• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.12
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• pp.1093-1105
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• 2012

We propose an interference space reuse (ISR) algorithm for the MU-MIMO design in 3-cell downlink interference channels. Also, we provide a strategy for the adoption of the ISR scheme in the cellular network. In the multicell interference channels, the cell edge users may undergo severe interferences and their signals should be protected from the interferers for reliable transmissions. However, the intra cell users do not only experience small interferences but also they require small transmission power for stable communication. We provide a vector design algorithm based on ISR, where intra cell users are served through reusing the cell edge users' interference space. The performance enhancement reaches 20% compared to the fractional frequency reuse (FFR) scheme combined with IA through the scheduling between the cell edge users and the intra cell users. Also, it can be used to enhance the cell edge throughput when the quality of service (QoS) requirements of the intra cell users are fixed.

• Journal of the Korean institute of surface engineering
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• v.49 no.1
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• pp.54-61
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• 2016

Screen printing of commercially available Ag paste is the most widely used method for the front side metallization of Si solar cells. However, the metallization using Ag paste is expensive and needs high temperature annealing for reliable contact. Among many metallization schemes, Ni/Cu/Sn plating is one of the most promising methods due to low contact resistance and mass production, resulting in high efficiency and low production cost. Ni layer serves as a barrier which would prevent copper atoms from diffusion into the silicon substrate. However, Ni based schemes by electroless deposition usually have low thermal stability, and require high annealing process due to phosphorus content in the Ni based films. These problems can be resolved by adding W element in Ni-based film. In this study, Ni-W-P alloys were formed by electroless plating and properties of it such as sheet resistance, resistivity, specific contact resistivity, crystallinity, and morphology were investigated before and after annealing process by means of transmission line method (TLM), 4-point probe, X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.2
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• pp.963-969
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• 2015

Bicycle is one of the most popular mode of transport due to the increase of interest in the well-being and environment pollution. Before fabricating a continuously variable transmission that is applied to the actual bicycle, for reducing the problems in the early stage, the reliable simulation program has been applied and the financial problem can be solved. In this paper, in order to confirm the design factor, the stress analysis has been applied. In all models, each link and the joint portion are assumed to be a major design factors, and impact of each link and joints received stress during the operation and it is confirmed by using the CAE. Also, for the analysis region, the special code has been developed to calculate pulsation phenomenon through appropriate mathematical modeling.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.3
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• pp.216-220
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• 2013

The rated voltage has been rising in order to minimize the losses in power transmission. The high voltage electric machines should be minimized due to the constraints of space. Therefore, the temperature of high voltage electric apparatuses easily exceeds the temperature limits. In this paper, it is investigated that how to minimize the internal temperature rising of a high voltage switchgear by adjusting the arrangement of bus bars. High voltage switchgears consist of a circuit breaker, a CT, a PT, a earthing switches, bus bars, and so on. It is very difficult to estimate the electromagnetic properties of a high voltage switchgear due to these various environments and structures. In this paper, analyses are focused on the electromagnetic characteristics of bus bars according to the arrangement method and the enclosures to simplify the electromagnetic characteristics of a switchgear. It is found that the characteristics of electric field intensity and electromagnetic losses in bus bars are influenced by the arrangement method of bus bars. However, it is confirmed that the electromagnetic characteristics of enclosures are not affected by the arrangement of bus bars. In this paper, the arrangement methods of bus bars to minimize the electric field intensity and electromagnetic losses are suggested. It is expected that the research results are helpful to design and develop an electrically reliable high voltage switchgear.

• Journal of Advanced Navigation Technology
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• v.17 no.6
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• pp.712-719
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• 2013

This paper studies the security module for the reliable transmission of the meter reading and the control data between the remote terminals and the upper server-side in smart water grid. The proposed security module was implemented to make it attachable to the remote terminal without security function. In particular, unlike the smart grid of electric field, the low power is considered due to the use of battery power in the smart water grid, and the ARIA-GCM-128 symmetric key method is adopted taking into the account that the damp and constrictive environments by the installed meter location in the underground occur a communication obstacle on building of the large-scale network system. The encryption module of this paper was devised to ensure the safety between the reading data on the terminal and the control data from the upper server, and secure the stability of the remote meter reading system by taking protection against an arbitrary alteration or modification.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.7
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• pp.1367-1372
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• 2007

