• Proceedings of the Korea Information Processing Society Conference
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• 2012.04a
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• pp.607-608
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• 2012

Data aggregation is a fundamental problem in wireless sensor networks which attracts great attention in recent years. Delay and energy efficiencies are two crucial issues of designing a data aggregation scheme. In this paper, we propose a distributed, energy efficient algorithm for collecting data from all sensor nodes with the minimum latency called Delay-aware Power-efficient Data Aggregation algorithm (DPDA). The DPDA algorithm minimizes the latency in data collection process by building a time efficient data aggregation network structure. It also saves sensor energy by decreasing node transmission distances. Energy is also well-balanced between sensors to achieve acceptable network lifetime. From intensive experiments, the DPDA scheme could significantly decrease the data collection latency and obtain reasonable network lifetime compared with other approaches.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.2
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• pp.462-483
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• 2016

The research on optimization of cellular network's energy efficiency (EE) towards environmental and economic sustainability has attracted increasing attention recently. In this survey, we discuss the opportunities, trends and challenges of this challenging topic. Two major contributions are presented namely 1) survey of proposed energy efficiency metrics; 2) survey of proposed energy efficient solutions. We provide a broad overview of the state of-the-art energy efficient methods covering base station (BS) hardware design, network planning and deployment, and network management and operation stages. In order to further understand how EE is assessed and improved through the heterogeneous network (HetNet), BS's energy-awareness and several typical HetNet deployment scenarios such as macrocell-microcell and macrocell-picocell are presented. The analysis of different HetNet deployment scenarios gives insights towards a successful deployment of energy efficient cellular networks.

• ETRI Journal
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• v.33 no.6
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• pp.973-976
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• 2011

This letter describes an efficient technique for maximum power point tracking (MPPT) of an energy harvesting device. It is based on controlling the device voltage at the point of maximum power. Using a microcontroller with a power saving technique, the MPPT algorithm maintains the maximum power with low power consumption. An experiment shows that the algorithm maximizes the energy transfer power using an energy management IC fabricated in a 0.18-${\mu}m$ process. Compared to direct energy transfer to a battery, the proposed technique is more efficient for low-energy harvesting under variable conditions.

• Journal of the Korean Solar Energy Society
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• v.40 no.3
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• pp.33-42
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• 2020

Operational energy is the energy that is used during the occupancy stage of building life cycle. It is associated with relatively longer proportion of infrastructure's service life and can constitute 80-90% of the total energy. Assessing the energy use in buildings is essential since they are significant contributors to energy demand. In this regard, energy performance of buildings has become the focus of many regulations. This paper aimed to review the regulations about the energy performance of buildings during their operational stage in Korea. For energy efficient operation program for existing buildings, governments should implement policies and support voluntary programs that rely on collecting and managing building performance data and using this data to inform public and private-sector operation and maintenance strategies. Implementing these policies and programs requires tools and processes for collecting, curating, managing, analyzing, and publishing this data. Energy assessment tool, that is a data resource management tool that enables to assess energy use across the entire portfolio of buildings, is also required.

• Smart Media Journal
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• v.4 no.1
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• pp.25-32
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• 2015

Powering wireless sensors with energy harvested from the environment is coming of age due to the increasing power densities of both storage and harvesting devices and the electronics performing energy efficient energy conversion. In order to maximize the functionality of the wireless sensor network, minimize missing packets, minimize latency and prevent the waste of energy, problems like congestion and inefficient energy usage must be addressed. Many sleep-awake protocols and efficient message priority techniques have been developed to properly manage the energy of the nodes and to minimize congestion. For a WSN that is operating in a strictly energy constrained environment, an energy-efficient transmission strategy is necessary. In this paper, we present a novel transmission priority decision scheme for a heterogeneous body sensor network composed of normal nodes and an energy harvesting node that acts as a cluster head. The energy harvesting node's decision whether or not to clear a normal node for sending is based on a set of metrics which includes the energy harvesting node's remaining energy, the total harvested energy, the type of message in a normal node's queue and finally, the implementation context of the wireless sensor network.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.2
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• pp.700-713
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• 2015

