• The Journal of Korean Institute of Communications and Information Sciences
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• v.11 no.3
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• pp.179-196
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• 1986

In this paper, the peformance of a statistical packet voice/data multiplexer is studied. In ths study we assume that in the packet voice/data multiplexer two separate finite queues are used for voice and data traffics, and that voice traffic gets priority over data. For the performance analysis we divide the output link of the multiplexer into a sequence of time slots. The voice signal is modeled as an (M+1) - state Markov process, M being the packet generation period in slots. As for the data traffic, it is modeled by a simple Poisson process. In our discrete time domain analysis, the queueing behavior of voice traffic is little affected by the data traffic since voice signal has priority over data. Therefore, we first analyze the queueing behavior of voice traffic, and then using the result, we study the queueing behavior of data traffic. For the packet voice multiplexer, both inpur state and voice buffer occupancy are formulated by a two-dimensional Markov chain. For the integrated voice/data multiplexer we use a three-dimensional Markov chain that represents the input voice state and the buffer occupancies of voice and data. With these models, the numerical results for the performance have been obtained by the Gauss-Seidel iteration method. The analytical results have been verified by computer simylation. From the results we have found that there exist tradeoffs among the number of voice users, output link capacity, voic queue size and overflow probability for the voice traffic, and also exist tradeoffs among traffic load, data queue size and oveflow probability for the data traffic. Also, there exists a tradeoff between the performance of voice and data traffics for given inpur traffics and link capacity. In addition, it has been found that the average queueing delay of data traffic is longer than the maximum buffer size, when the gain of time assignment speech interpolation(TASI) is more than two and the number of voice users is small.

• Korean Journal of Remote Sensing
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• v.34 no.2_2
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• pp.431-437
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• 2018

We analyzed the feasibility of detecting wave gliders moving on the sea surface using SAR images. For the experiment, a model was constructed and placed on the sea using a towing ship before and after the satellite observation time. In the acquisition of KOMPSAT-5 image, high resolution SAR data of spotlight mode was collected considering the small size of wave glider. As a result of the backscattering intensity analysis around the towing ship along with wave glider, several scattering points away from the ship were observed, which are not strong but clearly distinguished from the surrounding clutter values. Considering the distance from the center of the ship, it seems to be a signal by the wave glider. On the other hand, it is confirmed that the wave glider can be detected even at the very low false alarm rate ($10^{-6}$) of the target detection using CFAR. Although the scatter signal by the wave glider could be distinguished from the surrounding ocean clutter in the high resolution SAR image, further research is needed to determine if actual wave gliders are detected in various marine environments.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.7 s.361
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• pp.9-15
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• 2007

In this paper, we present the design of Schottky diodes and voltage multiplier for UHF-band passive RFID applications. The Schottky diodes were fabricated using Titanium (Ti/Al/Ta/Al)-Silicon (n-type) junction in $0.35\;{\mu}m$ CMOS process. The Schottky diode having $4{\times}10{\times}10\;{\mu}m^{2}$ contact area showed a turn-on voltage of about 150 mV for the forward diode current of $20\;{\mu}A$. The breakdown voltage is about -9 V, which provides sufficient peak inverse voltage necessary for the voltage multiplier in the RFID tag chip. The effect of the size of Schottky diode on the turn-on voltage and the input impedance at 900 MHz was investigated using small-signal equivalent model. Also, the effect or qualify factor of the diode on the input voltage to the tag chip is examined, which indicates that high qualify factor Schottky diode is desirable to minimize loss. The fabricated voltage multiplier resulted in a output voltage of more than 1.3 V for the input RF signal of 200mV, which is suitable for long-range RFID applications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.5A
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• pp.490-496
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• 2007

