• 한국통신학회논문지
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• 제19권5호
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• pp.892-900
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• 1994

ITU-TSS에서는 최근 B-ISDN의 신호 전송을 위하여 service specific connection oriented protocol(SSCOP)을 권고하였다. SSCOP에서는 오류 제어 및 흐름 제어를 위하여 주기적으로 상태 정보를 교환한다. 본 논문에서는 SSCOP를 end-to-end의 경우와 link-by-link인 경우로 나누어 이산 대기 모델로 분석하였다. 메시지의 에러율, 트래픽 부하, 상태 정보의 교환주기 등의 영향을 고려하여 성능 측정값으로써 지연기산, 수신단 버퍼 크기, 그리고 전송 효율의 평균값을 구하고 성능 분석의 결과를 검증하기 위하여 시뮬레이션을 수행하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1992년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 19-21 Oct. 1992
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• pp.632-637
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• 1992

Recently many dynamics control algorithms using robot dynamic equation have been proposed. One of them, Kawato's feedback error learning scheme requires neither an accurate model nor parameter estimation and makes the robot motion closer to the desired trajectory by repeating operation. In this paper, the feedback error learning algorithm is implemented to control a robot system, 5 DOF revolute type movemaster. For this purpose, an actuator dynamic model is constructed considering equivalent robot dynamics model with respect to actuator as well as friction model. The command input acquired from the actuator dynamic model is the sum of products of unknown parameters and known functions. To compute the control algorithm, a parallel processing computer, transputer, is used and real-time computing is achieved. The experiment is done for the three major link of movemaster and its result is presented.

• Current Optics and Photonics
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• 제5권2호
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• pp.114-120
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• 2021

Free-space optical (FSO) communication is considered to be a potential solution to congestion in the radio-frequency spectrum and last-mile-access bottleneck issues in future cellular communication networks, such as 5G and beyond. However, FSO link performance may degrade significantly due to irradiance fluctuations and random temporal fluctuations from atmospheric turbulence. Therefore, in this work the main objective is to reduce the effect of the atmospheric turbulence by considering a multihop FSO communication system with amplify-and-forward relaying supported by a radio-frequency (RF) link, which form a hybrid FSO/RF communication system. The FSO link is assumed to follow the gamma-gamma fading model, which represents strong turbulence. Also, the RF link is modeled by a Rayleigh distribution. The performance of the considered system, in terms of the outage probability and average bit-error rate (BER), is investigated and analyzed under various weather conditions and pointing errors. Furthermore, the effect of the number of employed relay nodes on the performance of the system is investigated. The results indicate that the considered system reduces outage probability and average BER significantly, especially for low channel quality. Finally, the closed-form expressions derived in this work are compared to the results of Monte Carlo simulations, for verification.

• 한국정밀공학회지
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• 제18권6호
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• pp.87-92
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• 2001

An error analysis is very important for a precision machine to estimate its performances. This study proposes a new parallel device, cubic parallel manipulator. Errors of the proposed cubic parallel manipulator include upper and down universal joint errors, due to the directional changes in the forces in the links, and actuation errors. An error analysis is presented based on an error model formed through the relation between the universal joint errors of the cubic parallel manipulator and the end effector accuracy. The analysis shows that the method can be used in predicting the accuracy of other cubic parallel devices.

• 한국정밀공학회지
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• 제18권4호
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• pp.97-103
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• 2001

Accuracy of a machined part is determined by the relative motion between the cutting tool and the workpiece. One of the important factors which affects the relative motion is the geometric errors of a machine tool. In this study, firstly, geometric errors are measured by laser interferometer, and the positioning error of each control point selected uniformly on the control surface CAD model can be estimated from th oirm shaping model and geometric error data base. Where a form shaping function is derived from the link of homogeneous transformation matrix. Secondly, control points are shifted to the estimated amount of positioning errors. A new control surface is modeled with NURBS(Non Uniform Rational B-Spline) surface approximation to the shifted control points. By generating tool paths to the redesigned control surface, we reduce the machining error quite.

• 한국통신학회논문지
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• 제42권2호
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• pp.383-385
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• 2017

For the purpose of providing high data rate real-time services, radio transmission technologies for ship ad-hoc network based on the Recommendation ITU-R 1842-1 are designed. In order to increase the link throughput of real-time services, in this paper, we investigate the performance of the SANET with the spatial transmit diversity techniques are employed. Based on the analysis of the packet error rate and throughput, we select the efficient multiple antenna schemes for SANET to improve the link reliability.

