• Computational Structural Engineering
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• v.15 no.2
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• pp.34-41
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• 2002

• Journal of KIISE
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• v.41 no.10
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• pp.832-837
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• 2014

Application loading speed can be improved by timely prefetching disk blocks likely to be needed by an application. However, existing prefetchers -- if they are not specialized to a particular application -- incur high overheads and are poor at identifying the blocks that will actually be required. There are many sequences in which blocks may be needed and, even if two access sequences are identical, block tracing and access timings can be affected significantly by the state of the buffer cache. We propose a new application-independent software-based prefetching technique, in which breakpoints are inserted at appropriate places in an application to collect the information on correlations between the blocks and to prefetch the potential blocks ahead of their schedule based on it. Experiments on an HDD-based desktop PC demonstrated an average 30% reduction in application launch time and 15% in general I/O, while reducing the wasted overhead.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.3
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• pp.28-38
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• 2003

Finite element analysis of cylinder heat/block compound under assembly, thermal and firing condition were performed. FE model including two cylinders with gasket, head bolts, liners and valve seats was used. FE modeling method and boundary conditions were introduced. Stress distribution and deformation of cylinder head and block under each loading condition were presented. Gasket pressure distribution and bore distortion level were predicted. Measured data of bore distortion was compared with the analysis results. The analysis result showed similar trends with the experimental data. High cycle fatigue analysis on the basis of this result has been performed in order to find the critical areas of the engine assembly.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06d
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• pp.181-183
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• 2012

WBAN(Wireless body area network)에서 사용되는 저 출력 센서 디바이스는 상당한 패킷 손실률을 발생시키며 데이터의 신뢰성을 떨어뜨리는 원인이 된다. 기존의 IEEE 802.15.4 MAC 프로토콜은 데이터 오류 발생 시 수신한 전체 데이터를 재전송하기 때문에 불필요한 에너지 소모와 오버헤드가 발생된다. 특히 WBAN 환경에서 인체 내부에 이식되는 디바이스의 경우 배터리 교체의 어려움과 초 저전력을 요구하기 때문에 노드의 수명 유지를 위해 사용되는 전력 소모량도 중대한 문제가 되고 있으며, 전체 데이터를 재전송하는 기존의 방식에서 발생하는 에너지 소모는 노드의 수명을 단축시키는 원인이 된다. 본 논문에서는 저전력과 신뢰성을 요구하는 WBAN 환경에서 수신 오류율 변화에 따른 데이터 동적 블록화 기법을 사용하여 재전송 데이터의 크기를 줄인다.

• Proceedings of the Korea Information Processing Society Conference
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• 2004.05a
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• pp.101-104
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• 2004

R-Tree 색인은 기존의 공간 데이터베이스관리시스템에서 공간 데이터 검색을 위하여 많이 사용되고 있는 공간 색인기법이다. 하지만 R-Tree 색인에서 기존의 잠금(Lock) 기반 동시성 제어는 갱신연산의 잠금으로 인해 검색연산의 블록킹 오버헤드(blocking overhead)가 발생한다. 본 논문에서는 R-Tree 색인에서 검색연산의 블록킹 오버헤드의 주요 원인이 되는 노드 분할 연산과 MBR(Minimum Bounding Rectangle) 갱신연산에 대해 각각 노드단위와 노드엔트리 단위의 버전(Version)을 생성하고 유지하여 동시에 발생하는 검색연산이 갱신연산으로 인한 지연이 없이 자신에 알맞은 버전을 읽음으로써, 검색성능을 높일 수 있는 버전 기반의 동시성 제어 기법을 제안한다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.1
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• pp.136-140
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• 2015

Linux environment that is commonly used at embedded systems supports various file systems as Ext2, FAT, NTFS, etc. The file system that is equiped on the embedded system is mostly implemented on mini hard disk or flash memory. The types of the file system of the system make an effect on the performance of a application programs. The factors of file system performance on a same media are block read, block write and block free time. On these factors, block read and block free time are not so different according to the type of file systems. This paper evaluates the performance benchmark of file systems supported by linux about block allocation and write performance. The results obtained from various experiments shows the characteristics of each file system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.8
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• pp.981-987
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• 2019

