• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2021.10a
• /
• pp.469-471
• /
• 2021

As wireless communication technology advances to ensure high accuracy and safety at high speeds, research and development of Visible Light Communication (VLC) technology has been accelerated as an alternative to traditional radio frequency (RF) technology. As the radio spectrum of RF communication becomes more congested and demand for bandwidth continues to increase, VLCs that can use unlicensed frequency band are proposed as a solution. However, VLC channels have broadcasting characteristics that make them easily exposed to eavesdropping and jamming attacks, and are vulnerable to MITM (Man-In-The-Middle) due to their line of sight (LOS) propagation characteristics. These attacks on VLC channels compromise the confidentiality, integrity, and availability of communications links and data, resulting in higher data retransmission rates, reducing throughput and increasing power consumption, resulting in lower data transmission efficiency. In this work, we model vulnerable VLC channels to analyze the impact of attacks and communications vulnerabilities by malicious jammers.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2021.10a
• /
• pp.606-608
• /
• 2021

Humans and various devices are interconnected using the Internet of Things and are used in various ways. In this study, a synchronization control system with remote locations was constructed using ICT, and a signal system for pedestrians was implemented using the system. PLC circuits were used to implement controllers, through which wireless control signal transmission and reception, LED lamp emission control, and power control were performed. It was confirmed that signal synchronization from the main controller to the remote sub-controller was possible by establishing a controller and pedestrian traffic light system, and lamp signal synchronization of the pedestrian traffic light system installed on both sides of the road was implemented. As a result, it was confirmed that 1:1 remote control or 1:N remote group control was possible, and this result can be used in various fields.

• Journal of Aerospace System Engineering
• /
• v.17 no.2
• /
• pp.1-8
• /
• 2023

Power transmission shafts in rotary wing aircraft use a hollow shaft to reduce weight. We can apply linear elastic fracture mechanics to predict crack propagation behavior. This paper predicted crack growth life of a hollow shaft with a circumferential through-type crack by finite element analysis. A 2D finite element model was created by applying a torsion and forming elements considering cracks. We defined the initial crack length and performed the finite element analysis by increasing the crack length to derive stress intensity factor at crack tips. We defined the length just prior to the stress intensity factor exceeding the fracture toughness as the crack limit length. We calculated the crack limit length using a handbook and numerically integrated the crack growth rate equation to derive growth life of each crack. The growth life of each crack was compared to verify the proposed finite element analysis method.

• Journal of Hydrogen and New Energy
• /
• v.34 no.5
• /
• pp.535-548
• /
• 2023

The intermittent nature of renewable energy is a challenge to overcome for safety and stable performance in water electrolysis systems linked to renewable energy. Oxygen removal using the catalyst is suitable for maintaining the oxygen concentration in hydrogen below the explosive level (4%) even in intermittent power supply. Metals such as Pd, Pt, and Ni are expected to be effective materials due to their hydrogen affinity. The oxygen removal performance was compared under high hydrogen concentration conditions by loading on γ-Al₂O₃ with high reactivity and large surface area. The characteristics of the catalyst before and after the reaction were analyzed through X-ray diffraction, transmission electron microscope, H₂-temperature programmed reduction, X-ray photoelectron spectroscope, etc. The Pd catalyst that showed the best performance was able to lower 2% oxygen to less than 5 ppm. Changes in catalyst characteristics after the reaction indicate that oxygen vacancies are related to oxygen removal performance and catalyst deactivation.

• Current Optics and Photonics
• /
• v.7 no.6
• /
• pp.738-744
• /
• 2023

Graphene-based saturable absorbers (SAs) are widely used as laser mode-lockers at various laser oscillators. In particular, transmission-type graphene-SAs with ultrabroad spectral coverage are typically manufactured on transparent substrates with low nonlinearity to minimize the effects on the oscillators. Here, we developed two types of transmitting graphene SAs based on CaF₂ and ZnSe. Using the graphene-SA based on CaF₂, a passively mode-locked mid-infrared Cr:ZnS laser delivers relatively long 540 fs pulses with a maximum output power of up to 760 mW. In the negative net cavity dispersion regime, the pulse width was not reduced further by inhomogeneous group delay dispersion (GDD) compensation. In the same laser cavity, we replaced only the graphene-SA based on CaF₂ with the SA based on ZnSe. Due to the additional self-phase modulation effect induced by the ZnSe substrate with high nonlinearity, the stably mode-locked Cr:ZnS laser produced Fourier transform-limited ~130 fs near 2,340 nm. In the stable single-pulse operation regime, average output powers up to 635 mW at 234 MHz repetition rates were achieved. To our knowledge, this is the first attempt to achieve shorter pulse widths from a polycrystalline Cr:ZnS laser by utilizing the graphene deposited on the substrate with high nonlinearity.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.34 no.3
• /
• pp.379-392
• /
• 2024

