• 한국수산과학회지
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• 제23권6호
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• pp.451-456
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• 1990

Underwater acoustic navigation and position fixing systems have been extensively used not only in surface position fixing but also in underwater position fixing. Tn recently, application of these systems has been in the field of underwater inspection of offshore platforms, where it is vital to track the position of an unmanned submersible or diver carrying underwater cameras and nondestructive testing equipment. But these systems are included the fixing errors as results of a signal with additive noise, the attenuation of sound and the interference effects due to multipath reflection and forward scattering. In this paper to improve the position fixing by the supershort baseline acoustic position system, a method to apply the Kalman filter to the fix of the system is proposed and the digital simulation under noise condition is conducted. The optimal positions by the Kalman filter are compared with original positions, and it is confirmed that the results of the pro-posed method are evidently more accurate.

• 한국위성정보통신학회논문지
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• 제12권1호
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• pp.120-124
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• 2017

본 본문에서는 Code division multiple access (CDMA) 사용자와 협대역 사용자가 동일 주파수 대역에 존재하는 곳에서 direct sequence/CDMA (DS/CDMA) 오버레이 시스템에 대해 pseudorandom noise (PN) 코드 획득 성능 상의 안테나 다이버시티의 효과가 분석되고 시뮬레이션 되었다. 시뮬레이션 결과는 안테나 다이버시티가 PN 획득 성능에 매우 효과적임을 보인다. 이 논문의 결과는 DS/CDMA 오버레이 환경에서 동기 구조의 설계에 적용될 수 있다.

• Journal of Communications and Networks
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• 제5권2호
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• pp.150-156
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• 2003

In this paper, an uplink MC-CDMA system incorporating multiuser detection and smart antennas has been considered. The performance of asynchronous as well as synchronous system is studied over a correlated Rayleigh multipath slow fading channel. A simplified array-processing algorithm suitable for slow fading situation is investigated to overcome the heavy computational complexity associated with Eigen solutions. The effect of variable data rate in the system performance is considered and effectiveness of antenna array to handle high data rate is discussed. A brief investigation on the system performance degradation due to correlated channel is also carried out. Based on the extensive simulation carried out, the performance of the asynchronous uplink system is found dramatically improved with antenna array and multiuser detection. Asynchronicity and channel correlation are found to affect the system performance significantly. The investigated simpli- fied algorithm produces similar results as Eigen solutions in slow fading situation with much reduced complexity.

• Journal of Communications and Networks
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• 제11권1호
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• pp.42-46
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• 2009

Superimposed training (SIT) design for estimating of time-varying multipath channels is investigated for mobile orthogonal frequency division multiplexing (OFDM) systems. The design of optimum SIT consists of two parts: The optimal SIT sequence is derived by minimizing the channel estimates' mean square error (MSE); the optimal power allocation between training and information data is developed by maximizing the averaged signal to interference plus noise ratio (SINR) under the condition of equal powered paths. The theoretical analysis is verified by simulations. For the metric of the averaged SINR against signal to noise ratio (SNR), the theoretical result matches the simulation result perfectly. In contrast to an interpolated frequency-multiplexing training (FMT) scheme or an SIT scheme with random pilot sequence, the SIT scheme with proposed optimal sequence achieves higher SINR. The analytical solution of the optimal power allocation is demonstrated by the simulation as well.

• 대한전기학회논문지:시스템및제어부문D
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• 제53권4호
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• pp.286-292
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• 2004

This paper presents a polyphase filtered orthogonal frequency division multiplexing (PF-OFDM) technique. The proposed structure uses a modified discrete Fourier transform (MDFT) transmultiplexer to achieve greater spectral efficiency than an OFDM system, while preserving backward compatibility with it. The prototype PF-OFDM filter has excellent time and frequency localization properties, which matte it possible to eliminate a guard interval (or cyclic prefix) and easily suppress interchannel interference (ICI). This modulation technique uses a single DFT structure, in contrast to a MDFT transmultiplexer, which requires two DFT polyphase filter banks. The PF-OFDM modulation is .justified over multipath Rayleigh fading channels.

