• Proceedings of the Korean Information Science Society Conference
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• 2006.06d
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• pp.235-237
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• 2006

최근 분산 해쉬 테이블(Distributed Hash Table)을 이용한 구조적 P2P(peer-to-peer) 시스템에서 로드 밸런싱에 관한 연구가 활발하게 진행되고 있다. 일반적으로 P2P 시스템에서의 피어들은 빈번하게 참여하는 동시에 탈퇴하기도 하기 때문에 로드의 불균형이 심화되는 문제점이 있다. 본 논문에서는 구조적 P2P 시스템에서 피어의 참여와 탈퇴 시 발생하는 가상서버의 이동을 효과적으로 관리하는 기법인 PALB(Peer Activity-aware Load Balancing)를 제안한다. 제안하는 PALB는 피어의 참여, 탈퇴 시에 발생하는 로드 불균형을 해결하기 위하여 적절한 수의 가상서버를 가장 적합한 피어에게 분산시킨다. 또한 이전 연구에서 제안한 OLAB(Object Lifetime-aware Load Balancing)와 함께 사용하여 로드 밸런싱 성능을 향상시킬 수 있다. PALB의 성능 평가를 위하여 동적 P2P 시스템 환경을 구성하였고, 피어와 오브젝트의 랜덤 데이터 셋을 이용하여 시뮬레이션을 수행하였다. 시뮬레이션 결과 PALB가 기존의 시스템에 비하여 더 적은 비용으로 더 나은 로드 밸런싱을 수행함을 확인하였다. 또한 OLAB와 동시에 사용하였을 경우, 매우 뛰어난 성능을 보임을 확인하였다.

• The Korean Journal of Applied Statistics
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• v.26 no.5
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• pp.747-758
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• 2013

The covariance matrix is important in multivariate statistical analysis and a sample covariance matrix is used as an estimator of the covariance matrix. High dimensional data has a larger dimension than the sample size; therefore, the sample covariance matrix may not be suitable since it is known to perform poorly and event not invertible. A number of covariance matrix estimators have been recently proposed with three different approaches of shrinkage, thresholding, and modified Cholesky decomposition. We compare the performance of these newly proposed estimators in various situations.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.4
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• pp.447-451
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• 2010

Monitoring and analyzing the status of smart objects, the ubiquitous smart monitoring system provides several information such as user-state index, service states and system operation among the services in real time. It also provides self-optimization and self-management for enhancing the performance of services. In order to expand the application scope of this real-time monitoring system, it is indispensible to process huge amount of stream data. In this paper, we propose a load balancing scheme to solve the overload of the monitoring agents. Our proposed scheme reduces deadline miss ratio of entire data by more than 80%.

• The KIPS Transactions:PartB
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• v.8B no.3
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• pp.283-287
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• 2001

컴퓨터를 이용한 협동작업은 공간적으로 분산되어 있는 여러 작업자들이 동기적 EH는 비동기적으로 협력할 수 있게 함으로써 보다 신속하고 정확하게 작업을 진행할 수 있게 한다. 최근의 협동작업 분야의 급속한 발전은 이제 더 이상 웹 상에서의 협동작업 도구를 메일, 채팅, 화이트보드, 화상회의 등에 한정하지 않고 웹 응용 프로그램들을 협동작업 도구에 포함시키기에 이르렀다. 본 논문에서는 공간적으로 분산되어 있는 여러 작업자들이 상용 웹 브라우저를 이용하여 웹 문서와 웹 데이터베이스 내용을 공유함으로써 보다 효율적인 협동작업을 할 수 있는 시스템을 소개한다. 본 논문에서 소개하는 시스템은 주소 동기화(URL Synchronization), 스크롤 동기화(Scroll Synchronization) 및 윈도우 크기 동기화(Window Size Synchronization) 기능을 제공하여 사용자들이 서로 다른 터미널에서 웹 브라우저를 동기적으로 이용할 수 있게 한다. 주소 동기화는 인터넷 브라우징의 이동과 방향을 동기적으로 제어해주고, 폼 동기화는 웹 페이지 입력을 실시간으로 보여준다. 스크롤 동기화는 웹 페이지의 스크롤을 동기적으로 제어하여 웹 브라우저의 출력 내용이 길어질 경우에도 문서 안의 같은 부분을 공유 할 수 있게 하며 윈도우 크기 동기화는 윈도우의 길이와 넓이를 맞춰준다.

