• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.2A
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• pp.34-42
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• 2005

In orthogonal frequency-division multiple access (OFDMA) uplink environments, asynchronously received signals can cause multiple access interference (MAI). This paper focuses on the performance degradation due to the MAI over frequency-selective fading channels. We first introduce the timing misalignment, which is defined as the relative timing difference between asynchronous timing error of uplink user and reference time of the base station, and analytically derive the MAI using the power delay profile of wide-sense stationary uncorrelated scattering (WSSUS) channel model. Then, the effective signal-to-noise ratio (SNR) and the average symbol error probability (SEP) are derived. The proposed analytical results are verified through simulations with respect to the region of the timing misalignment and the number of asynchronous users.

• Journal of electromagnetic engineering and science
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• v.4 no.4
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• pp.183-189
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• 2004

In this paper, the Eigen-RAKE receiver in wideband direct sequence code-division multiple access(DS-CDMA) systems with downlink smart antenna is analyzed for different spreading bandwidths(1.25 MHz, 5 MHz, 10 MHz) and different channel environments(macro, micro). The realistic spatio-temporal wideband multipath channel is assumed, one of which is standardized multiple-input single-output(MISO) radio channel model for WCDMA link-level simulations proposed by $3^{rd}$ generation partnership project(3GPP) contributions. We assumed spatial scattering phenomenon in which many unresolvable path signals within a limited range of spatial angle simultaneously contribute to the signals received at the receiver. Several multipaths within one chip are distinguished into each one and the first multipath components are selected as the desired signal and the others are considered self-interference. Downlink DS-CDMA system with eigenbeamformer using wider bandwidth present better performance than that using narrow bandwidth system by employing Eigen-RAKE receiver of many number of branches. It is shown that the downlink eigenbeamformer is more effective in typical urban macro cellular environments when using Eigen-RAKE receiver.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.6
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• pp.735-745
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• 1998

The method of moments has been widely used in the analysis of TM scattering problems. Recently, significant advances in the development of fast and efficient techniques for solving large problems have been reported. In such methods, iterative matrix solvers are preferred by virtue of their speed and low memory requirements. But for near resonant and strong multiple scattering problems, e.g., involving an aircraft engine inlet, a large number of iterations is required for convergence. In this paper, an efficient approximate inverse based preconditioner is used to reduce this number of iterations. By using the matrix partitioning method, the computational is used to reduce this number of iterations. By using the matrix partitioning method, the computational cost for obtaining the approximate inverse is reduced to O(N). We apply this preconditioner to an O(NlogN) algorithm, the multilevel fast multipole algorithm, for the aircraft engine inlet problem. The numerical results show the efficiency of this preconditioner.

• Korean Journal of Optics and Photonics
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• v.30 no.1
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• pp.1-7
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• 2019

MANPADS (man-portable air defense system) is a counterweapon system against enemy aircraft, tracking the MWIR (mid-wavelength of infrared) signature of the plume. Under foggy conditions, however, multiple scattering phenomenon caused by the particles affects the MWIR transmittance, and the MANPADS detection performance. Therefore, in this study we analyzed the lock-on range of MANPADS with varying fog conditions and plume characteristics. To analyze the optical extinction properties and transmittance in fog, Mie scattering theory and analytic solution of the radiative-transfer equation are utilized. In addition, we used flare signature as an alternative MWIR light source. We confirmed that the lock-on range could be noticeably reduced under conditions of mist, and proportional to the flare temperature.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.60.1-60.1
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• 2014

The star ${\zeta}$ Ophiuchi (HD 149757) is one of the brightest massive stars in the northern hemisphere and was widely studied in various wavelength domains. We report the analysis results of far ultraviolet (FUV) observations with other wavelengths for around ${\zeta}$ Ophiuchi. We study the correlation of between multi wavelength observations. We have developed a Monte Carlo code that simulates dust scattering of light including multiple encounters. The code is applied to the present Oph HII region to obtain the geometrical information of dust such as distance and thickness. Also We apply three-dimensional photoionization code to model Wisconsin $H{\alpha}$ Mapper observations of the H II region surrounding the star.

