• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.157-158
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• 2008

This paper examines an adaptive coding scheme for flat fading channels to maximize the average code rate of a coded system. The proposed adaptation technique is employed by using the required free distance of a rate compatible code depending on the channel realization. First, the system will calculate the required free distance based on the instantaneous channel gain. Based on this channel gain we will select a set of convolution code to optimize the code rate with a certain performance requirement. Simulation results show that our proposal can achieve a higher code rate.

• 전기학회논문지
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• 제64권12호
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• pp.1737-1741
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• 2015

A multi-channel CMOS transimpedance amplifier(TIA) array is realized in a $0.18-{\mu}m$ CMOS technology for the applications of panoramic scan LADAR systems. Each channel consists of a PIN photodiode and a feed-forward TIA that exploits an inverter input stage followed by a feed-forward common-source amplifier so as to achieve lower noise and higher gain than a conventional voltage-mode inverter TIA. Measured results demonstrate that each channel achieves $76-dB{\Omega}$ transimpedance gain, 720-MHz bandwidth, and -20.5-dBm sensitivity for $10^{-9}$ BER. Also, a single channel dissipates the power dissipation of 30 mW from a single 1.8-V supply, and shows less than -33-dB crosstalk between adjacent channels.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권3호
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• pp.945-964
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• 2014

In this paper, we investigate the performance of Signal to Leakage and Noise Radio (SLNR) based user scheduling in uplink of multi-cell with large-scale antenna system. Large antenna array is desired to improve the performance in future system by providing better beamforming capability. However, some studies have found that the signal channel is 'hardened' (becomes invariant) when the antenna number goes extremely large, which implies that the signal channel aware user scheduling may have no gain at all. With the mathematic tool of order statistics, we analyzed the signal and interference terms of SLNR in a homogeneous multicell network. The derived distribution function of signal and interference shows that the leakage channel's variance is much more influential than the signal channel's variance in large-scale antenna regime. So even though the signal channel is hardened, the SLNR-based scheduling can achieve remarkable multiuser diversity (MUD) gain due to the fluctuation of the uplink leakage channel. By providing the final SINR distribution, we verify that the SLNR-based scheduling can leverage MUD in a better way than the signal channel based scheduling. The Monte Carlo simulations show that the throughput gain of SLNR-based scheduling over signal channel based scheduling is significant.

• 대한전자공학회논문지TE
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• 제37권2호
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• pp.54-61
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• 2000

본 논문은 레일레이 페이딩 채널 환경에서 IMT-2000 파일럿 심볼 구조의 W-CDMA 시스템 역방향 링크의 채널 추정에 관한 RLS 적응형 알고리즘 성능을 WMSA(K=1,3)와 Constant gain 방식의 성능과 비교 분석하였다. 본 논문의 모델은 IMT-2000 시스템 규격의 W-CDMA 채널 구조, 변조 및 파일럿 패턴을 이용하였다. 파일럿 심볼 위치의 채널추정은 RLS 적응형 알고리즘을 이용하고 데이터 심볼 위치의 채널 보상은 선형보간으로 수행하였다. RLS 적응형 알고리즘 성능은 저속 페이딩에서 WMSA(K=1,3) 성능과 유사하지만 Constant gain 알고리즘 성능보다는 약간 우수하다. 도플러 주파수 320㎐, BER=2.0×10/sup -2/에서 RLS 적응형 알고리즘 성능이 WMSA(K=1)과 Constant gain 성능에 비해 4㏈의 성능 우위를 보여주고 있으며, WMSA(K=3)의 성능과는 커다란 차이를 보여준다. 따라서 페이딩이 고속화 될수록 RLS 알고리즘 의 성능이 전반적으로 WMSA(K=1,3)와 Constant gain 알고리즘 성능보다 우수함을 확인하였다.

• 대한전자공학회논문지TC
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• 제45권2호
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• pp.60-66
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• 2008

본 논문에서는 직교주파수분할다중접속(Orthogonal Frequency Division Multiple Access) 하향링크 시스템에서 부반송파 별 채널 이득(channel gain)이 다름을 이용하여 시스템의 용량을 향상시킬 수 있는 핸드오버 기법을 제안한다. 제안하는 기법에서 핸드오버 중인 사용자는 소스 기지국(source base station)과 타겟 기지국(target base station)에서 할당 받은 부반송파 중 강한 채널이득을 가진 부반송파를 선택해 줌으로써 이득을 얻는다. 부반송파 선택 과정에서 탈락한 부반송파에 대한 정보는 기지국으로 피드백(feedback)되어 사용하지 않도록 하여 시스템 전체의 간섭(interference)량을 줄인다. 제안하는 기법은 핸드오버하고 있는 사용자의 오수신 확률을 22% 줄였으며, 이에 따라 시스템 전체의 전송률이 향상된다.

