• Journal of Advanced Marine Engineering and Technology
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• v.36 no.2
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• pp.309-314
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• 2012

In this paper, we present surface-to-underwater visible light communication systems using white LEDs. Pulse position modulation (PPM)-based analogue data communications and on-off keying-based digital data communications systems are developed. Inexpensive and commercial power-LEDs and photo-diodes are used to construct two types of systems. We report the experimental results obtained from the prototype systems to show the possibility of an optical underwater visible light transceiver as a basis for short range underwater wireless network. Their performance deteriorates more than the atmosphere's one because of attenuation and scattering of the light in water, but these results are promising for the potential to create more robust network interface that improve medium performance such as a LED modulation and a photo-detector demodulation.

• Journal of Digital Contents Society
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• v.19 no.7
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• pp.1245-1251
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• 2018

Communication skills are emphasized as one of the key competencies of the people who are living in the fourth industrial revolution era. However, it is widely believed that traditional education systems focused on individual learning do not provide sufficient communication opportunities. This paper proposes a method to activate communication using mobile app. In this study, app was developed and used by college students for two days, and then analyzed the communication-related effects through questionnaires. The results showed that both fun and communication were effective. Based on the experimental results, it is expected that the proposed app in this paper will contribute to activation of communication among people, increase of interest among members, and improvement of cooperative thinking ability.

• Journal of Navigation and Port Research
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• v.47 no.6
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• pp.419-429
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• 2023

The pinnacle of rapidly changing and advancing maritime transportation technology is expected to be the Maritime Autonomous Surface Ship (MASS). The implementation of various services within the MASS is likely to be feasible through the ship-centric network known as the S2X communication system. However, existing communication systems face issues such as service traffic saturation and failure to meet demanded functionalities, necessitating the proactive introduction of additional communication technologies. In this study, the concept of S2X communication for the MASS was redefined, deriving required functionalities and ultimately selecting frequencies suitable for utilization. Candidate frequency groups suitable for the derived communication requirements were identified, and communication frequencies prioritized for the initial application were chosen through expert consensus. It is anticipated that through further research, including experimentation to validate these frequencies, they could be utilized in implementing services for autonomous ship navigation in the future.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.10
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• pp.1773-1778
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• 2006

This paper propose the method of constructing the Digital Logic Systems based on the Improved Automatic Theorem Proving Techniques(IATP) over Finite Fields. The proposed method is as following. First, we discuss the background and the important mathematical properties for Finite Fields. Also, we discuss the concepts of the Automatic Theorem Proving Techniques(ATP) including the syntactic method and semantic method, and discuss the basic properties for the Alf. In this step, we define several definitions of the IAIP, Table Pseudo Function Tab and Equal. Next, we propose the T-gate as Building Block(BB) and describe the mathematical representation for the notation of T-gate. Then we discuss the important properties for the T-gate. Also, we propose the several relationships that are Identity relationship, Constant relationship, Tautology relationship and Mod R cyclic relationship. Then we propose Mod R negation gate and the manipulation of the don't care conditions. Finally, we propose the algorithm for the constructing the method of the digital logic systems over finite fields. The proposed method is more efficiency and regularity than my other earlier methods. Thet we prospect the future research and prospects.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1355-1359
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• 2004

The two way subscriber transmission systems have tendency to spread its carrier frequency bandwidth or information bit rate and average bit error rate according to popularization of high speed information through the digital communication system, transmission medium and the Internet. This fact is an important incentive to realize new systems. These two way subscriber transmission systems usually use same cable or same carrier frequency bandwidth for up stream channel and down stream channel. In the systems, the disturbances of noise, crosstalk or fading affect the characteristics. Specifically, these disturbances cause the decrease of information bit rate and degradation of transmission quality. This paper proposes the improved method of their degradations using the particular feature of two way subscriber transmission systems and it makes clear proposed method is effective by theoretically and some numerical examples.

