• Journal of Advanced Marine Engineering and Technology
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• v.41 no.1
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• pp.70-75
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• 2017

In this paper, we studied the RF characteristics of a voltage-controlled artificial transmission line employing periodically arrayed diodes for application to highly miniaturized wireless communication systems on an MMIC (monolithic microwave integrated circuit). According to the results, the novel voltage-controlled artificial transmission line employing periodically arrayed diodes exhibited a short wave length, which was only 35.2% that of the conventional transmission line, owing to increasing capacitance. In addition, it's effective permittivity and effective propagation constant exhibited considerably higher values than those of the conventional transmission line. Furthermore, attenuation constant of the voltage-controlled artificial transmission line was far higher than that of the conventional transmission line. Using the closed-form equation, we theoretically analyzed the equivalent circuit of the voltage-controlled artificial transmission line.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.4
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• pp.445-450
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• 2018

AIS is the most important navigation equipment for the identification of other ships, etc. However, the AIS overload problem has been raised recently due to an increase in AIS equipped vessels. The government is planning to introduce the wireless LTE network at 100 km offshore as part of the SMART-Navigation project. Continuous development and dissemination of the services available through such platforms will be necessary to achieve major goals such as marine accident prevention and environmental protection. In this study, we applied a WAVE communication system, which could be the basis for the development of such services. As a result, reliable data transmission was confirmed for a range of communication of approx. 5 miles, although the service was limited to 1 km in road traffic. Therefore, it is expected that WAVE communication technology will be used to prevent marine accidents through such efforts as collision avoidance and the transfer of marine safety information between ships.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.7
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• pp.3329-3350
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• 2017

Installing caching and computing facilities in mobile edge networks is a promising solution to cope with the challenging capacity and delay requirements imposed on future mobile communication systems. The problem of optimal facility placement in mobile edge networks has not been fully studied in the literature. This is a non-trivial problem because the mobile edge network has a unidirectional topology, making existing solutions inapplicable. This paper considers the problem of optimal placement of a fixed number of facilities in a mobile edge network with an arbitrary tree topology and an arbitrary demand distribution. A low-complexity sequential algorithm is proposed and proved to be convergent and optimal in some cases. The complexity of the algorithm is shown to be $O(H^2{\gamma})$, where H is the height of the tree and ${\gamma}$ is the number of facilities. Simulation results confirm that the proposed algorithm is effective in producing near-optimal solutions.

• International Journal of Advanced Culture Technology
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• v.8 no.3
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• pp.269-274
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• 2020

It has used buoy for efficient domestic farm operations and fishermen fish. Buoy uses IoT-based communication to transmit water temperature, salinity, humidity, wind speed, etc. to fishers in real time. In this paper, we utilize LoRa, which enables communication in the marine environment, to construct a network and apply it to an actual buoy for monitoring. The implemented LoRa uses the 900MHz band to configure the network. The sensor consisted of a sensor that can monitor the atmospheric environment and a sensor that can monitor the marine environment. In addition, the information received in real time will be provided to the fishing village host. The fishermen were fully aware of this and took appropriate measures to conduct sea trials.

• Journal of information and communication convergence engineering
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• v.8 no.6
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• pp.651-654
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• 2010

In this paper, we propose two power randomization schemes for the random beamforming (RBF) based MIMO systems in cellular downlink. In the proposed system, a BS randomizes not only the pre-coding matrix but also the power allocation matrix, while the conventional RBF system allocates an equal power to each transmit stream. The proposed water-filling based power randomization scheme (Scheme-I) is proper in the low SNR values and the proposed random-power based randomization scheme (Scheme-II) is proper in the high SNR values. The proposed system with the power randomization outperforms the conventional RBF system which allocates the same power for each data stream.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.11
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• pp.1421-1427
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• 2018