With the rapid increase in data, saving storage space and improving the efficiency of data transmission have become critical issues, making the research on the efficiency of data compression technologies increasingly important. Lossless algorithms can precisely restore original data but have limited compression ratios, whereas lossy algorithms provide higher compression rates at the expense of some data loss. There has been active research in data compression using deep learning-based algorithms, especially the autoencoder model. This study proposes a new side-channel analysis data compressor utilizing autoencoders. This compressor achieves higher compression rates than Deflate while maintaining the characteristics of side-channel data. The encoder, using locally connected layers, effectively preserves the temporal characteristics of side-channel data, and the decoder maintains fast decompression times with a multi-layer perceptron. Through correlation power analysis, the proposed compressor has been proven to compress data without losing the characteristics of side-channel data.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
• /
• v.17 no.1
• /
• pp.25-30
• /
• 2024

Smart City, a key application area of the AIoT (Artificial Intelligence of Things), provides various services in safety, security, and healthcare sectors through location tracking and location-based services. an IPS (Indoor Positioning System) is required to implement location-based services, and wireless communication technologies such as WiFi, UWB (Ultra-wideband), and BLE (Bluetooth Low Energy) are being applied. BLE, which enables data transmission and reception with low power consumption, can be applied to various IoT devices such as sensors and beacons at a low cost, making it one of the most suitable wireless communication technologies for indoor positioning. BLE utilizes the RSSI (Received Signal Strength Indicator) to estimate the distance, but due to the influence of multipath fading, which causes variations in signal strength, it results in an error of several meters. In this paper, we conducted research on a path loss model that can be applied to BLE IPS for proximity services, and confirmed that optimizing the free space propagation loss coefficient can reduce the distance error between the Tx and Rx devices.

• The Journal of the Convergence on Culture Technology
• /
• v.10 no.2
• /
• pp.525-530
• /
• 2024

The need for an environmental monitoring system that obtains and provides environmental information in real time is increasing. In particular, in the case of water quality management in public waters, regular management must be conducted through manual and automatic measurement by law, and air pollution also requires regular measurement and management to reduce fine dust and exhaust gas in connection with the realization of carbon neutrality. In this study, we implemented a system that can measure and monitor water pollution and air pollution information in real time. A hovercraft capable of moving on land and water simultaneously was used as a measurement tool. Water quality measurement and air pollution measurement sensors were installed on the hovercraft body, and a communication module was installed to transmit the information to the monitoring system in real time. The structure of a hovercraft for environmental measurement was designed, and a LoRa module capable of low-power, long-distance communication was applied as a real-time information transmission communication module. The operational performance of the proposed system was confirmed through actual hardware implementation.

• Smart Media Journal
• /
• v.13 no.1
• /
• pp.52-59
• /
• 2024

This paper proposes a plan to improve the reception radio environment of the mobile terminal and maintain a constant reception electric field by using small cells in a small closed environment. In order to configure an efficient communication infrastructure for small cells, both ends of wireless transmission and reception of an Ethernet-based wireless video recording system are connected using an L2 switch. The small cell connected to the receiving side L2 switch shares the wireless network section of the wireless video recording system and connects to the transmitting side L2 switch. After that, when it is normally linked to FMS, a management system for small cells, through the Internet network, the output of small cells is checked. In order to verify the results, a proposed network is formed on the elevator inside the building with a poor radio wave environment, and the radio wave environment is measured before and after the small cell application in the section where the elevator operates. As a result, the main parameters of the radio wave environment in all sections of the elevator are improved, as well as a constant receiving electric field strength within the moving elevator.

• Journal of Space Technology and Applications
• /
• v.4 no.2
• /
• pp.87-104
• /
• 2024

CubeSats are being utilized in various fields such as Earth observation, space exploration, and verification of space science and technology due to their low cost, short development period, enhanced mission-oriented performance, and ability to perform various missions through constellation and formation flights. Recently, as the availability of CubeSats has increased and their application areas have expanded, the demand for high-speed transmission of large amounts of data obtained by CubeSats has increased unprecedentedly. Laser-based free space optical communication technology is capable of transmitting large amounts of data at high speeds compared to the existing radio communication methods, and provides various advantages such as use of unlicensed spectrum, low cost, low power, high security characteristics, and of use a small communication platform. For this reason, it is suitable as a high-performance communication technology to support CubeSat missions. In this paper, we will present the core components and characteristics of CubeSat-based space laser communication system, and recent research trends, as well as representative technology development results.