• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.5A
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• pp.305-315
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• 2003

MC-CDMA(Multicarrier code division multiple access), which is based on a combination of OFDM(orthogonal frequency division multiplexing) and CDMA(code division multiple access), has gained a lot of interests in wireless multimedia communications, as high speed data transmission is required for mobile services. MC-CDMA has many advantages for broadband high speed data transmission in multipath environment because it can offer both advantages of the CDMA and the OFDM. However, A high PAPR(peak to average power ratio) problem, which is a major drawback of OFDM, is also shown in the MC-CDMA. In this paper, we propose a new phase factor optimization scheme to reduce complexity in PTS(partial transmit sequence) to reduce PAPR. We also analyze the performance of the MC-CDMA with various PTS schemes to investigate the relations between PAPR characteristics and effect of nonlinear distortion of a high power amplifier. Our simulation results reveal that the proposed PTS scheme reduces PAPR about 0.2∼0.5 dB even with 25% reduced- complexity compared to the conventional scheme.

• Journal of the Korea Society of Computer and Information
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• v.15 no.9
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• pp.25-33
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• 2010

We propose a retouching method that converts a general photography to a watercolor painting image using bilateral filtering and mean shift segmentation which are mostly used in image processing. The first step is to weaken high frequency components of the image, while preserving the edge of image using the bilateral filtering. And after that we perform DoG(Difference of Gradient) edge extraction and mean shift segmentation respectively from the bilateral filtered image. The DoG edge extraction is performed using luminance component of the image whose RGB color space is transformed into CIELAB space. Experimental result shows that our method can be applied to various types of image and bring better result, especially against the photo taken in daylight.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.4
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• pp.343-350
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• 2014

Divisive hierarchical clustering algorithms iterate the process of decomposition and clustering data recursively. In each recursive call, data in each cluster are arbitrarily selected and thus, the total clustering time can be increased, which causes a problem that it is difficult to apply the process of clustering neighbor vehicular position data in vehicular localization. In this paper, we propose a new heuristic algorithm for speeding up the clustering time by eliminating randomness of the selected data in the process of generating the initial divisive clusters.

• Proceedings of the Korean Information Science Society Conference
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• 1999.10a
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• pp.231-233
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• 1999

시공간 상에서 움직이는 물체의 이동경로는 일반적으로 MBR이 매우 크므로, R-tree 계열의 다차원 인덱싱 기법을 적용할 때 질의시 겹침 영역이 많이 발생하는 문제점이 있다. 본 논문에서는 이러한 문제점을 해결하기 위해 time slice에 따라 이동경로의 MBR을 나누어 별도의 인덱스에 저장하는 기법을 제안한다. 이 기법을 적용하면 MBR의 평균 크기가 줄어들어 인덱스 페이지 및 데이터 페이지 접근횟수를 감소시킬 수 있을 뿐만 아니라, 시간이 지나 질의가 매우 드물게 수행되는 데이터에 대한 엔트리를 삭제하여 검색 범위를 줄이는 것이 용이하다. 또한 본 논문에서는 질의 성능을 최적화하기 위해서 time slice를 어떻게 설계해야 하는지에 대해서도 논의한다.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.155-159
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• 2010

홍수 예 경보 및 강우-유출의 관계에 의한 홍수량 산정은 수자원 계획과 관리에 있어 중요한 요소라 할 수 있다. 이러한 강우-유출의 관계를 표현할 수 있는 모형은 최근 분포형 모형으로 발전하게 되었지만, 유역수문 모형의 비약적인 발전과는 다르게 강우자료는 점 강우량을 유역내 평균강우량으로 산정하는 것이 일반적이다. 그러나, 실제 유역에서 강우의 분포는 다양한 이동속도와 방향을 가지고 있기에 유역 내 평균강우량이 발생한다고 가정하기에는 어려운 상황이 많다. 본 연구에서는 격자로 분할된 섬진강 유역에 임의로 생성한 중앙집중형 강우와 2009년 7월 12일부터 2009년 7월 15일까지의 레이더 강우 자료를 실제 이동방향과 수직된 나머지 세 방향으로 각각 공간분포 시켰으며, 강우의 이동과 공간분포를 함께 고려할 수 있는 준분포형인 Modified Clark 방법으로 유출량을 모의하였다. 실측된 유출량 및 강우이동에 대하여 모형을 검 보정한 후 직각된 4방향성으로 강우를 이동시켜 유역출구의 홍수량 변화를 비교 분석하였다. 그 결과 강우이동형태에 따라 첨두유량이 변화함을 알 수 있었으며, 가상의 이동강우 및 레이더 강우가 하류에서 상류로의 이동보다 상류에서 하류로 이동하는 특성이 유역출구에서의 첨두유량이 크고 지체시간을 지속시킴을 알 수 있었다. 본 연구를 통해 강우이동 특성을 고려할 수 있는 레이더 강우를 이용함으로써 홍수 유출특성의 변화 정도에 대한 신뢰도를 높일 수 있을 것으로 기대한다.

