• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.481-486
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• 2007

The Zienkiewicz-Zhu(Z/Z) error estimate is slightly modified for the hierarchical p-refinement, and is then applied to L-shaped plates subjected to bending to demonstrate its effectiveness. An adaptive procedure in finite element analysis is presented by p-refinement of meshes in conjunction with a posteriori error estimator that is based on the superconvergent patch recovery(SPR) technique. The modified Z/Z error estimate p-refinement is different from the conventional approach because the high order shape functions based on integrals of Legendre polynomials are used to interpolate displacements within an element, on the other hand, the same order of basis function based on Pascal's triangle tree is also used to interpolate recovered stresses. The least-square method is used to fit a polynomial to the stresses computed at the sampling points. The strategy of finding a nearly optimal distribution of polynomial degrees on a fixed finite element mesh is discussed such that a particular element has to be refined automatically to obtain an acceptable level of accuracy by increasing p-levels non-uniformly or selectively. It is noted that the error decreases rapidly with an increase in the number of degrees of freedom and the sequences of p-distributions obtained by the proposed error indicator closely follow the optimal trajectory.

• 대한인간공학회지
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• 제7권2호
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• pp.31-44
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• 1988

If an error occurs in the automatic mode when the advanced teleoperator system performs a task in hostile environment then the automatic mode changes into the manual mode. The operation by the control program and the operation by a human recover the error in the manual mode. The system resumes the automatic mode and continues the given task. It is necessary to improve the manual mode in order to make the best use of a man-robot system, as a part of the human interface technique. Therefore, the error recovery task is performed by combining the operation by the control program representing autonomy of a robot and the operation by a human representing versatility of a human operator effectively in the view point of human factors engineering. The geometric inverse kinematics is used for the calculation of the robot joint values in the operation by the control program. The singularity operation error and the parameter operation error often occur in this procedure. These two operation errors increase the movement time of the robot and the coordinate reading time, during the error recovery task. A singularity algorithm, parameter algorithm and fuzzy control are studied so as to remove the disadvantages of geometric inverse kinematics. And the geometric straight line motion is studied so as to improve the disadvantages of the operation by a human.

• 한국컴퓨터정보학회논문지
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• 제25권3호
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• pp.89-96
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• 2020

본 논문은 시스템 내부에서 소프트웨어 오류가 발생하였을 경우 컨트롤러 내의 Watchdog Timer를 이용하여 시스템의 상태를 오류 발생시점 이전 상태로 복구하는 시스템을 설계 구현하고, 하드웨어 오류 발생 시 별도의 리셋 회로를 통해 시스템을 재실행할 수 있는 기술을 제안한다. 제안 시스템은 외부 지원 없이 시스템 자체적으로 반영구적으로 작동 할 수 있도록 함으로써, 시스템의 안정적인 작동, 유지비용 절감 및 신뢰성을 제공하며, 고 신뢰성 응용분야에서 요구되는 자가 동작, 진단 및 복구 기능을 통한 시스템의 항상성 유지를 위한 적용이 가능하다.

• 한국통신학회논문지
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• 제24권6A호
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• pp.920-930
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• 1999

멀티 레벨(Multi-level) QAM(Quadrature Amplitude Modulation)은 전송대역의 효율적인 사용을 위한 전송방식의 하나로 많은 연구가 이루어져 실용화가 진행되고 있다. 이러한 전송방식을 사용하는 수신기에는 전송과정 중 채널에서 발생하는 ISI(Intersymbol Interference) 및 위상 오차(phase error)를 보상하기 위해서는 등화기(equalizer)와 위상 복구(carrier recovery) 회로를 사용해야 한다. 본 논문에서는 멀티 레벨 QAM 시스템에 적용할 수 있는 효과적인 수신기의 모델을 제안한다. 제안된 수신기에는 Godard 알고리즘을 사용하는 자력(blind) 등화기와 등화기의 출력 신호에 포함된 위상 에러를 복원하기 위해 $\theta$-정합을 이용하여 위상 오차를 복원하는 위상 복구 회로를 포함한다. 또한 다양한 채널모델에 대하여 제안한 수신기의 성능을 평가한다.

• 한국통신학회논문지
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• 제38A권7호
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• pp.545-551
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• 2013

MQASK 수신기에서 수신 심볼의 타이밍 동기에 사용되는 타이밍 복원 루프 Timing Error Detector(TED) 와 입력신호의 표본화율을 제어하는 VCO또는 NCO 및 루프 필터로 구성된다. 여기서 수신신호의 심볼율과 수신기의 표본화율의 시간 축에서의 위상차를 검출하는 TED는 심볼율과 표본화율의 주파수차가 클 경우 정상동작을 하지 못하는 단점이 있다. 본 논문에서는 PLL의 주파수 검출기와 같은 역할을 타이밍 복원 루프에서 수행하여 타이밍 복원 입력 신호의 주파수 차가 매우 큰 경우에도 타이밍 복원을 가능하게 할 수 있는 심볼율 변별기(Symbol Rate Discriminator SRD) 와 이를 사용한 타이밍 복원루프 구조를 제안 하였으며 이를 통해 심볼율이 가변되는 신호에 대한 타이밍 동기 획득이 가능함을 모의실험을 통해 입증하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1999년도 하계종합학술대회 논문집
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• pp.77-80
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• 1999

