• Journal of Korea Multimedia Society
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• v.12 no.12
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• pp.1769-1777
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• 2009

With the advent of the ubiquitous technology age, the progress of network technology has enabled a robust sensor communication, not just in cities, but also in poor surroundings such as deserts, polar regions, or underwater environments. In this paper, we propose a Multiple Acknowledgement (MA) technique to replace the conventional Automatic Repeat request (ARQ) technique. The MA mechanism is to send an Ack to many receivers simultaneously. The CH (master, coordinator) of the unit cluster broadcasts a Beacon frame where Ack information of the previously transmitted data is included. This technique can reduce the number of transmissions and overhead significantly. The proposed technique is a scheme improving the efficiency of an underwater sensor network where the uplink data transmission is the mainstream. The Performance of the ARQ, Block Ack, Pervasive Block Ack and the proposed method were compared with one another and analyzed. The proposed method showed significant performance improvement as compared with the ARQ, BA, and PBA in its channel efficiency.

• Proceedings of the KIPE Conference
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• 2015.11a
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• pp.52-53
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• 2015

This paper introduces a novel hybrid converter combining a full-bridge soft switching converter and a full-bridge LLC converter. In this topology all the primary switches can achieve ZVS and ZCS all over the operation range. An additional switch and a diode are added in the secondary side of full-bridge converter to eliminate the circulating current and to provide a separate freewheeling path. The hybrid structure makes it possible to deliver the power to the secondary all the time of operation, thereby improving the efficiency. The proposed topology is suitable for the applications such as on-board chargers for electric vehicles and high power dc-dc converters. A 6.6-kW prototype converter was implemented and 97.5% efficiency was obtained through the experiments.

• Journal of Power Electronics
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• v.17 no.4
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• pp.874-883
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• 2017

T-type isolated DC/DC converters have recently attracted attention due to their numerous advantages, including few components, low cost, and symmetrical operation of transformers. This study proposes an improved control strategy for increasing the efficiency of T-type isolated DC/DC converters. Under the proposed strategy, the primary circulating current flows through the auxiliary switches (metal-oxide-semiconductor field-effect transistors) instead of their body diodes in free-wheeling periods. Such feature can reduce conduction losses, thereby improving the efficiency of T-type isolated DC/DC converters. The operation principles and performances of T-type isolated DC/DC converters under the proposed control strategy are analyzed in detail and verified through the simulation and experimental results.

• Journal of the Korea Safety Management & Science
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• v.18 no.4
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• pp.179-183
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• 2016

The purposes of this research are to modelize test system of SM TESTING by ARENA, software, input several items of specimen's testing process, resources of system and transfer loop, etc, give a hypothesis and then, obtain results reducing the efficiency of the whole system finally by overload of specific facilities in the testing system through the simulation so as to obtain several materials such as specimen and testing facility, transfer loop, etc. by simple and various forms without any necessity of numerical modelization. It will add facilities of over load and reduce facilities with low operation rate, so increase the efficiency of the system.

• Proceedings of the KSR Conference
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• 2009.05b
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• pp.585-592
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• 2009

The performance of screw compressor depends on lots of design parameters of rotor profile, such as length of seal line, wrap angle, blow hole, suction and discharge port size, number of rotor lobe, etc. The optimum rotor profile makes it possible to increase the compression efficiency with low energy consumption, and to minimize the loss of power. In this research, a new rotor profile design and performance analysis are done by computer simulation. It is expected that the volumetric efficiency is improved because the internal leakage is reduced due to the minimization of blow hole and clearance, and the stiffness of rotors is increased due to the reduction of length to diameter ratio. Also, the specific power consumption will be secured for use ranging from low to high operation speed.

• ETRI Journal
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• v.43 no.3
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• pp.427-435
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• 2021

Data filtering is an essential task for improving the energy efficiency of radiofrequency identification (RFID) networks. Among various energy-efficient approaches, clustering-based data filtering is considered to be the most effective solution because data from cluster members can be filtered at cluster heads before being sent to base stations. However, this approach quickly depletes the energy of cluster heads. Furthermore, most previous studies have assumed that readers are fixed and interrogate mobile tags in a workspace. However, there are several applications in which readers are mobile and interrogate fixed tags in a specific area. This article proposes a model for dynamic clustering-based data filtering (DCDF) in mobile RFID networks, where mobile readers are re-clustered periodically and the cluster head role is rotated among the members of each cluster. Simulation results show that DCDF is effective in terms of balancing energy consumption among readers and prolonging the lifetime of the mobile RFID networks.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.5
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• pp.2768-2780
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• 2019

Ciphertext-policy attribute-based encryption (CP-ABE) is one of the practical technologies to share data over cloud since it can protect data confidentiality and support fine-grained access control on the encrypted data. However, most of the previous schemes only focus on data confidentiality without considering data receiver privacy preserving. Recently, Li et al.(in TIIS, 10(7), 2016.7) proposed a CP-ABE with hidden access policy and testing, where they declare their scheme achieves privacy preserving for the encryptor and decryptor, and also has high decryption efficiency. Unfortunately, in this paper, we show that their scheme fails to achieve hidden access policy at first. It means that any adversary can obtain access policy information by a simple decisional Diffie-Hellman test (DDH-test) attack. Then we give a method to overcome this shortcoming. Security and performance analyses show that the proposed scheme not only achieves the privacy protection for users, but also has higher efficiency than the original one.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.26 no.4
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• pp.142-148
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• 2018

In recent years, Korea's aviation industry has been developing rapidly due to the emergence of low-cost airlines. In order to survive in such competition, airlines are making various efforts to save the operation cost as much as possible. Fuel costs account for more than 25% of operating costs. For airlines, reducing aircraft fuel costs is an important part of improving profitability. In this study, analyzing the difference weight between flightplan and W&B Manifest for calculated the fuel that was unnecessarily loaded. As a method to calculate the unnecessary fuel was used by Airbus company flight planning program.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.68 no.2
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• pp.364-369
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• 2019

Generally, since memory chips should be tested all, considering its volume, the reduction in test time for detecting faults plays an important role in reducing the overall production cost. The parallel testing of chips in one ATE is a competitive solution to solve it. In this paper, NOC is proposed as test interface architecture between DUTs and ATE. Because NOC can be extended freely, there is no limit on the number of DUTs tested at the same time. Thus, more memory can be tested with the same bandwidth of ATE. Furthermore, the proposed NOC-based parallel test method can increase the efficiency of channel usage by packet type data transmission.

• Current Photovoltaic Research
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• v.10 no.3
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• pp.90-94
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• 2022

The screen-printing method is the most mature solar cell fabrication technology, which has the advantage of being faster and simpler process than other printing technology. A front metallization printed through screen printing influences the efficiency and manufacturing cost of solar cell. Recent technology development of crystalline silicon solar cell is proceeding to reduce the manufacturing cost while improving the efficiency. Therefore, screen printing requires process development to reduce a line width of an electrode and decrease shading area. In this paper, we will discuss the development trend and prospects of screen-printing metallization using metal paste, which is currently used in manufacturing commercial crystalline silicon solar cells.