This paper describes the design and implementation of an integrated LTCC front-end module for the IEEE802.11a WLAN applications by performing the behavioral-level simulation using measurement-based behavioral model. To meet the IEEE802.11a WLAN standard, a system transmitting 1024 symbols through 64-QAM process at the rate of 54Mbps should be implemented and nonlinear properties are confirmed by simulations of ACPR and EVM in this circumstance. The right offsets of ACPR which are 30MHz, 20MHz, and 11MHz distant from the center frequency of 5.8GHz are 49.36dBc, 36.90dBc, and 24.58dBc, respectively. The left offsets are 50.14dBc, 30.04dBc, and 28.85dBc, respectively and EVM is 2.94%. The size of the module implemented with LTCC five-layer substrates is $13.4mm{\times}14.2mm$. The measured characteristics of the transmitter show P1dB of 16.2dBm and power gain of 16.73dB. Those of the receiver exhibit the small signal gain of 16.24dB and noise figure of 7.83dB.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.40.1-40.1
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• 2017

The NISS (Near-infrared Imaging Spectrometer for Star formation history) is the near-infrared spectro-photometric instrument optimized to the Next Generation of small satellite series (NEXTSat). To achieve the major scientific objectives for the study of the cosmic star formation in local and distant universe, the spectro-photometric survey covering more than 100 square degree will be performed. The main observational targets will be nearby galaxies, galaxy clusters, star-forming regions and low background regions. The off-axis optics was developed to cover a wide field of view ($2deg.{\times}2deg.$) as well as the wide wavelength range from 0.95 to $2.5{\mu}m$, which were revised based upon the recent test and evaluation of the NISS instrument. The mechanical structure were tested under the launching condition as well as the space environment. The signal processing from infrared sensor and the communication with the satellite were evaluated after the integration into the satellite. The flight model of the NSS was assembled and integrated into the satellite. To verify operations of the satellite in space, the space environment tests such as the vibration, shock and thermal-vacuum test were performed. The accurate calibration data were obtained in our test facilities. Here, we report the test results of the flight model of the NISS.

• Journal of the Korea Computer Graphics Society
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• v.29 no.5
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• pp.21-30
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• 2023

Accurate segmentation of the kidney tumor is necessary to identify shape, location and safety margin of tumor in abdominal CT images for surgical planning before renal partial nephrectomy. However, kidney tumor segmentation is challenging task due to the various sizes and locations of the tumor for each patient and signal intensity similarity to surrounding organs such as intestine and spleen. In this paper, we propose a semi-supervised learning-based mean teacher network that utilizes both labeled and unlabeled data using a kidney local guided map including kidney local information to segment small-sized kidney tumors occurring at various locations in the kidney, and analyze the performance according to the kidney tumor size. As a result of the study, the proposed method showed an F1-score of 75.24% by considering local information of the kidney using a kidney local guide map to locate the tumor existing around the kidney. In particular, under-segmentation of small-sized tumors which are difficult to segment was improved, and showed a 13.9%p higher F1-score even though it used a smaller amount of labeled data than nnU-Net.

• Investigative Magnetic Resonance Imaging
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• v.11 no.1
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• pp.20-26
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• 2007

Purpose : The purpose of the present study was to develop and optimize solenoid coil for animal- model in 3 T MRI system and investigate and compare with the birdcage coil concerning the image quality with the various parameters such as SNR and Q-factor. Materials and Methods : Solenoid coil for animal-model was made on the acryl structure (diameter 4 cm, length 10 cm) 3 times-winding cooper tape of width 2 cm, thickness 0.05 cm and length 10 cm with 2 cm interval between winded tapes. Capacitors from 2 pF to 100 pF were used, and the solenoid coil was designed for receiver only coil. Results : SNR of the developed solenoid was 985 in CuSO4 0.7 g/L and 995 in rat experiment. Q-factor was 84-89 in unloaded condition and 203-206 in loaded condition. Conclusion : The resolution of the image obtained from solenoid was relatively higher than that of the conventional birdcage coil. In addition, the homogeneity of RF field by coil simulation was significantly excellent. The present study demonstrated that the solenoid coil could be useful to obtain small animal images with better contrast, resolution, visibility than images from birdcage.

