• Journal of Communications and Networks
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• v.15 no.1
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• pp.102-110
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• 2013

This paper considers a cooperative orthogonal frequency division multiple access (OFDMA)-based cognitive radio network where the primary system leases some of its subchannels to the secondary system for a fraction of time in exchange for the secondary users (SUs) assisting the transmission of primary users (PUs) as relays. Our aim is to determine the cooperation strategies among the primary and secondary systems so as to maximize the sum-rate of SUs while maintaining quality-of-service (QoS) requirements of PUs. We formulate a joint optimization problem of PU transmission mode selection, SU (or relay) selection, subcarrier assignment, power control, and time allocation. By applying dual method, this mixed integer programming problem is decomposed into parallel per-subcarrier subproblems, with each determining the cooperation strategy between one PU and one SU. We show that, on each leased subcarrier, the optimal strategy is to let a SU exclusively act as a relay or transmit for itself. This result is fundamentally different from the conventional spectrum leasing in single-channel systems where a SU must transmit a fraction of time for itself if it helps the PU's transmission. We then propose a subgradient-based algorithm to find the asymptotically optimal solution to the primal problem in polynomial time. Simulation results demonstrate that the proposed algorithm can significantly enhance the network performance.

• Journal of the Korean Data and Information Science Society
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• v.23 no.4
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• pp.777-785
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• 2012

Recently, the rapid development of internet and information technology has led to rapid changes in many industries. One of the most rapidly developing industries is the call centers. Almost all public institutions, financial institutions including insurance companies, and shopping malls, many call center staffs are proceeding with the consultation. However, lack of call center staffs is leading to a lot of customers complaints. The function of outbound call centers such as promotion and sale of products is also arising some problems due to insufficient number of consulting staffs. In this study, we propose the call center model for maximizing the rate of call connection time and suggest the best way of call centers model to be the channel distributions using the data mining techniques.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.1
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• pp.227-232
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• 2000

This study applied asynchronous W-CDMA(3GPP) system that is suggested as an access method of IMT-2000, multimedia communication in next generation, and estimated fading channel by using pilot symbol different from traditional IS-95. And then, it applied PIC(Parallel Interference Cancellation) as multiple access interference cancellation and analyzed performance depending on the power rate between DPCCH(Control) and DPDCH(Data). As a result of simulation, it showed the best performance in C:D = 3:7 and 4:6, where set up as five users in case of hand design, and showed the best performance in C:D = 3:7, where did as ten users.

• Design & Manufacturing
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• v.11 no.3
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• pp.51-55
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• 2017

Micro fuel cells have high reliability and long usage time. Among them, PEMFC (polymer Electrolyte Membrane Fuel Cell) is suitable as a portable power source because it is easy to fix electrolyte and simple structure. The bipolar plate, a key component of the fuel cell, is produced by cutting. In the case of micro fuel cell separator, burr is very small and the flow channel size in the separator is very small. Therefore, it is difficult to remove burrs in the usual way such as a brushing or ultra-sonic method. Therefore, this study proposed electrolytic polishing process and analyzed the characteristics of each condition by introducing the concept of roughness reduction rate. In addition, the ultrasonic process was added to analyze the effect of ultrasonic addition.

• Nuclear Engineering and Technology
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• v.50 no.6
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• pp.869-876
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• 2018

The force of a direct current (DC) electromagnetic pump used to transport liquid lithium was analyzed to optimize its geometrical and electrical parameters by numerical simulation. In a heavy-ion accelerator, which is being developed in Korea, a liquid lithium film is utilized for its high charge-stripping efficiency for heavy ions of uranium. A DC electromagnetic pump with a flow rate of $6cm^3/s$ and a developed pressure of 1.5 MPa at a temperature of $200^{\circ}C$ was required to circulate the liquid lithium to form liquid lithium films. The current and magnetic flux densities in the flow gap, where a $Sm_2Co_{17}$ permanent magnet was used to generate a magnetic field, were analyzed for the electromagnetic force distribution generated in the pump. The pressure developed by the Lorentz force on the electromagnetic force was calculated by considering the electromotive force and hydraulic pressure drop in the narrow flow channel. The opposite force at the end part due to the magnetic flux density in the opposite direction depended on the pump geometrical parameters such as the pump duct length and width that defines the rectangular channels in the nonhomogeneous distributions of the current and magnetic fields.

