• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.249-256
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• 2004

KRISO/KORDI is currently developing a deep-sea unmanned underwater vehicle (UUV) system which is composed of a launcher, an ROV, and an AUV. Two USBL acoustic positioning systems will be used for UUV's navigation. One is for the deep sea positioning of all three vehicles and the other is for AUV's guidance to the docking device on the launcher. In order to increase the position accuracy MFSK(Multiple Frequency Shift Keying) broadband signal will be used. As the first step to the implementation of a USBL system, this paper studies USBL positioning algorithm using MFSK signals. Firstly, the characteristics of MFSK signal is described with various MFSK parameters: number of frequencies, frequency step, center frequency, and pulse length. Time and phase delays between two received signals are estimated by using cross-correlation and cross-spectrum methods. Finally an USBL positioning algorithm is derived by converting the delays to difference of distances and applying trigonometry. The simulation results show that the position accuracy is improved highly when both cross-correlation and cross-spectrum of MFSK signals are used simultaneously.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.5 s.96
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• pp.488-493
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• 2005

In this study, waveguide-to-CPW transitions were developed for integrating waveguide and MMIC at V-band. The finite element method for numerical analysis and repeated experiments were performed to propose two types of waveguide-to-CPW transition. Using quartz substrate, proposed structures were designed for low loss as well as broadband characteristics. These waveguide-to-CPW transitions showed a good reliability and insensitivity to matching precision, and they could be fabricated with lower cost than that of the conventional connectors. Proposed two types of the structure showed insertion loss less than 1.9 dB and return loss better than 14 dB from 53 GHz to 60 GHz except unwanted resonance region, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.2 s.105
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• pp.171-177
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• 2006

A low-cost, high-performance 40 Gb/s clock recovery module using a phase-locked loop(PLL) for a 40 Gb/s optical receiver with the clock-hold function has been designed and implemented. It consists of a clock extractor circuit, an RF mixer and a frequency discriminator for phase/frequency detection, a VC-DRO, a phase shifter, and a clock-hold circuit. The extracted 40 GHz clock is synchronized with a stable 10 GHz VC-DRO. The clock stability and jitter characteristics of the implemented PLL-based clock recovery module are significantly improved as compared with those of the conventional open-loop type clock recovery module with a DR filter. The measured peak-to-peak RMS jitter is about 230 fs. When an input signal is dropped, the 40 GHz clock is maintained continuously by the hold circuit.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.3
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• pp.276-282
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• 2015

Until recently, power amplifiers using LDMOS were Class-AB and Doherty type, and showed 55 % efficiency for narrowband of 60 MHz bandwidth. However, owing to the RRH application of base stations power amplifier module, a bandwidth expansion of at least 100 MHz and high efficiency power amplifiers of at least 60 % power efficiency are required. In this study, a Class-J power amplifier was designed by optimizing an output matching circuit so that the second harmonic load will contain a pure reactance element only and have broadband characteristics by using GaN HEMT. The measurements showed that a 45 W Class-J power amplifier with a power added efficiency of 60~75 % was achieved when continuous wave signals were input at 1.6~2.3 GHz, including W-CDMA application.

• Information Systems Review
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• v.8 no.1
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• pp.159-179
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• 2006

With the advances in information technologies and the wide acceptance of IT outsourcing practices, subscription-based information & telecommunications services(ITS) become more available. Convergence and intensified industry competition have made it an imperative for the ITS providers to keep their current customers and acquire new customers at the same time. In this study, we developed a framework for effective customer management based on the factors influencing the post-purchase customer choice: stay with the present provider or switch to another one. Specifically, we classified the factors into four categories: Holding factors, Defect factors, Inducement factors, and Hurdle factors depending on the characteristics of the influence and direction of the influence. Based on the classification, we developed a post-purchase customer choice model for the subscription-based ITS providers. Then, we illustrated a possible application of the model in the context of the broadband Internet access service. The model could be used to increase the competitive advantage of service providers through the effective customer management in the subscription-based ITS market.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.11
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• pp.84-90
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• 2010

