• Korean Journal of Remote Sensing
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• v.31 no.2
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• pp.101-110
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• 2015

Synthetic Aperture Radar Interferometry (InSAR) is affected by various noise source such as atmospheric artifact, orbital error, processing noise etc.. Especially, one of the dominant noise source for long-wave SAR system, such as ALOS PALSAR (L-band SAR satellite) is the ionosphere effect because phase delays on radar pulse through the ionosphere are proportional to the radar wavelength. To avoid misinterpret of phase signal in the interferogram, it is necessary to detect and correct ionospheric errors. Recently, a MAI (Multipler Aperture SAR Interferometry) based ionospheric correction method has been proposed and considered one of the effective method to reduce phase errors by ionospheric effect. In this paper, we introduce the MAI-based method for ionospheric correction. Moreover we propose an efficient method that apply the method over non-coherent area using directional filter. Finally, we apply the proposed method to the ALOS PALSAR pairs, which include the west sea coast region in Korea. A polynomial fitting method, which is frequently adopted in InSAR processing, has been applied for the mitigation of phase distortion by the orbital error. However, the interferogram still has low frequency of Sin pattern along the azimuth direction. In contrast, after we applied the proposed method for ionospheric correction, the low frequency pattern is mitigated and the profile results has stable phase variation values within ${\pm}1rad$. Our results show that this method provides a promising way to correct orbital and ionospheric artifact and would be important technique to improve the accuracy and the availability for L-band or P-band systems.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.82.1-82.1
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• 2015

We investigate the long-term spatial drift of the center and the temporal variation of the shutter delay time map of Y4KCam mounted on the CTIO 1.0m telescope. We have collected shutter delay time maps for over 7 years as a part of long-term survey program. We find that the center of the shutter delay time map can drift up to $450{\mu}m$ on the CCD. This effect can result in a small amount of error unless the proper shutter delay time correction, but it does not appear to cause any significant problems in photometric measurements. We obtain the mean value of the shutter delay time of $69.1{\pm}0.9$ msec and find no temporal variation of the shutter delay time of Y4KCam for over 7 years, indicative of the mechanical stability of the shutter. We suggest that using a master shutter delay time correction frame would be sufficient to achieve high precision photometry and this does not add up errors more than ~ 2.5 mmag across the CCD frame with exposure times longer than 1 sec.

• Journal of Advanced Navigation Technology
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• v.8 no.1
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• pp.1-9
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• 2004

In this paper, we have studied the reliable scheme for transmission of digital watermarking-inserted image data through wireless channel. Multimedia data and watermarking data are degraded because of the high BER (Bit Error Rate) and the effect of fading in wireless channel. We adapt the error correction scheme for mitigating the degradation in watermarking data. We have evaluated the error performance of watermarking data modulated by OFDM/16QAM and sent through Rician fading channel. The simulation results show that when error correcting scheme is used the watermarking data can be detected without severe error even though watermarking-inserted image data is suffered from severe damage.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.12
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• pp.77-84
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• 2005

The orthogonal frequency division multiplexing (OFDM) technique and the single carrier with cyclic prefix (SC-CP) scheme are very attractive solutions for wireless applications, being computationally efficient since equalization is performed in the frequency domain. The equalizer could not entirely handle significant mean. Doppler shift. This motivates the use of a phase error tracking loop that operates jointly with the frequency equalizer. This paper describes the effect of the mean phase error and the performance of the proportional equalizer coupled with a phase error tracking loop based on decision-directed method. Furthermore, simulation results show that we can reduce the computational toad of the tracking loop with minimal performance degradation.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.2
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• pp.151-156
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• 2017

Communication performance requirements are described as QoS parameters in multimedia communication Protocols including SCTP. One of the important QoS parameters is the reliability of the transfer. As a QoS parameter, the reliability defines error detection, report and correction mechanisms. Including SCTP, conventional error control mechanisms, however, do not consider the integrated viewpoint of multimedia data. In this paper, I have designed and proposed the multimedia oriented error control method based on multimedia characteristics. The proposed scheme should have the reduction effect of the communication resources such as frame buffer, procesing power and bandwidth as well as satisfy the requirements of users.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1984.10a
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• pp.11-14
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• 1984

When the received sequence is not identical to the transmitted code word due to the channel nose effect, it is necessary to detect and correct errors. In this paper, it is shown how to construct the encoder and the decoder using cyclic product codes. this system combines random and burst error correction and is easily decodable. Performance has been obtained as expected.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.9C
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• pp.721-728
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• 2010

