• ETRI Journal
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• 제35권4호
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• pp.578-586
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• 2013

Using a sub-terahertz (sub-THz) wave generated using a photonics-based technology, a high-speed wireless link operating at up to 10 Gbps is designed and demonstrated for realization of seamless connectivity between wireless and wired networks. The sub-THz region is focused upon because of the possibility to obtain sufficient bandwidth without interference with the allocated RF bands. To verify the high-speed wireless link, such dynamic characteristics as the eye diagrams and bit error rate (BER) are measured at up to 10 Gbps for non-return-to-zero pseudorandom binary sequence $2^{31}-1$ data. From the measurement results, a receiver sensitivity of -23.5 dBm at $BER=10^{-12}$ is observed without any error corrections when the link distance between the transmitter and receiver is 3 m. Consequently, we hope that our design and experiment results will be helpful in implementing a high-speed wireless link using a sub-THz wave.

• International journal of advanced smart convergence
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• 제7권4호
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• pp.92-100
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• 2018

This paper presents a link adaptation scheme for adaptive full duplex (AFD) systems. The signal modulation levels and communication link patterns are adaptively selected according to the changing channel conditions. The link pattern selection process consists of two successive steps such as a transmit-receive antenna pair selection based on maximum sum rate or minimum maximum symbol error rate, and an adaptive modulation based on maximum minimum norm. In AFD systems, the antennas of both nodes are jointly determined with modulation levels depending on the channel conditions. An adaptive algorithm with relatively low complexity is also proposed to select the link parameters. Simulation results show that the proposed AFD system offers significant bit error rate (BER) performance improvement compared with conventional full duplex systems with perfect or imperfect self-interference cancellation under the same fixed sum rate.

• 한국전자파학회논문지
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• 제9권5호
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• pp.589-602
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• 1998

무선 ATM통신망에서 ATM기술올 무선링크에 적용하는 경우에 Rayleigh 및 Rician 페이딩 채널특성, 전력 제한, 단일 및 버스트 에러로 인해 유선링크에서 보다 상당한 전송성능 열화가 예상되며 이를 보상하기 위한 방안들이 강구되어야 한다. 본 논문에서는 무선 ATM통신망에서 무선링크률 통한 ATM 데이터의 전송시 전송성 농을 단일 및 버스트 에러환경으로 구분하여 정량적으로 분석하였으며 전송성능 열화현상이 발생된다는 것을 확 인하였다. 그려고 이러한 전송성능 열화현상올 극복하기 위한 FEC, ARQ, Hybrid ARQ 기법 동의 적용방안 검 토 후, ATM QoS(Quality of Service) 파라메터를 이용한 성능 분석올 통해 성놓개선 효과가 있음올 확인하였 다. 또한 이들 기법들간의 성능을 패킷 에러율 및 처리융 측면에서 비교 분석하였으며 이를 바탕으로 무선 ATM 방의 성능개선을 위해 트래픽 속성에 따라 효율적으로 적용하기 위한 통합 에러제어 구조를 제안하였다.

• International Journal of Precision Engineering and Manufacturing
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• 제6권2호
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• pp.61-71
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• 2005

The study reported deals with investigating the feasibility of control strategy for a serial rigid link manipulator that applies impulsive torques at the joints. The strategy is illustrated for a planar three rigid link manipulator. An impulse-based concept which uses successive torque impulses on rigid link as the controller for motion correction was introduced. This control strategy was tested over the entire trajectory to demonstrate that the tracking error could be reduced effectively. The best condition for minimizing the tracking error with the least impulse input at each joint is investigated by considering one design and one operating parameter. The first was the damping in the system, and the second was the sampling time during operation. The results show that this approach can provide useful guidance for the design and control of robot manipulators that require minimum impulse feedback for accurate tracking.

• International Journal of Precision Engineering and Manufacturing
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• 제2권4호
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• pp.75-80
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• 2001

An error analysis is very important to estimate performance of a precision machine. This study proposes an error analysis for a new parallel device, a cubic parallel device. The cubic parallel manipulator has error sources including upper and lower universal joint errors due to the directional changes in the link and actuation errors. The maximum errors of the end effector are affected by the axial direction changes of each links and the clearances of the universal joints when the parallel manipulator is moving along a path. It is found that the changes of errors mostly occur at the positions where the directions of exerting link forces shift. The error analysis is based on an error model formed from the relation between the universal point errors and the end-effector accuracy. The analysis method can be also used in predicting the accuracy of other parallel devices.