It is critical to design energy-efficient routing protocols for battery-limited mobile ad hoc networks, especially in which the energy-consuming MIMO techniques are employed. However, there are several challenges in such a design: first, it is difficult to characterize the energy consumption of a MIMO-based link; second, without a careful design, the broadcasted RREP packets, which are used in most energy-efficient routing protocols, could flood over the networks, and the destination node cannot decide when to reply the communication request; third, due to node mobility and persistent channel degradation, the selected route paths would break down frequently and hence the protocol overhead is increased further. To address these issues, in this paper, a novel Greedy Energy-Efficient Routing (GEER) protocol is proposed: (a) a generalized energy consumption model for the MIMO-based link, considering the trade-off between multiplexing and diversity gains, is derived to minimize link energy consumption and obtain the optimal transmit model; (b) a simple greedy route discovery algorithm and a novel adaptive reply strategy are adopted to speed up path setup with a reduced establishment overhead; (c) a lightweight route maintenance mechanism is introduced to adaptively rebuild the broken links. Extensive simulation results show that, in comparison with the conventional solutions, the proposed GEER protocol can significantly reduce the energy consumption by up to 68.74%.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.6
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• pp.516-521
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• 2019

The top seeded solution growth (TSSG) method is an alternative technique to grow high-quality SiC crystals that has been actively studied for the last two decades. However, the TSSG method has different issues that need to be resolved when compared to the commercial SiC crystal growing method, i.e., physical vapor transport (PVT). A particular issue of the TSSG method of results from the presence of liquid droplets on the grown crystal that can remain even after crystal growth; this induces residual stress on the crystal surface. Hence, the residual droplet causes several unwanted effects on the crystal such as the initiation of micro-cracks, micro-pipes, and polytype inclusions. Therefore, this study investigated the formation of the residual droplet through multiphysics simulations and lead to the development of a liquid droplet removal method. As a result, we found that although residual liquid droplets significantly apply residual stress on the grown crystal, these could be vaporized by adopting thermal annealing processes after the relevant crystal growing steps.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.54 no.8
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• pp.396-400
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• 2005

This paper proposes the cost analysis on the energy efficient equipment when this equipment is participated in the demand-side bidding. Conventional demand-side bidding is exercised through load re-distribution. However if this load reduction is exercised by the use of high efficient equipment, its effect will be assumed to be more economical. This paper analyses this cost-benefit effect of high efficient equipment in the demand-side bidding.

• IEMEK Journal of Embedded Systems and Applications
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• v.11 no.1
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• pp.1-8
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• 2016

We proposed a load unbalancing scheduling method for energy-efficient multi-core embedded systems considering DVFS (Dynamic Voltage/Frequency Scaling) power consumption and task characteristics. It is a new kind of scheduler which combines load balancing and load unbalancing technique. The purpose of the method is to effectively utilize energy without much effect in performance. In this paper, we conduct experiments on energy consumption and performance using the previous load balancing and unbalancing techniques and our proposed technique. The proposed technique reduced energy consumption more than 13.7% when compared to other algorithms. As a result, the proposed technique shows low energy consumption without much decline in the performance and is adequate for energy-efficient multi-core embedded systems.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.165.2-165.2
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• 2010

The objective of this study is to analyze the energy saving rate by retrofitting multi air conditioner from conventional type to high efficient type using Energyplus 4.0 which was developed for simulating a building energy by D.O.E. Generally, Multi air conditioner system was installed for both the cooling and the heating in a building. However, it was difficult to estimate the energy saving rate in the case of retrofitting multi air conditioner from conventional type to high efficient type. In the present study, annual energy consumptions of them were evaluated for same building and climate condition.