• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.928-931
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• 2003

본 논문에서는 고속 광대역의 정보신호를 효율적으로 전송하기 위한 무선 LAN 채널환경에서 OFDM 전송방식을 사용할 때 반송파의 주파수 오프셋이 발생하는 동기 오차가 수신시스템에 미치는 영향으로 인한 수신 성능을 분석하였다. 성능개선 기법으로 Convolution Coding 기법을 적용함으로써 반송파 주파수 오프셋에 따른 성능 열화를 보상하였다. 성능 해석 결과, OFDM 시스템에서 주파수 오프셋이 커짐에 따라 성능이 열화됨을 알 수 있었고, (BER=$10^{-3}$)를 목표로 하는 경우 OFDM 시스템에 Convolution Coding 기법을 적용함으로써 성능 개선이 나타났지만 64QAM방식인 경우 주파수 오프셋 0.05, 0.1에서 주파수 오프셋에 의한 캐리어간 간섭의 영향이 지배적임을 알 수 있다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.3B
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• pp.251-258
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• 2002

In this paper, an adaptive convolutional coding method in multicarrier direct sequence code division multiple access (DS/CDMA) systems is considered. In order to accommodate a number of coding rates easily and make the encoder and decoder structure simple, we use the rate compatible punctured convolutional (RCPC) code. To achieve maximum data throughput, an adaptive rate system based on the channel state information (the SINR estimate) is proposed. We show that the proposed adaptive rate convolution coded multicarrier DS/CDMA systems can enhance spectral efficiency and provide frequency diversity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4A
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• pp.378-383
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• 2004

Orthogonal Frequency Division Multiplexing (OFDM) transmits high-speed data by splitting the transmission bandwidth into a number of subcarriers. The bandwidth of each subcarrier is ensured to be smaller than the coherence bandwidth. This paper presents an OFDM system incorporated with the Carrier Interferometry (CI) codes to improve the performance by enhancing frequency diversity effect. The performances of CI-OFDM with multilevel modulations are investigated in highly dispersive fading channels. For the investigation of performance improvement of CI-OFDM, a simulator has been developed using a well-known SPW simulation platform. The simulation results show that the CI-OFDM provides both performance improvement and robustness against dispersive fading channel behavior. The performance of CI-OFBM with multilevel modulations demonstrates that CI-OFDM outperforms a traditional OFDM system, particularly in highly dispersive channels. With a relatively large delay spread of 151㎱ compared to the guard interval of 800㎱, CI-OFDM provides a BER of 10$^{-3}$ if sufficient signal power is present.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.12A
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• pp.1217-1224
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• 2008

The carrier tracking has to be basically completed for accurate positioning of Galileo satellite system. The FLL for tracking frequency errors is robust to dynamic stress causing changes of propagation time but hardly tracks accurate carrier tracking. The PLL for tracking phase errors provides accurate carrier tracking but is sensitive to dynamic stress and its tracking performance is decreased when high dynamics exist. In this paper, we design the carrier tracking loop with the FLL-assisted PLL loop filter and co-operations of FLL and PLL to achieve accurate carrier tracking in high dynamic stress. we prove the performance of designed carrier tracking loop via simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.9C
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• pp.1279-1288
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• 2004

In this paper, the DMR(Digital Microwave Radio) system-based OFDM(Orthogonal Frequency Division Multiplexing) scheme in microwave channel environments has been proposed and system performances have been evaluated. The existing single carrier DMR system has a complex system structure due to using high-level QAM(Quadrature Amplitude Modulation) modulation scheme and so charmel capacity is limited by sensitive effects from fading. Therefore, in the proposed DMR system, it uses that the OFDM scheme for enhancement of fading distortion and also uses that the band-limited pulse shaping filter instead of windowing for no additional data such as GI/GB and for using efficient of IFFT/FFT block. The performance of OFDM/QPSK-DMR system and single carrier DMR system are analysed by computer simulation using two-ray model under the microwave channel environments The computer simulation results confirm that the fade margin of the proposed OFDM/QPSK-DMR system is highly increased as the number of sub-carriers is larger.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.55-58
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• 2000