• Journal of Power Electronics
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• 제15권6호
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• pp.1593-1600
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• 2015

This paper proposes a novel compensation algorithm of current offset error for single-phase linear compressor in home appliances. In a half-bridge inverter, current offset error may cause unbalanced DC-link voltage when the DC-link is comprised of two serially connected capacitors. To compensate the current measurement error, the synchronous reference frame transformation is used for detecting the measurement error. When an offset error occurs in the output current of the half-bridge inverter, the d-axis current has a ripple with frequency equal to the fundamental frequency. With the use of a proportional-resonant controller, the ripple component can be removed, and offset error can be compensated. The proposed compensation method can easily be implemented without much computation and additional hardware circuit. The validity of the proposed algorithm is verified through experimental results.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2002년도 전력전자학술대회 논문집
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• pp.343-346
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• 2002

In recent, complex SVPWM (Space Vector PWM) algorithm can be easily implemented by high performance microprocessor and DSP. Various SVPWM techniques are widely studied due to the advantages of low harmonic distortion and high use ratio of D.C. link voltage. Most of various studies for improving of VS-PWM inverter performance are concentrated about switching pattern and zero pulse pattern split algorithms. However, dc link voltage that is determined at rated load and speed conditions is not proper in the low speed and under rated load. In this paper, analysis of current ripple with digitally implemented SVPWM inverter is introduced according to link voltage. The optimal link voltage in the designed inverter system and load condition is provided in order to suppress output voltage error and current ripple. As remaining the effective voltage vector interval per sampling period sufficiently, additional voltage error and current ripple are suppressed. The proposed algorithm is verified through digital simulation and experimental results.

• 한국통신학회논문지
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• 제24권6B호
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• pp.1088-1097
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• 1999

이 논문에서는 무선접속노드와 무선링크로 구성되는 무선 ATM접속망에서 ATM 셀손실율을 정량적으로 분석하였다. 무선접속노드는 ND/D/1 queue로 모델링하였고 무선링크는 단일 및 버스트 에러환경으로 구분하였으며 단일 비트에러 환경보다 버스트 에러환경에서의 셀손실 확률이 더 높다는 것을 확인하였다. 무선 ATM접속망에서 ATM기술을 무선링크에 적용하는 경우에 Rayleigh 및 Rician 페이딩 채널특성, 전력제한, 버스트 에러 특성으로 인해 단일 비트에러 환경의 유선링크에서 보다 상당한 전송성능 열화가 발생하는 것은 필연적이며 이를 보상하기 위한 방안들이 강구되어야 한다. 이러한 무선 채널의 전송성능 열화현상을 극복하기 위해 CBR 트래픽에 적합한 FEC(Forward Error Correcting) 기법의 적용방안을 검토한 후, 이 중 대표적인 concatenated FEC 기법의 성능을 셀 손실율 측면에서 분석하였다.

• Current Optics and Photonics
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• 제3권3호
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• pp.210-214
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• 2019

The allowable path-deviation time of aircraft in a free-space optical communication system has been estimated from various trajectories, using different values of aircraft speeds and turn rates. We assumed the existence of a link between the aircraft and a ground base station. First, the transmitter beam's divergence angle was calculated through two different approaches, one based on a simple optical-link equation, and the other based on an attenuation coefficient. From the calculations, the discrepancy between the two approaches was negligible when the link distance was approximately 110 km, and was under 5% when the link distance ranged from 80 to 140 km. Subsequently, the allowable path-deviation time of the aircraft within the tracking-error tolerance of the system was estimated, using different aircraft speeds, turn rates, and link distances. The results indicated that the allowable path-deviation time was primarily determined by the aircraft's speed and turn rate. For example, the allowable path-deviation time was estimated to be ~3.5 s for an aircraft speed of 166.68 km/h, a turn rate of $90^{\circ}/min$, and a link distance of 100 km. Furthermore, for a constant aircraft speed and turn rate, the path-deviation time was observed to be almost unchanged when the link distance ranged from 80 to 140 km.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.211-214
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• 2000

An error analysis is very important for a precision machine tool to estimate its performance. This study proposes a new parallel device, a cubic parallel manipulator. Errors of the proposed cubic parallel manipulator include universal joint errors, errors occurring due to changes in the fore directions in the links, and actuation errors. An error analysis is performed for the manipulator platform moving at uniform velocity. The analysis shows how the position and orientation of the platform influences the directional link forces that change the errors in the manipulator. The analysis shows that the method can be used in predicting the accuracy of parallel devices.