• IEMEK Journal of Embedded Systems and Applications
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• v.9 no.3
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• pp.165-171
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• 2014

In this paper, we propose the hardware and software of a test-bed of a hovering AUV (autonomous underwater vehicle). Test-bed to develop as the underwater robot for the hovering -type is planning to apply for marine resource development and exploration for deep sea. The RTU that controls a azimuth thruster and a vertical thruster of test-bed is a intergrated-type thruster. The main control unit that collects sensor's data and performs high-speed processing and controls a movement of test-bed is a underwater hybrid navigation system. Also it transfers position, posture, state information of test-bed to the host PC of user using a wireless communication. The host PC checks a test-bed in real time by using a realtime monitoring system that is implemented by LabVIEW.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.29 no.2
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• pp.109-116
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• 1993

Underwater acoustic positioning systems have been extensively used not only in surface position fixing but also in underwater position fixing. Recently, these systems have been applied in the field of installation and underwater inspection of offshore platforms etc. But in these systems are included the fixing errors as results of a signal with additive noise and irregular motion of vessel by ocean waves. To improve the accuracy of the position fixing a Kalman filter is applied to the supershort baseline (SSBL) acoustic positioning system with beacon mode in noise conditions. The position data obtained by the Kalman filter is compared with raw position data and it is confirmed in the simulation that the former is more accurate than the latter. And an indicator monitoring the filtering effect is described while ship's moving.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.372-378
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• 2016

A mound was constructed to install a caisson and sofa blocks underwater. The mound riprap, which were of uniform grade, size, shape, and specific gravity, formed the foundation for the support superstructure. Also, rubble leveling works were performed before installing structures such as caissons. In this study, underwater construction equipment was developed with a remotely controlled operating system and underwater environment monitoring system for unmanned underwater rubble leveling work. The performance of the developed equipment was verified using on-land and underwater tests. In addition to the performance verification, the construction process and economic efficiency of the equipment should be checked before applying it to the real construction field for commercial purposes. In this paper, a construction process using the developed equipment was proposed and compared with the existing rubble leveling method. The results demonstrated that the new construction method has higher economic efficiency and safety than the existing construction method.

• 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.

• Journal of the Institute of Convergence Signal Processing
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• v.23 no.2
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• pp.50-61
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• 2022

This work demonstrates the design and evaluation of Aqua-Aware, a lightweight miniaturized light emitting diode (LED) based underwater compact sensor node which is used to obtain different characteristics of the underwater environment. Two optical sensor nodes have been designed, developed, and evaluated for a short and medium link range called as Aqua-Aware short range (AASR) and Aqua-Aware medium range (AAMR), respectively. The hardware and software implementation of proposed sensor node, algorithms, and trade-offs have been discussed in this paper. The underwater environment is emulated by introducing different turbulence effects such as air bubbles, waves and turbidity in a 4-m water tank. In clear water, the Aqua-Aware achieved a data rate of 0.2 Mbps at communication link up to 2-m. The Aqua-Aware was able to achieve 0.2 Mbps in a turbid water of 64 NTU in the presence of moderate water waves and air bubbles within the communication link range of 1.7-m. We have evaluated the luminous intensity, packet success rate and bit error rate performance of the proposed system obtained by varying the various medium characteristics.

• Journal of Korea Multimedia Society
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• v.14 no.2
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• pp.258-268
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• 2011

Underwater acoustic sensor networks can be used disaster prevention and environmental monitoring systems in underwater environments. Because, the underwater environment is different from the ground, the long propagation delay, low transfer rates and limited bandwidth characteristics should be considered. In this, paper will propose the MAC protocol that allocates time slot into each node according to priority policy through the period of contention-free slot reservation in underwater acoustic sensor networks in order to avoid collision and minimize energy consumption waste. We perform mathematical analysis to evaluate the performance of the proposed protocol with regard to the collision probability, the energy consumption by collision, throughput and channel utilization. We compare the proposed protocol with the conventional protocol, and the performance results show that the proposed protocol outperforms the conventional protocol.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.6
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• pp.360-369
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• 2014

Underwater Acoustic Sensor Networks(UASN) enables varied study from collected data of underwater environments such as pollution monitoring, disaster prevention. The collected data is transmitted from underwater to terrestrial communication entity by acoustic communication. Because of the constraints of underwater environments include low data rate and propagation delay, it is difficult to apply cryptographic techniques of terrestrial wireless communication to UASN. For this reason, if the cryptographic techniques are excluded, then collected data will be exposed to security threats, such as extortion and forgery, during transmission of data. So, the cryptographic techniques, such as the authentication and key establishment protocol which can confirm reliability of communication entities and help them share secret key for encryption of data, must need for protecting transmitted data against security threats. Thus, in this paper, we propose the light weight authentication and key establishment protocol.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.10
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• pp.645-653
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• 2014

Recently, the ocean field researches such as offshore plant, ocean survey and underwater monitoring systems are garnering the attention from both academy and industry. However, the communication in underwater environment is very difficult because of the unique irregular features in water. This is the reason that the application of terrestrial protocols to the water environment is not proper. This paper proposes a routing algorithm that can enhance communication reliability by utilizing channel properties in underwater environment. We address two problems that lead to the poor communication performance, signal attenuation and multi-path problem in water. Overcoming these problems, the proposed algorithm ensures high packet delivery ratio and low transmission delay. Also, this paper evaluates the performance through simulation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.2
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• pp.143-150
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• 2023

Underwater wireless communication is a challenging issue for realizing the smart aqua-farm and various marine activities for exploring the ocean and environmental monitoring. In comparison to acoustic and radio frequency technologies, the visible light communication is the most promising method to transmit data with a higher speed in complex underwater environments. To send data at a speedier rate, high-performance photodetectors are essentially required to receive blue and/or cyan-blue light that are transmitted from the light sources in a light-fidelity (Li-Fi) system. Here, we fabricated high-performance organic phototransistors (OPTs) based on P-type donor polymer (PTO2) and N-type acceptor small molecule (IT-4F) blend semiconductors. Bulk-heterojunction (BHJ) PTO2:IT-4F photo-active layer has a broad absorption spectrum in the range of 450~550 nm wavelength. Solution-processed OPTs showed a high photo-responsivity >1,000 mA/W, a large photo-sensitivity >10³, a fast response time, and reproducible light-On/Off switching characteristics even under a weak incident light. BHJ organic semiconductors absorbed photons and generated excitons, and efficiently dissociated to electron and hole carriers at the donor-acceptor interface. Printed and flexible OPTs can be widely used as Li-Fi receivers and image sensors for underwater communication and underwater internet of things (UIoTs).

• Smart Structures and Systems
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• v.3 no.3
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• pp.357-372
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• 2007

Parametric density concept is proposed for a long-range pipeline health monitoring. This concept is designed to obtain the attenuation of ultrasonic guided waves propagating in underwater pipelines without complicated calculation of attenuation dispersion curves. For the study, three different pipe materials such as aluminum, cast iron, and steel are considered, ten different transporting fluids are assumed, and four different geometric pipe dimensions are adopted. It is shown that the attenuation values based on the parametric density concept reasonably match with the attenuation values obtained from dispersion curves; hence, its efficiency is proved. With this concept, field engineers or inspectors associated with long-range pipeline health monitoring would take the advantage of easier capturing wave attenuation value, which is a critical variable to decide sensor location or sensors interval.