• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.4
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• pp.810-816
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• 2011

The existing underwater acoustic communications modem is developing based on commercial products, so it is possible on functionality and performance of underwater acoustic communications modem implementation. But the production of development system is required to single platform system implementation at the system's size and cost. So this paper designs and implements the signal processing module as an important role to single hardware platform production of underwater acoustic communication modem by using TigerSHARC DSP processor.

• Journal of Korea Multimedia Society
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• v.17 no.5
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• pp.631-639
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• 2014

Recently, research on Media Access Control (MAC) techniques for underwater acoustic communication has been conducted actively. For successful acoustic communication in underwater conditions, development of environmentally adaptive MAC techniques, which is taking narrow bandwidth, distance, depth, noise level, salinity, multipath and etc into account, is an especially important work. In this paper, knowledge based system is introduced not only to obtain adaptive and optimal communication parameters but also increase network efficiency and availability by requesting change of MAC techniques based on decisions from knowledge-based system Smart Decision Block (SDB). Computer simulations were also conducted to verify the performance of the proposed system in underwater conditions.

• Journal of the Korea Institute of Military Science and Technology
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• v.11 no.3
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• pp.19-29
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• 2008

Underwater acoustic(UWA) communication is one of the most difficult field in terms of severe channel environments such as multipath propagation, high temporal and spatial variability of channel conditions. Therefore, it is important to model and analyze the characteristics of underwater acoustic channel such as multipath propagation, transmission loss, reverberation, and ambient noise. In this paper, UWA communication channel is modeled with a ray tracing method and applied to image transmission. Quadrature phase shift keying(QPSK) and multichannel decision feedback equalizer(DFE) are utilized as phase-coherent modulation method and equalization technique, respectively. The objective is to improve the performance of the image transmission using vertical sensor array instead of single sensor in the viewpoint of bit error rate(BER), constellation diagram, and received image quality.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.6 no.1
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• pp.29-36
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• 2013

The inter-symbol interference(ISI) is one of the main obstacles to reliable high-rate data communication in the shallow underwater acoustic channel. This paper studies on the simulation of adaptive equalizer used as a means of mitigating the ISI in the shallow underwater acoustic communication system. The underwater channel is modeled as a superposition of multiple paths, whose lengths and relative delays are calculated from the channel geometry. Based on this channel model, computer simulations are carried out to investigate the performance of adaptive equalizer in the shallow underwater acoustic channel.

• Journal of the Institute of Convergence Signal Processing
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• v.19 no.3
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• pp.139-146
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• 2018

Underwater acoustic communication can be applied to various area such as scientific, commercial and military survey using Autonomous Underwater Vehicles and Unmanned Underwater Vehicles. Underwater communication is studying very actively by advanced country like United States. But differ from wireless communication in the air, underwater acoustic communication has some difficult problems, ISI(Inter Symbol Interference) due to multipath and limit of transmission bandwidth due to slow propagation of sound wave. In this paper, SC-FDE and OFDM transmission system for the cancellation of ISI in conjunction with underwater acoustic channel modeling are applied to the underwater simulation of communication. The performance of these methods in the simulation guide to possibility of adopting in underwater acoustic communication algorithm. For this purpose, we compare SER performance of SC-FDE with that of OFDM for modelled underwater channel. Underwater channel is generated by Bellhop model. Simulation results show above 5dB SNR gain at 10-3 SER. And it demonstrate SC-FDE is efficient method for underwater acoustic communication.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.04b
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• pp.168-171
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• 2000

Underwater acoustic communications have made considerable advances in the past decade. The purpose of this paper is to achieve the underwater communication by ultrasonic sensors and to investigate conditions of good underwater acoustic communicators. As a result of this experiments, the ultrasonic sensors, MA40E7R/S, made by Nicera can be used as ultrasonic transducers for underwater communication using AM(Amplitude Modulation) signal and Transmission Loss is 17.328[dB] at 65[cm]. To make a good underwater communicator, proper diameter of disk PZT transduers is the one of most important factors, because radiation of acoustic wave depends on proper diameter of transduers and the transmission loss strongly depends on the spreading loss.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.165-169
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• 2007

Due to the complexity of underwater acoustic channel, signal estimation in underwater acoustic communication field is considerably affected from time-varying multipath fading channels. On this reason, the original signals should have many long training signals to estimate the channel and the purposed signals, and the bit rate of signals having information may have small rate. In order to avoid this loss of efficiency in underwater communication, this paper employed a blind channel identification method which don't use training signals. Simulations have predicted performance of the employed method in multipath environment and an aquatic plant experiment has verified the simulation results.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.227-234
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• 2022

Covert Underwater Communication (CUC) signals should not be detected by other unintended users. Similar to the method used in Radio Frequency (RF), covert communication technique sending information underwater is designed in consideration of the characteristics of Low Probability of Detection (LPD) and Low Probability of Intercept (LPI). These conventional methods, however, are difficult to be used in the underwater communications because of the narrow frequency bandwidth. Unlike the conventional methods of reducing transmission power or increasing the modulation bandwidth, a method of mimicking the acoustic signal of an underwater mammal is being studied. The biomimetic underwater acoustic communication mainly mimics the click or whistle sound produced by dolphin or whale. This paper investigates biomimetic communication method and introduces research trends to understand the potential for the development of such biomimetic covert underwater acoustic communication and future research areas.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.3
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• pp.405-411
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• 2020

Recently, studies on underwater communication, related to the development of underwater resources, disaster monitoring and defense, have been actively carried out. In the design of wireless communication systems, path loss is the most important information to derive a link budget that is required to guarantee communication reliability by calculating received power level for the given communication link. The underwater acoustic channel have different characteristics according to geographical location and relevant environmental factors such as water temperature, depth, wave height, algae, and turbidity. Subsequently, many research institutes aiming to develop underwater acoustic communication systems are researching actively on the underwater acoustic channels in various sea areas. In Korea, however, studies on the path loss of the acoustic channel are still insufficient. Therefore, in this study, the path loss of the acoustic channel are studied based on measurement data of the at-sea experiment conducted at Geohae-do, southern sea of Korea.

• The Journal of the Korea institute of electronic communication sciences
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• v.5 no.5
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• pp.509-515
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• 2010

Such as disaster rescue in deep water, undersea exploration and monitering for environmental pollution, many applications require the acoustic communication for high data rate over underwater acoustic channel. As underwater channel is very complex and is time-varying, conventional single carrier communication has good performance. In this paper, An adaptive OFDM system is analyzed for high data rate and reliability and rubust service over UWA channels. Through the adaptive system, we show threshold switching for an adaptive algorithm.