In this paper, the reduced size of broad bandpass filter with parallel coupled line structure is presented. This proposed filter can control bandwidth of narrow to broadband by adjusting the coupling coefficient. The conventional filter is operated with a narrow band. If a higher bandwidth is desired than the conventional narrow bandwidth, it is hard to realize due to the coupling coefficient between feeding line and resonator. In this paper, to overcome this limitation, a proposed bandpass filter is designed with reduced size due to SIR(Stepped Impedance Resonator) and multi-grade type structures than conventional one, and it has characteristics of adjusting bandwidth freely as per quantity of coupling coefficient. The proposed bandpass filter that, experimental results of insertion and return losses are 0.42 dB and 20.9 dB with bandwidth of 60 % at the center frequency of 5.8 GHz, respectively.

• THE INTERNATIONAL COMMERCE & LAW REVIEW
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• v.26
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• pp.285-313
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• 2005

Online game business has emerged as the most lucrative entertainment industry, with over 10 million players in South Korea and over 30 million in Japan in 2005. The popularity of online games can be attributed to the availability of broadband network, pushing online games into the mainstream entertainment culture. The age distribution of online game players is expanding and a variety of new games are under development to target certain age groups. While the interactive entertainment market continues to expand, with many new online game publishers entering Japan, relatively little is known about which factors influence online game players' behavioral intentions to play continuously in this area. It appears that in this extremely attractive and growing services segment, academics, as well as practitioners, would benefit from investigating the difference, among the types of players, in demographic and social trends, perceptions related to game-design factors, and attitude toward the games. Based on data collected from online questionnaire survey, the differences between hardcore and casual players have been analyzed, and interesting conclusions have been provided concerning the online-game design and development strategies for Japan online-game players.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.6
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• pp.303-309
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• 2014

Chaos communication system can improve a system security due to characteristics of non-periodic, non-predictability, broadband signal and easy implementation. Also, chaos signal is sensitive to initial conditions of chaos map. By these reasons, security of chaos communication system is superior to digital communication system. BER performance of COOK modulation system is better than other chaos modulation systems, even if COOK modulation system uses an asynchronous receiver. However, security and safety of COOK modulated signal are worse than other chaos modulation systems, because information bits can be easily predicted from COOK modulated signal. In this paper, for security improvement of COOK modulated signal, we propose a novel Scrambling COOK modulation system by applying the scrambling method. Conventional COOK modulated signal can be predicted, because chaos signal is generated when data is only 1. However, proposed system cannot be predicted, because chaos signal is generated when data is 0 or 1. Therefore, security and safety of transmitted signal in scrambling COOK modulation system is superior to conventional COOK modulation system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.2
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• pp.364-369
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• 2009

Today, as various access technologies appear, for example WiMax, WiBro, the demand for spectrum is increasing rapidly. Spectrums are a national resource with scarcity value so that we need to a]locate them effectively for the national economy and industry. Accordingly, In the paper, we proposed several factors and new model for estimating spectrum requirements of a next generation mobile network with multimedia data services. These are self-similarity characteristics of data traffic, engineered capacity considering QoS, structure of FA increase, asymmetry of data traffic between uplink and downlink, handoff traffic, and uneven traffic pattern among base stations. It can applied mobile WiMax or other wireless broadband systems in general.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.2A
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• pp.86-96
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• 2006

In recent year, EPON(Ethernet PON) system is expected to be more attractive solutions for high speed, broadband access networks in next generation access networks due to the conversionce of low-cost ethernet equipment and low-cost fiber infrastructure. Upstream channel control algorithm is essential to hare upstream bandwidth in EPON. In this paper, we suggest HUHG(High Utilization and Hybrid Granting) algorithm for supporting high bandwidth utilization and QoS for different service class. This algorithm improves bandwidth utilization as removing or diminishing idle time of upstream channel using characteristics of fixed EF(Expedited Forwarding) sub-cycle. The proposed algorithm also minimizes the packet delay and delay variation of EF class. We conduct detailed simulation experiments using OPNET to study the performance and validate the effectiveness of the proposed algorithm.