• 대한디지털의료영상학회논문지
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• 제13권2호
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• pp.63-69
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• 2011

Table strapis patient fixture for securing the patient movements and falls. if it designed to measure the abdominal circumference and used as an indicator of dose selection at CT scan. it will prevent the overexposure of dose without degradation of image quality and efficiently manage dose of each type of body to technician to deal with CT. First, in order to compare the dose used in CT image and qualitative characteristics. reference image is obtained by examining the abdominal phantom in same conditions with the hospital 120 kVp, 200 mAs, D-Dom (Dynamic Dose Of Modulation). SNR, PSNR, RMSE, MAE, CTDIvol of CT images are compared with reference image. for comparing with reference image, the image that Umbilicus level image of Abdomen CT is stored in the PACS were used. For comparison, the top 12 o'clock portion of the air drawn from the same ROI was measured. CTDIvol, mAs, etc. In order to analyze the characteristics of the image, by measuring the length of the umbilicus circumference, pattern of the dose was analyzed. by using the analyzed perimeter and dose information, To be identified visually, fixed band that scale marked were produced. Use them, If the length of circumference of less than 60 cm 100 mAs, Case of 61~80 cm 120 mAs, Case of 80~100 cm 150 mAs, more than 100 cm 200 mAs, dose selection based on the perimeter, the image was applied. by compare analyzed with the Reference Image, image quality was assessed. by compare with existing tests that equally 200 mAs applied, How much was confirmed that the dose reduction. 1. Depending on the Abdominal circumference, the average PSNR(dB) of the image that differently dose applied was 45.794. 2. Comparing with existing test. the dose of scan that adjusted the mAs depending on the circumference was decreased about 40%. SNR and PSNR of the image that obtained by adjusting the standard mAs based on dose modulation were not much different. Therefore, By choosing a low mAs. dose reduction can be obtained. and the dose selection method that measured Abdominal circumference using a fixed band can protect the overexposure and uniformly apply dose of each type of body to technician to deal with CT.

• 대한전자공학회논문지TC
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• 제43권12호
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• pp.61-67
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• 2006

본 논문에서는 고속무선통신에 널리 사용되고 있는 직교 주파수 분할 다중화 데이터 전송시스템에서 반송파주파수 옵셋(Offset)에 의한 잔류 위상 오차와 샘플링 주파수 옵셋에 의한 잔류 오차를 추적하고 보상하는 알고리즘을 제안한다. 직교 주파수 분할 다중화 시스템에서는 서로 직교성을 가지는 부반송파들이 디지털 데이터에 의해 변조되어 동시에 전송된다 반송파 주파수 옵셋이 존재하는 경우에는 신호 대 잡음비의 감소 그리고 인접 부반송파의 간섭 등이 발생한다. 또한 송신단과 수신단에서의 샘플링 주파수의 차이로 인한 샘플링 시점의 오차도 직교 주파수 분할 다중화 시스템에서 성능저하의 주요한 요인으로 작용한다. 반송파 주파수의 오차와 샘플링 주파수의 오차는 직교 주파수 분할 다중화 시스템에서 중요한 성질중의 하나인 직교성 상실을 초래하며 이는 성능저하의 원인으로 작용하므로 수신단에서는 지속적으로 잔류 오차를 추적하여 보상해 주는 방식의 적용이 필수적이다. 본 논문에서는 주파수 선택적 페이딩 무선 채널 환경에서 파일롯 데이터뿐만 아니라 채널이득 정보 및 페이로드 데이터를 주파수 오차 추정에 반영하여 추정오차를 줄이고 이 추정 값을 주파수 오차 보상에 반영하여 성능 향상을 달성할 수 있는 방식을 제안한다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 하계종합학술대회 논문집(1)
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• pp.43-46
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• 2004

In this paper, we present a carrier phase estimation algorithm for LDPC coded systems. LDPC coded system can not achieve the ideal performance if phase offset is introduced by channel. However, the estimation of phase offset is very hard since the operating point of LDPC is very low SNR. To solve this problem, the algorithm using the tentative soft decision value and based on Maximum Likelihood (ML), was proposed in [2]. But this algorithm has problem which works only under constant phase offset. If phase offset is time variant, it has a severe degradation in performance. To solve this problem. we propose two types of estimators. symbol by symbol estimator: Unidirectional estimator (UDE) and hi-directional estimator (BDE), and sub-block estimator (SBE).

• 한국광학회지
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• 제10권1호
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• pp.64-67
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• 1999

전송용 고아섬유로 320km의 분산천이 광섬유를 사용하여 10Gb/s 광링크를 구성하고 전송실험을 수행하였다. 광링크는 10Gb/s 광송수신기, 광전력 증폭기, 3개의 광전로 증폭치 증폭기 및 전송용로 구성되어Tdmaum 전송거리에 따른 비트 오율 특성에 대하여 조사하였다. 전송실험 결과 광선로 증폭기의 입력세기가 -18dBm이고, 이득이 28dB인 경우 수신기 입력단에서 측정된 광학적 신호대 잡음비는 28dB로 나타났으며, 광섬유를 사용하지 않은 경우와 비교하여 2dB의 전력 패널티가 발생한 것으로 나타났다. 광섬유 전송 후 발샹한 2dB의 전력 패널티는 광학적 신호대 잡음비 열화에 의해 1dB, 경로 패널티에 의해 1dB가 발생하는 것으로 조사되었다.

