• 한국인터넷방송통신학회논문지
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• 제10권2호
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• pp.19-24
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• 2010

본 논문은 방송통신위원회의 정책에 따라 DTV 전환시 예상할 수 있는 DTV 서비스가 인접채널에 할당될 무선 마이크에 간섭을 주는 영향을 분석하였다. 분석을 위해 DTV 서비스가 채널 51(692 MHz ~ 698 MHz)에 할당되고 무선 마이크가 채널 52(698 MHz ~ 704 MHz)에 할당되는 시나리오를 가정하였다. Minimum Coupling Loss(MCL)를 이용하여 보호 이격거리를 산출하고 몬테 칼로(Monte Carlo) 분석을 이용하여 간섭 확률 0 %를 위한 보호 대역을 산출하였다. 그 결과 실내의 경우 1.71 km의 보호 이격거리와 2.4 MHz의 보호 대역이 산출되었고 실외의 경우 18.86 km의 보호 이격거리와 5.7 MHz의 보호 대역이 산출되었다.

• 한국통신학회논문지
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• 제30권12A호
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• pp.1161-1167
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• 2005

본 논문에서는 주파수 재사용률이 1인 OFDM(Orthogonal Frequency Division Multiplexing) 기반의 셀룰러 시스템을 위한 가상 스마트 안테나 개념을 소개한다. OFDM 기반의 셀룰러 시스템은 다중경로 채별에 강건한 장점이 있으나, 셀 경계에서 인접 셀에 의한 셀 간 간섭이 큰 단점이 있다. 본 논문예서는 다수의 기지국으로부터 수신되는 OFDM 신호의 심볼 타이밍 오프셋 추정 기법을 유도하고 준정칙 페이딩 채널에서 이러한 심볼 타이밍 오프셋에 의하여 형성된 조정백터(steering vector)을 이용한 가상 스마트 안테나 기반의 셀 간 간섭 제거 기법을 제안한다.

• Journal of Communications and Networks
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• 제10권2호
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• pp.118-126
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• 2008

The use of beamforming is effective for users in limited power environments. However, when it is applied to the downlink of a cellular system with universal frequency reuse, users near the sector boundary may experience significant interference from more than one sector. The use of a minimum mean square error (MMSE)-type receiver may not sufficiently cancel out the interference unless a sufficient number of receive antennas are used. In this paper, we consider the use of inter-sector beamforming that cooperates with a neighboring sector in the same cell to mitigate this interference problem in time-division duplex (TDD) environments. The proposed scheme can avoid interference from an adjacent sector in the same cell, while enhancing the transmit array gain by using the TDD reciprocity. The performance of the proposed scheme is analyzed in terms of the output signal-to-interference-plus-noise power ratio (SINR) and the output capacity when applied to an MMSE-type receiver. The beamforming mode can be analytically switched between the inter-sector and the single-sector mode based on the long-term channel information. Finally, the effectiveness of the proposed scheme is verified by computer simulation.

• JSTS:Journal of Semiconductor Technology and Science
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• 제3권1호
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• pp.47-54
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• 2003

New efficiency enhancement techniques have been devised and implemented to InGaP/GaAs HBT MMIC power amplifiers for W-CDMA mobile terminals applications. Two different types of bias current control circuits that select the efficient quiescent currents in accordance with the required output power levels are proposed for overall power efficiency improvement. A dual chain power amplifier with single matching network composed of two different parallel-connected power amplifier is also introduced. With these efficiency enhancement techniques, the implemented MMIC power amplifiers presents power added efficiency (PAE) more than 14.8 % and adjacent channel leakage ratio(ACLR) lower than -39 dBc at 20 dBm output power and PAE more than 39.4% and ACLR lower than -33 dBc at 28 dBm output power. The average power usage efficiency of the power amplifier is improved by a factor of more than 1.415 with the bias current control circuits and even up to a factor of 3 with the dual chain power amplifier.

• 한국전자파학회논문지
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• 제15권12호
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• pp.1199-1206
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• 2004

본 논문에서는 나카가미-m 페이딩 채널에서 정규화된 부반송파의 간격에 따라 구분되는 직교 MC DS- CDMA 시스템과 오브래핑 되지 않는 MC DS-CDMA시스템을 분석하였다. 다중 반송파 시스템에서 발생하는 선택 경로수를 줄이기 위하여 Hybrid SC/MRC 방식이 적용되어 MRC 방식을 사용한 경우와 비교 분석하였다. 분석 결과, Hybrid SC/MRC 방식을 MRC 방식으로 대체할 수 있으며, 주어진 대역폭이 고정되어 있는 경우 부반송파의 수를 증가시키면 부반송파 간격이 증가하고 필요한 대역폭이 더 많이 필요함으로 부반송파의 수는 주어진 대역폭을 고려하여 선택하여야함을 확인하였다.