• 전자공학회논문지B
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• 제32B권5호
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• pp.777-787
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• 1995

This paper presents a new method for automatically calibrating robot link (Kinematic) parameters during the process of estimating motion parameters of a moving object. The motion estimation is performed based on stereo cameras mounted on the end-effector of a robot manipulator. This approach significantly differs from other calibration approaches in that the calibration is achieved by simply observing the motion of the moving object (without resorting to any other external calibrating tools) at numerous and widely varying joint-angle configurations. A differential error model, which expresses the measurement errors of a robot in terms of robot link parameter errors and motion parameters, is developed. And then a measurement equation representing the true measurement values is derived. By estimating the above two kinds of parameters minimizing the difference between the measurement equations and the true moving pattern, the calibration of the robot link parameters and the estimation of the motion parameters are accomplished at the same time.

• 제어로봇시스템학회논문지
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• 제7권7호
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• pp.597-604
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• 2001

Recently, the study of the moving sliding mode in the variable structure control is in progress ac-tively. The conventional time-invariant sliding model control can\`t guarantee the sliding mode in the reaching phase, which is robust against the uncertainty. But with the time-varying method, the controller makes the states track the desired trajectories and keeps the sliding mode. Nevertheless, the piecewise continuous method of the past still has the reaching mode. Thus we propose the continuously moving sliding surface by the fuzzy algorithm. The proposed algorithm is made of the fuzzy rule considering both the error and the error velocity, and may apply to the entire phase plane without sacrificing sliding mode. Especially the proposed scheme can rotate tot he slope-decreasing direction, needless to say rotating to the slope-increasing direction. For showing that the proposed controller guarantees the sliding model and ensures the robustness, we apply the proposed method to the two-link robot manipulator simulation.

• 한국통신학회논문지
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• 제29권10B호
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• pp.831-840
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• 2004

무선 링크 상에서의 QoS 제공을 위해서는 트래픽 소스와 무선 채널 그리고 오류 제어 방식간의 상호 작용에 대해 정확히 이해하여야 하고 또한 이를 계량화 하는 것이 필요하다. 이 논문에서는 이와 같은 상호작용을 네트워크 계층 관점에서 분석하고 이를 딜레이 성능의 분석에 적용하였다. 시간에 따라 전송 용량이 변하는 무선 링크 상에서 on/off 트래픽 소스가 데이타를 전송하는 시나리오를 가정하였다. 패킷 딜레이 분포는 uniformization과 Laplace transform이라는 두 가지 방식으로 유도 되었고 두 방식간의 장단점이 비교되었다. 수식으로 표현된 딜레이 분포는 다시 딜레이에 대한 서비스 요건이 주어진 경우, 무선 유효 대역폭 (wireless effective bandwidth) 이라는 양을 계산하기 위해 사용되었다. 수치적인 분석과 시뮬레이션을 통해서 이 논문에서 제안한 분석의 정확도를 검증하였고 오류 제어와 대역폭 할당이 패킷 딜레이 성능에 미치는 영향을 분석하였다.

• 한국전자파학회논문지
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• 제14권3호
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• pp.268-275
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• 2003

본 논문에서는 멀티 미디어 서비스를 지원하는 VSG-CDMA 시스템의 역방향 링크 용량을 전력 제어와 사용자 분포에 따라 두 모델로 가정하여 해석적으로 분석한다. 분석 모델 I은 완벽한 전력제어와 사용자의 균일 분포로 가정하여 블록킹 확률식을 계산하고 1 %의 블록킹 확률에 일치하는 최대 음성과 데이터 사용자수를 산출한다. 분석 모델 II은 전력제어오차와 사용자의 비균일(셀 경계 부분에 위치)분포로 가정하여 분석한다. 모델 I의 분석 결과는 5 MHz의 광대역 VSG-CDMA 시스템 용량의 상한선(upper bound)이며 모델 II의 분석 결과는 시스템 용량의 하한선(lower bound)을 제시한다. 또한 모델 II에서 데이터 활동율과E$_{b}$/N$_{o}$ 값에 따른 사용자 용량을 분석하여 VSG-CDMA 시스템의 성능 개선 방안을 제안한다.