• The Korean Journal of Financial Management
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• v.6 no.1
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• pp.31-62
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• 1989

By using deterministic dynamic models, we observe the behavior of the foreign exchange rate of a small open economy with rational expectation formation and different restrictions on the international economic integrations. First, an economy connected to the world by purchasing power parity and uncovered interest parity is studied in the next section. In both sections, financial assets available in the economy are domestic money and bonds. Stocks are added as a financial instrument in the next section, and real capital accumulation is also taken into account. Furthermore, the economy concerned there is fairly autonomous, and not directly governed by either purchasing power parity or uncovered interest parity. The expectation formation used throughout the whole paper is complete perfect foresight, which is the certainty version of rational expectation and free from any forecast errors. It is found that upon monetary expansion the short run depreciation of the foreign exchange rate is a fairly robust result regardless of the degree of the international economic integration, while it is not true for fiscal expansion. The expectation on the long run state significantly affects the short run response of the exchange rate. All of our models postulate that the current account should be balanced eventually. As the result, the short run behavior of the exchange rate is affected by the expectation on the long run balance and may well be a blend of the traditional flow view and modem asset view. The initial overshooting of the exchange rate is easily observed even in the fairly autonomous economy Furthermore, the initial overshooting is not reduced over time, but augmented for some time before it is eventually eliminated. As long as we maintain rational expectaion, introducing time delay in the adjustment of the foreign goods price to the foreign exchange rate does not make much difference.

• The Journal of the Acoustical Society of Korea
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• v.32 no.1
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• pp.14-21
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• 2013

The erosion, suspension, and transport of sediment frequently occur in the coastal waters and estuarine. These processes often generate the so-called fluid mud layer, which is defined as a high-concentration aqueous suspension of fine grained sediment (> 10 g/l), consisting mainly of silt and clay-size particles. Therefore the high-resolution ultrasound is mostly used to detect or monitor the fluid mud layer. Because the sound attenuation tends to increase rapidly with the suspended sediment concentration, it is necessary to consider the accurate attenuation correction to estimate the backscattering strengths from the suspended sediment layers. In this paper, the volume backscattering strengths with various suspended sediment concentrations were measured using 5-MHz ultrasound signal in a small-scale water tank. The sound attenuation due to the viscosity and scattering from suspended sediment particles was predicted by the Richard's model and applied to the sonar equation to estimate the volume backscattering strengths from the suspended sediment concentrations. For the case that the additional attenuation was not considered, the volume backscattering strengths increased to the concentration of 20 g/l, and over this point, the backscattering strengths were roughly constant. However, for the case that the attenuation due to the suspended sediment concentration was considered, the backscattering strengths increased with the concentration.

• Korean Journal of Remote Sensing
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• v.33 no.6_1
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• pp.961-970
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• 2017

Despite of large demand for high spatial resolution products of aerosol properties from satellite remote sensing, it has been very difficult due to the weak signal by a single pixel and higher noise from clouds. In this study, aerosol retrieval algorithm with the high spatial resolution ($500m{\times}500m$) was developed using Geostationary Ocean Color Imager (GOCI) data during the Korea-US Air Quality (KORUS-AQ) period in May-June, 2016.Currently, conventional GOCI Yonsei aerosol retrieval(YAER) algorithm provides $6km{\times}6km$ spatial resolution product. The algorithm was tested for its best possible resolution of 500 m product based on GOCI YAER version 2 algorithm. With the new additional cloud masking, aerosol optical depth (AOD) is retrieved using the inversion method, aerosol model, and lookup table as in the GOCI YAER algorithm. In some cases, 500 m AOD shows consistent horizontal distribution and magnitude of AOD compared to the 6 km AOD. However, the 500 m AOD has more retrieved pixels than 6 km AOD because of its higher spatial resolution. As a result, the 500 m AOD exists around small clouds and shows finer features of AOD. To validate the accuracy of 500 m AOD, we used dataset from ground-based Aerosol Robotic Network (AERONET) sunphotometer over Korea. Even with the spatial resolution of 500 m, 500 m AOD shows the correlation coefficient of 0.76 against AERONET, and the ratio within Expected Error (EE) of 51.1%, which are comparable to the results of 6 km AOD.