• Journal of Satellite, Information and Communications
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• v.8 no.2
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• pp.74-79
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• 2013

For the purpose of drawing out a requirements (draft) for the development of low Earth orbit meteorological satellite payload, the present development situation of the foreign low Earth orbit meteorological satellite payload was analyzed, and survey and analysis on the questionnaire of the low Earth orbit meteorological satellite payload users' requirements were carried out. Through this research, some key required performance specifications (draft) were made on the basis of technological requirements such as frequency, radiation measurement, spacial, and antenna efficiency requirements, and the low Earth orbit meteorological satellite payload users' requirements.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.7
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• pp.554-559
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• 2010

In this paper, we analyzed the frequency spectrum of radiated electromagnetic pulses generated by series arc- and corona- discharges as a basic study to develop an on-line diagnostic technique for power facilities installed inside closed-switchboards. To simulate series arc and corona discharges, five types of electrode system which consists of needle and plane electrodes were arranged. The experiment was carried out in an electromagnetic shielding room, and the measurement system consists of an ultra log antenna and an EMI receiver. From the experimental results, the frequency spectrum exists in ranges from 30 MHz to 2 GHz for a series arc discharge and 30 MHz to 1.2 GHz depending on defects for a corona discharge. The peak frequency of the series arc- and corona- discharges were 100 MHz to 160 MHz and 40 MHz to 80 MHz, respectively.

• Steel and Composite Structures
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• v.36 no.1
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• pp.31-45
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• 2020

The purpose of this study is to develop an effective iterative two-stage method (ITSM) for structural damage identification of offshore platform structures. In each iteration, a new damage index, Modal Energy-Based Damage Index (MEBI), is proposed to help effectively locate the potential damage elements in the first stage. Then, in the second stage, the beetle antenna search (BAS) algorithm is used to estimate the damage severity of these elements. Compared with the well-known particle swarm optimization (PSO) algorithm and genetic algorithm (GA), this algorithm has lower computational cost. A modal energy based objective function for the optimization process is proposed. Using numerical and experimental data, the efficiency and accuracy of the ITSM are studied. The effects of measurement noise and spatial incompleteness of mode shape are both considered. All the obtained results show that under these influences, the ITSM can accurately identify the true location and severity of damage. The results also show that the objective function based on modal energy is most suitable for the ITSM compared with that based on flexibility and weighted natural frequency-mode shape.

• Journal of Astronomy and Space Sciences
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• v.35 no.4
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• pp.295-308
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• 2018

In this study, orbit determination (OD) simulation for the Korea Pathfinder Lunar Orbiter (KPLO) was accomplished for investigation of the observational arc-length effect using a sequential estimation algorithm. A lunar polar orbit located at 100 km altitude and $90^{\circ}$ inclination was mainly considered for the KPLO mission operation phase. For measurement simulation and OD for KPLO, the Analytical Graphics Inc. Systems Tool Kit 11 and Orbit Determination Tool Kit 6 software were utilized. Three deep-space ground stations, including two deep space network (DSN) antennas and the Korea Deep Space Antenna, were configured for the OD simulation. To investigate the arc-length effect on OD, 60-hr, 48-hr, 24-hr, and 12-hr tracking data were prepared. Position uncertainty by error covariance and orbit overlap precision were used for OD performance evaluation. Additionally, orbit prediction (OP) accuracy was also assessed by the position difference between the estimated and true orbits. Finally, we concluded that the 48-hr-based OD strategy is suitable for effective flight dynamics operation of KPLO. This work suggests a useful guideline for the OD strategy of KPLO mission planning and operation during the nominal lunar orbits phase.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.6
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• pp.163-168
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• 2018

We developed W-band transceiver module using open MMIC chip such as receiver single chip and transmitting power amplifier. In order to calculate the noise figure and output power value, we analyzed the W-band transition loss from the antenna to MMIC connection and constructed the 12 channel receiver and the 5 channel transmitter. And compared with the results of the measurement. As a result, the output power of the transmitter was similar to the analytical results and the measured results at room temperature and environmental conditions. The noise figure of the receiver was also similar, but some channels showed error of about 3 dB due to manufacturing error.

• Journal of Navigation and Port Research
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• v.45 no.5
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• pp.231-237
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• 2021

Enhancing the performance of maritime wireless communication has been highlighted by the issue of cell planning in the sea area because of lack of an appropriate Propagation Loss Model (PLM). To resolve the cell planning issue in vast sea areas, it was essential to develop the (PLM) matching the intended sea area. However, there were considerable gaps between the prediction of legacy PLMs and field measurement in propagation loss and there was a need to develop the adjusted PLM (A-PLM). Therefore, cell planning was performed on this adjusted model, including modification of the base station's location, altitude, and antenna azimuth to meet the quality objectives. Furthermore, in order to verify the availability of the cell planning, Communication Service Quality Monitoring System (CS-QMS) was developed in the LTE-Maritime project to collect LTE signal quality information from the onboard equipment at regular intervals and to ensure that the service quality was high enough to satisfy the goals in each designated grid. As a result of verification, the success rate of RSRP was 95.7% for the intensive management zone (IMZ) and 96.4% for the interested zone (IZ), respectively.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.24 no.3
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• pp.35-40
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• 2024