• Asian Journal of Atmospheric Environment
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• v.4 no.3
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• pp.115-140
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• 2010

Great concerns about atmospheric aerosols are attributed to their multiple roles to atmospheric processes. For example, atmospheric aerosols influence global climate, directly by scattering or absorbing solar radiations and indirectly by serving as cloud condensation nuclei. They also have a significant impact on human health and visibility. Many of these effects depend on the size and composition of atmospheric aerosols, and thus detailed information on the physicochemical properties and the distribution of airborne particles is critical to accurately predict their impact on the Earth's climate as well as human health. A single particle analysis technique, named low-Z particle electron probe X-ray microanalysis (low-Z particle EPMA) that can determine the concentration of low-Z elements such as carbon, nitrogen and oxygen in a microscopic volume has been developed. The capability of quantitative analysis of low-Z elements in individual particle allows the characterization of especially important atmospheric particles such as sulfates, nitrates, ammonium, and carbonaceous particles. Furthermore, the diversity and the complicated heterogeneity of atmospheric particles in chemical compositions can be investigated in detail. In this review, the development and methodology of low-Z particle EPMA for the analysis of atmospheric aerosols are introduced. Also, its typical applications for the characterization of various atmospheric particles, i.e., on the chemical compositions, morphologies, the size segregated distributions, and the origins of Asian dust, urban aerosols, indoor aerosols in underground subway station, and Arctic aerosols, are illustrated.

• Korean Chemical Engineering Research
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• v.59 no.3
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• pp.443-449
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• 2021

A biodegradable shatterproof thin film material having excellent water resistance and applicability was prepared by crosslinking through esterification of starch and citric acid. In order to improve the thin film formation and physical properties of these materials, PVA and glycerin were added to secure the flexibility of the applied thin film. In addition, conditions for optimizing material functionality such as swelling degree and solubility in water according to reaction time, temperature, and concentrations of raw materials and additives were analyzed. The crosslinking reaction of starch and citric acid was confirmed by FT-IR analysis, and it was found that single and multiple esterification reactions occurred simultaneously in these reaction processes. It can be seen that the crosslinked starch-citric acid thin film material was decomposed about 95% after 12 weeks after landfilling, and thus biodegradability was excellent.

• Journal of IKEEE
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• v.1 no.1 s.1
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• pp.73-82
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• 1997

In this paper we analyzed, using Markov modeling, the performance of CSMA/CD over the wireless channel which is characterized by near-far effect, shadowing and Rayleigh fading. The analysis shows that throughput of CSMA/CD is degraded by channel error. However, if capture effect which arises from the randomness of power level of received signal due to the fading phenomena of electromagnetic waves is taken into consideration, the system performance is much improved and the system stability is also made better.

• Progress in Medical Physics
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• v.15 no.3
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• pp.140-148
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• 2004

The absorbed dose for proton beam in water was calculated using the PTRAN code system. The proton interactions with water and the description on absorbed dose calculations are discussed, and the file structure and an execution example of the PTRAN codes are described. For 60, 100, 150, 200, and 250 MeV proton beams it is demonstrated that the absorbed dose is determined from the sum of Coulomb interactions and nuclear reactions, and that the Bragg peak feature depends On the energy straggling and multiple scattering. The PTRAN code was useful for studying the fundamental mechanism of the absorbed dose to water for clinical proton beams.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2002.11a
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• pp.169-174
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• 2002

It has known that the DCMP(Directionally Constrained Minimization of power)and the ZF(Zero Forcing) can improve the SINR performance of an array antenna system by using spatial signature of wireless channel. This paper analyzes performance of DCMP and ZF in multiple scattering environments. To obtain the spatial signature of wireless channel. bothe DOA(Directional of Arrival) and AS(Angular Spread) of the received signals were estimated by using ESPRIT. The performance of the DCMP and the ZF was analyzed theoretically. Through computer simulation, the SINR performance were evaluated.