• Journal of Korean Orthopaedic Sports Medicine
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• v.1 no.1
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• pp.102-107
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• 2002

Purpose: The aim of this retrospective study were to report the short-term results of inferior capsular shift procedure using splitting subscapularis and capsule for the patients who had shoulder instability and were apt to recur after arthroscopic stabilization procedure. Materials & Methods : Fifteen cases of instability of the shoulder were included with an average follow-up of 2 years (range: 1$\~$3 years). There were 13 men and 2 women with an average age of 27years. Multidirectional instability was found in 4 cases, voluntary instability in 3 cases, bony Bankarte lesion in 2 cases and 6 cases were contact sportmen. Thirteen shoulders underwent the inferior capsular shifts and Bankart repairs and 2 shoulders without Bankart lesion underwent the inferior capsular shift only. Average 19 mm of shift (range: 10$\~$25 mm) was done. Results : Fourteen patients showed good and excellent results with one subluxation and one positive apprehension test. Postoperative ranges of motions did not change in forward elevation, external rotation at side and external rotation at 90$^{\circ}$ abduction (p>0.05). Conclusion : Inferior capsular shift procedure using splitting subscapularis and capsule can be helpful in shoulder instability patients who were high-risk group of recurrence with arthroscopic procedure.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.5B
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• pp.871-878
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• 2000

A divided matched filter-reference filter(MF-RF) technique for LEO satellite packet transmission is proposed to increase the packet throughput in the presence of severe Doppler shift and fading. To overcome the severe Doppler shift, the divided matched filter is adopted where the integration region of matched filter is divided and ouputs of divided matched filer are added to decide the correct pseudo-noise (PN) phase. To maintain the constant false alarm rate in time varying interference and fading channel, the adaptive threshold for acquisition is obtained from the reference filter. As a performance measure, average acquisition time and packet throughput are used, and the effets of the parameters, i.e., Doppler shift, chip energy to noise ratio, user velocity, standard deviation of shadowing, and preamble length are shown.

• Journal of KIISE:Databases
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• v.31 no.2
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• pp.150-162
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• 2004

Moving objects have characteristics that they change continuously their positions over time. The movement of moving objects should be stored on trajectories for processing past queries. Moving objects databases need to provide spatio-temporal index for handling moving objects queries like combined queries. Combined queries consist of a range query selecting trajectories within a specific range and a trajectory query extracting to parts of the whole trajectory. Access methods showing good performance in range queries have a shortcoming that the cost of processing trajectory Queries is high. On the other hand, trajectory-based index schemes like the TB-tree are not suitable for range queries because of high overlaps between index nodes. This paper proposes new TR(Trajectory Riving)-tree which is revised for efficiently processing the combined queries. This index scheme has several features like the trajectory preservation, the increase of the capacity of leaf nodes, and the logical trajectory riving in order to reduce dead space and high overlap between bounding boxes of nodes. In our Performance study, the number of node access for combined queries in TR-tree is about 25% less than the STR-tree and the TB-tree.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.4 s.316
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• pp.78-85
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• 2007

This paper presents a segmental scheme for regions-composed images in local normalization process. The scheme is based on local statistics computed through a moving window. The normalization algorithm uses linear or nonlinear functions to transfer the pixel distribution and the homogeneous affine of regions which is corrupted by additive noise. It adjusts the mean and standard deviation for nearest-neighbor interpoint distance between current and the normalized image signals and changes the segmentation performance according to local statistics and parameter variation adaptively. The performance of newly advanced local normalization algorithm is evaluated and compared to the performance of conventional normalization methods. Experimental results are presented to show the region segmentation properties of these approaches.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.5
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• pp.117-121
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• 2014

In the orthogonal frequency division multiplexing system, the prefix inserted between data symbols should be eliminated to apply the Fourier transform on the valid symbol interval. This functional procedure should be based on the accurate symbol timing detection. The symbol timing detection at the receiver side provides the reference for determining the beginning time index of each symbol whose initial point is located at the boundary between the preamble and the payload part. Also, the detection error is one of the main factors in the overall system performance. In this paper the effect of the bandwidth of the moving average filter on the symbol timing detection is discussed. Simulations are carried out to analyze the detection performance for the varying values of the window size of the moving average filter which is related to the filter bandwidth.