• 한국통신학회논문지
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• 제21권5호
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• pp.1230-1239
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• 1996

This paper analyzes matched-filter acquistion performance of a direct-sequence spread-specturm multiple-access system in a Rayleigh fading channel. For an application of multiple access system, multiple access interference is considered in the performance analysis. A signal flow graph technique is used to derive mean acquisition time in terms of detection and false alarm probabilities. As aresult of performance analysis, it is shown that mean acquisition time increases as fading rate becomes faster andthe numbre of users increases, and it decreases as a matched-filter length becomes logner. The variation of parameter values hs much influence on acquisition performance as SNR/chip becomes smaller.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.85-88
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• 2008

수중에서는 매질과 채널의 특성으로 인해 가능한 최대 데이터 전송 속도는 지상통신에서의 데이터 전송 속도에 비해 매우 낮으며, 이를 어떻게 극복하느냐가 매우 중요하다. 특히 천해(shallow water)에서 다중경로(Multipath)로 인한 지연 확산은 심볼 사이의 ISI(Inter Symbol Interference)를 유발시켜 수중 통신 시스템의 성능을 더욱 떨어뜨린다. 본 논문에서는 수중 음향 채널에서 고속 데이터 전송을 위해 OFDM(Orthogonal Frequency Division Multiplexing) 방식을 이용한 통신 시스템을 다룬다. 다중경로로 인한 심한 심볼간 간섭을 받는 수중 채널에서 고속 데이터 전송을 위해 OFDM 방식의 통신 시스템의 성능을 평가하였으며, 이를 위해 수중 채널 모델을 이용해 영상 데이타 전송 시뮬레이션을 수행하였다.

• 제어로봇시스템학회논문지
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• 제20권9호
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• pp.977-983
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• 2014

A repeat-back jamming signal is an intentionally re-broadcasted GNSS (Global Navigation Satellite System) interference. In this paper, a novel repeat-back jamming detection scheme is proposed. The proposed scheme uses a combined pseudo random noise signal (C-PRN) and is available for a generic GNSS receiver with a single antenna. The C-PRN signal is made by combining several received pseudo random noise signals that had been transmitted from the visible GNSS satellites. Through a Monte-Carlo simulation, the detection probability of a repeat-back jamming signal detected with the proposed scheme is presented.

• 센서학회지
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• 제23권1호
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• pp.1-6
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• 2014

In many medical image devices, dc noise often prevents normal diagnosis. In wireless capsule endoscopy systems, multipath fading through indoor wireless links induces inter-symbol interference (ISI) and indoor electric devices generate impulsive noise in the received signal. Moreover, dc noise, ISI, and impulsive noise are also found in optical fiber communication that can be used in remote medical diagnosis. In this paper, a blind signal processing method based on the biased probability density functions of constant modulus error that is robust to those problems that can cause error propagation in decision feedback (DF) methods is presented. Based on this property of robustness to error propagation, a DF version of the method is proposed. In the simulation for the impulse response of optical fiber channels having slowly varying dc noise and impulsive noise, the proposed DF method yields a performance enhancement of approximately 10 dB in mean squared error over its linear counterpart.

• 한국컴퓨터산업학회논문지
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• 제7권1호
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• pp.39-46
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• 2006

고속의 데이터 전송에 대한 채널의 왜곡을 보상하기 위해 다중 경로 다이버시티 수신을 수행하였다. 다이버시티 가지에 보상 알고리즘을 결합한 수신 구조를 갖는 DS/BPSK 시스템을 구성하고 시스템의 성능을 SNR에 따른 평균 비트 에러율 관점에서 평가하였다. 상호부호간 간섭을 극복하기 위해 L 개의 다이버시티 가지에 비선형 탭 지연선 구조를 사용하고 보상 알고리즘에 따라 탭 계수가 시변채널에 적응하도록 하였다. 그 결과 일반적인 보상 알고리즘에 비해 제안한 알고리즘의 평균 비트 에러율이 $10^{-2}$ 정도 개선되었다.