• 한국전자파학회논문지
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• 제10권1호
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• pp.54-62
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• 1999

본 논문에서는 실내 무선광연결에 사용될 수 있는 차동검출기에서 잡음광의 결합비와 차동이득비에 따른 신호대 잡음비의 개선에 대하여 분석하고 실험하였다. 차동검출기는 2개의 포토다이오드와 1개의 차동증폭기 로 이루어지며, 차동이득비가 잡음광의 결합비와 같을 때 잡음광이 소거되어 약 20 dB의 선호대잡음비를 개 선하였다. 차통검출기는 실내의 무선광연결에서 주변의 강한 잡음광의 영향을 개선하거나 인접된 채널광에 의한 혼선의 영향을 없애는 데에 매우 효과적이다. 이 방법은 선호광과 유사한 파장의 잡음광이 발생하는 경 우에도 잡음개선효과가 았다.

• Journal of electromagnetic engineering and science
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• 제9권2호
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• pp.78-84
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• 2009

This paper represents the effects of drain bias on the linearity and efficiency of an analog pre-distortion power amplifier(PA) for wideband code division multiple access(WCDMA) repeater applications. For verification, an analog predistorter(APD) with three-branch nonlinear paths for memory-effect compensation is implemented and a class-AB PA is fabricated using a 30-W Si LOMaS. From the measured results, at an average output power of 33 dBm(lO-dB back-off power), the PA with APD shows the adjacent channel leakage ratio(ACLR, ${\pm}$5 MHz offset) of below -45.1 dBc, with a drain efficiency of 24 % at the drain bias voltage($V_{DD}$) of 18 V. This compared an ACLR of -36.7 dEc and drain efficiency of 14.1 % at the $V_{DD}$ of 28 V for a PA without APD.

• Journal of Mechanical Science and Technology
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• 제15권12호
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• pp.1784-1793
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• 2001

The flow fields around an elliptic cylinder of axis ratio AR=2 adjacent to a free surface were investigated experimentally using a water channel. The main objective is to understand the effect of the free surface on the flow structure in the near-wake. The flow fields were measured by varying the depth of cylinder submergence, for each experimental condition, 350 velocity fields were measured using a single-frame PIV system and ensemble-averaged to obtain the spatial distribution of turbulent statics. For small submergence depths a large-scale eddy structure was observed in the near-wake, causing a reverse flow near the free surface, downstream of the cylinder. As the depth of cylinder submergence was increased, the flow speed in the gap region between the upper surface of the cylinder and the free surface increased and formed a substantial jet flow. The general flow structure of the elliptic cylinder is similar to previous results for a circular cylinder submerged near to a free surface. However, the width of the wake and the angle of downward deflection of the shear layer developed from the lower surface of the elliptic cylinder are smaller tan those for a circular cylinder.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(2)
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• pp.233-236
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• 2001

We have designed and fabricated ASK modulator MMIC operating at 5.8GHz for OBE used in AGPS (Automatic Gate Passing System). ASK modulator MMIC was designed to apply a sing1e supply voltage of 3V to the drain in order to decrease ACP (Adjacent Channel Power). The measurement result of this chip exhibits on/off characteristic over 30dB. The design parameters are optimized through ADS simulation tool. The layouts and fabrication o( ASK Modulator MMIC were designed and fabricated by using ETRI 0.5${\mu}{\textrm}{m}$ MESFET library. The chip sizes were 1mm $\times$1mm. The performance analysis of the implemented ASK Modulator based on the design parameters is accomplished.

• 전자공학회논문지D
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• 제34D권4호
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• pp.106-112
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• 1997

We demonstrate a novel wavelength -division add/drop multiplexer employing fiber bragg gratings and polarization beam splitters. the multiplexer is easy to fbricate without any special technique such as UV trimming, and yet shows very stable performance with less than 0.3-dB crosstalk power penalty in a 0.8-nm-spaced, 2.5Gbps-per-channel WDM transmission system. We find that the rejection of adjacent channels is more than -6dB, and the signal leakage through output port is less than -34dB.