• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.5
• /
• pp.550-558
• /
• 2019

As the scale of the Internet of Things (IoT) environment grows and develops day by day, the information collected and shared through IoT devices becomes increasingly diverse and more common. However, because IoT devices have limitations on computing power and a low power capacity due to their miniaturized size, it is difficult to apply security technologies like encryption and authentication that have been directly applied in the previous Internet environment, making the IoT vulnerable to security threats. Because of this weakness, important information that needs to be delivered safely and accurately is exposed to the threat of malicious exploitation, such as data forgery, data leakage, and infringement of personal information. In order to overcome this threat, various security studies are being actively conducted to compensate for the weaknesses in IoT environment devices. In particular, since various devices interact, and share and communicate information collected in the IoT environment, each device should be able to communicate with reliability. With regard to this, various studies have been carried out on techniques for device authentication. This study examines the limitations and problems of the authentication techniques that have been studied thus far, and proposes technologies that can certify IoT devices for safe communication between reliable devices in the Internet environment.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.14 no.2
• /
• pp.309-316
• /
• 2019

In this paper, a low-jitter delay-locked loop that compensates for local clock skew is presented. The proposed DLL consists of a phase splitter, a phase detector(PD), a charge pump, a bias generator, a voltage-controlled delay line(VCDL), and a level converter. The VCDL uses self-biased delay cells using current mode logic(CML) to have insensitive characteristics to temperature and supply noises. The phase splitter generates two reference clocks which are used as the differential inputs of the VCDL. The PD uses the only single clock from the phase splitter because the PD in the proposed circuit uses CMOS logic that consumes less power compared to CML. Therefore, the output of the VCDL is also converted to the rail-to-rail signal by the level converter for the PD as well as the local clock distribution circuit. The proposed circuit has been designed with a $0.13-{\mu}m$ CMOS process. A global CLK with a frequency of 1-GHz is externally applied to the circuit. As a result, after about 19 cycles, the proposed DLL is locked at a point that the control voltage is 597.83mV with the jitter of 1.05ps.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.16 no.3
• /
• pp.485-492
• /
• 2021

The wind turbines with a rated capacity of 50kW or less are generally considered as small class. Small wind turbines are an attractive alternative for off-grid power system and electric home appliances, both as stand-alone application and in combination with other energy technologies such as energy storage system, photovoltaic, small hydro or diesel engines. The research objective is to develop the 50kW scale wind turbine blades in ways that resemble as closely as possible with the construction and methods of utility scale turbine blade manufacturing. The mold process based on wooden form is employed to create a hollow, multi-piece, lightweight design using carbon fiber and fiberglass with an epoxy based resin. A hand layup prototyping method is developed using high density foam molds that allows short cycle time between design iterations of aerodynamic platforms. A production process of five blades is manufactured and key components of the blade are tested by IEC 61400-23 to verify the appropriateness of the design. Also, wind system with developed blades is tested by IEC 61400-12 to verify the performance characteristics. The results of blade and turbine system test showed the available design conditions for commercial operation.

• The Journal of the Convergence on Culture Technology
• /
• v.7 no.1
• /
• pp.654-661
• /
• 2021

Air pollution caused by industrial development has become a level that can seriously threaten human health. In general, indoor air pollution is considered to be lower than outdoors, but modern people live indoors most of the time, thus it is essential to keep the indoor air quality comfortable in order to take care of one's own health and improve the quality of life. Therefore, the development of an indoor environment management platform using Internet of Things and data processing technology, which is currently drawing attention, is considered a very meaningful study. In this paper, we designed an IoT-based management platform that can remotely monitor and control indoor environments. In addition, the functions of the IoT terminal, gateway, and data server constituting the platform were implemented using open source and open libraries, and all functional operations were also verified. In particular, the IoT terminal and the gateway in this paper exchange data using BLE communication, so they can operate with relatively low power and since the gateway uses the BLE Advertising mode, it has the advantage of automatically recognizing IoT terminals that have not been previously configured.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
• /
• v.14 no.1
• /
• pp.56-69
• /
• 2021

In this paper, the PV system with a link to the commercial system needs some advantages like small capacity, high power factor, high reliability, low harmonic output, maximum power operation of solar cell, and low cost, etc. as well as the properties of inverter. To transfer the PV energy of photovoltaic power generation system to the system and load, it requires PCS in both directions. The purpose of this paper is to confirm the stable power supply through the load leveling by presenting the PCS considering ESS of photovoltaic power generation. In order to achieve these purpose, 5 step process of operation mode algorithm were used according to the solar insolation amount and load capacity and the controller for charging/ discharging control was designed. For bidirectional and effective energy transfer, the bidirectional converter and battery at DC-link stage were connected and the DC-link voltage and inverter output voltage through the interactive inverter were controlled. In order to prove the validity of the suggested system, the simulation using PSIM was performed and were reviewed for its validity and stability. The 3[kW] PCS was manufactured and its test was conducted in order to check this situation. In addition, the system characteristics suggested through the test results was verified and the PCS system presented in this study was excellent and stronger than that of before system.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.27 no.1
• /
• pp.47-52
• /
• 2021

