• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.15 no.1
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• pp.84-89
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• 2001

This paper deals with multiresolution analysis of wavelet transform for partial discharge(PD), composite discharge(corona + surlace discharge). Multiresolution analysis was used for performing discrete wavelet transform PD signals was decomposed into "approximation" and "detail" cOmpJnents until 4 levels by using discrete wavelet analysis. In this paper, daubechies family is adopted for the research of the characteristics of PD signals. 1be results show that in corona discharge the segment 7, 8, 9, 10, 1] values of defined variable is increased with discharge process, so phase distribution is characterized by 210~330 ranges. In case surface discharge in expoxy insulator inserted, defined variable values is fairly symmetric chscharge pattern because coupled both corona and dielectric oounded discharges. We can confimJly discriminate the type of PD source.

• The KIPS Transactions:PartC
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• v.8C no.6
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• pp.703-710
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• 2001

In this paper, we consider a multiple watermarking for image copyright protection. Multiple watermarking can be defined that two or more watermarks are inserted into the same content. Multiple watermarking using spread spectrum technique is able to extract the correct watermarks from the watermarked content when the orthogonality among keys should be guaranteed only. To keep the orthogonal property between keys, we perform the process of Gram-Schmidt on the random sequences. The orthogonalized sequences are used as keys to embed the watermarks. The proposed method can not only extract correctly the embedded watermarks but also show the robustness against various attacks such as Gaussian noise addition, histogram equalization, gamma correlation, sharpening and brightness/contrast adjustment.

• The KIPS Transactions:PartC
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• v.13C no.6 s.109
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• pp.677-684
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• 2006

This paper investigates the link margin of MB-OFDM UWB system quantitatively. Various simulations are performed considering the implementation loss by imperfect synchronization unit and the effect of multi-path fading channels. MB-OFDM UWB system uses ZP(Zero Padding) instead of CP(Cyclic Prefix) and supports two transmission modes; one is TFI(Time Frequency Interleaving) mode that transmits OFDM symbols using different carrier frequency from symbol to symbol according to Time Frequency(TF) codes, the other is FFI(Fixed Frequency Interleaving) mode that transmits OFDM symbols using a specific carrier frequency. The advantage of if and TFI is to be able to increase the transmitting power effectively compared to the existed OFDM systems that transmit the signal continuously at the same average transmitting power. From the analysis results of Ink margin, to guarantee the service range of 4m in 200Mbps mode, TFI mode must necessarily be implemented and the service range of 480Mbps mode is estimated about 1-2m in the line-of-sight multi-path channel (CMI).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.7A
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• pp.554-561
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• 2009

In this paper, we propose a novel Vehicular Ad-hoc Network(VANET) which includes communication and ranging features, using Spread Spectrum(SS) multi-carrier modulation scheme. In existing methods, a spread spectrum technique was used to communicate with other vehicles and raging was possible by detecting phase difference between transmission/reception of the PN signal. However, the use of high-speed PN signals is mandatory to detect possible errors of phase difference and to increase the analysis capacity. In the proposed system, multi-carrier modulation scheme was used as solution of mentioned problem. The multi-carrier modulation scheme uses smaller PN signal and chip-rate than the single-carrier modulation, so it is possible to send multiple carrier waves using the same frequency range. This technique (multiple carrier waves) allows to have the Equal Gain Combing (EGC) diversity effect, providing better result in phase difference error detection and raging accuracy.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.4
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• pp.377-387
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• 2016

Design of X-band frequency FMCW based imaging radar with multi-resolutions and performances of the self-manufactured radar system are presented in this study. In order to implement the multi-bandwidths, a ramp sequence of the FMCW signal is consisting of two kinds of 'saw-tooth' waveform with different bandwidth, and a receiver circuit consisting of L-band source and frequency converter circuit is used to effectively extract spectra of beat-frequency from the received signal of X-band frequency. The system setups for performance measurement of self-manufactured radar system are maximum output power of 35 dBm, sampling frequency of 1.2 MHz and sweep time of 1 ms. Then, the measured resolutions of the modulated signal having bandwidth of 500 MHz and 300 MHz in range & azimuth-direction are (0.28 m, 0.26 m) and (0.44 m, 0.27 m), respectively.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.5
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• pp.344-352
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• 2020

Covertness and performance are very important design goals in the underwater communications. To satisfy both of them, we proposed efficient underwater communication model which combined multiband and direct sequence spread spectrum method in order to improve performance and covertness simultaneously. Turbo coding method with 1/3 coding rates is used for channel coding algorithm, and turbo equalization method which iterately exchange probabilistic information between equalizer and decoder is used for receiver side. After optimal threshold value was set in Rake processing, this paper analyzed the performance by varying the number of chips were 8, 16, 32 and the number of bands were from 1 to 4. Through the simulation results, we confirmed that the performance improvement was obtained by increasing the number of bands and chips. 2~3 dB of performance gain was obtained when the number of chips were increased in same number of bands.

