• Proceedings of the Korea Society for Industrial Systems Conference
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• 2006.05a
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• pp.143-147
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• 2006

Wireless sensor networks(WSN) technology has various applications such as surveillance and information gathering in the uncontrollable area of human. One of major issues in WSN is the research for reducing the energy consumption and reliability of data. A system with forward error correction(FEC) can provide an objective reliability while using less transmission power than a system without FEC. In this paper, we propose to use LDPC codes of various code rate(0.53, 0.81, 0.91) for FEC for WSN. Also, we considered node-to-node interference in addition to AWGN channel. The proposed system has not only high reliable data transmission at low SNR, but also reduced transmission power usage.

• Journal of information and communication convergence engineering
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• v.6 no.2
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• pp.158-163
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• 2008

The MB-OFDM based UWB communication system is a personal area network specification aiming to provide 480Mbps peak data rate over 528 MHz spectrum. As the corresponding baseband modem operates at high clock rate, its complexity should be optimized for low power consumption. A set of modem design parameters is suggested including the AD bit width, the clipping level and the quantization level at the Viterbi decoder input as well as the trace-back depth of the Viterbi decoder. The data throughput is used to evaluate the performance of the receiver and a recommended set of design parameter values is presented to aid efficient modem implementation.

• Journal of information and communication convergence engineering
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• v.10 no.2
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• pp.117-122
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• 2012

We propose a hybrid multiple access (HMA) for uplink orthogonal frequency division multiple access (OFDMA) systems, which combines two resource sharing schemes: a scheduling-based resource allocation (SBRA) scheme and a contentionbased resource allocation (CBRA) scheme. The SBRA scheme is appropriate for non-real time high data rate traffic, and, CBRA is appropriate for near-real time low/medium data rate traffic. Thus, the proposed HMA scheme supports various types of traffic. As a CBRA scheme, our proposed random frequency hopping (RFH)-OFDMA scheme was presented. Simulation results show that the proposed HMA yields the best performance among various resource allocation schemes for uplink OFDMA systems.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.2
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• pp.194-201
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• 2015

A frequency modulated ultra-wideband (FM-UWB) transmitter with a high-robust relaxation oscillator for subcarrier generation and a dual-path Ring VCO for RF FM is proposed, featuring low power and low complexity. A prototype 3.65-4.25 GHz FM-UWB transceiver employing the presented transmitter is fabricated in $0.18{\mu}m$ CMOS for short-range wireless data transmission. Experimental results show a bit error rate (BER) of $10^{-6}$ at a data rate of 12.5 kb/s with a communication distance of 60 cm is achieved and the power dissipation of 4.3 mW for the proposed transmitter is observed from a 1.8 V supply.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.6
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• pp.819-827
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• 2013

Compared to legacy frequency hopping communications, future radio communications are required the secure and high data rate, ad-hoc network communication. In this paper, we have designed the network communication structure on the frequency hopping mode, and analyzed the performance of synchronization on the frequency hopping network radio systems. The design results are shown the initial sync. phase of approximately 9 hops and the traffic packet phase of approximately 30 hops. Also, we have simulated the performance on the communication conditions which are carrier bandwidth of 50kHz, user data rate of 64kbps and OQPSK modulation scheme in AWGN. In the simulation, we analyzed the correlation and the performance of synchronization success. The result of simulation show 99% probability for synchronization success at $E_b/N_o$ -4dB.

• Journal of the Korea Society of Computer and Information
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• v.24 no.3
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• pp.29-39
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• 2019

In this study, we introduce a model that satisfies energy efficiency and economical efficiency by introducing and demonstrating cogeneration generators in industrial complexes using various actual data collected at the site. The proposed model is composed of three scenarios, ie, full - time operation, scenario operated according to demand, and a fusion type. In this study, the power generation profit and surplus thermal energy are measured according to the operation of the generator, and the thermal energy is traded according to the demand of the customer to calculate the profit and loss including the heat and evaluate the economic efficiency. As a result of the study, it is relatively profitable to reduce the generation of the generator under the condition that the electricity rate is low and the gas rate is high, while the basic charge is not increased. On the contrary, if the electricity rate is high and the gas rate is low, The more you start up, the more profit you can see. These results show that even a cogeneration power plant with a low economic efficiency due to a low "spark spread" has sufficient economic value if it can sell more than a certain amount of heat energy from a nearby customer and adjust the applied power through peak management.