This paper deals with a design of a symbol timing recovery circuit of QAM using the interpolation in AWGN channel. To reduce timing jitter and the amount of processing data, we employ MGA (Modified Gardner Algorithm) as a symbol timing error detector which is called NDA(Nondecision Directed Algorithm). We show the characteristics (S-curve and the variance) of timing error detector with the roll-off factor of a shaping filter, which are compared with GA. Also, we compare the BER curve of interpolation method with that of ideal case. The performance of the STR is shown to be close to that of ideal case. This result shows that this method can be useful to implement symbol timing recovery circuit for multi-level modulation.

• Journal of Information Technology Applications and Management
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• 제11권2호
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• pp.29-43
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• 2004

As the development of an information technique, gradually, mobile device is going to be miniaturized and operates at high speed. By such the requirements, the devices using a flash memory as a storage media are increasing. The flash memory consumes low power, is a small size, and has a fast access time like the main memory. But the flash memory must erase for recording and the erase cycle is limited. JFFS is a representative filesystem which reflects the characteristics of the flash memory. JFFS to be consisted of LSF structure, writes new data to the flash memory in sequential, which is not related to a file size. Mounting a filesystem or an error recovery is achieved through the sequential approach. Therefore, the mounting delay time is happened according to the file system size. This paper proposes a MJFFS to use a multi-checkpoint information to manage a mass flash file system efficiently. A MJFFS, which improves JFFS, divides a flash memory into the block for suitable to the block device, and stores file information of a checkpoint structure at fixed interval. Therefore mounting and error recovery processing reduce efficiently a number of filesystem access by collecting a smaller checkpoint information than capacity of actual files. A MJFFS will be suitable to a mobile device owing to accomplish fast mounting and error recovery using advantage of log foundation filesystem and overcoming defect of JFFS.

• International Journal of Aeronautical and Space Sciences
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• 제11권2호
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• pp.98-109
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• 2010

This paper deals with a new method of unmanned aerial vehicle (UAV) recovery when a UAV fails to get a global positioning system (GPS) signal at an unprepared site. The proposed method is based on the simultaneous localization and mapping (SLAM) algorithm. It is a process by which a vehicle can build a map of an unknown environment and simultaneously use this map to determine its position. Extensive research on SLAM algorithms proves that the error in the map reaches a lower limit, which is a function of the error that existed when the first observation was made. For this reason, the proposed method can help an inertial navigation system to prevent its error of divergence with regard to the vehicle position. In other words, it is possible that a UAV can navigate with reasonable positional accuracy in an unknown environment without the aid of GPS. This is the main idea of the present paper. Especially, this paper focuses on path planning that maximizes the discussed ability of a SLAM algorithm. In this work, a SLAM algorithm based on extended Kalman filter is used. For simplicity's sake, a blimp-type of UAV model is discussed and three-dimensional pointed-shape landmarks are considered. Finally, the proposed method is evaluated by a number of simulations.

• 한국정보처리학회논문지
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• 제3권2호
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• pp.327-338
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• 1996

본 논문은 분산 트랜잭션 처리 시스템에서 분산 트랜잭션들이 사용한 자원들을 들을 일관성 있게 유지하는 검사점 설정 및 오류 복구 기법에 관한 연구이다. 기존 의 방법과 비교하여 제안하는 검사점 설정 방법은 검사점을 설정하는 동안 수행되고 있는 분산 트랜잭션들에 간섭 현상과 저장 비용을 최소화 할 수 있고, 검사점을 설정 하기 위한 별도의 메세지를 사용하지 않기 때문에 추가의 검사점을 설정하기 위한 메세지 비용이 없다. 또한 제안하는 알고리즘은 도미노 현상과 순환적 재시작 현상을 제거할 수 있다. 본 논문에서는 제안하는 알고리즘의 정확성과 성능을 설명하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2003년도 봄 학술발표회 논문집
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• pp.288-295
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• 2003

An adaptive procedure in finite element analysis is presented by p-refinement of meshes in conjunction with a posteriori error estimator that is based on the recovery technique. In case of the recovery technique, the SPR(superconvergent patch recovery) approach has been modified for p-adaptive mesh refinement. The strategy of finding a nearly optimal distribution of polynomial degrees on a fixed finite element mesh is discussed such that a particular element has to be refined automatically to obtain an acceptable level of accuracy by increasing p-levels non-uniformly. To verify the proposed algorithm, the limit value approach is proposed which utilizes the exact strain energy computed from the extrapolation equation. A new pre-processor is developed for the p-version finite element program in which the vector graphic editor is used for the automatic generation of node connection and coordinate by halfedge solid data structure according to uniform or nonuniform p-distribution. The general 2-D algorithm is also developed to generate face modes and internal modes in accordance with different mesh types. The quality of the error estimator is investigated with the help of two mumerical examples. The results show that the sequences of p-distributions obtained by the proposed error indicator closely follow the optimal trajectory.