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Baek, Chang-uk;Jung, Ji-won
- Journal of the Korea Institute of Information and Communication Engineering
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- v.19 no.7
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- pp.1531-1538
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- 2015
In this paper, we proposed receiver structure based on an iterative turbo equalization to cope with phase difference between two sensors in MIMO underwater communication channel. In a space-time coded system, it is often assumed that there are no phase errors among the multiple transmitter and receiver chains. In this paper, we have studied the effect of the phase errors between different transmit sensors and different propagation paths in the environment of MIMO underwater communication system, and have shown through BER performance by computer simulations that the bit-error-rate performance can be severely degraded. A decision-directed estimation and compensation algorithm has been proposed to minimize their effects on the system performance. In this paper, we investigate the phase differences and their effects on multiple-input and multiple-output systems, and propose a compensation algorithm for underwater channel model to minimize their effects.
https://doi.org/10.6109/jkiice.2015.19.7.1531 인용 PDF KSCI KPUBS HTML

Park, SungJun;Kim, Jedo
- The Journal of the Acoustical Society of Korea
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- v.38 no.1
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- pp.67-72
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- 2019
In this study, we investigate the echo reduction performance of miniaturinzed Helmholtz resonators using smaller than wavelength acoustic metamaterial structures. The Helmholtz resonators are formed using air structures which exhibit large impedance mismatch with the surrounding underwater environment. Using the multi-physics software package, we find that significant reduction in the sonar signature is expected and frequency tailoring is possible by controlling the degree of space coiling and inner volume of the resonators. We find that for the basic Helmholtz resonators, up to 7 dB reduction in echo is expected at 10,000 Hz while when the miniaturized Helmoholtz resonators are used, up to 14 dB reduction in echo is expected at 5,000 Hz. In addition, frequency tailoring is demonstrated by varying the internal volume of the Helmholtz resonators and broadband characteristic is shown using superposition of various degree of space coiled structures. Through this study we investigate the effectiveness of the miniaturized Helmholtz resonators formed using air structures and the echo reduction results show promisses in the application of achieving underwater stealth.
https://doi.org/10.7776/ASK.2019.38.1.067 인용 PDF KSCI HTML

Jeong, Yoo-Jin;Shin, Soo-Young;Park, Soo-Hyun
- Journal of the Korea Society for Simulation
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- v.15 no.4
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- pp.79-86
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- 2006
Data transmission in poor environment like underwater has considerably serious delay rate and ewer rate. Like this environment usually has heavy fluctuation of error rate and limited wireless communication state. Therefore, mechanism using in such environment has to be efficient and simple. This paper suggests a new block ack mechanism, called the Pervasive Block ACK (PBA), which transmits aggregated ACKs. This mechanism takes effect on reducing number of traffic, decreasing overhead and delay rate in poor environment networks like underwater. Additionally, we can expect energy consumption. We verify propriety and efficiency of PBA through describing numerical result based analytical formula in this paper.
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박민수;김승일;성하종;이충용;윤대희
- The Journal of the Acoustical Society of Korea
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- v.18 no.2
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- pp.25-31
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- 1999
An array aperture synthesis technique is proposed. The proposed method does not require the condition that the overlapped hydrophones have the identical position in space to estimate the phase correction factors. while the existing ETAM algorithm does. Therefore the proposed method increases the available data applied to extend the effective aperture length of the towed array. From the numerical experiments, the proposed method can reduce the mean square error in estimating the direction of a target signal.
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