• Journal of Navigation and Port Research
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• v.34 no.3
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• pp.181-187
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• 2010

The performance of underwater wireless communication system is influenced on channel characteristic. Especially, a delay spread cause by reverberation and multi-path happen the ISI (Inter Symbol Interference) and reduces the communication performance. In this paper, we study the application of high speed data transmission in underwater to use the OFDM (Orthogonal Frequency Division Multiplexing) technique for robust the reverberation and multi-path. we confirm the performance of communication in underwater to use the model for actually underwater channel simulation model. As a result, we acquired the BER of modulation techniques. The BER of single carrier is $2{\times}10^{-1}$ and BER of multi carrier is $8{\times}10^{-2}$ in 1000m.

• Journal of Convergence for Information Technology
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• v.10 no.5
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• pp.1-7
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• 2020

This paper proposes a link adaptation method for Underwater Internet of Things (IoT), which reduces power consumption of sensor nodes and improves the throughput of network in underwater IoT network. Adaptive Modulation and Coding (AMC) technique is one of link adaptation methods. AMC uses the strong correlation between Signal Noise Rate (SNR) and Bit Error Rate (BER), but it is difficult to apply in underwater IoT as it is. Therefore, we propose the machine learning based AMC technique for underwater environments. The proposed Modulation Coding and Scheme (MCS) prediction model predicts transmission method to achieve target BER value in underwater channel environment. It is realistically difficult to apply the predicted transmission method in real underwater communication in reality. Thus, this paper uses the high accuracy BER prediction model to measure the performance of MCS prediction model. Consequently, the proposed AMC technique confirmed the applicability of machine learning by increase the probability of communication success.

• Journal of Convergence for Information Technology
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• v.10 no.7
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• pp.33-40
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• 2020

This work tackles the problem of conventional reinforcement learning scheme which has a relatively long training time to reduce energy consumption in underwater network. The enhanced scheme adjusts the learning range of reinforcement learning based on distance estimation. It can be reduce the scope of learning. To take account the fact that the distance estimation may not be accurate due to the underwater wireless network characteristics. this research added noise in consideration of the underwater environment. In simulation result, the proposed AQ-NAV scheme has completed learning much faster than existing method. AQ-NAV can finish the training process within less than 40 episodes. But the existing method requires more than 120 episodes. The result show that learning is possible with fewer attempts than the previous one. If AQ-NAV will be applied in Underwater Networks, It will affect energy efficiency. and It will be expected to relieved existing problem and increase network efficiency.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.10a
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• pp.402-404
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• 2013

The wireless communication channel different speed by depth of water or salt and it is influenced by multi-path according underwater. In the paper, MIMO(Multi-input-Multi-Output) system used turbo Equalizer combining Equalizer with Turbo codes for data rates by multi-path channel. we proposed and simulated that the Decision-Directed method used for phase offset. The simulation of proposed method show that the bit-error rate performance can be severely affected by phase errors.

• The Journal of the Acoustical Society of Korea
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• v.27 no.6
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• pp.279-285
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• 2008

This study includes the efficiency assessment of a multiple access protocol for UUV (Underwater unmanned vehicle) control. Most of UUVs are controled by wire now; however, wireless control is demanded because of the demerit of the wire control that limits the place and activity. This study simulates efficiency of a standardization multiple access protocol (Pure ALOHA, Slotted ALOHA, Nonpersistent CSMA, Slotted Nonpersistent ISMA) formed for the purpose of performing wireless communication controlled by the ship or communication buoy at the sea surface and by the under water communication node at the bottom in order to efficiently control the UUV's. Results show that no significant changes occur related to changing type of the mother ship and the communication node; In addition, the Non-persistent CSMA and the Slotted Non-persistent ISMA show relatively high efficiency for underwater acoustic communication.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.10
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• pp.1780-1786
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• 2008

The performance of underwater wireless communication system is influenced on channel characteristic. Especially, a delay spread cause by reverberation and multi-path happen the ISI (Inter Symbol Interference) and reduces the communication performance. In this paper, we study the application of high speed data transmission in underwater to use the OFDM (Orthogonal Frequency Division Multiplexing) technique for robust the reverberation and multi-path. we confirm the performance of communication in underwater to use the model for actually underwater channel simulation model. As a result, we acquired the BER of modulation techniques. The BER of single carrier is $2{\times}10^{-1}$ and BER of multi currier is $8{\times}10^{-2}$ in 1000m. Transmission of single carrier is 5 kbps.

• Journal of Korea Multimedia Society
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• v.13 no.11
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• pp.1657-1666
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• 2010

Underwater wireless sensor networks (UWSN) need stable efficient data transmission methods because of environmental characteristics such as limited energy resource, limited communication bandwidth, variable propagation delay and so on. In this paper, we explain an enhanced hybrid transmission method that uses a hexagon tessellation with an ideal cell size in a two-dimensional underwater wireless sensor network model (2D) that consists of fixed position sensors on the bottom of the ocean. We also propose an energy efficient sensing and communication coverage method for effective data transmission in a three-dimensional underwater wireless sensor network model (3D) that equips anchored sensors on the bottom of the ocean. Our simulation results show that proposed methods are more energy efficient than the existing methods for each model.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.23 no.4
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• pp.409-417
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• 2005

This study is aimed to develop a remote control robot-ship system using wireless communication and DGPS, which it is an automatic system for measuring exact depth and bed topography of reservoir or dam. Robot-ship is equipped with GPS and echosounder, and it is controled remotely using wireless internet. Robot-ship is consist of frame, each module and control board. Control segment is consisted of a processing system for positioning data and remote control system. A wireless communication system is developed which can communicate interactively between robot-ship and control segment, and it is developed in two channel system of RF modem and wireless internet. The robot-ship could be used acquire economically and exactly the water depth and bed topography of reservoirs, dams, rivers and so on.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.1
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• pp.45-49
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• 2011

Cooperative multihop communications support effective transmissions over underwater acoustic channels as inferior wireless channels. But the performance of cooperative multihop systems may degrade due to the lack of cooperative nodes at the initial operation time duration. At the initial time duration, the lack of cooperative nodes causes more errors, and the multihop network propagates these errors. In this paper, we apply fountain code to the cooperative multihop system at the initial time duration, and show performance improvements by simulations.

• Journal of Korea Multimedia Society
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• v.13 no.1
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• pp.122-132
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• 2010

The analysis of ocean environment offers us essential information for ocean exploration. But ocean environment has a lot of environmental variables such as the movements of nodes by an ocean current, corrosion by salt water, attenuation of radio wave, occurrences of multi-path and difficulty of sensor nodes' deployment. It is accordingly difficult and complex to gather and process the environmental information through ocean data communication due to these constraints of ocean environment unlike the terrestrial wireless networks. To overcome these problems, we organized ocean communication network for monitoring underwater environment by real experiment in Gyeongpoho similar to ocean environment. Therefore, this paper aims at overcoming major obstacles in ocean environment, effectively deploying sensor nodes for ocean environment monitoring and defining an efficient structure suitable for communication environment by the implementation of ocean environment monitoring system in Gyeongpoho.