• The Journal of the Korea institute of electronic communication sciences
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• v.8 no.1
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• pp.27-40
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• 2013

This study is about development of technology system for an advanced deep-sea unmanned underwater robot of S. Korea analysed by the application of scenario planning. It was developed a 6000m class next-generation deep-sea unmanned underwater vehicle(or robot, UUV) system, soonly ROV 'Hemire' and Depressor 'Henuvy' in 2006 at S. Korea and motion control, adaptive control algolithm, a work-space manipulator control algolithm, especially the underwater inertial-acoustic navigation system robust to initial errors and sensor failures. But there are remained matters on position tracking of the USBL, inertial-acoustic navigation system, attitude sensor, designed sonar sensors. So this study suggest the new idea for settle the matters and then this idea help the development of the underwater inertial-acoustic navigation system robust to initial errors and sensor failures, such as acoustic signal drop-out, by modifying the error covariance of the failed sonar signal when drop-out occurs. As a result, the future policy for deep-sea unmanned underwater robot of S. Korea is to further spur the development of new technology and more improvement of the technology level for deep-sea unmanned underwater robot system with indicator and imaginary wall as external device.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.89-90
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• 2008

We present an implementation and it's real-sea test of an underwater acoustic communication system, which allows the system to reduce complexity and increase robustness in time variant underwater environments. For easy adaptation to complicated and time-varying environments of the ocean, all-digital transmitter and receiver systems were implemented. For frame synchronization the CAZAC sequence was used, and QPSK modulation/demodulation method with carrier frequency of 25kHz and a bandwidth of 5kHz were applied to generate 10kbps transmission rate including overhead. To improve transmission quality, we used several techniques and algorithms such as adaptive beamforming, adaptive equalizer, and convolution coding/Viterbi decoding. For the verification of the system performance, measurement of BER has been done in a very shallow water with depth of 20m at JangMok, Geoje. During the experiment, image data were successfully transmitted up to about 9.6km.

• The Journal of the Acoustical Society of Korea
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• v.32 no.2
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• pp.124-130
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• 2013

The performance of underwater acoustic communication system is sensitive to the ISI(Inter-Symbol Interference) due to delay spread develop of multipath signal propagation. The equalizer is used to combat the ISI. In this paper, the performances of underwater acoustic communication with turbo equalizer were evaluated by real data collected in Korean littoral sea. As a result, when one iterative decoding using turbo equalizer is applied, the performance was improved 1.5 dB than the case of the non-iterative equalizer at BER $10^{-4}$. In the case of two or three iterations the performance was enhanced about 3.5 dB, but the performance wasn't improved any more in the case of more than three times.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.1
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• pp.325-339
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• 2018

In this paper, we propose a joint adaptive combining and variable tap-length multiuser detector (MUD) for amplify-and-forward (AF) underwater acoustic cooperative interleave-division multiple access (IDMA) communication system. The proposed MUD jointly realizes tap-length adjustment, adaptive combining, and multiuser detection. In contrast to the existing methods, the proposed detector can adaptively combine the received signals from different nodes at destination, and does not need the assumption that full and perfect channel state information (CSI) of all the links at the receiver is known. Moreover, the proposed detector can adaptively adjust the tap coefficient vector and tap-length of each branch according to the specific channel profile of each branch. Simulation results validate the feasibility and show the advantages of the proposed detector against existing counterparts.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.923-928
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• 2014

Communication underwater is severely limited when compared to communications in air because water is essentially opaque to electromagnetic radiation except in visible range. Acoustic systems are capable of long range communication, but offer limited data rates and significant latency due to the speed of sound in water. On the other hand, optical wireless communication has been proposed as one of the best alternatives to meet the requirements of the underwater observation and subsea monitoring systems. It will help In this study, we are developing an underwater optical communication system that integrates with a depot ship floating on the water. An interface between LED lighting communication system and Bluetooth module is presented to support the underwater-to-air communications. Error free image and text transmission at 3 m of water were achieved at bit rates of 230.4 kbps. This development effort will enhance infrastructure to efficiently interconnect between underwater wireless systems and command ship networks for underwater monitoring.

