006

Energy consumption is an important design parameter for battery-operated embedded systems. Dynamic power management is one of the most well-known low-power design techniques. This paper proposes an online realtime scheduling algorithm, which we call energy-aware realtime scheduling using slack stealing (EARSS). The proposed algorithm gives the highest priority to the task with the largest degree of device overlap when the slack time exists. Scheduling result enables an efficient power management by reducing the number of state transitions. Experimental results show that the proposed algorithm can save the energy by 23% on average compared to the DPM-enabled system scheduled by the EDF algorithm.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.7
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• pp.22-28
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• 2009

As multiprocessors have been widely adopted in embedded systems, task computation energy consumption should be minimized with several low power techniques supported by the multiprocessors. This paper proposes an energy-aware task scheduling algorithm that adopts both dynamic voltage scaling and power shutdown in multiprocessor environments. Considering the timing and energy overhead of power shutdown, the proposed algorithm performs an iterative task assignment and task ordering for multiprocessor systems. In this case, the iterative priority-based task scheduling is adopted to obtain the best solution with the minimized total energy consumption. Total energy consumption is calculated by considering a linear programming model and threshold time of power shutdown. By analyzing experimental results for standard task graphs based on real applications, the resource and timing limitations were analyzed to maximize energy savings. Considering the experimental results, the proposed energy-aware task scheduling provided meaningful performance enhancements over the existing priority-based task scheduling approaches.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.45 no.1
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• pp.78-85
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• 2008

Most researches for power management have focused on increasing the utilization of system performance by scaling operating frequency or operating voltage. If operating frequency is changed frequently, it reduces the real system performance. To reduce power consumption, alternative approaches use the limited number of operating frequencies or set the smoothing frequencies during execution to increase the system performance, but they are not suitable for real time applications. To reduce power consumption and increase system performance for real time applications, this paper proposes a new power-aware schedule method by allocating operating frequencies and by setting smoothing frequencies. The algorithm predicts so that frequencies with continuous interval are mapped into discrete operating frequencies. The frequency smoothing reduces overheads of systems caused by changing operating frequencies frequently as well as power consumption caused by the frequency mismatch at a wide frequency interval. The simulation results show that the proposed algorithm reduces the power consumption up to 40% at maximum and 15% on average compared to the CC RT-DVS.