• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.98-101
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• 1998

The intermodulation distortion(IMD) due to laser diode nonlinearity of an asynhcronous direct sequence code diviion multiple access(DS/CDMA) system in wireless-optical transmission system model is analzed. A third order polynomial is used to represent laser diode nonlinearity. In DS/CDMA system, only one harmonic of the third-order intermodulation term falls on the signal frequency band and influences the system performance characteristics. To cancel multi-user interference and nonlinear distortion in a DS/CDMA wireless-optical transmission system model, the simple transversal filter structure with N-taps of (N-1) tap delay of 1 chip time delay line is used. It is necessary to select an optimal modulation index that provides a maximum signal-to-noise ratio and the results are useful for CDMA system design.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.28A no.11
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• pp.855-865
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• 1991

A simple method for analysis of serial search burst-format direct-sequence spread-spectrum (DS-SS) code acquisition system had been recently proposed, and therein, the effect of the code autocorrelation sidelobes on the performance of DS-SS code acquisition system has been assessed [4],[5]. In this paper, a new hybrid scheme which combines the serial search with maximum likelihood search is proposed to eliminate the deleterious effect of code autocorrelation sidelobes, and the performance is analyzed for the additive withe Gaussian noise (AWGN) channels. To analyze the performance of this system, we have generalized the method used in [4],[5] to arbitrary burst-format DS-SS acquisition schemes. The results show that a new hybrid scheme has good immunity against the effect of code autocorrelation sidelobes. Thevalidity of the presented approach has been confirmed form the results of simulation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.1
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• pp.67-73
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• 2005

In order to compensate for the degradation caused by the frequency shift under the Rayleigh fading with the balanced QPSK DS-SS communication, it is necessary to devise an efficient phase estimation method. In this paper, using the pilot signal, three conventional methods and a complex number method are presented and compared. The performance comparison results show that the combination complex number method is better than the other conventional methods, which have some limiting conditions.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.1316-1319
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• 2002

In this paper, an online SNR estimator is derived for turbo coded multicode DS/SS systems in Nakagami fading channels. The multicode DS/SS approach is one of promising solutions to obtain higher-rate data transmission in DS/SS technologies. Turbo coding has paid much attention because of the significant improvements on error rate performances in various communication systems including multicode DS/SS systems. However, in the turbo decoding, channel state information, especially signal-to-noise ratio (SNR) at the correlator outputs, is desired in order to obtain such improvements. We evaluate the accuracy of the derived SNR estimation. It is shown that the bit error rate performance using our SNR estimation is close to the performance with perfect knowledge of channel state information.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.126-129
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• 1999

In this paper, it is assumed that a mobile radio channel is a Rayleigh distributed multipath fading channel and Erlang capacity and equivalent channel numbers are calculated for the reverse link of a imperfect power controlled DS/CDMA cellular system considering both shadowing and multipath fading. The DS/CDMA blocking probability is calculated based on a new analysis method that considers Erlang capacity and ICF(interference correction factor) using the median value of $E_{b(i)}$/ $I_{o}$ corresponding to each reverse link user. It is showed that the effect of multipath fading must not be ignored in Erlang capacity of the IS-95 DS/CDMA cellular system and the Erlang capacity is decreased according to the increase of the deviation of the imperfect power control, to the decrease of the processing gain, to the increase of the voice activity.y.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.3 s.246
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• pp.349-355
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• 2006

The gas turbine components is used on high temperature conditions which under severely circumstance with start-up and stop several times. Therefore, it is used nickel-base superalloys like and GTD-111DS. Damaged buckets on the t긴ade tip during operating are repaired per 24,000 hr to three times according to repair specification of manufacture. It is applied pre-heat, HIP(hot isostatic pressing) and post-heat treatment to support welding repair on blade tip effectively. On this study, It is utilize of $WRAP^{TM}$ (welding repair advanced process) method to make tension test specimens for this study, And then, material strength and characteristic for GTD-111DS was analyzed.

