• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4C
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• pp.391-399
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• 2006

We propose a novel low complexity video encoder, at the expense of a complex decoder, where video frames are intra-coded periodically and frames in between successive intra-coded frames are coded efficiently using a proposed irregular binning technique. We investigate a method of forming an irregular binning which is capable of quantizing any value effectively with only small number of bins, by exploiting the correlation between successive frames. This correlation is additionally exploited at the decoder, where the quality of reconstructed frames is enhanced gradually by applying POCS(projection on the convex sets). After an image frame is reconstructed with the irregular binning information at the proposed decoder, we can further improve the resulting quality by modifying the reconstructed image with motion-compensated image components from the neighboring frames which are considered to contain image details. In the proposed decoder, several iterations of these modification and re-projection steps can be invoked. Experimental results show that the performance of the proposed coding scheme is comparable to that of H.264/AVC coding in m mode. Since the proposed video coding does not require motion estimation at the encoder, it can be considered as an alternative for some versions of H.264/AVC in applications requiring a simple encoder.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.12A
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• pp.1006-1014
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• 2011

Recently, as CSMA technique has been increasingly adopted in various wireless networks, extensive researches to analyze the statistical characteristics of CSMA-based wireless networks have been done. Despite the ongoing efforts, there still remain many difficulties in the analysis because of unexpectable operational behavior of CSMA. Previous literature studying CSMA networks used the concept of the carrier sensing radius to reflect the carrier sensing function. However, since the carrier sensing radius based on the protocol model is not affected by the aggregate interference from other nodes, the derived statistical models cannot avoid approximation errors especially if the network is under high interference. In this paper, we propose an algorithm to derive the carrier sensing radius considering the physical model, where the carrier sensing radius reflecting the aggregate interference is found. For the purpose of this, we analyze the aggregate interference model and the behavior of CSMA function. Based on the analysis, we propose an iterative approximation algorithm for the physical carrier sensing radius. Extensive simulations and results show that the proposed algorithm can contribute to considerably reduce the statistical modeling error of a CSMA network under various channel conditions.

• Korean Journal of Remote Sensing
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• v.35 no.5_2
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• pp.819-829
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• 2019

In the disaster of collapse, an immediate response is needed to prevent the damage from worsening, and damage area calculation, response and recovery plan should be established. This requires accurate detection of the damage affected area. This study performed the detection of the damaged area by using UAV which can respond quickly and in real-time to detect the collapse accident. The study area was selected as B-05 housing redevelopment area in Jung-gu, Ulsan, where the demolition of houses and apartments in progress as the redevelopment project began. This area resembles a collapsed state of the building, which clear changes before and after the demolition. UAV images were acquired on May 17 and July 9, 2019, respectively. The changing area was considered as the damaged area before and after the collapse of the building, and the changing area was detected using CVA (Change Vector Analysis) the Representative Change Detection Technique, and SLIC (Simple Linear Iterative Clustering) based superpixel algorithm. In order to accurately perform the detection of the damaged area, the uninterested area (vegetation) was firstly removed using ExG (Excess Green), Among the objects that were detected by change, objects that had been falsely detected by area were finally removed by calculating the minimum area. As a result, the accuracy of the detection of damaged areas was 95.39%. In the future, it is expected to be used for various data such as response and recovery measures for collapse accidents and damage calculation.

• Journal of the Korean Association of Geographic Information Studies
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• v.23 no.4
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• pp.253-265
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• 2020

As the risk of landslide is recently increasing due to the typhoons and localized heavy rains, effective techniques for the landslide damage detection are required to support the establishment of the recovery planning. This study describes the analysis of landslide-damaged areas using ISODATA(Iterative Self-Organizing Data Analysis Technique Algorithm) with Sentinel-2 image, regarding the case of Gokseong in August 7, 2020. A total of 4.75 ha of landslide-damaged areas was detected from the Sentinel-2 image using spectral characteristics of red, NIR(Near Infrared), and SWIR(Shortwave Infrared) bands. We made sure that the satellite remote sensing is an effective method to detect the landslide-damaged areas and support the establishment of the recovery planning, followed by the field surveys that require a lot of manpower and time. Also, this study can be used as a reference for the landslide management for the CAS500-1/2(Compact Advanced Satellite) scheduled to launch in 2021 and the Korean Medium Satellite for Agriculture and Forestry scheduled to launch in 2024.