CAMC (constant amplitude multi-code) has a better performance of error correction in iterative decoding than SPCPC (single parity check product code). CAMC benefits from a processing gain since it belongs to a spread spectrum signal. We show that the processing gain enhances the performance of CAMC. Additional correction of bit errors is achieved in the de-spreading of iteratively decoded signal. If the number of errors which survived the iterative decoding is less than or equal to ($\sqrt{N}/2-1$), all of the bit errors are removed after the de-spreading. We also propose a stopping criterion in the iterative decoding, which is based on the histogram of EI (extrinsic information). The initial values of EI are randomly distributed, and then they converge to ($-E_{max}$) or ($+E_{max}$) over the iterations. The strength of the convergence reflects how successfully error correction process is performed. Experimental results show that the proposed method achieves a gain of 0.2 dB in Eb/No.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.382-385
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• 2007

Constantly enhancing positioning accuracy by the Global Positioning System (GPS) technique is of great importance, but challenging, especially after the GPS positioning technique has been improved considerably during the past two decades. The associated main error sources have been reduced substantially, if not eliminated. Troposhpeic influence with its highly temporal and spatial variability appears to be one of the major error sources. It is hence an increased interest among GPS researchers to reduce the tropospheric influence or delay. Two techniques have been commonly implemented to correct the tropospheric impact. The first technique, known as parameter estimation, characterizes the path delay with empirical models and the parameters of interest are determined from the GPS measurements. The second strategy, termed as external correction, involves independent path delay measurements. The present study is an integration of both techniques in which the parameter estimation as well as external correction are used to correct the path delay for $110{\sim}210$ km range baselines. Twenty-four parameters have been obtained in 24 hours solution by setting the cutoff angle at 3 and 15 degrees for parameter estimation strategy. Measurements from meteorological instruments and water vapor radiometer (WVR) are applied in the GPS data processing, separately, as an external strategy of present research work. Interesting results have been found, indicating more stable repeatability in baseline when the external correction strategy is applied especially with the inclusion of WVR observations. The offset of an order of 1 cm is found in the baselines determined by the two strategies. On the other hand, parameter estimation exhibits more stable in terms of GPS height repeatability. The offset in the GPS height determined by the two strategies is on the order of few centimeters.

• English Language & Literature Teaching
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• v.16 no.4
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• pp.133-152
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• 2010

There is disagreement, among researchers, on the benefits of corrective feedback on L2 learners' written output. Some scholars advocate the usefulness of corrective feedback while some claim that error correction is ineffective and even harmful. So far, however, research outcomes cannot settle this debate. Based on this debate, this study examines whether there is a difference among diverse types of feedback on the effects of L2 learners' writing improvement. This study found that teacher's direct feedback was more effective than any other types of feedback on the effect of participants' writing improvement. In particular, teacher's direct feedback helped their improvement on grammar, mechanics, and form. Among the types of peer feedback, self-correction was the most effective. In teacher feedback, form-focused feedback had more effects than content-focused feedback, but no difference with regard to peer feedback. In addition, teacher's content-focused feedback was more effective than peer's content-focused feedback. Overall, in all types of feedback, teacher feedback was more effective than peer feedback. However, direct (form-focused) feedback was the most effective in teacher feedback, and self-correction in peer feedback. The least effective feedback in both teacher and peer feedback was indirect (form-focused) feedback, which is simple underlining of errors.

• Quantitative Bio-Science
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• v.37 no.2
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• pp.133-141
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• 2018

Graphical lasso is one of the most popular methods to estimate a sparse precision matrix, which is an inverse of a covariance matrix. The objective function of graphical lasso imposes an ${\ell}_1$-penalty on the (vectorized) precision matrix, where a tuning parameter controls the strength of the penalization. The selection of the tuning parameter is practically and theoretically important since the performance of the estimation depends on an appropriate choice of tuning parameter. While information criteria (e.g. AIC, BIC, or extended BIC) have been widely used, they require an asymptotically unbiased estimator to select optimal tuning parameter. Thus, the biasedness of the ${\ell}_1$-regularized estimate in the graphical lasso may lead to a suboptimal tuning. In this paper, we propose a two-staged bias-correction procedure for the graphical lasso, where the first stage runs the usual graphical lasso and the second stage reruns the procedure with an additional constraint that zero estimates at the first stage remain zero. Our simulation and real data example show that the proposed bias correction improved on both edge recovery and estimation error compared to the single-staged graphical lasso.