• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.2
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• pp.168-180
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• 1992

Commumication technology has been continuously developed to overcome the distance and time for the transmission of information to the human society. Wireless mobile communication, which had been used mostly in the military and police is widely used these days for enterprise and individuals. Therefore the domestic usage of the advanced mobile phone service are progressively gaining wide popularity. The modulation techniques used usually in mobile communications were the analog techniques such as AM and FM, but they are getting replaced by the digital techniques, However, the major disadvantage of the digital communications is the increase of the transmission bandwidth. Therefore, it is very important to use efficiently the limited frequency bandwidth. The domestic research and development on the subject seems quite limited and in order to establish the technology of the digital mobile communications. This thesis presents the design of the frequency hopping synthesizer providing 124 channels with a channel spcing of 200KHz. VCD used in the synthesizer employs a semi-rigid cable for higher purity of signal spectrum, and a hybrid pgase detector is realized with a sample hold phase detector in conjuction with a tri-state phase detedctor.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11B
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• pp.1501-1509
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• 2001

Recently, the use of wireless communication systems has been rapidly increasing, which results in a difficult problem in efficient control of limited frequency resources. As a way of solving this problem, the ultra wideband time hopping impulse radio system attracts much attention. The impulse radio system communicates pulse position modulated data using Gaussian monocycle pulses of very short duration less than 1 nsec. Thus the transmitted signal has very low power spectral density and ultra wide bandwidth from near D.C. to a few GHz. It is blown that it hardly interferes with the existing communication systems because of its very low power spectral density. The purpose of this paper is to characterize multipath propagation of the impulse radio signal and to evaluate the performance of the correlator-based receiver for the multipath environments. In this paper, we consider the deterministic two-path model and the statistical indoor multipath model of Saleh and Valenzuela. For the two-path model the output of the correlator with the ideal reference waveform varies according to the relative difference between the indirect path delay and the time interval of PPM, and to the indirect path gains. In addition, the characteristics of bit error rates is measured for the two models through computer simulation. The simulation results indicate that the performance of the impulse radio system depends both on the relative difference between the indirect path delay and the time interval of PPM, and on the indirect path gains. Furthermore, it is observed that the reference signal designed for the AWGN channel can not be applied to the multipath channels.

• Journal of the Korean Society for Railway
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• v.15 no.6
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• pp.631-637
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• 2012

New Opening of Suseo-Pyeongteak High Speed Railway (HSR) will be a new leap in the Korean railway history. However if this section of HSR line around Seoul Metropolitan Area opens, the confluence of new HSR and existing HSR line in Pyeongteak-Osong section will cause a bottle neck problem. In other words, the opening of Suseo-Pyeongteak HSR line will make the capacity of track reach the limit and the section of railroad between Pyeongteak and Osong will be saturated. This will also make such troubles as restricting the number of train which stops at Cheonan-Asan station. In this study, based on the train assignment theory of TVM430 signal system, the methods of calculating headway and number of train are reviewed and the plan for application of optimal operation pattern during peak hour between Pyeongteak-Osong section is also suggested. To remove the bottle neck problem in this HSR section, 3 alternatives are suggested and the expected effects and problems of each alternative are also analyzed. The results show that the troubles caused by excess of track capacity can be removed without any additional cost if the minimum headway in operating system for HSR is adopted in this section. In the future, if these alternatives are considered to the long-term plan for operating train and signal systems, this will improve the efficiency of train operation, which can remove the bottle neck in the HSR line.

• Journal of the Korea Convergence Society
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• v.8 no.8
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• pp.9-15
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• 2017

With the development of semiconductor integration technology, central processing units and storage devices have been miniaturized and performance has been rapidly developed, interconnection network technology is becoming a more important factor in terms of the performance of high performance computing system. In this paper, we analyze the trend of interconnection network technology used in high performance computing. Interconnect technology, which is the most widely used in the Supercomputer Top 500(2017. 06.), is an Infiniband. Recently, Ethernet is the second highest share after InfiniBand due to the emergence of 40/100Gbps Gigabit Ethernet technology. Gigabit Ethernet, where latency performance is lower than InfiniBand, is preferred in cost-effective medium-sized data centers. In addition, top-end HPC systems that demand high performance are devoting themselves from Ethernet and InfiniBand technologies and are attempting to maximize system performance by introducing their own interconnect networks. In the future, high-performance interconnects are expected to utilize silicon-based optical communication technology to exchange data with light.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.3
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• pp.319-325
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• 2004

FHMA(frequency hopping multiple access) communication system has good performance for the LPI and AJ(low probability of intercept and anti-jamming) application. However, high PAPR(peak to average power ratio) happens in the base-station or the repeater system because of a large number of users. In general, predistorter is used to complete the HPA(high power amplifier) nonlinear characteristics. This paper analyzes BER performance when magnitude of IBO(input back oft) and the number of user are considered as the system parameters. In case of the SSPA(solid state power amplifier), the predistorter does not always work as a complete nonlinear compensator. We find that there is a minimum value of IBO for the predistorter to compensate for the nonlinear SSP A, which is changed as the number of user. If IBO is lower than 6 ㏈ at the user number of 16 and p=1, the system with predistorter is poorer than the one without predistorter. Only when the IBO is over 6 ㏈, predistorter does work as a nonlinear compensator. We call it as cross-over IBO value. TWTA improves the more compensation performance than SSPA because characteristic AM/AM of TWTA has more nonlinear than SSPA. At the BER=10$\^$-3/, there are SNR power gains of about 2.5 ㏈ and 3 ㏈ due to the predistorter when the numbers of users are 16 and 32, respectively.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2009.06a
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• pp.452-455
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• 2009

The Nakdong Delta can be identified by two different geomorphic units. The first one is the upper delta. This is mostly composed of inter-distributary islands that are largely influenced by fluvial processes and attributed to the development of these islands along the river. The other one is the lower delta which is mostly composed of beach ridges. Barrier islands are largely effected by wave processes promoted by the development almost at a right angle to the river. Influenced by the longshore current which flows to the same direction, barrier islands located in the Nakdong river estuary are developing from east to west direction. As a result, the eastern end of the barrier islands are growing toward the north-west direction effected by tidal current which moves toward the same direction. Barrier islands include the Sinho Island, the Jinwoo Island, the Daema deung, the Janga Island, the Baghap deung, the Sae deung, and the Chulsae deung(Doyeo deung). They have orderly emerged from the sea since 1861. Since 2008, a new Deung, a sand dune growing under sea, has been developing rapidly from Chulsae deung to the Dadaepo beach. It made the sailing of small fisher boats impossible. Tidal currents transported a lot of sand and silt around the barrier islands. The landscape of Nakdong river estuary where many barrier islands are distributed will change rapidly affecting land environment.