• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.6
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• pp.1243-1249
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• 2004

In this paper, the multipath effect on underwater acoustic channel bandwidth and BFSK and BPSK bit error dependancy on channel bandwidth are analyzed. The multipath is modeled as a discrete multipath and a continuous multipath and the channel bandwidth is expressed as a function of multipath delay spread constant. Bit error characteristics on the channel bandwidth and the criteria of the multipath delay spread constant are found through the numerical simulation. The transmission bit rate of less than 100bps in the water tank which has a channel bandwidth of 100Hz, is a consistent result with the numerical simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10B
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• pp.1210-1215
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• 2011

In this paper, a supervised adaptive equalization algorithm based on probability density function (PDF) matching method is introduced and its decision-feedback version is proposed for underwater communication channels with strong impulsive noise and severe multipath characteristics. The conventional least mean square (LMS) algorithm based on mean squared error (MSE) criterion has shown to be incapable of coping with impulsive noise and multipath effects commonly shown in underwater communications. The linear PDF matching algorithm, which shows immunity to impulsive noise, however, has revealed to yield unsatisfying performance under severe multipath environments with impulsive noise. On the other hand, the proposed nonlinear PDF matching algorithm with decision feedback proves in the simulation to possess superior robustness against impulsive noise and multipath characteristics of underwater communication channels.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.2
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• pp.299-306
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• 2011

In this paper, a blind adaptive equalization algorithm based on PDF-distance minimization and a set of Delta functions is introduced and its superior robustness against impulsive noise and multipath characteristics of underwater communication channels is proved. The conventional CMA based on MSE has shown to be incapable of coping with impulsive noise, and correntropy blind algorithm has also revealed to yield not satisfying performance for the mission. On the other hand, the blind adaptive equalization algorithm based on PDF-distance minimization and a set of Delta functions has been proved to solve effectively the problem of impulsive noise and multipath characteristics of underwater communication channels through theoretical and simulation analysis.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.359-362
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• 2001

Analog communication systems using AM, FM modem have been developed. Digital communication systems using digital modems, which is by expansion of digital hardware skill have been recently developed. In order to accomplish a reliable communication it is important to overcome ocean environmental channel characteristics such as transmission loss, ambient noise and multipath effect etc. Specially, the effect of multipath is the most important element that determines the performance of underwater communication system in shallow water. Multipath channel can be divided a vertical and horizontal channel. the former is defined the channel to have large path-delay times between a direct wave and reflected waves. The latter shows relatively small path-delay times between a direct and reflected waves in compared with a vertical channel. In this paper, The performance of FSK, PSK and DPSK modem with respect to the vertical and horizontal multipath communication channels it described and compared.

• The Journal of the Convergence on Culture Technology
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• v.3 no.4
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• pp.191-198
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• 2017

In this paper, we compare the transmission performance of Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplexing (OFDM) under long duration multipath channel environments. This paper generates underwater channels through Bellhop based on the underwater environmental data of the west sea. BER performance of CDMA and OFDM are analyzed through various underwater channels based on the channels. Computer simulations result show that CDMA has better performance than OFDM when multipath delay time of underwater channel is shorter than spreading factor (SF). However, OFDM has better BER performance than CDMA as multi-path delay time increases.

• Proceedings of the IEEK Conference
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• 2008.06a
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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.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.10
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• pp.2207-2214
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• 2010

Underwater acoustic(UWA) communication has multipath error because of reflection by sea-level and sea-bottom. The multipath of UWA channel causes signal distortion and error floor. In this paper, we proposed split input bits of channel decoder using method of maximum value, average value, LLR value for optimal estimation. Channel coding method is LDPC(N size=16000) standard in DVB-S2. As shown in simulation results, the performance of LLR value method is better than other methods.

• 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.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.401-404
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• 2004

수중음향통신 관점에서 바다와 같은 수중채널은 수십심벌에 이르는 다중경로와 빠르게 변화하는 도플러 효과가 존재한다. 따라서 신뢰성 있는 수중음향통신을 위해서는 채널 등화가 반드시 필요하다. 본 논문에서는 이차 통계량 기반의 Blind Identification 알고리듬을 이용한 수중음향 채널추정 기법을 이용하여 무향수조의 채널응답을 분석하였다. 실험을 통하여 알고리듬의 추정 정확도 및 트랜스듀서 특성을 포함한 무향수조의 채널 응답 특성에 대하여 논한다.

• The Journal of the Acoustical Society of Korea
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• v.27 no.6
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• pp.286-295
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• 2008

Underwater acoustic communication has multi path error because of reflection by sea-level and sea-bottom. The multipath of underwater channel causes signal distortion and error floor. In this paper, we consider the use of various channel coding schemes such as RS code, convolutional code, cross-layer code and LDPC code in order to compensate the multipath effect in underwater channel. As shown in simulation results, characteristic of multipath error is similar to that of random error, so interleaver has little effect for error correcting. For correcting of error floor by multipath error, it is necessary strong channel codes like LDPC code that is similar to Shannon's limit. And the performance of concatenated codes including RS codes has better performance than using singular channel codes.