• Journal of Communications and Networks
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• v.12 no.3
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• pp.222-230
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• 2010

In this paper, we present a closed-form approximation of the average sum rate of zero-forcing (ZF) beamforming (BF) with semi-orthogonal user selection (SUS). We first derive the survival probability associated with the SUS that absolute square of the channel correlation between two users is less than the orthogonalization level threshold (OLT).With this result, each distribution for the number of surviving users at each iteration of the SUS and the number of streams for transmission is calculated. Secondly, the received signal power of ZF-BF is represented as a function of the elements of the upper triangular matrix from QR decomposition of the channel matrix. Thirdly, we approximate the received signal power of ZF-BF with the SUS as the maximum of scaled chisquare random variables where the scaling factor is approximated as a function of both OLT and the number of users in the system. Putting all the above derivations and order statistics together, the approximated ergodic sum rate of ZF-BF with the SUS is shown in a closed form. The simulation results verify that the approximation tightly matches with the sample average for any OLT and even for a small number of users.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.3A
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• pp.353-361
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• 2000

The performance of a multi-carrier CDMA system is analyzed considering frequency selective multipath fading and Near/Far effects. The number of multicarrier, multiuser, and arms of RAKE receiver, and the decay ratio of frequency selective multipath fading are used as a parameter for the performance analysis. More over, the distribution and the strength of multiuser interference are also considered. To evaluated the Near/Far effects in a multi-carrier CDMA system, three distribution models are assumed. In the first model. interference to carrier Ratio, I/C, ranges form -4 dB to 4dB, and at each 2 dB interval 20 % of multiuser is assumed to be uniformly distributed. In the second one, I/C ranges from -2 dB to 2 dB, and 33.3% of multiuser is assumed to be equally dispersed at each 2dB interval. The third model is 0 dB of I/C, that is, with perfect power control, multiuser are assumed to be evenly located. In this paper, multi-carrier CDMA system adoption RAKE receiver is proposed to mitigate the frequency selective multipath fading. Form the results, the third model(i.e. perfect power control)shows the best performance, and the narrower range of I/C causes the less effects to the desired signal, which reads to the better performance.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.6
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• pp.36-42
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• 2020

Nowadays, the touch screen panel (TSP) cover glass for mobile smart devices is being developed with a curved glass shape due to different design requirements. Because the sizes of mobile smart devices continue to increase, there has also been a great increase in the demand for large-area curved glass greater than 20 inches. In this study, heat and fluid flow analysis using CFD was performed to optimize the heating surface temperature distribution of the large curved glass formation system. Five cooling water flow paths in the cooling block were designed and analyzed for each case. A function that can quantitatively calculate the temperature uniformity of the heating surface was proposed and these values were obtained for the five models. The temperature distributions of the heating surface and the energy consumption of the heating system were also compared and comprehensively analyzed. Based on the analysis results of the five different cooling channel path models, the optimal path design could be presented.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2458-2473
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• 2024

The turbulent flow in reactor pressure vessel (RPV) of pressurized water reactor (PWR) is important for the flow rate distribution at core inlet. Thus, it is vital to study the turbulent flow phenomena in RPV. However, the complicated fluid channel consisted of inner structures of RPV will block or refract the laser sheet of particle image velocimetry (PIV). In this work, the matched index of refraction (MIR) of sodium iodide (NaI) solution and acrylic was applied to support optical path for flow field measurements by PIV in the 1/10th scaled-down RPV model. The experimental results show detailed velocity field at different locations inside the scaled-down RPV model. Some interesting phenomena are obtained, including the non-negligible counterflow at the corner of nozzle edge, the high downward flowing stream in downcomer, large vortices above vortex suppression plate in lower plenum. And the intensity of counterflow and the strength of vortices increase as inlet flow rate increasing. Finally, the case of asymmetry flow was also studied. The turbulent flow has different pattern compared with the case of symmetrical inlet flow rate, which may affect the uniformity of flow distribution at the core inlet.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.1
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• pp.1-11
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• 1997

We examine the DS/SSMA system which is employing coherent BPSK with RAKE receiver. We adop Nakagami m-distribution as a multipath fading model. First, we analyze the performances of the system in the single cell environment and obtain the other-cell interference according to power control error. And considering the other-cell interference into the analysis of single cell system, we examine the cellular CDMA network. The average BER and outage probability are the figures of merit that characterize the system performance. The required BER, 1E-3, and required outage probability are the figures of merit that characterize the system performance. The requeired BER, 1E-3, and required outage probability, 1% for the voice transmission is considered to acquire the capacity of system.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.8
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• pp.7-18
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• 1999

