• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.11
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• pp.78-87
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• 1996

in urban cross-roads with dense buildings, receiving power and delay spread were computed when doing these, we were able to develope codes to be executed in a very fast time by combining image method and algorithm for propagation paths compairing with ray launching technique. And receiving power and delay spread could be viewed in 3-dimensional picture by virtue of computing electric fields in arbitrary receiving point. For numerical computation, receiving power of wide and anrrow band and delay spread were computed, and extension method of ray numbers was facilitated for handling infinite number of rays.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.4
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• pp.297-305
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• 2018

The role of UCAV is to carry out various missions in hostile situations such as penetration and attack on the enemy territory. To this end, application of RF stealth technology is indispensable so as not to be caught by enemy radar. The X-47B UCAV with blended wing body configuration is a representative aircraft in which modern RCS reduction schemes are heavily applied. In this study, a model UCAV was first designed based on the X-47B platform and then an extensive RCS analysis was conducted to the model UCAV in the high-frequency regime using the Ray Launching Geometrical Optics (RL-GO) method. In particular, the effects of configuration of UCAV considering IR reduction on RCS were investigated. Finally, the effects of RAM optimized for the air intake of the model UCAV were analyzed.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.2
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• pp.1-6
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• 2010

Short-range wireless communication systems are expanding at rapid rate, finding application in offices and homes. Development of wireless local network is accompanied by steady increase in the demand for ever higher data rates. This in turn entails the necessity to develop communication systems which operate at higher frequencies. It can be expected that short-rage wireless communication networks will soon push towards the THz frequency range. We use a 3D ray-launching for analysis of propagation environments at the indoor fixtures. We extended the approach from the modeling of the reflectivity of optically thick, smooth building materials at THz frequencies to materials with a rough surface. The simulation result of propagation environment is similar to average received power of reference paper. The RMS delay spread was calculated to be 9.11 ns in a room size of $6m(L){\times}5m(W){\times}2.5m(H)$ for the concrete plaster.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.6
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• pp.1511-1519
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• 2010

In this paper, we proposed and analyzed a RSSI based cooperative localization algorithm considering wireless propagation characteristics in indoor and outdoor environments for wireless sensor networks, which can estimate the BN position. The conventional RSSI based estimation scheme has low precision ranging due to instability propagation characteristics by time variable. Hence, we implemented ray-launching simulator for analysis of propagation characteristics in 4 case, and experimented proposed localization scheme with 4 RN and 1 to 5 BN. Simulation results show that NLCA has estimation error as 2m-3.5m, however, proposed CLA/ECLA has 1.3m-2.5m/0.5m-1.2m by same environments. Therefore, if we can consider channel characteristics, the proposed algorithm provides higher localization accuracy than RSSI based conventional one.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.05a
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• pp.875-878
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• 2010

In this paper, we proposed a RSSI based cooperative localization algorithm considering wireless propagation characteristics in indoor environment for wireless sensor networks, which can estimate the BN position. The conventional RSSI based estimation scheme has low precision ranging according to time variable propagation characteristics. Hence, we implemented ray-launching simulator for analysis of propagation characteristics in $13.65m{\times}8.7m$, and performed proposed localization scheme with 4 RN and 1 to 5 BN. From the results, if we can consider channal characteristic in proposed ranging scheme, the cooperative localization algorithm with propagation characteristics provides higher localization accuracy than RSSI based conventional one.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.64.1-64.1
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• 2013

The point spread function (PSF) of an optical system is in general defined as a two-dimensional intensity distribution which results from a single point source at infinity. It is an important key for the evaluation of the optical performance of an astronomical telescope. The PSFs of the soft X-ray telescope (SXT) aboard Yohkoh were measured in a wide range of the field-of-view under the in-flight configuration at White Sands Missile Range prior to launching the satellite. It has been known that the SXT PSF has a sharp peak at the core and the intensity drops very fast as it goes distant from the center. Due to the combination of this sharp peak at the PSF core and the effect of undersampling by a large pixel size, a carefully designed method is requested in the examination of the PSF data. The pattern of the SXT PSF is determined by the fitting of a mathematical functional form to the pre-launch experimental data. The elliptical Moffat function has been adopted for the evaluation of the SXT PSF. It is revealed from our study that the SXT PSF shows a peculiar characteristics, and thus a careful consideration on the undersampling effect and also a proper choice of statistics are necessary for the determination of the best fit function of the PSF. Details on the on- and off-axis SXT PSF in the field-of-view will be introduced and discussed in our presentation.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.35.1-35.1
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• 2018