• The Journal of the Korea Contents Association
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• v.7 no.8
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• pp.21-30
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• 2007

Due to the growth of embedded systems and the development of semi-conductor and storage devices, digital convergence devises is ever growing. Digital convergence devices are equipments into which various functions such as communication, playing movies and wave files and electronic dictionarys are integrated. Example are portable multimedia players(PMPs), personal digital assistants(PDAs), and smart phones. Therefore, these devices need an efficient file system which manages and controls various types of files. In designing such file systems, the size constraint for small embedded systems as well as performance and compatibility should be taken into account. In this paper, we suggest the partial buffer cache technique. Contrary to the traditional buffer cache, the partial buffer cache is used for only the FAT meta data and write-only data. Simulation results show that we could enhance the write performance more than 30% when the file size is larger than about 100 KBytes.

• Journal of Institute of Control, Robotics and Systems
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• v.6 no.8
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• pp.659-665
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• 2000

In this paper a platoon merging control system is considered as a remotely located system with state represented by a stochastic process. in the system it is common to encounter situations where a single decision maker controls a large number of subsystems and observation and control signals are sent over a communication channel with finite capacity and significant transmission delays. Unlike a classical estimation problem where the observation is a continuous process corrupted by additive noise there is a constraint that the observation must be coded and transmitted over a digital communication channel with fintie capacity. A recursive coder-estimator sequence is a state estimation scheme based on observations transmitted with finite communication capacity constraint. in this paper we introduce a stochastic model for the lead vehicle in a platoon of vehicles in a lane considering the angle between the road surface and a horizontal plane as a stochastic process. In order to merge two platoons the lead vehicle of the following platoon is controlled by a remote control station. Using the observation transmitted over communication channel the remote control station designs the feedback controller. The simulation results show that the intervehicle spacings and the deviations from the desired intervehicle spacing are well regulated.

• Nuclear Engineering and Technology
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• v.50 no.5
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• pp.780-787
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• 2018

This article presents a security module based on a field programmable gate array (FPGA) to mitigate man-in-the-middle cyber attacks. Nowadays, the FPGA is considered to be the state of the art in nuclear power plants I&C systems due to its flexibility, reconfigurability, and maintainability of the FPGA technology; it also provides acceptable solutions for embedded computing applications that require cybersecurity. The proposed FPGA-based security module is developed to mitigate information-gathering attacks, which can be made by gaining physical access to the network, e.g., a man-in-the-middle attack, using a cryptographic process to ensure data confidentiality and integrity and prevent injecting malware or malicious data into the critical digital assets of a nuclear power plant data communication system. A model-based system engineering approach is applied. System requirements analysis and enhanced function flow block diagrams are created and simulated using CORE9 to compare the performance of the current and developed systems. Hardware description language code for encryption and serial communication is developed using Vivado Design Suite 2017.2 as a programming tool to run the system synthesis and implementation for performance simulation and design verification. Simple windows are developed using Java for physical testing and communication between a personal computer and the FPGA.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.9C
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• pp.905-913
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• 2006

In the impulse radio ultra-wideband communication systems, the residual timing offset exists when the acquisition and tracking of the timing synchronization is well done. And the offset affects the performance of the system dramatically. In order to compensate the offset, we present the digital phase-locked loop that uses the reference signal in the correlation detection receiver. First, we show the degradation of BER performance that is caused by the offset, and then compensation process of the timing tracker and performance improvement. In this paper, the timing detector in the tracker operates at the sampling period of frame level uses the correlation between received and reference signal. Also, we present the performance comparison by using the computer simulation results for different Gaussian monocycle pulses.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.5
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• pp.879-886
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• 2003

Agile frequency synthesizers are the common device used for commandable, wide-band frequency hopping in frequency-hopped (FH) communications. In this paper, synthesizer phase transient effect and its compensation methods in an FH/FSK(Frequency Hopped Frequency Shift Keying) system are studied. Models for these analysis are developed and resulting performance degradations are computed. The basic PLL is difficult to implement for fast frequency hopping in narrowband radio communication systems. To solve this problem, digital frequency synthesizer/CPM (Continuous Phase Modulation)modulator is proposed. And it's performance is analyzed theoretically. The analysis show that fast frequency hopping is possible in frequency hopping system that use digital frequency synthesizer/CPM modulator.