• International Commerce and Information Review
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• v.9 no.2
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• pp.103-120
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• 2007

The knowledge based economy requires more and more people to learn new knowledge and skills in a timely and effective manner. These needs and new technology such as computer and Internet are fueling a transition in e-learning. According to specialist's opinion, imagination experience studying is generalized, and learning environment that language barrier by studying, multi-language studying Machine that experience past things that disappear through simulation, and travel area, and experience future changed state disappears is forecasting to come. This is previewing finally that it may become future education that education and IT, element of entertainment is combined. Already, became story that argument for party satellite of e-Learning existence passes one season already. e-Learning is utilized already in all educations that we touch by effectiveness by corporation's competitive power improvement and implement of lifelong education in educational institutions through present e-Learning. It is obvious that when see from our viewpoint which is defining e-Learning by one industry and rear by application to education as well as one new growth power about these, e-Learning industry becomes very important means that can solve dilemma of growth real form. Only, special quality of digital industry that e-Learning is being same with other digital industry and repeat putting out a fire rapidly, and is repeating sudden change that these evolution is not gradual growth of accumulation and improvement of technology that is appearing consider need to. In the meantime, we need to observe about evolution of Information Technology. Because there is some scholars who e-Learning's concept foresees to evolve by u-Learning.(although, a person who see that these concept is not more in marketing terminology by some scholars' opinion is). This u-Learning's concept means e-Learning that take advantage of ubiquitous technology as Ubiquitous-Learning's curtailment speech. Ubiquitous, user means Information-Communication surrounding that can connect to network freely regardless of place without feeling network or computer. There is controversy about introduction time regarding these direction, but e-Learning is judged to evolve by u-Learning necessarily. Because keep in step and age that study all contents that learner wants under environment of 3A (any time, any whrer, any device) by individual order thoroughly is foreseen to come in ubiquitous learning environment that approach more festinately.

• Journal of Advanced Navigation Technology
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• v.21 no.3
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• pp.272-278
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• 2017

In order to meet performance requirements specified by the ICAO in drone operation, a system that provides augmentation information such as SBAS is needed. However, the operating range of the drone is limited in situation where the drone can not received the SBAS message continuously. In this paper, we propose a system to transmit SBAS augmentation message using a separate communication channel assuming the SBAS satellite signal to the drone has been shielded. We implemented the proposed system and verified its performance in the static environment. The DGPS positioning results showed that the accuracy difference is about 10cm, which means the accuracy performance was very similar. In addition, the protection level calculated by the system also shows the difference within 2m from the value calculated by the airborne receiver.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.5
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• pp.885-892
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• 2017

In this paper, we proposed a novel crowbar circuit for high-speed discharge charge switching to solve discharge charge-time delay of supply voltage in the conventional crowbar circuit. The proposed circuit is designed to increase the charge-speed after high-speed discharge of supply voltage, thereby reducing the time exposed to radiation damage and, the normal operation time of electronic system after passing the pulse radiation. The simulation of the discharge charge-times before the implement of the hardware is conducted using Cadence's pspice tool, and DUT (Device Under Test) board is fabricated in the device level. The comparison measurement of the crowbar circuits is performed on the satellite-electronic device for 24V. As the result, we confirmed the high-speed function of the proposed circuit by improvement of the discharge-speed 96.8% and the charge-speed 27.3% as compared with the conventional circuit.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2C
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• pp.210-218
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• 2010

In order to improve the efficiency of frequency bandwidth, various modulation methods such as QAM and PSK have been widely used, and their variation APSK(Amplitude Phase Shift Keying) type modulation methods were proposed and are being used in some satellite communication systems. In this paper, a new constellation method named as $4L^2$-APSK is proposed, which places symbol points circularly as the existing APSK constellations do, but has different number of points and different distance between adjacent points on each layer. An equation for error probability in AWGN channel is also induced for $4L^2$-APSK. In addition, a new Gaussian noise channel is proposed in which noise variances are in the amplitude and in the phase and the two are not equal, and a method of obtaining error probabilities in this channel is also suggested. The equations for error probabilities are verified by computer simulations, and error probabilities of $4L^2$-APSK and QAM are analyzed and compared in the AWGN channel and the proposed noise channel, respectively.