Recently, the share of wind power in energy markets has sharply increased with the active development of renewable energy internationally. In particular, large-scale wind farms are being developed far from the coast to make use of abundant wind resources and to reduce noise pollution. In addition to the electromagnetic interference (EMI) caused by offshore wind farms to coastal or air surveillance radars, it is necessary to investigate the EMI on global maritime distress and safety system (GMDSS) communications between ship and coastal stations. For this purpose, this study investigates whether the transmitted field of MF/HF band from a ship would be subject to interference or attenuation below the threshold at a coastal receiver. First, using geographic information system digital maps and 3D CAD models of wind turbines, the area of interest is electromagnetically modeled with patch models. Although high frequency analysis methods like Physical Optics are appropriate to analyze wide areas compared to its wavelength, the high frequency analysis method is first verified with an accurate low frequency analysis method by simplifying the surrounding area and turbines. As a result, the received wave power is almost the same regardless of whether the wind farms are located between ships and coastal stations. From this result, although wind turbines are large structures, the size is only a few wavelengths, so it does not interfere with the electric field of MF/HF distress communications.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.17 no.3
• /
• pp.537-542
• /
• 2022

There is a limit to the current indoor air quality (IAQ) monitoring method using fixed sensors and devices. A mobile robot for IAQ monitoring was developed by mounting IAQ monitoring sensors on a small multi-legged robot to minimize vibration and protect the sensors from vibration while robot moves. The developed mobile robot used a simple gait mechanism to enable the robot to move forward, backward, and turns only with the combination of forward and reverse rotation of the two DC motors. Due to the simple gait mechanism, not only IAQ data measurements but also gait motion control were processed using a single Arduino board. Because the mobile robot has small number of electronic components and low power consumption, a relatively low-capacity battery was mounted on the robot to reduce the weight of the battery. The weight of mobile robot is 1.4kg including links, various IAQ sensors, motors, and battery. The gait and turning speed of the mobile robot was measured at 3.75 cm/sec and 14.13 rad/sec. The maximum height where the robot leg could reach was 33 mm, but the mobile robot was able to overcome the bumps up to 24 mm.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
• /
• v.15 no.5
• /
• pp.405-412
• /
• 2022

This paper studies the method of estimating power loss and classifying the factors for improving the power generation efficiency through O&M. It is installed under various climatic conditions worldwide, operational and maintenance technologies suitable for the characteristics of the installation location are required. Existing studies related to solar power generation efficiency have been actively quantifying the impact on short-term losses by environmental factors such as high temperature, dust accumulation, precipitation, humidity, and wind speed, but analysis of the overall impact from a long-term operation perspective is limited. In this study, the potential for efficiency improvement was analyzed by re-establishing a loss classification system according to the power flow of solar power to derive a comprehensive efficiency model for long-term operation and estimating power loss through a case study for each region where climate conditions are classified. As a result of the analysis, the average annual potential for improving soiling loss was 26.9%, Death Valley 7.2%, and Seoul 3.8%. Aging losses was 6.6% in the 20th year as a cumulative. The average annual potential due to temperature loss was 2.9 % for Doha, 1.9% for Death Valley, and 0.2% for Seoul.

• Journal of Appropriate Technology
• /
• v.6 no.2
• /
• pp.136-145
• /
• 2020

Agriculture is the backbone of the economy of most developing countries. In these countries, agriculture or farming is mostly done manually with little integration of machinery, intelligent systems and data monitoring. Irrigation is an essential process that directly influences crop production. The fluctuating amount of rainfall per year has led to the adoption of irrigation systems in most farms. The absence of smart sensors, monitoring methods and control, has led to low harvests and draining water sources. In this research paper, we introduce a 433 MHz Radio Frequency and 2G based Smart Irrigation Meter System and a water prepayment system for rural areas of Tanzania with no reliable internet coverage. Specifically, Ngurudoto area in Arusha region where it will be used as a case study for data collection. The proposed system is hybrid, comprising of both weather data (evapotranspiration) and soil moisture data. The architecture of the system has on-site weather measurement controllers, soil moisture sensors buried on the ground, water flow sensors, a solenoid valve, and a prepayment system. To achieve high precision in linear and nonlinear regression and to improve classification and prediction, this work cascades a Dynamic Regression Algorithm and Naïve Bayes algorithm.

• Journal of Broadcast Engineering
• /
• v.27 no.6
• /
• pp.936-939
• /
• 2022

As air combat system technologies developed in recent years, the development of air defense systems is required. In the operating concept of the anti-aircraft defense system, selecting an appropriate armament for the target is one of the system's capabilities in efficiently responding to threats using limited anti-aircraft power. Much of the flying threat identification relies on the operator's visual identification. However, there are many limitations in visually discriminating a flying object maneuvering high speed from a distance. In addition, as the demand for unmanned and intelligent weapon systems on the modern battlefield increases, it is essential to develop a technology that automatically identifies and classifies the aircraft instead of the operator's visual identification. Although some examples of weapon system identification with deep learning-based models by collecting video data for tanks and warships have been presented, aerial vehicle identification is still lacking. Therefore, in this paper, we present a model for classifying fighters, helicopters, and drones using a convolutional neural network model and analyze the performance of the presented model.