• Korean Journal of Radiology
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• v.22 no.1
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• pp.131-138
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• 2021

Objective: Iterative reconstruction degrades image quality. Thus, further advances in image reconstruction are necessary to overcome some limitations of this technique in low-dose computed tomography (LDCT) scan of the chest. Deep-learning image reconstruction (DLIR) is a new method used to reduce dose while maintaining image quality. The purposes of this study was to evaluate image quality and noise of LDCT scan images reconstructed with DLIR and compare with those of images reconstructed with the adaptive statistical iterative reconstruction-Veo at a level of 30% (ASiR-V 30%). Materials and Methods: This retrospective study included 58 patients who underwent LDCT scan for lung cancer screening. Datasets were reconstructed with ASiR-V 30% and DLIR at medium and high levels (DLIR-M and DLIR-H, respectively). The objective image signal and noise, which represented mean attenuation value and standard deviation in Hounsfield units for the lungs, mediastinum, liver, and background air, and subjective image contrast, image noise, and conspicuity of structures were evaluated. The differences between CT scan images subjected to ASiR-V 30%, DLIR-M, and DLIR-H were evaluated. Results: Based on the objective analysis, the image signals did not significantly differ among ASiR-V 30%, DLIR-M, and DLIR-H (p = 0.949, 0.737, 0.366, and 0.358 in the lungs, mediastinum, liver, and background air, respectively). However, the noise was significantly lower in DLIR-M and DLIR-H than in ASiR-V 30% (all p < 0.001). DLIR had higher signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) than ASiR-V 30% (p = 0.027, < 0.001, and < 0.001 in the SNR of the lungs, mediastinum, and liver, respectively; all p < 0.001 in the CNR). According to the subjective analysis, DLIR had higher image contrast and lower image noise than ASiR-V 30% (all p < 0.001). DLIR was superior to ASiR-V 30% in identifying the pulmonary arteries and veins, trachea and bronchi, lymph nodes, and pleura and pericardium (all p < 0.001). Conclusion: DLIR significantly reduced the image noise in chest LDCT scan images compared with ASiR-V 30% while maintaining superior image quality.

• Geophysics and Geophysical Exploration
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• v.2 no.1
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• pp.26-32
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• 1999

Among the various seismic data processing sequences, the velocity analysis is the most time consuming and man-hour intensive processing steps. For the production seismic data processing, a good velocity analysis tool as well as the high performance computer is required. The tool must give fast and accurate velocity analysis. There are two different approches in the velocity analysis, batch and interactive. In the batch processing, a velocity plot is made at every analysis point. Generally, the plot consisted of a semblance contour, super gather, and a stack pannel. The interpreter chooses the velocity function by analyzing the velocity plot. The technique is highly dependent on the interpreters skill and requires human efforts. As the high speed graphic workstations are becoming more popular, various interactive velocity analysis programs are developed. Although, the programs enabled faster picking of the velocity nodes using mouse, the main improvement of these programs is simply the replacement of the paper plot by the graphic screen. The velocity spectrum is highly sensitive to the presence of the noise, especially the coherent noise often found in the shallow region of the marine seismic data. For the accurate velocity analysis, these noise must be removed before the spectrum is computed. Also, the velocity analysis must be carried out by carefully choosing the location of the analysis point and accuarate computation of the spectrum. The analyzed velocity function must be verified by the mute and stack, and the sequence must be repeated most time. Therefore an iterative, interactive, and unified velocity analysis tool is highly required. An interactive velocity analysis program, xva(X-Window based Velocity Analysis) was invented. The program handles all processes required in the velocity analysis such as composing the super gather, computing the velocity spectrum, NMO correction, mute, and stack. Most of the parameter changes give the final stack via a few mouse clicks thereby enabling the iterative and interactive processing. A simple trace indexing scheme is introduced and a program to nike the index of the Geobit seismic disk file was invented. The index is used to reference the original input, i.e., CDP sort, directly A transformation techinique of the mute function between the T-X domain and NMOC domain is introduced and adopted to the program. The result of the transform is simliar to the remove-NMO technique in suppressing the shallow noise such as direct wave and refracted wave. However, it has two improvements, i.e., no interpolation error and very high speed computing time. By the introduction of the technique, the mute times can be easily designed from the NMOC domain and applied to the super gather in the T-X domain, thereby producing more accurate velocity spectrum interactively. The xva program consists of 28 files, 12,029 lines, 34,990 words and 304,073 characters. The program references Geobit utility libraries and can be installed under Geobit preinstalled environment. The program runs on X-Window/Motif environment. The program menu is designed according to the Motif style guide. A brief usage of the program has been discussed. The program allows fast and accurate seismic velocity analysis, which is necessary computing the AVO (Amplitude Versus Offset) based DHI (Direct Hydrocarn Indicator), and making the high quality seismic sections.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.37 no.1
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• pp.27-36
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• 2000

