• Journal of information and communication convergence engineering
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• v.12 no.2
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• pp.97-103
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• 2014

In spectrum sensing, there is a tradeoff between the probability of missed detection and the probability of a false alarm according to the value of the sensing threshold. Therefore, it is important to determine the sensing threshold suitable to the environment of cognitive radio networks. In this study, we consider a cognitive radio-based ad hoc network where secondary users directly communicate by using the same frequency band as the primary system and control their transmit power on the basis of the distance between them. First, we investigate a condition in which the primary and the secondary users can share the same frequency band without harmful interference from each other, and then, propose an algorithm that controls the sensing threshold dynamically on the basis of the transmit power of the secondary user. The analysis and simulation results show that the proposed sensing threshold control algorithm has low probabilities of both missed detection and a false alarm and thus, enables optimized spectrum sharing between the primary and the secondary systems.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.5
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• pp.173-178
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• 2011

In this paper, we analyze the total performance according to transmit probability of interfering transmitter in hetero systems. We analyze this criteria as a parameter for co-use when hetero systems share the same frequency channels. In order to make an analysis of relationship between transmit probability and performances of two systems. We take into consideration on the case that WLAN is a victim receiver and WiBro is an interfering transmitter. Analyzed coexistence results may be widely applied into the technique developed to get the coexisting condition for wireless devices using many communication protocols in same frequency.

• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.90-94
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• 1998

The parallel inverter is popularly used because of its fault-tolerance capability, high-current outputs at constant voltages and system modularity. The conventional parallel inverter usually employes active and reactive power control or frequency and voltage droop control. However, these approaches have the disadvantages that the response time of parallel inverter control is slow against load and system parameter variation to calculate active, reactive power, frequency and voltage. This paper describes a novel control scheme for power equalization in parallel connected inverter. The proposed scheme has a fast power balance control response, a simplicity of implementation, and inherent peak current limiting capability since it employes a instantaneous current/voltage control with output voltage and current balance and output voltage regulation. A design procedure for the proposed parallel inverter controller is presented. Futhermore, the proposed control scheme is verified through the simulation in various cases such as the system parameter variation, the control parameter variation and the nonlinear load condition.

• Journal of Information Processing Systems
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• v.10 no.3
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• pp.384-394
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• 2014

The femtocell overlaid cellular network (FOCN) has been used to enhance the capacity of existing cellular systems. To obtain the desired system performance, both cross-tier interference and co-tier interference in an FOCN need to be managed. This paper proposes an interference management scheme that adaptively constructs a femtocell cluster, which is a group of femtocell base stations that share the same frequency band. The performance evaluation shows that the proposed scheme can enhance the performance of the macrocell-tier and maintain a greater signal to interference-plus-noise ratio than the outage level can for about 99% of femtocell users.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2002.05a
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• pp.144-151
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• 2002

Future wireless communication systems are expected to provide a broad range of multimedia services in which the asymmetry of traffic load between uplink and downlink is a significant feature. The rode division multiple access system with tune division duplex mode (CDMA/TDD) is a good solution to cope with the traffic asymmetry problem. However. the TDD system is subject to inter-cell interference compared to frequency division duplex (FDD) system. Since both uplink and downlink share the same frequency in TDD. uplink and downlink may interfere each other especially when neighboring cells require different rates of asymmetry. Thus, time slot allocation for tells is an important issue in TDD. In this paper. we propose a genetic algorithm based time slot allocation scheme which maximizes the residual system capacity. The proposed scheme allows that each cell employ different level of uplink/downlink asymmetry and satisfies the interference requirement.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2004.05a
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• pp.526-529
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• 2004

A new SEPIC-Flyback convater is proposed. The proposed converter is the superposition of SEPIC and Flyback converter. Not only SEPIC output but also Flyback output could be fully regulated by constant frequency PWM control. Merged SEPIC and Flyback topology could share the transformer and power MOSFET. When the switch turns of one topology operates via capacitive energy transfer. Another topology acts as powering mode while the switch is off. So, it could increase power falsify per one cycle. The operating principle of the proposed converter is described below. Prototype featuring 24V input 48V output, 100kHz switching frequency, and 100W output is simulated under the proposed topology.