• 한국통신학회논문지
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• 제31권9C호
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• pp.897-904
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• 2006

여러 입력 여러 출력 시스템은 주파수 효율이 높으며, 가장 비슷함 검파기를 쓸 때 성능이 가장 뛰어나다. 가장 비슷함 검파기는 송신 안테나와 별자리의 신호수가 많아지면 지수적으로 복잡해지므로, 성능은 가장 비슷함 검파기보다 떨어지지만 복잡하기는 덜한 영 만들기 검파기가 제안된 바 있다. 이 논문에서는 가장 비슷함 검파기보다 덜 복잡하고 영 만들기 검파기보다 성능이 나은 새로운 검파 기법을 제안한다. 제안한 기법은 신호대잡음비가 높을 때 더욱 효과적임을, 곧, 가장 비슷함 검파기보다 덜 복잡하고 성능은 거의 같음을, 보인다.

• The Journal of the Acoustical Society of Korea
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• 제21권2E호
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• pp.71-80
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• 2002

This paper suggests the Cardioid beamforming algorithm of the doublet sensors employing DIFAR (directional frequency analysis and recording) sensor signals in the frequency domain. The algorithm enables target bearing estimation using the signals from directional sensors. The algorithm verifies its applicability by successfully estimating bearings of a target projecting ten narrow-band signals in shallow water. The estimated bearings agree very well with those from GPS (global positioning system) data. Assuming the bearings from GPS data to be real values, the estimation errors are analyzed statistically. The histogram of estimation errors in each frequency have Gaussian shape, the mean and standard deviation dropping in the ranges -1.1°∼ 6.7°and 13.3∼43.6°, respectively. Estimation errors are caused by SNR (signal to noise ratio) degradation due to propagation loss between the source and receiver, daily fluctuating geo-magnetic fields, and non-stationary background noises. If multiple DIFAR systems are employed, in addition to bearing, range information could be estimated and finally localization or tracking of a target is possible.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권1호
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• pp.253-271
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• 2017

In this paper, considering that perfect channel state information (CSI) is hard to achieve in practice, the downlink capacity of distributed antenna systems (DAS) with imperfect CSI and multiple receive antennas is investigated over composite Rayleigh fading channel. According to the performance analysis, using the numerical calculation, the probability density function (PDF) of the effective output SNR is derived. With this PDF, accurate closed-form expressions of ergodic capacity and outage probability of DAS with imperfect CSI are, respectively, obtained, and they include the ones under perfect CSI as special cases. Besides, the outage capacity of DAS in the presence of imperfect CSI is also derived, and a Newton's method based practical iterative algorithm is proposed to find the accurate outage capacity. By utilizing the Gaussian distribution approximation, another approximate closed-form expression of outage capacity is also derived, and it may simplify the calculation of accurate outage capacity. These theoretical expressions can provide good performance evaluation for downlink DAS for both perfect and imperfect CSI. Simulation results verify the effectiveness of the theoretical analysis, and the system capacity can be improved by increasing the receive antennas, and decreasing the estimation error or path loss. Moreover, the system can tolerate the estimation error variance up to about 0.01 with a slight degradation in the capacity.

• 천문학회보
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• 제37권2호
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• pp.157.2-157.2
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• 2012

Direct-conversion receivers often suffer from a DC-offset that is a by-product of the direct conversion process to baseband. In general, a basic approach to reduce the DC-offset is to do simple average of the baseband signal and remove the DC by subtracting the average. However, this gives rise to a residual DC offset which degrades the performance when the receiver adopts the coding schemes with high coding rates such as 8-PSK. Therefore, more advanced methods should be additionally required for better performance. While the training sequences are basically designed to have good auto-correlation properties to facilitate the channel estimation, they may be not good for the simultaneous estimation of the channel response and the DC-offset. Also the DC offset compensation under a bad condition does not give good results due to the estimation error. Correspondingly, the proposed scheme employs the two important points. First, the training sequence codes are divided into two groups by MSE(Mean Squared Errors) for estimating the channel taps and then SNR calculated from each group is compared to predefined threshold to do fine DC-offset estimation. Next, ON/OFF module is applied for preventing performance degradation by large estimation error under severe channel conditions. The simulation results of the proposed scheme shows good performances compared to the existing algorithm. As a result, this scheme is surely applicable to the receiver design in many communications systems.

• ETRI Journal
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• 제41권5호
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• pp.626-636
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• 2019

A novel algorithm for joint user selection and optimal power allocation for Stackelberg game-based revenue maximization in a downlink non-orthogonal multiple access (NOMA) network is proposed in this study. The condition for the existence of optimal solution is derived by assuming perfect channel state information (CSI) at the transmitter. The Lagrange multiplier method is used to convert the revenue maximization problem into a set of quadratic equations that are reduced to a regular chain of expressions. The optimal solution is obtained via a univariate iterative procedure. A simple algorithm for joint optimal user selection and power calculation is presented and exhibits extremely low complexity. Furthermore, an outage analysis is presented to evaluate the performance degradation when perfect CSI is not available. The simulation results indicate that at 5-dB signal-to-noise ratio (SNR), revenue of the base station improves by at least 15.2% for the proposed algorithm when compared to suboptimal schemes. Other performance metrics of NOMA, such as individual user-rates, fairness index, and outage probability, approach near-optimal values at moderate to high SNRs.

• 대한전자공학회논문지
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• 제24권3호
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• pp.400-407
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• 1987

Thin film filter type 4-channel wavelength division multiplexing(WDM) device was designed and fabricated for the application in optical subscriber loop system. It has multi-mode fiber pigtails and four wavelength division consisting of 0.81, 0.89, 1.2 and 1.3 um. The evaluated performances are 1-2d B of insertion loss(connector loss excluded)and 30-35d B of crosstalk attenuation for all channels. The performance of the fabricated device was tested in the wideband optical transmission experiment, where the SNR degradation due to the crosstalk of the device was found to be within a measurement error.