• The Journal of the Acoustical Society of Korea
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• v.38 no.5
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• pp.494-510
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• 2019

Underwater acoustic communication channel parameters consist of impulse response, delay spreading, scattering function, coherence bandwidth, frequency selective fading, coherence time and time variant magnitude fading statistics on which communication system modem and channel coding are designed. These parameters are influenced by sound velocity profile, platform motion and sea surface roughness in given acoustical oceanography condition. In this paper, channel model based on phasor, channel simulator, measurement and analysis method of channel parameters are given in a fixed source-to-receiver system and the parameters are analyzed using shallow water experimental data. For two different source-to-receiver ranges of 300 m and 600 m, the parameters are characterized by three multipaths such as a direct, a surface reflection path with time variant scattering and a bottom reflection path. The results present a channel modelling method of a fixed source source-to-receiver system, channel parameters measurement and analysis methods and a system design and performance assessment method in shallow water.

• Journal of Advanced Navigation Technology
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• v.24 no.5
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• pp.343-347
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• 2020

This paper presents the development of a software for tracking the location of objects in the water and for creating a three-dimensional hull map. The objective of this software, as a software for underwater hull cleaning robot, is to map the location of underwater hull cleaning robot and to locate the position of sensor by identifying the shaded area of acoustic communication. For the software designed for mapping the location of cleaning robot in the water, the height and intensity were applied as variables for underwater ultrasonic communication. The software for creating a three-dimensional hull was developed by OpenGL using scanned lines from a blueprint of a ship. This software can help identifying the location of underwater hull cleaning robot without actual visibility and can be used to maintain a stable communication status by locating the position of sensor by easily spotting the shaded area of acoustic communication caused by the curved area of the bottom of the ship.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.5
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• pp.1042-1050
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• 2014

The performance of underwater acoustic(UWA) communication system is sensitive to the Inter-Symbol Interference(ISI) due to delay spread develop of multipath signal propagation. And due to limited frequency using acoustic wave, UWA is a low transmission rate. Thus, it is necessary technique of Space-time code, equalizer and channel code to improve transmission speed and eliminate ISI. In this paper, UWA communication system were analyzed by simulation using these techniques. In the result of simulation, the proposed Turbo Equalization method based on layered Space Time Codes has improved performance compared to conventional UWA communication.

• The Journal of the Acoustical Society of Korea
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• v.23 no.2
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• pp.134-145
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• 2004

The study aims to develop the underwater wireless telephone system. The system is designed based on the underwater acoustic communication channel parameters such as ambient noise, multipath effect and diver breathing noise. The system adopts SSB modem and its carrier frequency is about 33 kHz in which ambient noise level is low and therefore a high S/N ratio is easily obtained. The source level of the transmitter is designed as 131 dB re 1μPa. Its intelligibility index of sentence shows as 80% or mure in the range of less than 300m in the sea trial.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.7
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• pp.1577-1582
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• 2013

In this paper, we have analyzed the performance of MIMO (Multi-Input Multi-Output) underwater acoustic communication by using the acquired data via the experiments in water tank. First of all, in the pursuit of this aim, we have measured the channel transfer characteristics at several transceiver locations. The transmitted signal was modulated by QPSK(Quadrature Phase Shit Keying) and the received signal was recovered through the detector that contains the zero forcing equalizer. A maximum 30~40 ms delay was appeared because of physically closed water tank environment that has the harsh multi-path transmission conditions. In result of experiment, even though the bit error rate showed comparatively large when $2{\times}2$ MIMO system with two transmitters and receivers was considered. However, we confirmed it has approximately 15% enhanced performance compared with SISO (Single-Input Single-Output) system.