• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.6 no.3
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• pp.15-23
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• 1995

The antenna height of the mobile communications lower than its typical surroundings causes multipath fading usually resulting in fast fluctuations of both signal strength and wave length in mobile radio communications. Therefore, there have been developed and used various wave be- havior prediction models, in some other foreign countries, based on the measurement data rather than on theoretical derivation. The main purpose of this paper is to examine the wave propagation characteristics particularly in Korean terrain with the measurements made in four types of different areas - a large city area, a small city area, a flat terrain area, and a mountain area. Those areas have been classified according to the terrain characteristics with which the particular area contains, such as scale and number of buildings, highways, trees, and so on. With the measured data of the field strength in the frequency band of pager system obtained from those four different areas, we compared the calculated ones from both Hata's and TIREM prediction models which are often applied in Korea.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.5
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• pp.921-927
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• 2006

The current DGPS technique is many problems that is permission of radio station using RF Wireless Modem, that is influence of geographic obstacle using radio wave, that is frequency interference, that is finiteness of frequency resources. In this paper, we are solved many elements, IM(Interface Module) replaces RF Wireless Modem, we suggest transmission technique of correction message using mobile phone, we researched Interface Module development which is linkage of DGPS receiver and mobile phone. IM can transmit correction message passing RS-232 port and modem communication control. IM of base station is initialized RS-232 port and modem to move station for correction message transmission, IM waited response mode. IM of move station is initialized RS-232 port and modem, IM requests hand shaking to base station, completed connection establishment. Users are worked Differential surveying using receiving correction message between mobile phones.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.4
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• pp.453-461
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• 2011

In order to use more efficiently limited frequency resources at the broadcasting band and to eliminate blanket area of the terrestrial broadcasting and to improve broadcasting quality. The importance of repeaters has increasing continuously. However, in case of T-DMB digital on channel repeater in OFDM systems, some of the signal radiated feedback again at the receiver antenna. So it generates feedback signal interference in repeater system. Also phase noise increases ICI(Inter Carrier Interference). It affects seriously the frequency domain equalizer. In this paper, we remove the feedback signal interference by LMS with correlation. Also we propose an effective equalizer algorithm that can remove ICI caused by phase noise and the power amplifier's back-off. In this simulation results, this system is satisfied the performance of BER=$10^{-4}$ at less than SNR=14 dB after compensation of phase noise.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.05a
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• pp.197-200
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• 2002

The current Inn technique is many problems that is permission of radio station using RF Wireless Modem, that is influence of geographic obstacle using radio wave, that is frequency interference, that is finiteness of frequency resources. In this paper, we are solved many elements, IM replaces RF Wireless Modem, we suggest transmission technique of correction message using mobile phone, we researched Interface Module development which is linkage of DGPS receiver and mobile phone. IM can transmit correction message passing RS-232 port and modem communication control. IM of base station is initialized RS-232 port and modem to move station for correction message transmission, IM waited response mode. IM of move station is initialized RS-232 port and modem, IM requests hand shaking to base station, completed connection establishment. Users are worked Differential surveying using receiving correction message between mobile phones.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.3
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• pp.93-98
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• 2005

STSAT-2 will be launched on December 2007 by the first Korean launch vehicle KSLV-1, and its one of the main instruments is DREAM (Dual Channel Radio Frequency and Environment Atmosphere Monitoring) which detects a signal for atmosphere from the Earth by using micro-wave signal. The STSAT-2 has many units for technology demonstration such as FDSS (Fine Digital Sun Sensor) and DHST (Dual Head Star Tracker) including PPT (Pulsed Plasma Thruster) for attitude control and momentum dumping in the space. In this paper, the power budget analysis for STSAT-2 will be studied and provided for supporting the whole mission life time during the mission of its spacecraft.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.8
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• pp.1052-1057
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• 2020

With the development of new ICT technology, smart keys for vehicles are terminals with ICT technology. Therefore, when the vehicle and the smart key communicate with RF, a cyber hacking attack is possible. Cyber-attacks on smart keys can pose a threat to vehicle theft and vehicle control. Therefore, it is necessary to study hacking attacks and vulnerabilities of smart keys for autonomous vehicles. In this paper, we analyze the cyber attack case of RF communication for vehicles and smart keys. In addition, a real RF cyber attack on the smart key is performed, and the vulnerability of radio wave replication in the same frequency band is found. In this paper, we analyze the vulnerability of RF communication between vehicles and smart keys, and propose a countermeasure against cyber security. In the future, plans to strengthen cyber attacks and security through the popularization of autonomous vehicles will become basic data to protect human and vehicle safety.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.422-428
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• 2023

