• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.05a
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• pp.852-854
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• 2015

In this letter, we designed and fabricated the paper-based ring-type frequency selective surface(FSSs) using inkjet printing method for practicable building wall applications to enhancement of the indoor communication environment, including low cost and ease of fabrication. Designed FSS has the band-stop characteristics at X-band, stable angle of incidence and wide bandwidth. Comparisons between measured and simulated results showed the good agreements.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2004.11a
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• pp.165-168
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• 2004

본 논문에서는 OFDM(orthogonal frequency division modulation) 시스템의 비터비 복호기 출력을 이용한 주파수 동기추적알고리듬을 제안한다 OFDM 시스템은 직교성이 보장된 부반송파에 데이터를 실어 전송함으로, 부반송파간 직교성 유지가 매우 중요하다. 부반송파간 직교성을 해치는 가장 큰 원인으로써 주파수 옵셋을 들 수 있다. OFDM 시스템의 안정적인 신호 수신을 위해서는 잔존 주파수까지 제거할 수 있는 고성능 주파수 동기 알고리듬이 필수적으로 요구된다. 본 논문에서는 다중변조 OFDM 시스템에서, 주파수 옵셋을 블라인드 모드로 추적하여 보상 할 수 있는 알고 리듬을 제안한다 전산실험을 통해 주파수 선택적 채널에서 제안한 알고리듬의 우수성을 보인다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2019.05a
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• pp.25-28
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• 2019

Along with the development of information and communication technology, maritime communication systems also have been actively studied for navigation and communication equipment aiming at safety, efficiency, accuracy and security. However, for fishing ship over 100km far from the coast, it is difficult to manage such as location and status of ship. Therefore, in this study, for the safety of the long distance ship through Digital-HF communication system, we use method to choose the optimum frequency and it enables to check the position of ship.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.10A
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• pp.1794-1801
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• 2001

다중 반송파 변조의 일종인 OFDM(Orthogonal Frequency Division Multiplexing) 방식은 기존의 주파수 분할 다중화 기법에 각 부 채널들 사이의 직교성까지 보장함으로써 사용 주파수 효율을 극대화시킬 수 있는 방식이다. 그러나 주파수 비 선택적 다중경로 채널에서 높은 데이터 율을 갖는 OFDM 신호의 전송은 주파수 영역에서 인접 심벌간 간섭과 동일한 형태를 갖는 승산성 왜곡에 의해 영향을 받는다. 본 논문에서는 결정 궤환 시퀀스 등화기를 OFDM 시스템에 적용하여 신호를 등화하고, 등화를 통하여 주파수 영역에서의 인접 심벌간 간섭을 보상하는 방법을 제안한다. 결정 궤환 시퀀스 등화를 이용하여 최우 시퀀스 등화가 갖는 복잡도를 크게 줄이면서 주파수 오프셋이 추정될 수 있음을 설명하고 모의 실험을 통해 OFDM 시스템의 성능 개선을 보인다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.10
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• pp.2247-2255
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• 2015

In very shallow water acoustic communication channel, underwater acoustic (UWA) communication signal is observed as frequency selective fading signal due to time-varying multipath. This induces a time and frequency dependent inter-symbol-interference (ISI) and degrades the UWA system performance. There is no study about how the performances of the error correction codes are related to a multipath fading statistics in very shallow water. In this study, the characteristics of very shallow water multipath fading channel is analyzed and the performances of two different forward error correction (FEC) codes are compared. The convolution code (CC) and Reed-Solomon (RS) code are adopted. Sea experimental results show that RS code is better choice than CC in frequency selective channel with fading.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.8
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• pp.55-61
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• 2010

In this paper, we proposed selective extraction method of frequency information and PCA-ELM based diagnosis system for three-phase induction motors. As the first step for diagnosis procedure, DFT is performed to transform the acquired current signal into frequency domain. And then, frequency components are selected according to discriminate order calculated by variance As the next step, feature extraction is performed by principal component analysis (PCA). Finally, we used the classifier based on Extreme Learning Machine (ELM) with fast learning procedure. To show the effectiveness, the proposed diagnostic system has been intensively tested with the various data acquired under different electrical and mechanical faults with varying load.

• Journal of Satellite, Information and Communications
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• v.10 no.2
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• pp.34-39
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• 2015

In this paper, a design of an offset Cassegrain antenna is proposed for Ku and Ka dual-band without increasing the antenna size. For Efficiency of computation and implementation, the frequency selectivity surface (FSS) of reflecting the Ka-band signal and passing the Ku-band is provided for the sub-reflector instead of the main reflector. The proposed FSS hyperboloid sub-reflector is the periodic structure of a unit cell comprising octagon metal rings embedded in the multiple layers. The proposed design is verified for 19 GHz and 45 GHz bands by the use of precise electromagneitc-field simulations.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.11
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• pp.33-38
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• 2004

In this paper, we review a trellis-coded orthogonal frequency division multiplex (TC-OFDM) system, which combines OFDM with trellis-coded modulation, for overcoming the frequency selective and multipath fading of time dispersive channels. We simulate and analyse the BER performance of rate 2/3 trellis coded 8DPSK-OFDM over time dispersive channels. Design of the trellis codes at different carrier numbers of OFDM is discussed. Results show that TC-OFDM system can provide 6 dB coding gain at a BER of 10$^{-3}$ compared with OFDM system without coding.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1A
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• pp.44-50
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• 2007

In typical MC-CDMA systems, different frequency-domain scrambling codes are randomly chosen from a given code set and then assigned to different subscriber stations using the same subcarrier set. When orthogonal codes are employed for the frequency-domain scrambling, the choice of the scrambling code does not affect the detection performance if the timing and frequency synchronizations are perfect and the channel characteristic is flat. However, in practical cases, inter-code interference often appears due to the broken code orthogonality. In this paper, the optimal order of allocating the orthogonal frequency-domain scrambling codes to new subscriber stations is derived under non-negligible timing offsets in MC-CDMA system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.9C
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• pp.898-907
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• 2003

In this paper, we propose a new blind watermarking method that embeds a watermark on the lowest wavelet subband coefficients, while most watermarking techniques embed watermarks in the middle frequency range for robustness and fidelity. A new embedding algorithm for watermarking is proposed that embeds a bi-level watermark sequence into randomly selected wavelet coefficients on the lowest subband(LL) using a quantization in order to be robust. Experimental results prove our novel embedding strategy is invisible and good rate-distortion-robustness performance.