본 논문에서는 제한된 통신 채널의 대역에서 주파수 효율이 높은 OFDM 시스템을 위한 반송파 주파수 동기 알고리즘을 제안한다. OFDM 시스템에서의 반송파 주파수 옵셋은 부반송파 간격의 정수배와 소수배로 나누어진다 소수배 주파수 옵셋이 ± 0.5 근처의 값을 가질 경우에는 정확한 정수배 주파수 옵셋 추정이 어렵고 반송파 동기 PLL이 소수배 주파수 옵셋을 추적하는데 많은 시간이 소요된다. 제안한 알고리즘은 정수배 주파수 옵셋을 제거하기 위해 2개의 심볼 만을 이용하고 다중경로 패널에서도 정확한 정수배 주파수 옵셋의 추정이 가능하다 또한, 소수배 주파수 옵셋이 ± 0.5 근처의 값을 가질 경우 적은 계산량으로 주파수 옵셋을 ± 0.1 이내로 보상할 수 있다.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2004.05a
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• pp.433-436
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• 2004

반도체 및 LCD 제조 라인의 물류 제어 시스템을 위하여 시스템의 현재 및 미래의 Look ahead 정보를 사용하고 반송장비의 운반 상황을 동시에 고려하면서 디스패칭(dispatching) 과정을 수행하는 RTLAD(Real Time Look Ahead Dispatcher)를 위한 핵심 기법들을 개발한다. 특히, 베이(bay) 내에서 로트의 가공이 완료 되었을 때 다음 스텝 공정을 위하여 목적지 장비를 실시간으로 결정하는 절차를 제시하며, 동시에 목적지 장비까지의 반송장비를 선택하는 절차를 제시한다. 목적지 장비 결정 과정에서 반송장비의 상황을 함께 고려한다.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1998.10a
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• pp.330-340
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• 1998

자율주행 반송차가 주어진 경로를 따라 주행 할 때 주행면의 불균일성과 같은 외란요인과 자율반송차 시스템 자체의 비선형성 등으로 인하여 원치 않는 경로추종오차가 발생하게 되는데 본 연구에서는 이러한 경로추종오차를 최소화하기 위해서 신경회로망을 이용한 경로추종 오차 보상방법을 제안한다. 본 방법에서는 신경회로망을 통하여 조향각 보상량을 제공하므로써 경로추종오차를 보상한다. 신경망은 다층 퍼셉트론을 채용하였으며 역전파 알고리즘의 최급강하규칙(Gradient descent rule)을 이용하여 학습을 수행하였다. 본 제안에서는 학습오차를 경로추종오차로부터 정의하므로써 경로추종오차가 최소화되록 신경회로망을 학습시켰다. 제안된 방법의 타당성은 다양한 경로에 대한 모의실험 및 실제 실험을 통하여 검증하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.2
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• pp.250-257
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• 2004

MC-CDMA and OFDM are digital modulation techniques where a single data symbol is transmitted at multiple subcarriers which we orthogonal to each other. With this technique, frequency diversity can be achieved. The performance of multi currier systems is analyzed. when data is transmitted over multi-path Rayleigh fading channel. The performance of this technique, gauged by the average bit error rate, is numerically analyzed for the system with the application of antenna diversity.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.5
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• pp.381-387
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• 2013

Nitrogen and phosphorus removal was investigated in an UASB-ABF (Up-flow anaerobic sludge blanket - aerated bio-filter) anaerobic sewage treatment system. Successful removal of nitrogen and phosphorus with organic matters was possible in the UASB-ABF system from the results of 160 days operation with the influent raw domestic sewage. Removal efficiencies of organic matter (as TCOD) showed 64% in UASB without recycle of the ABF effluent, however, they increased to 92%, 95%, 96% with 120%, 180% and 240% recycle of the ABF effluent, respectively. Increasement of the organic matter removal was not prominent at recycle ratio above 180%. Apparent increase in TN removal occurred with recycle of the ABF effluent. TN removal efficiency was 18% without recycle, but it increased to 82% with 240% recycle of the ABF effluent. And stable nitrification above 95% was possible as a result of efficient removal of organic matter in the UASB with and without recycle of the effluent. Removal of both TP and $PO{_4}^{3-}$-P also increased remarkably with recycle of the effluent. Without recycle of the effluent, that is at strict anaerobic condition in UASB, TP was not removed, however, its removal efficiency increased to 51%, 63%, 71% at recycle ratios of 120%, 180%, 240%, respectively mainly at UASB.