As a potential approach for non-destructive testing of concrete structures, we evaluate the time-of-flight (TOF) ultrasound tomography technique In conventional X ray tomography, the reconstructed Image corresponds to the internal attenuation coefficient However, in TOF ultrasound tomography, the reconstructed Image is proportional to the retractive index of the medium Because refractive effects are minimal for X-rays, conventional reconstruction techniques are applied to reconstruct the Image in X-ray tomography However, since ultrasound travels in curved path, due to the spatial variations in the refractive index of the medium, the path must be known to correctly reconstruct the Image. Algorithm for determining the ultrasound path is developed from a Geometrical Optics point view and the image reconstruction algorithm, since the paths are curved It requires the algebraic approach, namely the ART or the SIRT Here, the difference between the computed and the measured TOP data is used as a basis, for the iteration process First the initial image is reconstructed assuming straight paths. It then updates the path based on the recently reconstructed image This process of reconstruction and path determination repeats until convergence The proposed algorithm is evaluated by computer simulations, and in addition is applied to a real concrete structure.

• Progress in Medical Physics
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• v.17 no.1
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• pp.40-46
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• 2006

Hepatoma is one of 3 most common malignancies in Korea, the survival rate is not improved since last decades because of delayed diagnosis and limited treatment conditions. Radiation was one of treatment options but the impact on the survival is not remarkable. High dose exposure to target area was suggested for improved effect but low tolerance dose of normal liver tissue is the main limited factor. IMRT is the advanced form of 3DCRT, for focusing high dose on target with minimal dose to surrounding normal tissues. Motion of the tumor by respiration, cardiac pulsation and peristalsis is the main treatment harrier of IMRT for treatment of hepatoma patients. Development of QA technique for acceptable geometrical uncertainties and dose error on target volume is essential for IMRT in clinical treatment but proper QA technique is not yet developed. This study compared the verification film dosimetry with measured dose in phantom and calculated dose in planning computer on exactly same conditions of patient treatments. Within 3% dose differences between 3 groups were confirmed. We suggest that our verification QA technique is easy, economic, iterative and acceptable in clinical application for advanced hepatoma patients.

• Aerospace Engineering and Technology
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• v.13 no.2
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• pp.177-184
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• 2014

Flight safety analyses concerned with Launch Vehicle are performed to measure the risk to the people, ship and aircraft using impact point and impact dispersion area of debris generated by on-trajectory failures and malfunction turns. Predictions of impact point and impact dispersion area are essential for launch vehicle's flight safety analysis. Usually, impact dispersion area can be estimated in using Monte-Carlo simulation. However, Monte-Carlo method requires more several hundreds of iterative calculations which requires quite some time to produce impact dispersion area. Herein, we check the possibility of applying JU(Julier Uhlmann) transformation and Taguchi method instead of Monte-Carlo method and we propose a best method in terms of compuational time to produce impact dispersion area by comparing the results of the three methods.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.1
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• pp.48-58
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• 2012

New digital predistortion technique is proposed for power amplifier linearization in multi-band transmission systems. We consider a system where muli-band signals are combined and amplified by a single power amplifier (PA). In this system, the PA output is distorted by the nonlinear cross-products between different band signals as well as their own nonlinear self-products. To compensate these nonlinear effects, we propose a multiple PD structure. Each PD removes the nonlinear cross-products and self-products to mitigate the spectral regrowth for the corresponding band. Since the PD parameters for different bands are linked together, it is difficult to find the PD parameters separately. Thus, we propose an iterative method for finding the PD parameters jointly. For demonstration of the proposed method, multi-band characteristics of PA are extracted from a commercial power amplifier. Computer simulation was executed based on the PA parameters. The simulation results show that the proposed method can effectively linearize the PA and remove spectral regrowth at each signal band.