• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5841-5846
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• 2013

In this work, we consider the effect of doppler bandwidth on the performance of channel sounding. We develop the mathematical formulation of the problem and compare the MMSE channel estimator to the simple correlator. Examples of the performance of the MMSE and correlator estimators are presented for the single-input single-output (SISO) case with various values of Doppler bandwidth to assess the impact of time variation. The results show that as the $f_dT$ product increases the performance of both the MMSE and correlator estimates gets worse, and that the performance of the MMSE estimator improves relative to the correlator.We also consider case that the exact statistics of the channel are unknown It is shown that when the mismatch is not too large, the MMSE estimator with mismatch still does better than the simple correlator, but if the mismatch is large, then the correlator can do better.

• Journal of the Korean Society of Radiology
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• v.11 no.5
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• pp.343-351
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• 2017

T1, T2 relaxation time and relaxation rates were measured and analyzed according to the change of RF coil channel number of MAGiC sequence. T1, T2, R1 and R2 maps were obtained by using MAGiC sequence with phantom (1.0, 0.6, 0.2, 0 mM) on the RF coil with channel number of 1, 8, 16 and 32 respectively. T1, T2, R1, R2 values and relaxation rates were measured for each channel number and concentration, and Relaxivity was calculated according to each concentration. T1, T2, R1, and R2 values were measured in each coil. There was no significant difference between T1 and R1 values (p> 0.05). However, T2 and R2 values were significantly different (p <0.05). In the post-analysis results, T2 value was significantly different from that measured on 1, 8, 16, and 32 channel coils (p <0.05) and There was no difference between 8, 16, and 32 channel coils (p> 0.05). The R2 value was significantly different from that measured on the 8, 16, and 32 channel coils in the 1 channel coil, and the results on the 8 channel coils and the 16 channel coils showed a significant difference (P <0.05). In conclusion, T1 and R1 values were not significantly different according to the number of channels in the coil, but T2 and R2 values were significantly different. Therefore, when quantitative measurement of T2 and R2 values using the MAGiC sequence, the same number of coils should be used for reproducibility.

• Journal of KIISE:Databases
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• v.33 no.1
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• pp.86-101
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• 2006

The bandwidth of channel and the power of the mobile devices are limited on a wireless environment. In this case, data broadcast has become an excellent technique for efficient data dissemination. A significant amount of researches have been done on generating an efficient broadcast program of a set of data items with different access frequencies over multiple wireless broadcast channels as well as single wireless broadcast channel. In this paper, an efficient data allocation method over multiple wireless broadcasting channels is explored. In the traditional approaches, a set of data items are partitioned into a number of channel based on their access probabilities. However, these approaches ignore a variation of access probabilities of data items allocated in each channel. In practice, it is difficult to have many broadcast channels and thus each channel need to broadcast many data items. Therefore, if a set of data items broadcast in each channel have different repetition frequencies based on their access frequencies, it will give much better performance than the traditional approaches. In this paper, we propose an adaptive data allocation technique based on data access probabilities over multiple broadcast channels. Our proposed technique allows the adaptation of repetition frequency of each data item within each channel by taking its access probabilities into at count.

• Journal of Korea Multimedia Society
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• v.8 no.12
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• pp.1623-1630
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• 2005

Adaptive modulation and coding (AMC), which has a number of variation levels in accordance with the fading channel variation, is a promising technique for communication systems. In this paper, we present an AMC method using the cluster in OFDM system for bandwidth efficiency and performance improvement. The AMC schemes applied into each cluster or some clusters are determined by the minimum or the average SNR value among all the sub carriers within the corresponding cluster. It is important to find the optimal information on cluster because AMC performance can be varied according to the number and position of cluster. It is shown by computer simulation that the AMC method outperforms the fixed modulation in terms of bandwidth efficiency and its performance can be determined by the position and number of clusters.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.27-30
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• 2005