• Journal of Korean Society on Water Environment
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• v.22 no.3
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• pp.437-443
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• 2006

The Water usage is relationship which is close with the administrative cost from industrial facility. It is not easy to reduce a water usage. This research is the optimization of the waste water quantity which process waste water integration of the standard thermal power plant in system operate time. The turbine rotates by force of the steam and it produces an electricity. Demineralization Water is manufacture purity manufacturing equipment and it is supplied in power plant channel. We knew a possibility of reducing from pure control process. When it is reduced the Back Washing time, Rinsing time of the gravity filter and the activated carbon filter. Also, It is possible even from regeneration phase in Condensate Polishing Demineralization System. In addition, There is also the water which the drain of the sampling water for watching the condition of power plant process will be able to use. Integrates these processes it will be able to reduce an annual 30,000 ton degree. The research is want to use the fundamental data for the water curtailment of the power plant.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.604-607
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• 2005

In the electro-discharge machining the machining performance is closely related to the characteristics of discharge which can be identified from electrical behavior in gap between workpiece and electrode. Therefore, the accurate prediction of electrical behavior in electro-discharge machining (EDM) is useful to process control and optimization. However, any simulation model fur prediction of electrical behavior in EDM process has never been reported until now. In this study, a simulation model is developed to analyze the electrical behavior of electro-discharge plasma which significantly influences electrical behavior in EDM process. For the purpose of this the fundamentals of electro-discharge mechanism such as inception, propagation, formation of plasma channel and termination are investigated to accurately predict the cycle of discharge plasma in EDM. As a result, a mathematical model of electro-discharge plasma is constructed with considering the fundamentals of electro-discharge plasma. Consequently, it is demonstrated that the developed model can predict the electrical behavior of plasma such as electron density in various conditions.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.7
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• pp.1354-1358
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• 2007

Nowaday, the wideband multimedia service, high speed and great capacity internet service etc. are increasing, so the network construction with the base of optical subscriber network is necessary. As efficient and economic optical subscriber networks are developed, so efficient network construction is possible. The most technology of them is WDM(Wavelength Division Multiplexing)-PON technology of ONU(Optical Network Unit) jointing method using PON(Passive Optical Network). In this paper, we have studied on a method for automatic optimization of data modulation current as optical power when the data is transmitted.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.4
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• pp.657-662
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• 2019

The power consumption of wearable sensors and electrocardiogram regulators should be very low to extend the network lifetime and anticipated QoS( : Quality of Service) control such as error correction and authentication of data processed by WBAN( : Wireless Body Area Network) nodes is important. Therefore, QoS control is the most urgent concern to implement WBAN in health monitoring regulations. For optimal QoS control, we compare the energy efficiency and the average number of transmissions with IEEE 802.15.6 and the error correction method considering energy efficiency. The performance of the proposed error correction technique shows that the energy efficiency and the transmission rate are improved by adjusting the coding rate appropriately using the channel estimation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2019.05a
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• pp.603-606
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• 2019

In this paper, we propose a slotted-ALOHA-based random access protocol and derive the optimal number of random slots that maximize channel throughput when multiple energy harvesting sensor devices perform random access in wireless-powered sensor networks (WPSN). Throughput numerical analysis, we prove that the throughput has a concavity with respect to the number of random slots and obtain the optimal number of slots. Simulation results show that the throughput of the proposed slotted ALOHA-based random access protocol is maximize when the derived optimal number of slots is employed in the considered WPSN.