• Journal of Internet of Things and Convergence
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• v.8 no.4
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• pp.9-15
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• 2022

NAND flash memory is used as a medium for various storage devices due to its high data processing speed with low power consumption. However, since the read processing speed of data is about 10 times faster than the write processing speed, various studies are being conducted to improve the speed difference. In particular, flash dedicated buffer management policies have been studied to improve write speed. However, SSD(solid state disks), which has recently been used for various purposes, is more vulnerable to read performance than write performance. In this paper, we find out why read performance is slower than write performance in SSD composed of NAND flash memory and study buffer management policies to improve it. The buffer management policy proposed in this paper proposes a method of improving the speed of a flash-based storage device by analyzing the pattern of read data and applying a policy of pre-reading data to be requested in the future from NAND flash memory. It also proves the effectiveness of the read-ahead policy through simulation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.05a
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• pp.82-84
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• 2022

In recent years, research has been actively conducted to solve overhead problems caused by the increase in the number of IoT devices. MQTT, one of the IoT lightweight protocols for resolving performance degradation in IoT environments, is standardized to enable efficient operation in many-to-many communication environments, but there is a security vulnerability as it does not provide encryption by default. Although TLS communication technology can be applied to solve these problems, it is difficult to meet IoT's lightweight power-saving requirements. This paper introduces the latest MQTT communication encryption trends and analyzes IoT applicability by comparing TLS encryption and payload encryption methods.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.3
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• pp.397-404
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• 2023

This paper designs a wind turbine test site based on international regulations for the certification of wind turbine prototypes. The maximum height of the meteorological mast installed at the test site is 140m, and power facilities capable of testing up to three wind turbines of 5MW or more are installed. The weather resources measured at the mast can be recorded and analyzed using a monitoring system. Wind turbine manufacturers can use this test site during the certification period, and the installed wind turbines can be used for continuous power generation projects. Therefore, this test site can provide fundamental data for measuring the long-term performance and durability of wind turbines, which can be used to improve models or develop new wind turbines.

• Journal of IKEEE
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• v.26 no.1
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• pp.1-9
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• 2022

In order to secure the reliability of the power system and to increase the penetration level of distributed energy resources (DERs), requirements such as IEEE 1547 have been revised to strengthen the grid connection standards for DER. This paper proposes a control scheme for smart inverter functions based on IEEE 1547-2018 that satisfy these standards, and introduces a power HILS-based test platform built for verification of smart inverter. Among the smart inverter functions, Volt-var and Frequency-watt allow the curve to be set from the upper level to comply with the interoperability and operation time of enable signals for each function are controlled by references from the upper level. According to the requirement, Volt-var and Frequency-watt are performed via power HILS platform and verified through the measurement results that all of the specified type tests were satisfied.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.6
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• pp.107-112
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• 2022

In an embedded system such as a drone, it is difficult to store, transfer and analyze the entire hyper-spectral image to a server in real time because it takes a lot of power and time. Therefore, the hyper-spectral image data is transmitted to the server through dimension reduction or compression pre-processing. Feature selection method are used to send only the bands for analysis purpose, and these algorithms usually take a lot of processing time depending on the size of the image, even though the efficiency is high. In this paper, by improving the temporal disadvantage of the band selection algorithm, the time taken 24 hours was reduced to around 60-180 seconds based on the 40000*682 image resolution of 8GB data, and the use of 7.6GB RAM was significantly reduced to 2.3GB using 45 out of 150 bands. However, in terms of pixel classification performance, more than 98% of analysis results were derived similarly to the previous one.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.12
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• pp.1855-1862
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• 2022

Various indoor location-based services can be provided through indoor presence determination and indoor positioning technology using Beacon. However, since the BLE signal advertised by the beacon has an unstable RSSI due to problems such as multi-path fading, it is difficult to guarantee the accuracy of indoor presence determination. In this paper, data were collected while the classroom door was open to ensure accuracy in various situations. Based on the collected data, we propose an indoor presence determination method considering the characteristics of the signal. The proposed method uses support vector machine, showed about 10% accuracy improvement compared to the results using raw RSSI only. This method has the advantage of being able to accurately determine indoor presence with only one receiver. It is expected that the proposed method can implement a low-cost system for determining indoor presence with high accuracy.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.05a
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• pp.519-521
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• 2022

As appearance of diverse electric power supplies and fuel cells have been emerging, UAVs have capacity to prolong their flight missions. Nowadays, the rotary based UAVs that are commonly distributed on the open market, adapt rechargeable batteries and have around 50 centimeters in width and generally within 30 minutes in hovering flight capacities. UAV's flight time highly depends on the capacity and the weight of its batteries. To cope with the flight time, recharging methods are also being researched. their researches are mainly divided into coupled and decoupled in manner. In this article, we propose the method to refine the position more effectivly and precisely adapting QR Code and 3-D position estimation so that UAVs enable to land on the recharging system successfully.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2022.06a
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• pp.339-343
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• 2022

In this study, a method for simplifying the structure of the VDES RF receiver, and the gain control method of the receiver to comply with the international standard in this structure was described. The input level of the wanted signal and unwanted signal to the receiver was defined, and when the two signals were input, the saturation state at the ADC was checked at the receiver output. As a result of the simulation by the circuit simulator, it was satisfied that the output power of the receiver was in the SFDR region of ADC with respect to the adjacent channel interference ratio, intermodulation, and blocking level. Through this study, it was found that the structure of th proposed RF receiver conforms to the international standard.

• Journal of Software Assessment and Valuation
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• v.15 no.1
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• pp.71-78
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• 2019

Lasers for optical broadband communication systems should have excellent frequency selectivity and modal stability. DFB lasers have low lasing frequency shift during high speed current modulation. In this paper, we have developed a simulation software and analysed beam profiles of a lasing mode in longitudinal direction of an 1.55um DFB laser with two mirrors and without anti-reflection coatings, that have both an index- and gain-gratings. As the phases of the index and gain gratings on the mirror faces are varied, the beam profiles |R(z)| and |S(z)| of the lasing mode with the emitted power ratio P_l/p_r are analysed and examined. In order to reduce the threshold current of a lasing mode and enhance the frequency stability, κL should be greater than 8, regardless of the grating phases on the mirror faces.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.1
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• pp.101-105
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• 2024

4H-SiC power metal-oxide-semiconductor field effect transistors (MOSFETs) have been developed to achieve lower specific-on-resistance (R_on,sp), and the gate oxides have been thermally grown. The poor channel mobility resulting from the high interface trap density (D_it) at the SiO₂/4H-SiC interface significantly affects the higher switching loss of the power device. Therefore, the development of novel fabrication processes to enhance the quality of the SiO₂/4H-SiC interface is required. In this paper, NO post-oxidation annealing (POA) by using the conditions of N₂ diluted NO at a high temperature (1,300℃) is proposed to reduce the high interface trap density resulting from thermal oxidation. The NO POA is carried out in various NO ambient (0, 10, 50, and 100% NO mixed with 100, 90, 50, and 0% of high purity N₂ gas to achieve the optimized condition while maintaining a high temperature (1,300℃). To confirm the optimized condition of the NO POA, measuring capacitance-voltage (C-V) and current-voltage (I-V), and time-of-flight secondary-ion mass spectrometry (ToF-SIMS) are employed. It is confirmed that the POA condition of 50% NO at 1,300℃ facilitates the equilibrium state of both the oxidation and nitridation at the SiO₂/4H-SiC interface, thereby reducing the D_it.