In this paper, we propose a new SC-FDE (single carrier frequency domain equalization) structure to cope with narrow band interference signals or jammers and reduce pilot overhead. The conventional SC-FDE structure has a problem that the receiver performance degrades severely due to difficulty in time-domain channel estimation when narrow band jammers exist. In addition, the spectral efficiency is lowered by transmitting pilot at every SC-FDE block to estimate channel response. In order to overcome those problems, the proposed structure is devised to estimate frequency domain channel directly without time domain channel estimation. To reduce the pilot overhead, several data blocks are transmitted between two pilots. The channel estimate of each data block is found through linear interpolation of two channel estimates at two pilots. By performing frequency domain channel equalization using this channel estimate, the distortion by the channel is well compensated when narrow band jammers exist. The performance of the proposed structure is confirmed by computer simulation.

• Journal of KIISE:Computer Systems and Theory
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• v.26 no.2
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• pp.242-260
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• 1999

실시간 데이터압축 기법은 저장 시스템의 용량과 저장 시스템간의 대역폭을 동시에 증가시킴으로써 프로세서-메모리, 메모리-디스크간의 성능 격차를 줄이기 위한 새로운 대안으로 연구되어 왔다. 하지만 압축데이타를 복원하는데 소요되는 시간은 압축 기법의 장점을 상쇄시킬 만큼 큰 오버헤드로 작용한다. 본 논문에서는 이러한 복원 오베헤드를 줄이기 위해 선택적 압축 기법과 복원 오버헤드 감춤 기법들을 적용한 선택적 압축 메모리 시스템을 제안하고 선택적으로 압축된 데이터를 효과적으로 접근하기 위한 캐쉬 구조와 메모리 운용방법을 제시한다. 제안된 선택적 압축 메모리 시스템의 성능은 분석적 모델과 트레이스 구동 방식의 실험을 통해 평가된다. 실험 결과에 따르면 선택적 압축 메모리 시스템의 성능은 데이터의 압축율과 응용 프로그램의 데이터 접근 유형에 따른 압축 블록의 참조율 및 복원 오버헤드를 줄이기 위해 장착된 복원 버퍼의 접근 성공률에 따라 좌우됨을 알 수있다. 복원 버퍼는 대부분의 벤치마크 프로그램들에 대해서 기존의 복원 오버헤드를 70% 이상 줄여 주며 이 경우 일반적인 메모리 시스템에 비해 최대 20%까지의 성능 향상을 보인다. 뿐만 아니라 선택적 압축 기법은 평균 47% 의 데이터 이동시간의 감소와 10%의 온 칩 캐쉬 접근 실패 횟수의 감소 효과를 제공한다.

• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.5
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• pp.598-603
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• 2004

An optical head actuator of an optical disk drive consists of two servo mechanisms for the focusing and the tracking to acquire data from disk. As the rotational speed of the disk grows, the utilized lag-lead-lead compensator has known to be above its ability for precisely controlling the optical head actuator. To overcome the difficulty, this paper propose a new controller design method for optical head actuator based fuzzy proportional-integral-derivative (PID) control and the genetic algorithm(GA). It employs a two-stage control structure with a fuzzy PI and a fuzzy PD control and is optimized by the GA to yield the suboptimal fuzzy PID control performance. It is shown the feasibility of the proposed method through a numerical tracking actuator simulation.

• KIPS Transactions on Computer and Communication Systems
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• v.2 no.10
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• pp.413-420
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• 2013

Redundant arrays of independent disks (RAID) without a power-fail-safe component in small and mid-sized business suffers from intolerably long resynchronization time after a unclean power-failure. Data blocks and a parity block in a stripe must be updated in a consistent manner, however a data block may be updated but the corresponding parity block may not be updated when a power goes off. Such a partially modified stripe must be updated with a correct parity block. However, it is difficult to find which stripe is partially updated (inconsistent). The widely-used traditional parity resynchronization manner is a intolerably long process that scans the entire volume to find and fix inconsistent stripes. This paper presents a fast resynchronization scheme with a negligible overhead for small and mid-sized RAIDs. The proposed scheme is integrated into a software RAID driver in a Linux system. According to the performance evaluation, the proposed scheme shortens the resynchronization process from 200 minutes to 5 seconds with 2% overhead for normal I/Os.