• 전자공학회논문지S
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• 제34S권1호
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• pp.80-93
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• 1997

This paper proposes a new technique of optimal codebook design in multistage gain-shape vector quantization (MS-GS VQ) for wireless image communication. An original image is divided into a smany blocks as possible in order to get strong robustness to channel transmission errors: the original image is decomposed into a number of subband images, each of which contains a sperate spatial frequency information and is obtained by the biorthogonal wavlet transform; each subband is separated into several consecutive VQ stages, where each stage has a residual information of the previous stage; one vector in each stage is divided into two components-gain and shape. But, this decomposition genrates too many blocks and it thus makes the determination of optimal codebooks difficult. We overcome this difficulty by evolving each block's codebook independently with different genetic algorithm that uses each stage's individual training vectors. Th eimpact of th eproposed VQ technique on the channel transmission errors is compared with that of other VQ techniques. Simulation results show that the proposed VQ technique (MS-GS VQ) with the optimal codebook designe dy genetic algorithms is very robust to channel transmission errors even under the bursty and high BER conditions.

• 한국항행학회논문지
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• 제12권1호
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• pp.54-60
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• 2008

일반적으로 무선통신 시스템은 채널 상에서 발생하는 페이딩, 음영효과, 전파감쇠, 잡음 및 간섭 등에 의해 신호의 신뢰성이 크게 저하된다. 따라서 멀티미디어 데이터들을 열악한 무선통신 채널에서 안정적으로 전송하기 위해서는 보다 신뢰성 있는 시스템이 필요하다. 본 논문에서는 무선통신 환경에서 보다 신뢰성 있는 정보 전송을 위해 STBC의 다이버시티 이득과 STTC의 채널 효율성, 코딩 이득 및 다이버시티 이득을 동시에 갖는 STTC 기반 STBC 시스템을 고려하고 송수신기 사이의 채널 간 상관 값을 갖는 슬로우 페이딩 채널환경에서 성능을 분석하였다.

• International Journal of Fluid Machinery and Systems
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• 제9권3호
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• pp.229-236
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• 2016

Exergetic analysis was introduced in optimization of a rotating equilateral triangular internal cooling channel with staggered square ribs to maximize the net exergy gain. The objective function was defined as the net exergy gain considering the exergy gain by heat transfer and exergy losses by friction and heat transfer process. The flow field and heat transfer in the channel were analysed using three-dimensional Reynolds-averaged Navier-Stokes equations under the uniform temperature condition. Shear stress transport turbulence model has been selected as a turbulence closure through the turbulence model test. Computational results for the area-averaged Nusselt number were validated compared to the experimental data. Three design variables, i.e., the angle of rib, the rib pitch-to-hydraulic diameter ratio and the rib width-to-hydraulic diameter ratio, were selected for the optimization. The optimization was performed at Reynolds number, 20,000. Twenty-two design points were selected by Latin hypercube sampling, and the values of the objective function were evaluated by the RANS analysis at these points. Through optimization, the objective function value was improved by 22.6% compared to that of the reference geometry. Effects of the Reynolds number, rotation number, and buoyancy parameter on the heat transfer performance of the optimum design were also discussed.

• 한국통신학회논문지
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• 제33권3A호
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• pp.248-255
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• 2008

OFDMA 시스템에서 주파수축에서의 다중사용자 스케줄링의 성능은 채널의 주파수 선택적 특성과 상관이 있다. 채널이 주파수축에서 평탄하면 다중사용자 스케줄링의 이득이 줄어들 수 있으며 반대로 주파수 선택적 특성이 너무 커서 할당 대역폭 내에서 채널의 변화가 심하게 일어난다면 충분한 스케줄링 이득을 얻기 어려워진다. 다중 사용자 스케줄링 이득을 최대화하기 위해서는 순환지연 다이버시티를 적용하여 채널의 주파수 선택적 특성을 조절할 수 있다. 이 논문에서는 할당 대역폭과 채널 특성을 고려하여 순환지연 다이버시티를 적용할 때의 최적의 지연값을 결정하는 방법을 제안한다.

• Journal of the Optical Society of Korea
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• 제18권2호
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• pp.118-123
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• 2014

For multi parameter optimization of Raman Fiber Amplifier (RFA), a simple genetic algorithm is presented in the scenario of a 320 channel Dense Wavelength Division Multiplexed (DWDM) system at channel spacing of 25 GHz. The large average gain (> 22 dB) is observed from optimized RFA with the optimized parameters, such as 39.6 km of Raman length with counter-propagating pumps tuned to 205.5 THz and 211.9 THz at pump powers of 234.3 mW, 677.1 mW respectively. The gain flattening filter (GFF) has also been optimized to further reduce the gain ripple across the frequency range from 190 to 197.975 THz for broadband amplification.