• Journal of the Korean Association of Geographic Information Studies
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• v.16 no.1
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• pp.36-46
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• 2013

The Geostationary Ocean Color Imager (GOCI), the first geostationary ocean color observation instrument launched in 2010 on board the Communication, Ocean, and Meteorological Satellite (COMS), has been generating the operational level 1 data. This study describes a methodology for creating the GOCI true color image and data processing software, namely the GOCI RGB maker. The algorithm uses a generic atmospheric correction and reprojection technique to produce the color composite image. Especially, the program is designed for educational purpose in a way that the region of interest and image size can be determined by the user. By distributing software to public, it would maximize the understanding and utilizing the GOCI data. Moreover, images produced from the geostationary observations are expected to be an excellent tool for monitoring environmental changes.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.5
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• pp.461-466
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• 2012

This paper describes the development and test result of X-band Transmitter flight model(FM) of STSAT-3 by satellite research center(SaTReC), KAIST. The communication sub-system of STSAT-3 is consist of two different frequency band channels. S-band frequency is used for Telemetry & Command, and X-band frequency is used for mission data. Payload observations data in Mass Memory Unit (MMU) is modulated by QPSK modulator in X-band Transmitter, and then QPSK modulation signal is transmitted to antenna through transfer switch. In this Paper, we described the results of modulation, low-pass filter design, power amp development, and switch test. The FM XTU is delivered Spacecraft Assembly, Integration and Test(AIT) level through the completion of functional Test and environmental(vibration, thermal vacuum) Test successfully.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.6
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• pp.879-888
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• 1999

A Study on the ARQ scheme of data error control is important for more reliable information transmission. Since performance difference is large by the long transmission delay time in satellite communication, the performances of SR ARQ and conventional type-I hybrid ARQ with fixed code rate are investigated by using the parameters of packet length, channel capacity, BER, and transmission delay time especially. BCH code is used in type-I hybrid ARQ for FEC method. This paper presents the throughput analyses according to such various parameters as BCH code rate, window size, data rate and round-trip delay time. Especially we derive a performance equation of type-I hybrid ARQ with the factor of the transmission delay time using the equation of SAW ARQ. Also, the performance of type-I hybrid ARQ specially considering transmission delay time is analyzed through numerical analysis and computer simulation so we can get a important characteristics variation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.8
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• pp.830-838
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• 2003

In this paper, TX/RX dual operation microstrip single antenna for satellite communication is designed, analyzed, fabricated and measured. TX/RX frequency ranges are 14.0∼l4.5 GHz, 11.7∼12.75 GHz in respectively and vertical and horizontal polarizations are used for TX and RX. This antenna uses microstrip direct feeding for RX and aperture coupled strip-line feeding for TX and accommodates stacked elements for a high directivity and wide impedance bandwidth. In an analysis of single element, FDTD and MOM was compared and FDTD analysis was more accurate because of the consideration of finite structure and imperfect two ground planes. The proposed structure facilitates generally to an extension of two dimensional array and lower an unwanted radiation by strip-line feed in TX. TX/RX 8${\times}$4 array has a return loss below -10 dB, -14 dB in TX, RX respectively and a gain ranging from 19.1∼20.7 dB in TX, 21.2∼21.8 dB in RX which has a radiation efficiency of 43∼5l %, 52∼57 %.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.4
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• pp.739-746
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• 2017

Orthogonal frequency division multiplexing(OFDM) systems have many advantages. However, OFDM systems are much affected by a nonlinear distortion because those systems have a high peak to average power ratio(PAPR) value. A selected mapping technology was suggested to reduce a PAPR value. The technology does not have data loss but receivers need side information to know modified phase sequence. Therefore, side information causes decreased a transmission efficiency. In this paper, we suggest a blind SLM receiver using a cross correlation technology. This receiver does not require side information. The proposed blind SLM receiver calculates sums of cross-correlation between transmitted pilot signals multiplied by each phase sequence and received pilot signals. So, this receiver detects side information which has a maximum sum cross-correlation value. We compared our proposed SLM receiver to a conventional blind SLM receiver through bit error rate(BER) and side information error rate(SIER) performances. Simulation results show that the proposed SLM receiver has improved BER and SIER performances than the conventional SLM receiver.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.5
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• pp.389-395
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• 2012

U-City has been promoted nation-wide by development of recent IT technology. This paper studied the concept of 3D-virtual city in order to realize the current Ubiquitous City(U-City) efficiently, and to manage all the RFID/USN monitoring data in the real U-City. 3D-Virtual City is the concept of the reproduction of real world U-City, for embodying Ubiquitous technology while using Digital map, satellite image, VRML(Virtual Reality Modeling Language). U&V-City is the four-dimensional future city that real-time wire/wireless communication network and 3D-web GIS shall be connected that massive database, intelligent service be perceived through employing EAI(External Authoring Interface) that provides HTML&JAVA, and interface for efficient removal/process of massive information/ service and also by employing GPS/LBS/Navigation in support of world-wide orientation concept, and RTLS(Real Time Location System).