• Korean Journal of Pharmacognosy
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• v.33 no.1 s.128
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• pp.69-73
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• 2002

The methanol extracts of 162 herbal medicines were screened for the inhibitory activity against VHR dualspecificity protein tyrosine phosphatase (DS-PTPase). Seventeen medicinal plants, Scutellaria baicalensis, Cuscuta chinensis, Caesalpinia sappan, Arecae pericarpium, Rubus coreanus, Machilus thunbergii, Amsonia elliptica Cinnamomum cassia, Arisaema erubescens, Pueraria thunbergiana, Dendrobium moniliforme, Mentha arvensis, Peucedanum japonicum, Salvia miltiorrhiza, Leonurus sibiricus, Siegesbeckia orientalis, Prunella vulgaris showed potent VHR DS-PTPase inhibitory activity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.11A
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• pp.1620-1629
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• 2000

본 논문에서는 켑춰를 갖는 슬랏 ALOHA 방식을 이용한 패킷 무선망의 성능을 분석하였다. 접속을 획득하기 위해서 켑춰효과를 이용하고 트래픽은 포아슨 랜덤프로세서로 가정하였을며 공간트래픽밀도는 실제적인 이동통신환경을 나타내는 puncturing 종형분포로 가정하였다. 패킷은 접속을 획득하는 헤더부분과 데이터 정보가 들어있는 데이터 부분으로 나눈다헤더부분은 공통확산부호를 갖는 DS에 의해 확산되고 데이터부분은 간섭전력과재밍에 강하고 고속의 데이터 전송시 성능향상을 기대할 수 있는 MC DS/FH에 의해 확산된다. 이동통신채널은 도심 전파의 다중경로 채널에 대한 다양한 헤이딩 환경을 제공해 주는 나카가미 페이딩 채널을 가정하였다. 동일한 지연시간에 반송주파수수를 증가시킴에 따라 높은 co널 처리 용량을 얻었으며 FH를 MC/DS/CDMA에 사용함으로서 간섭전력의 변화가 심한 환경에서 시스템의 성능을 일정하게 유지시켰다. 또한 Hard-limiting 상관수신기를 사용함으로써 페이딩이 심한 환경에서 패킷 무선망의 성능을 개선시켰다.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2001.06a
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• pp.9-12
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• 2001

In DS/CDMA system the number of output signal levels increases as multi-channel signals are summed, hence the power amplifier with high linearity is required. PW/CDMA is a transmission technique that performs pulse width modulation on the multilevel signal synthesized from multiple channel data. In PW/CDMA system the signal level is maintained to be binary, hence the modulation and demodulation circuits become simple. In this paper we derive the probability of bit error of the PW/CDMA system in AWGN environment. The results are compared with DS/CDMA system and are verified through the computer simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.5B
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• pp.545-553
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• 2001

다중 사용자 DS-CDMA 시스템에서 더 나은 성능을 얻고자 컨볼루션 코드와 차등 코드의 직렬 연쇄 구조를 제안한다. 시스템은 접속 간섭 (MAI: Multiple-access Interference)를 억제하기 위해 다른 사용자의 확산 코드, 동기, 그리고 전력 정보 등을 필요로 하지 않는 단일 사용자 검파기(SUD: Single User Detection)로 이루어진다. 채널 부호로 사용된 부호화율 1과 메모리 수 1을 가지는 차등 부호는 부호화로 인한 효율 저하를 가져오지 않으며 최소 상태수를 가지게 된다. 이러한 차등 부호와 컨볼루션 부호를 복호함에 있어서 서로간의 정보를 교환하는 반복 복호 처리를 이용한다. AWGN 채널에서의 분석 결과로부터 본 연쇄 부호 기법이 DS-CDMA 시스템에서 기존의 컨볼루션 코드보다 유사한 복잡도에서 더 나은 성능과 유연성을 제공함을 알 수 있다. 또한 제안한 기법이 SUD를 하는 DS-CDMA 시스템에 적용될 때, 처리 이득(Processing Gain)이나 간섭 억제 여파기의 탭 개수를 증가시킴으로써 성능 향상이 일어나며, 원근 간섭 전력 문제가 심한 경우에 성능 저하가 일어남을 알 수 있다.