• The KIPS Transactions:PartC
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• v.10C no.1
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• pp.103-110
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• 2003

In this paper, we propose and evaluate the performance distance-based registration considering call arrival. We propose the mobility model, which can be used to analyze the performance of proposed registration schemes. Numerical results show that zone-based registration needs less number of registration than distance-based registration. On the other hand, the registration load of the distance-based registration is equally distributed to all cells in a location area. However, the registration load of the distance-based registration considering cail arrival is similar to that of zone-based registration and equally distributed to all cells in a location area. Therefore, the proposed scheme can be effectively used restricted radio resources.

• Journal of Broadcast Engineering
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• v.10 no.2
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• pp.174-181
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• 2005

In this paper, we proposed new fast scattered pilot synchronization techniques to reduce the burst synchronization time for the DVB-H receiving system with robustness. DVB-H terminals employ a TDM system called 'Time-Slicing' to reduce power consumption. In order to fully exploit the potential power reduction, the synchronization time for the DVB-H receiver must be very short. A typical DVB-T system uses the TPS Synchronization to determine the position of scattered pilots which are used for channel estimation, and it takes 68 OFDM symbol time. In this paper, several new fast scattered pilot synchronization techniques are proposed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.6
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• pp.1045-1050
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• 2008

A GNSS augmentation system provides precision information using corrected GNSS pseudorange measurements. Common bias errors are corrected by PRC (Pseudorange Correction) between reference stations and a rover. However non-common errors (ionospheric and tropospheric noise error) are not corrected. Using position error variance this paper analyzes non-common error (noise errors) of ionosphere and troposphere wet vapor.

• Nuclear Engineering and Technology
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• v.26 no.3
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• pp.401-410
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• 1994

Validation study of two radionuclide migration models for single fracture developed in geologic medium the hydrodynamic dispersion diffusion model(HDDM) and the channeling dispersion diffusion model(CDDM), was studied by migration experiment of tracers through an artificial granite fracture on the labolatory scale. The tracers used were Uranine and Sodium lignosulfonate know as nonsorbing material. The flow rate ranged 0.4 to 1.5 cc/min. Related parameters for the models were estimated by optimization technique. Theoretical breakthrough curves with experimental data were compared. In the experiment, it was deduced that the surface sorption for both tracers did not play an important role while the diffusion of Uranine into the rock matrix turned out to be an important mass transfer mechanism. The parameter characterizing the rock matrix diffusion of each model agreed well The simulated result showed that the amount of flow rate could not tell the CDDM from the HDDM quantitatively. On the other hand, the variation of fracture length gave influence on the two models in a different degree. The dispersivity of breakthrough curve of the CDDM was more amplified than that of the CDDM when the fracture length was increased. A good agreement between the models and experimental data gave a confirmation that both models were very useful in predicting the migration system through a single fracture.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.38 no.5
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• pp.548-555
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• 2001

In this paper, we proposed a HVS(human visual system) model-based digital image watermarking which is not only invariant to rotation and translation but also more robust to lossy compression, cropping, and scaling as compared to the conventional method. Fourier transform and log-polar mapping is used to make the proposed algorithm invariant to rotation and translation, and in addition, watermark energy is embedded maximally based on spatial frequency sensitivity of HVS without the deterioration of the invisibility. As a result, the robustness of watermarking is improved both in general image processing operations such as cropping, low pass filtering, and lossy compression and in geometrical transforms such as rotation, translation, and scaling. And, by disjoint embedding of the watermark and the template without intersection, the deterioration of invisibility and robustness is prevented. Experimental results show that proposed watermarking is about 30~75 [%] more robust af compared to the conventional methods.

• Journal of the Korea Computer Industry Society
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• v.2 no.7
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• pp.983-996
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• 2001

Mobile Ad Hoc Network (MANET) is a network architecture which has no backborn network and is deployed temporarily and rapidly in emergency or war without fixed mobile infrastructures. All communications between network entities are carried in ad-hoc networks over the wireless medium. Due to the radio communications being extremely vulnerable to propagation impairments, connectivity between network nodes is not guaranteed. Therefore, previously developed routing algorithms in wired networks cannot be used. And many new algorithms have been undergone. This study proposes the Secondary Header approach to the cluster based routing protocol (CBRP). In case, the main header becomes abnormal status so that the main header can not participate the communications between network entities, the secondary header immediately replaces the primary header without selecting process of the new primary header. The performances of proposed algorithm CBRP-SH(Cluster Based Routing Protocol using Secondary Header) are compared with CBRP and results are presented in order to show the effectiveness of the algorithm.