Due to the rapid development of Internet-of-Things technology, different types of smart sensors are now devised and deployed widely. These smart sensors are now used in animal husbandry which was traditionally managed by the experience of farmers, such that wearable sensors for livestock, and the smart farm which is equipped with multiple sensors are utilized to increase the efficiency of livestock management. Herein, we consider a scheme in which the body temperature and the level of activity are measured by smart sensor which is attached to the neck of dairy cattle and the health condition is monitored based on collected data. Especially, we find that the estrous of dairy cattle which is one of most important metric in milk production, can be predicted with high precision using various machine learning techniques. By utilizing the proposed prediction scheme, estrous of cattle can be detected immediately and this can improve the efficiency of cattle management.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.11
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• pp.1201-1208
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• 2014

As the wireless communication technologies are being studied for application to marine communication networks in a fusion of marine industries and IT technology, this paper proposes a HARQ-ARQ interaction scheme for reliable communication between the smart ships. Moreover, this paper evaluates the performance of the HARQ-ARQ interaction schemes through the computer simulation. In the HARQ-ARQ interaction scheme for marine network systems, as a HARQ acknowledgement is implicitly utilized as an ARQ acknowledgement. Hence, the HARQ-ARQ interaction scheme can reduce the packet delay. However, the HARQ-ARQ interaction scheme has problems caused by the error of HARQ feedback messages. Hence, this paper considers the effect of error of HARQ feedback messages on the performance of the HARQ-ARQ interaction scheme, in marine network systems. The simulation results show that the HARQ-ARQ interaction scheme can improve the delay performance of the ships in the marine network systems.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.3
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• pp.256-265
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• 2017

In this paper, an ascheme is proposed for multiuser underwater acoustic communication by using the multi-chirp rate signals. It differs from the well known TDMA (Time Division Multiple Access), FDMA (Frequency Division Multiple Access) or CDMA (Code Division Multiple Access), by assigning each users with different chirp-rate carriers instead of the time, frequency or PN code. Multi-chirp rate signals can be separated from each other by FrFT (Fractional Fourier Transform), which can be regarded as the chirp-based decomposing, and superior to the match filter in the underwater acoustic channel. VTRM (Virtual Time Reverse Mirror) is applied into the system to alleviate the ISI caused by the multipatch and make the equalization more simple. Results of computer simulations and pool experiments prove that the proposed multiuser underwater acoustic communication based on the multi-chirp rate exhibit well performance. Outfield experments carrie out in Xiamen Port show that using about 10 kHz bandwidth, four users could communicate at the same time with 425 bps with low BER and can match the UAC application.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.8
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• pp.2736-2750
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• 2022

As demands for the maritime communications increase, a variety of functions and information are required to exchange via elements of maritime systems, which leads communication traffic increases in maritime frequency bands, especially in VHF (Very High Frequency) band. Thus, effective resource management is crucial to the future maritime communication systems not only to the typical terrestrial communication systems. VHF data exchange system (VDES) enables to utilize more flexible configuration according to the communication condition. This paper focuses on the VDES communication system among VDES terminals such as shore stations, ship stations and aids to navigation (AtoN) to address efficient resource allocation. We propose a resource management method considering a MIMO (Multiple Input Multiple Output) technique in VDES, which has been widely used for modern terrestrial wireless networks but not for marine environments by scheduling the essential communication resources. We introduce the general channel model in marine environment and give two metrics, spectral and the energy efficiencies to examine our resource scheduling algorithm. Based on the simulation results and analysis, the proposed method provides a possibility to enhance spectral and energy efficiencies. Additionally, we present a trade-off relationship between spectral and energy efficiencies. Furthermore, we examine the resource efficiencies related to the imperfect channel estimation.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2017.11a
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• pp.34-35
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• 2017

Under the STCW Convention, marine engineers are required to have a satisfactory level of maritime English proficiency so that they can successfully perform their duties on board or maintain and operate the various equipment and facilities installed in the ship. More specifically, the importance of the engineers' written communication skills has been highlighted since their documents (for instance, post-work records, legal, and/or internal reports) have a significant legal impact in the event of a marine casualty or maritime crime. To suggest the necessity of developing standard engineering logbook phrases (SELP), therefore, this paper will closely analyse three-month authentic marine engineers' work records written by Korean officers. From the analysis, the problems and errors in the logbook will be analysed, and considerations to be taken into account in the development of SELP will be illustrated. Finally, the future actions for this standardised written communication for the logbook entry will be sought.