• Journal of Korean Elementary Science Education
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• v.23 no.1
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• pp.27-36
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• 2004

This paper aims to examine how well university students, who are going to be primary school teachers, understand the International System of Units (SI), focusing on seven basic units such as 'm', '㎏', '㏖', 'A', 'K', 's', 'cd'. This study specifically investigates whether the students know the seven units and understand their uses and how they read and learn them. The subjects were 1030 students from the University of Education in Jinju, Geongsangnamdo. Data was collected through a questionnaire which was designed by this researcher and checked by an authority, and the frequency and percentage of reponses to each question were obtained and analysed. Findings show all the students knew very well that 'm' and '㎏' are included in the seven units, compared to the others which low percentage of the students considered as the elements. In terms of understanding of use, the units of the length 'm', the mass '㎏', and the time 's' are well understood, presumably, because they are often used in ordinary life and school, while the amount of substance '㏖', the electric current 'A', the thermodynamic temperature 'K', and the luminous intensity 'cd' are not as well understood. It is probably because 'A', 'cd', and 'K' are hardly used in everyday life. With respect to reading the units, the subjects read 'm', '㎏', '㏖', and's' much better than the others. As for the source of learning them, most students answered they learned them in schools, which implies school education is very important. From these results it is concluded that school education should be accompanied with use in everyday life for understanding and using the units. SI Base Units understanding was investigated by an academic year. According to this investigation, generally the right answer rate differed 4<2<3<1 by an academic year in order. For the Senior, Sophomore appeared the right answer rate more high. because, they learned before in deepening or elementary course on chemistry and physics related with SI Base Units. On the other hand, for the junior answered low rate by this reason that they couldn't remember about SI Base Units that learned before. For the Freshman appeared low rate by this reason that they were not learned or graduated from the department of liberal art in high school.

• Journal of Advanced Navigation Technology
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• v.6 no.1
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• pp.44-51
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• 2002

This paper describes the performance evaluation and analysis of an Orthogonal Frequency-Division Multiplexing (OFDM) system having the least Inter Symbol Interference (ISI) in a multi-path fading channel environment. Wireless Local Area Network (W-LAN) in accordance with IEEE 802.11a and IEEE 802.11b provides high-speed transmission to universities, businesses and other various places. In addition, service providers can offer a public W-LAN service on restricted areas such as a subway. The proliferation of W-LAN has led to greater W-LAN service demands, but problems are also on the rise in offering a good W-LAN service. In particular, urban areas with high radio wave interference and many buildings are vulnerable to deteriorated QoS including disconnected data and errors. For example, when high-speed data is transmitted in such areas, the relatively high frequency generates ISI between Access Points (AP) and Mobile Terminals (such as a notebook computer), leading to a frequency selective fading channel environment. Consequently, it is difficult to expect a goodW-LAN service. The simulation proves that the OFDM system enables W-LAN to implement QoS in high-speed data transmission in a multi-path fading channel environment. The enhanced OFDM performance with 52 sub-carriers is verified via data modulation methods such as BPSK, QPSK and 16QAM based on IEEE 802.11a and punched convolutional codes with code rate of 1/2 and 3/4 and constraint length of 7. Especially, the simulation finds that the OFDM system has better performance and there is no data disconnection even in a mobile environment by applying a single tap equalizer and a decision feedback equalizer to a mobile channel environment with heavy fading influence. Given the above result, the OFDM system is an ideal solution to guarantee QoS of the W-LAN service in a high-speed mobile environment.

• Journal of Mechanical Science and Technology
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• v.19 no.6
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• pp.1313-1320
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• 2005

Stenosed coronary artery may play an important role in various coronary heart diseases. However, it has not been known how much stenosed coronary artery affects coronary circulation system, quantitatively. The present study developed a mathematical model for microcirculation in the left common coronary artery (LCCA) with adopting a previously measured morphological data and mechanical properties of the coronary vessels. We examine the effect of percent diameter stenosis on blood flow rate and shear stress for two cases. Case I comprised of one-stenosed element at $10^{th}$ order ($\%$ diameter stenosis are 10, 30, and 50, respectively). Case II consisted of completely occluded element at $10^{th}$ order (number of occluded elements are 0, 1, and 2 out of 8, respectively). As the level of stenosis becomes severe, the shear stress increases significantly but the flow rate reduction was relatively small. However, for the occluded case, there was linearly proportional reduction of flow rate according to number of occluded elements. Either such high shear stress associated with coronary artery stenosis or reduced flow rate due to occlusion may cause atherosclerosis and myocardial ischemia.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.3
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• pp.209-222
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• 2014

NCW is a new operational concept for modern warfare to improve the ability to conduct combat by connecting command and control system via network. To realize NCW integrating information sharing system between multiple platforms, CDL is considered as a key component for high-speed transmission of ISR data. Accordingly, further studies to enhance the performance of CDL are being performed around the world, and our government has also developed self-reliant CDL, MPI-CDL. However, the maximum data rate and networking performance of current CDL still fall short of the objective to enable multiple systems to share the large ISR data. Therefore, in this paper, we analyze the development flow and international technical trends of CDL, and present an approach for enhancing data rate and networking capacity of the next generation CDL.