Ultrafast ultrasound imaging has been applied to various imaging approaches, including shear wave elastography, ultrafast Doppler, and super-resolution imaging. However, these methods are still challenging in real-time implementation for three Dimension (3D) or portable applications because of their massive data rate required. In this paper, we proposed an adaptive quantization method that effectively reduces the data rate of large Radio Frequency (RF) data. In soft tissue, ultrasound backscatter signals require a high dynamic range, and thus typical quantization used in the current systems uses the quantization level of 10 bits to 14 bits. To alleviate the quantization level to expand the application of ultrafast ultrasound imaging, this study proposed a depth-sectional quantization approach that reduces the quantization errors. For quantitative evaluation, Field II simulations, phantom experiments, and in vivo imaging were conducted and CNR, spatial resolution, and SSIM values were compared with the proposed method and fixed quantization method. We demonstrated that our proposed method is capable of effectively reducing the quantization level down to 3-bit while minimizing the image quality degradation.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.146-147
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• 2011

Processing a large area substrate for liquid crystal display (LCD) or solar panel applications in a capacitively coupled plasma (CCP) reactor is becoming increasingly challenging because of the size of the substrate size is no longer negligible compared to the wavelength of the applied radio frequency (RF) power. The situation is even worse when the driving frequency is increased to the Very High Frequency (VHF) range. When the substrate size is still smaller than 1/8 of the wavelength, one can obtain reasonably uniform process results by utilizing with methods such as tailoring the precursor gas distribution by adjustingthrough shower head hole distribution or hole size modification, locally adjusting the distance between the substrate and the electrode, and shaping shower head holes to modulate the hollow cathode effect modifying theand plasma density distribution by shaping shower head holes to adjust the follow cathode effect. At higher frequencies, such as 40 MHz for Gen 8.5 (2.2 m${\times}$2.6 m substrate), these methods are not effective, because the substrate is large enough that first node of the standing wave appears within the substrate. In such a case, the plasma discharge cannot be sustained at the node and results in an extremely non-uniform process. At Applied Materials, we have studied several methods of modifying the standing wave pattern to adjusting improve process non-uniformity for a Gen 8.5 size CCP reactor operating in the VHF range. First, we used magnetic materials (ferrite) to modify wave propagation. We placed ferrite blocks along two opposing edges of the powered electrode. This changes the boundary condition for electro-magnetic waves, and as a result, the standing wave pattern is significantly stretched towards the ferrite lined edges. In conjunction with a phase modulation technique, we have seen improvement in process uniformity. Another method involves feeding 40 MHz from four feed points near the four corners of the electrode. The phase between each feed points are dynamically adjusted to modify the resulting interference pattern, which in turn modulate the plasma distribution in time and affect the process uniformity. We achieved process uniformity of <20% with this method. A third method involves using two frequencies. In this case 40 MHz is used in a supplementary manner to improve the performance of 13 MHz process. Even at 13 MHz, the RF electric field falls off around the corners and edges on a Gen 8.5 substrate. Although, the conventional methods mentioned above improve the uniformity, they have limitations, and they cannot compensate especially as the applied power is increased, which causes the wavelength becomes shorter. 40 MHz is used to overcome such limitations. 13 MHz is applied at the center, and 40 MHz at the four corners. By modulating the interference between the signals from the four feed points, we found that 40 MHz power is preferentially channeled towards the edges and corners. We will discuss an innovative method of controlling 40 MHz to achieve this effect.

• Journal of Mechanical Science and Technology
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• v.17 no.6
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• pp.860-869
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• 2003

Dynamic characteristics of a catenary that supplies electrical power to high-speed railway is investigated. The catenary is a slender structure composed of repeating spans. Each span is in turn composed of the contact and messenger wires connected by the hangers in regular intervals. A finite element based dynamic model is developed, and numerical simulations are performed to determine the dynamic characteristics of the catenary The influence of the structural parameters on the response characteristics is investigated. The structural parameters considered include tension on the contact and messenger wires, stiffness of the hangers, and the hanger and span spacing. The hanger characteristics are found to be the dominant factors that influence the overall dynamic characteristics of the catenary.

• Journal of Institute of Control, Robotics and Systems
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• v.13 no.10
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• pp.956-961
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• 2007

We propose a new distance measurement method and local positioning system for the autonomous mobile robots localization. The distance measurement method is able to measure long-range distances with a high accuracy by using ultrasonic sensors. The time of flight of the ultrasonic waves include various noises is calculated accurately by the proposed period detecting method. The proposed local positioning system is composed of four ultrasonic transmitters and one ultrasonic receiver. The ultrasonic transmitter and receiver are separated but they are synchronized by RF (Radio frequency) signal. The proposed system using ultrasonic waves is represented as USAT(Ultrasonic Satellite System). USAT is able to estimate the position using the least square estimation. The experimental results show that the proposed local positioning system enables to estimate the absolute position precisely.