In this paper, the design, implementation, and analysis of a device capable of transmitting and receiving millimeter-wave signals and performing channel sounding measurements in atmospheric conditions at distances of up to approximately 10km outdoors are presented. The device is expected to be instrumental in studying the propagation characteristics of millimeter-wave frequencies. Utilizing data such as received power levels and power delay profiles (PDPs), comparisons with predicted values using path loss, K-factor, and other propagation models are facilitated. The mobile transceiver unit, integrated onto a vehicle platform, allows for flexible adjustment of transmitter and receiver positions, while synchronization issues with distance are mitigated using a rubidium atomic clock. Furthermore, automatic boresight alignment using scanning techniques is employed to locate the main sector of the antenna.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.7
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• pp.1774-1794
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• 2024

In the field of environmental sensing, it is necessary to develop radio planning techniques for the next generation Internet of Things (IoT) networks over mixed terrains. Such techniques are needed for smart remote monitoring of utility supplies, with links situated close to but out of range of cellular networks. In this paper, a three-dimension (3-D) geometric optimization algorithm is proposed, considering the positions of edge IoT devices and antenna coupling factors. Firstly, a multi-level single linkage (MLSL) iteration method, based on geometric objectives, is derived to evaluate the data rates over ISM 915 MHz channels, utilizing optimized power-distance profiles of continuous waves. Subsequently, a federated learning (FL) data selection algorithm is designed based on the 3-D geometric positions. Finally, a measurement example is taken in a meadow biome of the Mexican Colima district, which is prone to fluvial floods. The empirical path loss model has been enhanced, demonstrating the accuracy of the proposed optimization algorithm as well as the possibility of further prediction work.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.4
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• pp.285-293
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• 2020

In this paper, to improve Synthetic Aperture Radar (SAR) image quality, the effect of time synchronization error in the EGI/IMU (Embedded GPS/INS, Inertial Measurement Unit) integrated system is analyzed and state augmentation is applied to compensate it. EGI/IMU integrated system is widely used as a SAR motion measurement algorithm, which consists of EGI mounted to obtain the trajectory and IMU mounted on the SAR antenna. In an EGI/IMU integrated system, a time synchronization error occurs when the clocks of the sensors are not synchronized. Analysis of the effect of time synchronization error on navigation solutions and SAR images confirmed that the time synchronization error deteriorates SAR image quality. The state augmentation is applied to compensate for this and as a result, the SAR image quality does not decrease. In addition, by analyzing the performance and the observability of the time synchronization error according to the maneuver, it was confirmed that the time-variant maneuver such as rotational motion is necessary to estimate the time synchronization error adequately. In order to reduce the influence of the time synchronization error on the SAR image, the time synchronization error must be compensated by performing maneuver changing over time such as a rotation before SAR operation.

• Korean Journal of Soil Science and Fertilizer
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• v.46 no.6
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• pp.659-664
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• 2013

The aim of this study is to determine the drought stress index through photochemical analysis in red pepper (Capsiumannuum L.). The photochemical interpretation was performed in the basis of the relation between Kautsky effect and Photosystem II (PSII) following the measurement of chlorophyll, pheophytin contents, and $CO_2$ assimilation in drought stressed 5-week-old red pepper plants. The $CO_2$ assimilation rate was severely lowered with almost 77% reduction of chlorophyll and pheophytin contents at four days after non-irrigation. It was clearly observed that the chlorophyll fluorescence intensity rose from a minimum level (the O level), in less than one second, to a maximum level (the P-level) via two intermediate steps labeled J and I (OJIP process). Drought factor index (DFI) was also calculated using measured OJIP parameters. The DFI was -0.22, meaning not only the initial inhibition of PSII but also sequential inhibition of PSI. In real, most of all photochemical parameters such as quantum yield of the electron transport flux from Quinone A ($Q_A$) to Quinone B ($Q_B$), quantum yield of the electron transport flux until the PSI electron acceptors, quantum yield of the electron transport flux until the PSI electron acceptors, average absorbed photon flux per PSII reaction center, and electron transport flux until PSI acceptors per cross section were profoundly reduced except number of QA reducing reaction centers (RCs) per PSII antenna chlorophyll (RC/ABS). It was illuminated that at least 6 parameters related with quantum yield/efficiency and specific energy fluxes (per active PSII RC) could be applied to be used as the drought stress index. Furthermore, in the combination of parameters, driving forces (DF) for photochemical activity could be deduced from the performance index (PI) for energy conservation from photons absorbed by PSII antenna until the reduction of PSI acceptors. In conclusion, photochemical responses and their related parameters can be used as physiological DFI.