In a microfluidic chips pressure driven flow or electro-osmotic flow has been usually employed to deliver bio-samples. Flow in the chips is usually slow and the mixing performance is poor. A micro-mixer with a rapid mixing is important for practical applications. In this study a newly designed and electro-osmotic driven micro-mixer is proposed. This design is comprised of a channel and a series of metal electrodes periodically attached on the side surface. In this configuration electro-osmotic flows and the stirring effects are simulated three-dimensionally using a commercial code, CFD-ACE. Focus is given the effect on the electro-osmotic flow characteristics under the local variation of the electric field.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.5
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• pp.31-43
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• 1996

In this paper, we analyze the delay characteristics of the multimdedia traffic in B-ISDN, and propose a weighted variable-size window estimator considering the QoS characteristics of the media and the variable delay characteristics of the networks, and present a delay estimator-based synchronization protocol for the efficient synchronization in ATM-based B-ISDN. The proposed estimator assigns a high weight value to recent cells arrived in the receiver, and suitably adjusts window size in order to efficiently adapt to delay variation by the prameter to detect the delay variation of the networks. The proposed synchronization protocol estimates end-to-end delay by the weighted variable-size window estimator, and dynamically schedules th evirtual channel of the transmitter to playout multimedia data on time in the receiver. Also, we evaluate the performance of the delay estimator, which is the most importnat functional element in our proposed synchronization protocol, by the simulation and analyze the results of the simulation.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.5
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• pp.714-719
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• 2012

In this paper, the polishing force monitoring and the control method were implemented for the polishing machine with the airbag tool. Airbag tool has been known to be adaptable to the curvature variation such as the aspherical and the free-form surface. However, it was necessary to control the tool movement of vertical axis also because of the table rotational wobble and vibration. To solve it by the polishing force control, we installed another stepping motor to the z-axis. And the polishing force was measured with the load cell and controlled by the PID Labview controller. A few hundreds gram of the polishing force were well controlled under 0.8 second of the response time and 5% variation. An experiment was done to clean the edge burrs of the micro channel structure of width $87{\mu}m$ using the polishing force control.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.36 no.2
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• pp.170-177
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• 2003

This study is to analyze the influence of the Tsushima Warm Current (TWC) on the variation of sound speed in the southern part of the East Sea. Sound speed is calculated by method of Chen and Millero (1977:, based on the CTD data measured in June of 1996. Sound speed in the central part of the TWC is about $45ms^{-1}$ more fast than that in the other regions without the TWC. Sound speed minimum layer (SML) in the TWC region exists between loom and 341 m, while it exists between 260m and 290m in the non-TWC region. SML distributes along the path of TWC over continental shelf in the coastal waters of Japan.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1998.10a
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• pp.150-160
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• 1998

Measuring temperature with ultrasonic wave apparatus is desirable in the case of both below 300$0^{\circ}C$ and ideal gas because of the fact that the temperature of gas is the function of only sound velocity. In this study, being used a heatable wind channel and a blower, the variation of temperature is observed in accordance with diverse flow rate(air velocity). The frequency modulation method is used to measure the temperature which is varying in hot air flow till 10$0^{\circ}C$. The length changed in the position of ultrasonic sensors is considered. Also, the effects of air velocity at the same temperature and various facing angles of ultrasonic sensors are considered. As a result of this study, it has been found that the temperature in gas flow is correctly measured regardless of both the distance of ultrasonic sensors and the variation of air velocity, and that there is just a little influence of facing angles.

• Korean Journal of Optics and Photonics
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• v.8 no.6
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• pp.506-509
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• 1997

A novel narrowband wavelength bandpass filter with a large side-lobe suppression was proposed in vertical coupler structure using coupling variation in propagation direction. Combination of a half sinusoidal distributed and a slow coupling schmes was used for narrow bandwidth and small side-lobes. Simulation showed 1.5 nm passband at 1.5507 $\mu\textrm{m}$ and the side-lobes were suppressed more than 20 dB which is two times larger than that of a constant coupling filter. A monolithic two-channel wavelength demultiplexer was proposed and theoretically investigated.