• Proceedings of the Acoustical Society of Korea Conference
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• 1993.06a
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• pp.113-116
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• 1993

본 논문에서는 변형된 wavelet 변환을 통해 추출한 특징벡터를 이용하여 한국어 숫자음을 대상으로 한 음성인식기를 구현하였다. wavelet 변환은 시간 및 주파수 영역에 대해 다중해상도(multiresolution)를 가지는 신호분석법이다. 본 연구에서는 계산량의 감소와 넓은 주파수 대역을 분석하기 위해, mother wavelet의 형태를 분석 주파수 대역에 따라 변화시키는 방법을 제안하였다. 기존의 wavelet 변환으로 실험한 결과 86.5%의 인식율을 얻었고, 변형된 wavelet 변환의 경우 96%의 인식율을 얻었으며 계산량이 감소하였다. 이와 함께 음성인식에서 널리 사용되는 특징 파라미터인 멜켑스트럼과 FFT 멜스케일 필터 대역(mel scale filter bank)과 비교 실험한 결과 인식율의 향상을 보였다. 이는 제안한 방법이 고주파 대역의 세밀한 시간 해상도와 저주파 대역의 세밀한 주파수 해상도를 지니는데 기인하는 것으로 판단된다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.107-110
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• 2003

본 논문에서는 부분대역간섭 (PBI : Partial Band Interference)이 존재하는 다중경로 페이딩 환경에서 하이브리드 SC/MRC-Lc/L 다이버시티 수신 Multi-Carrier DS-CDMA 시스템의 성능을 알아보고, 광대역 DS-CDMA 시스템과 비교 분석하였다. 결과적으로 Multi-Carrier DS-CDMA 시스템에서 부분대역간섭에 대한 영향은 성능 열화정도가 전체 주파수 대역 중 일부대역에서만 받기 때문에 광대역 DS-CDMA 시스템보다는 심각하지 않았다. 또한, 하이브리드 SC/MRC-Lc/L 다이버시티 수신 Multi-Carrier DS-CDMA 시스템은 입력 다이버시티 가지의 수를 적절히 선택함으로서 시스템의 복잡성과 성능 대 비용을 결정할 수 있다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.1 s.92
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• pp.78-83
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• 2005

LTCC filters have been widely used to wireless terminals. They generally adopt the multilayer structure. Some of multilayer LTCC filters are made of symmetrical parallel-coupled lines and anti-symmetrical parallel-coupled lines to reduce the length of resonators. The equivalent circuit of parallel-coupled lines was analyzed and applied to bandpass filters using multilayer parallel-coupled line resonators. The three-pole bandpass filter with the center frequency of 2.45 GHz is designed by using the proposed equivalent circuit and the measured results have good agreement with the design results.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.3
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• pp.63-73
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• 2002

초광대역 통신 시스템은 광대역에 걸쳐 주파수 스펙트럼이 기저 대역 잡음과 같이 존재하여 기존의 통신 시스템에 간섭을 주지 않고 고속의 통신이 가능하며, 반송파를 사용하지 않기 때문에 송.수신기의 소비 전력을 감소시키고 그의 구조를 간략화 시킬 수 있다. 본 논문은 신호의 대칭성에 의해 평균값이 0인 안티포달 초광대역 신호를 구성하고 시간 도약 부호를 이용하여 다중접속, 주파수 영역에서 에너지의 평활화 및 재밍 저항(간섭 제거)을 위 한 초광대역 통신 시스템을 제안하였다. AWGN 및 다중접속 환경에서 안티포달 초광대역 통신 시스템의 오류확률, 다중접속시 전송속도에 대해 수치해석을 통해 시스템의 성능을 분석하였다.