• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.9C
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• pp.589-595
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• 2011

This paper proposes an improved multi-stage timing offset estimation scheme for orthogonal frequency division multiplexing (OFDM) systems in multipath fading channel environment. The conventional multi-stage timing offset estimation scheme is very sensitive to the random multipath components. By exploiting the sample standard deviation of the cross-correlation values, the proposed scheme achieves a robustness to the random multipath components. Simulation results demonstrate that the proposed scheme has a higher correct estimation probability and has a better mean square error (MSE) performance than the conventional scheme in multipath fading channels.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.3
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• pp.443-448
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• 2022

This paper presents a subband affine projection algorithm with variable step size to improve convergence performance in adaptive filtering applications with long adaptive filters and highly correlated input signals. The proposed algorithm can obtain fast convergence speed and small steady-state error by using different step sizes for each adaptive sub-filter in the subband structure to which polyphase decomposition and noble identity are applied. The step size derived to minimize the mean square error of the adaptive filter at each update time shows better convergence performance than the existing algorithm using a variable step size. In order to confirm the convergence performance of the proposed algorithm, which is superior to the existing algorithm, computer simulations are performed for mean square deviation(MSD) for AR(1) and AR(2) colored input signals considering the system identification model.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.24 no.1
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• pp.10-15
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• 2016

In this study, The code-carrier divergence test was applied to GPS measurements, and the results were compared and analyzed. The GPS data used for the threshold determination were obtained from Global Navigation Satellite System permanent stations built by the Korea Aerospace Research Institute. At each permanent station, identical dual-frequency receiver and choke ring antenna with radome are installed. The analysis method, root mean square values were compared and analyzed for each permanent station and satellite. As a result, the root mean square value generally decreased as the satellite elevation angle increased although the trend was gentle. Threshold were finally selected based on the average and standard deviation of root mean square for each permanent station. For improving of availability and continuity in real-time operation when the threshold is over the limits, Code-Carrier divergence test values are initialized.

• Journal of Korea Water Resources Association
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• v.39 no.8 s.169
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• pp.677-690
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• 2006

The LH-OAT (Latin Hypercube One factor At a Time) method for sensitivity analysis and SCE-UA (Shuffled Complex Evolution at University of Arizona) optimization method were applied for the automatic calibration of SWAT model in Bocheong-cheon watershed. The LH-OAT method which combines the advantages of global and local sensitivity analysis effectively identified the sensitivity ranking for the parameters of SWAT model over feasible parameter space. Use of this information allows us to select the calibrated parameters for the automatic calibration process. The performance of the automatic calibration of SWAT model using SCE-UA method depends on the length of calibration period, the number of calibrated parameters, and the selection of statistical error criteria. The performance of SWAT model in terms of RMSE (Root Mean Square Error), NSEF (Nash-Sutcliffe Model Efficiency), RMAE (Relative Mean Absolute Error), and NMSE (Normalized Mean Square Error) becomes better as the calibration period and the number of parameters defined in the automatic calibration process increase. However, NAE (Normalized Average Error) and SDR (Standard Deviation Ratio) were not improved although the calibration period and the number of calibrated parameters are increased. The result suggests that there are complex interactions among the calibration data, the calibrated parameters, and the model error criteria and a need for further study to understand these complex interactions at various representative watersheds.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.36 no.1
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• pp.9-15
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• 2018

Precise regional geoid heights on and around Mount Jiri were calculated and were compared to the KNGeoid14 (Korean National Geoid 2014) model. In this study, gravimetric geoid heights were calculated by using RCR (Remove-Compute-Restore) technique and then hybrid geoid heights were calculated by using the LSC (Least Square Collocation) method in the same area. In addition, gravity observation and GNSS(Global Navigation Satellite System) surveying performed in this study were utilized to determine gravimetric geoid heights and to compute hybrid geoid heights, respectively. The results of the study show that the post-fit error (mean and standard deviation) of hybrid geoid heights was evaluated as $0.057{\pm}0.020m$, while the mean and standard deviation of the differences were -0.078 and 0.085 m, respectively for KNGeoid14. Therefore, hybrid geoid heights in this study show more considerable progress than KNGeoid14.

• Journal of the Korean Society of Physical Medicine
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• v.9 no.1
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• pp.63-68
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• 2014