This paper suggests One-time Password key exchange authentication technique for a strong authentication based on MANET and through identify wireless environment security vulnerabilities, analyzes current authentication techniques. The suggested authentication technique consists of 3 steps: Routing, Registration, and Running. The Routing step sets a safe route using AODV protocol. The Registration and Running step apply the One-time password S/key and the DH-EKE based on the password, for source node authentication. In setting the Session key for safe packet transmission and data encryption, the suggested authentication technique encrypts message as H(pwd) verifiers, performs key exchange and utilizes One time password for the password possession verification and the efficiency enhancement. EKE sets end to end session key using the DH-EKE in which it expounds the identifier to hash function with the modula exponent. A safe session key exchange is possible through encryption of the H(pwd) verifier. The suggested authentication technique requires exponentiation and is applicable in the wireless network environment because it transmits data at a time for key sharing, which proves it is a strong and reliable authentication technique based on the complete MANET.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.05a
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• pp.313-316
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• 2009

A novel approach for electrocardiogram (ECG) analysis within a functional sensor node has been developed and evaluated. The main aim is to reduce data collision, traffic over loads and power consumption in healthcare applications of wireless sensor networks (WSN). The sensor node attached on the patient's bodysurface around the heart can perform ECG analysis based on a QRS detection algorithm to detect abnormal condition of the patient. Data transfer is activated only after detected abnormality in the ECG. This system can reduce packet loss during transmission by reducing traffic overload. In addition, it saves power supply energy leading to more reliable, cheap and user-friendly operation in the WSN based ubiquitous health monitoring.

• Smart Structures and Systems
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• v.15 no.1
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• pp.135-150
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• 2015

Large concrete structures are prone to cracks and damages over time from human usage, weathers, and other environmental attacks such as flood, earthquakes, and hurricanes. The health of the concrete structures should be monitored regularly to ensure safety. A reliable method of real time communications can facilitate more frequent structural health monitoring (SHM) updates from hard to reach positions, enabling crack detections of embedded concrete structures as they occur to avoid catastrophic failures. By implementing an unconventional mode of communication that utilizes guided stress waves traveling along the concrete structure itself, we may be able to free structural health monitoring from costly (re-)installation of communication wires. In stress-wave communications, piezoelectric transducers can act as actuators and sensors to send and receive modulated signals carrying concrete status information. The new generation of lead zirconate titanate (PZT) based smart aggregates cause multipath propagation in the homogeneous concrete channel, which presents both an opportunity and a challenge for multiple sensors communication. We propose a time reversal based pulse position modulation (TR-PPM) communication for stress wave communication within the concrete structure to combat multipath channel dispersion. Experimental results demonstrate successful transmission and recovery of TR-PPM using stress waves. Compared with PPM, we can achieve higher data rate and longer link distance via TR-PPM. Furthermore, TR-PPM remains effective under low signal-to-noise (SNR) ratio. This work also lays the foundation for implementing multiple-input multiple-output (MIMO) stress wave communication networks in concrete channels.

• 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.

• Journal of Magnetics
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• v.18 no.1
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• pp.43-49
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• 2013

A pulsed ferrite magnetic field generator (FMFG) was designed for the use in the 1000 m long through-the-earth (TTE) communication system for mining disaster situations. To miniaturize the TTE system, a ferrite core having 10,000 of permeability was used for the FMFG. Attenuation of the magnetic field intensity from the FMFG (200-turn and 0.18 m diameter) was calculated to be 89.95 dB at 1000 m depth soil having 0.1 S/m of conductivity. This attenuation was lower than 151.13 dB attenuation of 1 kHz electromagnetic wave at the same conditions. Therefore, the magnetic-field was found to be desirable as a signal carrier source for TTE communications as compared to the electromagnetic wave. The designed FMFG generates the magnetic field intensity of $1{\times}10^{-10}$ Tesla at 1000 m depth. This magnetic field is detectable by compact magnetic sensors such as flux gate or magnetic tunneling junction sensor. Therefore, the miniature FMFG TTE communication system can replace the conventional electromagnetic wave carrier type TTE system and allow reliable signal transmission between rescuer and trapped miners.