Shock waves have been observed in the outskirts of galaxy clusters. They are commonly interpreted as being driven by mergers of sub-clumps, so are called "merger shocks". We here report a study of the properties of merger shocks in merging galaxy clusters with cosmological hydrodynamic simulations. As a representative case, we describe the case where sub-clusters with mass ratio ~ 2 go through an almost head-on, binary-like merger. Because of the turbulent nature of hierarchical clustering, shock surfaces are not uniform, but composed of parts with different Mach numbers. As merger shocks expand from the core to the outskirts, the average Mach number, < $M_s$ >, increases. The shocks propagating along the merger axis could be observed as X-ray shocks and/or radio relics. The kinetic energy through the shocks peaks at ~ 1 Gyr after shock launching, or at ~ 1 - 2 Mpc from the core. The most energetic shocks are found to have the kinetic-energy weighted Mach number, < $M_s$ > $_{\phi}{\simeq}2-3$, and the CR-energy weighted Mach number, < $M_s$ > $_{CR}{\simeq}3-4$. We then discuss the observational implications of our results.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.35T no.3
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• pp.103-112
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• 1998

This paper proposes a propagation prediction model which can calculate a propagation path loss easily at option point in case of the propagation processing by repeat reflection when we analysis a propagation route, it makes the calculation speed which is the defect of a geometrical of image method and a ray-launching method improve and we develop and apply the algorithms which can do an angle of incidence, an angle of reflection with a propagation direct path, a reflection path and a maximum reflection number arithmetic process synchronously. Finally we choose as a sample which is the real road condition where is around SK telecoms chunnam branch office in wolgok-dong, kwangsan-ku, kwangju and simulate proposition model then we demonstrate the relative superiority with comparing the results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.1
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• pp.39-47
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• 2008

Automatic landing performance of UAV can be enhanced by adding Pseudolite(PL) to GPS. However, it is very hard to install and operate PL with confidence because GPS satellites are moving and the landing zone are usually changeable. The coverage and accuracy of combined GPS and PL can be estimated by using simulator and the correct information is very crucial to UAV operation. In this paper, design, implementation and evaluation of GPS/PL simulator for UAV landing are given. A very realistic coverage estimation is obtained using GIS data and ray launching method with considerations of the transmitter power level, altitude of UAV, number and location of PL. The expected accuracy is estimated using DOP and NSP computed using both GPS and PL. The performance of simulator is evaluated by comparing with the results of a real GPS receiver, and the certified simulator shows the required accuracy for UAV landing can be easily met by proper installation of at least 2 PLs.

• The Korean Journal of Air & Space Law and Policy
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• v.22 no.2
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• pp.155-175
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• 2007

As intellectual terror threats increase, we feel the limit in coping with those threats and the things we do are placing traditional X-ray machines & ETD and increasing aviation security staffs. In fact, even if air transportation system is the fast and most efficient transportation methods, it is true that there are many inconveniences to endure due to terror threats. In the name of security, even if we make a lot of efforts and time to screen both good-natured passengers, baggage, cargo and suspicious passengers, it is impossible to screen perfectly and it is not an efficient methods. Therefore, we introduce profiling system that reduce the effort to screen good-natured passengers but focus on screening dangerous passengers and baggages. Profiling system strengthens aviation security, using the concept "Selection & Concentration". Israel started to introduce manual profiling system in aviation security, which is interviewing suspicious passengers and it has been used in crime investigation since 1960. And it has been upgraded and diversified to CAPPS(Computer Assisted Passenger Screening Program) and SPOT(Screening Passenger by Observation). So, this theses is to study on the concept & kind of profiling and profiling methods adopted in airlines. Also it presents the method of introduction of profiling system in Korea and the necessity of making law on it.