We have designed and tuilt the quasioptical system for the dual channel receiver which is used for the simultaneous observation of the cosmic radio with 100GHz band and 150GHz band. The quasioptical system has been widely used to guide the beam for the millimeter and submillimeter waves. A Gaussian distribution of field and power transverse to their axis of propagation allow the simple and elegant theory of Gaussian quasioptics. Using the theory of Gaussian beam, we introduced the analysis of image beam which is applied for a wide range of frequency. In order to guide two beams from the Cassegrain antenna simultaneously, the quasioptical system and its components for the dual channel receiver were designed by using the image beam method. We have checked the characteristics of the quasioptical components and the system by using the heam measurement system, which is made by us. The quasioptical system has been installed in the dual channel receiver on the Cassegrain antenna. The performance of this system has been finally confimed through the successful simultaneous observation with two bands of the cosmic radio.

• The Journal of Society for e-Business Studies
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• v.7 no.2
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• pp.1-19
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• 2002

Lately, the Korean ginseng was confronted with the sale crisis in world markets from the various circumstance. One of important difficulties is overspreading of Korean ginseng imitative in foreign markets. In Korean markets also, chinese ginseng was imported illegally and manufactured as Korean ginseng, which was resulted in the damage of Korean ginseng brand. The most essential problem is misunderstanding of Korean ginseng's information in the foreigner. In this paper, we developed a genuine guarantee system to identify the true Korean ginseng through internet and geographic cording system of Korean ginseng products. This system can be applied to the enforcement of Korean ginseng sale to international markets.

• Nuclear Engineering and Technology
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• v.41 no.1
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• pp.135-142
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• 2009

In this investigation, we prepared a 1 and 3-parallel serpentine single PEMFC, which has an active area of $100\;cm^2$ and a flow channel cross section of $1{\times}1mm$. Distribution and transport of water in a non-operating PEMFC were observed by varying flow types and the flow rates (250, 400, and 850 cc/min). This investigation was performed at the neutron imaging facility at the CO1d Neutron RAdiography facility (CONRAD), HMI, Germany of which the collimation ratio and neutron fluence rate are 250, $1{\times}10^{6}n/s/cm^2$, respectively. The neutron image was continuously recorded by a scintillator and lens-CCD coupled detector system every 10 seconds. It has been observed that although the distilled water was supplied into the cathode channel only, the neutron image showed a water movement from the cathode to the anode channel. The water at the cathode channel was completely discharged as soon as the pressurized air was supplied. But the water at the anode channel was not easily removed by the pressurized air except for the 3-parallel serpentine type with 850cc/min of air flow rate. Moreover, the water at the MEA wasn't removed for any of the cases.

• Progress in Superconductivity
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• v.5 no.1
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• pp.38-44
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• 2003

The aim of this study is to confirm clinical usefulness of magnetocardiogram (MCG) by analyzing MCG data of health subjects and patients with Wolff-Parkinson-White (WPW) syndrome and dilated cardiomyopathy (DCM). Measurement of MCG signals was done with a home-made 40-channel SQUID system. MCG signals of 30 healthy subjects were measured as the reference of MCG signals. Among the DCM patients, 7 patients showed abnormal the direction of T wave vector. For a WPW syndrome patient, we measured the MCG signals before and after the surgery. and compared the difference. From the measured magnetic field distribution, current vector map was obtained to show the myocardium current activity. By comparing the MCG signals and current maps, we showed the differences in the analysis results between the healthy subjects and patients with heart diseases.

• Journal of Internet Computing and Services
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• v.18 no.6
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• pp.15-23
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• 2017

Wireless power transmission (WPT) for wireless charging is currently attracting much attention as a promising approach to miniaturize batteries and increase the maximum total range of an electric vehicle. The main advantage of the laser power beam (LPB) approach is its high power transmission efficiency (PTE) over long distance. In this paper, we present the design of a laser power beam based WPT system, which has a best WPT channel selection technique at the receiver end when multiple power transmitters and single power receiver are operated simultaneously. The transmitters send their transmission channel information via optically modulated laser pulses. The receiver uses the received signal strength indicator and digitized data to choose an optimum power transmission path. We modeled a vertical multi-junction photovoltaic cell array, and conducted an experiment and simulation to test the feasibility of this system. From the experimental result, the standard deviation between the mathematical model and the measured values of normalized energy distribution is 0.0052. The error between the mathematical model and measured values are acceptable, thus the validity of the model is verified.