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.47-48
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• 2016

Parallel distributed generators (DGs) in the islanded micro-grid are normally controlled with the aid of the droop control scheme. However, the traditional droop control methods which use the P-${\omega}$ and Q-E curve to share power between DGs are still concerned to improve the accurate of reactive power sharing and variation of frequency and voltage at the point of common coupling (PCC). This paper proposes a control scheme to solve the limitation of microgrid in islanded operation such as reactive power sharing accuracy and PCC voltage and frequency restoring. In order to achieve the control objective, a secondary control is implemented with both central controller and local controller by using the low bandwidth communications. The effectiveness of the proposed control scheme is analyzed through the simulation.

• Journal of Information Technology Applications and Management
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• v.22 no.3
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• pp.83-103
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• 2015

The rapid development of internet technologies and social media over the last few years has generated a huge amount of unstructured text data, which contains a great deal of valuable information and issues. Therefore, text mining-extracting meaningful information from unstructured text data-has gained attention from many researchers in various fields. Topic analysis is a text mining application that is used to determine the main issues in a large volume of text documents. However, it is difficult to identify related issues or meaningful insights as the number of issues derived through topic analysis is too large. Furthermore, traditional issue-clustering methods can only be performed based on the co-occurrence frequency of issue keywords in many documents. Therefore, an association between issues that have a low co-occurrence frequency cannot be recognized using traditional issue-clustering methods, even if those issues are strongly related in other perspectives. Therefore, in this research, a methodology to reorganize social issues from a research and development (R&D) perspective using social network analysis is proposed. Using an R&D perspective lexicon, issues that consistently share the same R&D keywords can be further identified through social network analysis. In this study, the R&D keywords that are associated with a particular issue imply the key technology elements that are needed to solve a particular issue. Issue clustering can then be performed based on the analysis results. Furthermore, the relationship between issues that share the same R&D keywords can be reorganized more systematically, by grouping them into clusters according to the R&D perspective lexicon. We expect that our methodology will contribute to establishing efficient R&D investment policies at the national level by enhancing the reusability of R&D knowledge, based on issue clustering using the R&D perspective lexicon. In addition, business companies could also utilize the results by aligning the R&D with their business strategy plans, to help companies develop innovative products and new technologies that sustain innovative business models.

• 한국태양에너지학회:학술대회논문집
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• 2008.04a
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• pp.43-48
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• 2008

Through simulations and field experiment on A.C. parallel operation of both Utility Interactive Photovoltaic System and Diesel Engine Revolving Field Type Synchronous Generator, following factors have been found. First, the inverter should be operated in three modes of frequency(mode.1: ${\pm}$0.3Hz, mode.2: ${\pm}$1Hz, mode.3: ${\pm}$2Hz) as default, considering properties of operating Synchronous Generator. Second, as a result of supplying 13.5kW of residual power, it has been found that Synchronous Generator takes the power input only as reactive power, because it was electrically stable with frequency of 60.14Hz and high voltage of 222.3V even when power factor was -0.94. Besides, it was mechanically stable, too, because the quake, noise, and temperature of Synchronous Generator in this case were 7.5mm/s, 97dB, and $6^{\circ}C$ respectively, which were lower than normal load connection of 145.6kW; 11.03mm/s. Thus, load share of Revolving Field Type Synchronous Generator reduces according to the supply of Photovoltaic System to the load power. In this experiment, 200kW of Synchronous Generator and 40kW of Photovoltaic System were operated in parallel. The load share was 20% in maximum. and 11.1lit/hr of fuel was saved.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.1
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• pp.32-42
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• 2015

In this paper, we considered the scenario that one cellular link and muti-D2D links share the same frequency resource which can improve the spectrum efficiency during uplink communication in LTE (Long Term Evolution)-Advanced network. In order to reduce the interference caused to the D2D users, we set DME (Discovery and Management Entity) which can send the area information to eNB(evolved Node B). We proposed a resource allocation scheme by using these assistant devices to reduce the interference that CUE (Cellular User Equipment) causes to DUE Rx (D2D UE Receiver). Basing on the area information, in order to mitigate the interference among the D2D pairs which share the same frequency resource, a power control scheme has been proposed. The simulation results prove that by using the DMEs, the proposed schemes improve the stability of D2D communication and bring the highest performance of the communication system when comparing to the other different schemes.