PURPOSE: The purpose of this study was to examine the position changes with tilt table on autonomic nervous system using heart rate variability analysis. METHODS: Fourty healthy adult males volunteered in this study. The low frequency, high frequency and low frequency/high frequency ratio and mean heart rate, standard deviation of all normal R-R intervals, root mean square of successive differences, heart rate variability index were measured at the tilt table angle of $0^{\circ}$, $45^{\circ}$ and $90^{\circ}$ with pulsoximeter. Data were analyzed one-way ANOVA and LSD post hoc test. RESULTS: The mean heart rate, low frequency and low frequency/high frequency ratio increased significantly at higher angle of tilt table(p<.05). The root mean square of successive differences, heart rate variability index decreased significantly at lower angle of tilt table(p<.05). The standard deviation of all normal R-R intervals, high frequency decreased at higher angle of tilt table did not show significant difference. CONCLUSION: The symphathetic activity increased significantly at higher angle of tilt table. The parasymphathetic activity decreased at higher angle of tilt table, but the difference were not significant. The autonomic adaptation, balance and heart rate variability decreased significantly at higher angle of tilt table. Based on these results, in the treatment of patients with a change in posture precedence should be carefully treated. Further studies are necessary to determine the most safety and effective methods.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.447-450
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• 2003

This paper concerns on application of active magnetic bearing(AMB) system to levitate the elevation axis of an electro-optical sight mounted on moving vehicles. In such a system. it is desirable to retain the elevation axis within the predetermined air-gap while the vehicle is moving. A disturbance compensation control is proposed to reduce the base motion response. In the consideration of the uncertainty of the system model, a filtered-x least-mean-square(FXLMS) algorithm is used to estimate adaptively the frequency response function of the feedforward control which cancels disturbance responses. The frequency response function is fitted to an optimal feedforward control. Experimental results demonstrate that the proposed control reduces the air-gap deviation to 27.7% that by feedback control alone.

• Smart Structures and Systems
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• v.19 no.4
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• pp.361-369
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• 2017

Electromechanical impedance method as an efficient tool in Structural Health Monitoring (SHM) utilizes the electromechanical impedance of piezoelectric materials which is directly related to the mechanical impedance of the host structure and will be affected by damages. In this paper, electromechanical impedance of piezoelectric patches attached to simply support rectangular plate is determined theoretically and experimentally in order to detect damage. A pairs of piezoelectric wafer active sensor (PWAS) patches are used on top and bottom of an aluminum plate to generate pure bending. The analytical model and experiments are carried out both for undamaged and damaged plates. To validate theoretical models, the electromechanical impedances of PWAS for undamaged and damaged plate using theoretical models are compared with those obtained experimentally. Both theoretical and experimental results demonstrate that by crack generation and intensifying this crack, natural frequency of structure decreases. Finally, in order to evaluate damage severity, damage metrics such as Root Mean Square Deviation (RMSD), Mean Absolute Percentage Deviation (MAPD), and Correlation Coefficient Deviation (CCD) are used based on experimental results. The results show that generation of crack and crack depth increasing can be detectable by CCD.

• Journal of Acupuncture Research
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• v.21 no.1
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• pp.176-188
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• 2004

This study was carried out to investigate statistical validity of medical articles that used various statistical techniques such as t-test, analysis of variance, correlation analysis, regression analysis and chi-square test. For study 429 original articles using those statistical methods were selected from Journal of Korean Acupuncture & Moxibusition Society published from 1984 to 2002. 429 original articles were reviewed to analyzed the statistical procedures. Results are summarized as follows : 1. In this study 93 articles(21.68%) of 429 ones didn't report statement of statistical method in detail. 2. 53 articles(12.53%) didn't report p-value in correctly, and 245 articles(57.11 %) used mean${\pm}$standard error (Mean${\pm}$SEM.) and 109 articles used mean${\pm}$standard deviation(Mean${\pm}$SD.). All of 23 articles using nonparametric statistical techniques made an error to central tendency or dispersion. 3. 175 articles(59.93%) and 14 articles(4.79%) of 292 ones made an error to description of equal variances and normal distribution. 4. 99 articles(50%) of 185 ones misused t-test and 4 articles of 5 ones misused chi-square test. 5. 28 articles(73.68%) of 38 ones using discrete variable misused parametric technique such as t-test or ANOVA. 2 articles and 1 article of 125 ones choosing paired samples misused independent t-test and Mann-Whitney U test. 6. 20 articles using analysis of variance didn't use multiple comparison.

• Structural Monitoring and Maintenance
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• v.5 no.2
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• pp.231-242
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• 2018

Subway tunnel structure has been rapidly developed in many cities for its strong transport capacity. The model-based damage detection of subway tunnel structure is usually difficult due to the complex modeling of soil-structure interaction, the indetermination of boundary and so on. This paper proposes a new data-based method for the damage detection of subway tunnel structure. The root mean square acceleration and cross correlation function are used to derive a statistical pattern recognition algorithm for damage detection. A damage sensitive feature is proposed based on the root mean square deviations of the cross correlation functions. X-bar control charts are utilized to monitor the variation of the damage sensitive features before and after damage. The proposed algorithm is validated by the experiment of a full-scale two-rings subway tunnel lining, and damages are simulated by loosening the connection bolts of the rings. The results verify that root mean square deviation is sensitive to bolt loosening in the tunnel lining and X-bar control charts are feasible to be used in damage detection. The proposed data-based damage detection method is applicable to the online structural health monitoring system of subway tunnel lining.