• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.6 no.4
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• pp.272-277
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• 2013

In this paper the effect of instability and chaos in optical fiber networks based on the Internet is described. Nonlinear optical fiber effect especially Brillouin scattering in networks has emerged as the essential means for the construction of active optical devices used for all-optic in-line switching, channel selection, amplification, oscillation in optical communications and a host of other applications. The inherent optical feedback by the back-scattered Stokes wave in optical networks also leads to instabilities in the form of optical chaos. This paradigm of optical chaos in fiber Internet serves as a test for fundamental study of chaos and its suppression and exploitation in practical application in optical fiber communication. This paper attempts to present a survey and some of our research findings on the nature of Brillouin chaotic effect on Internet based optical communication.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.1
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• pp.22-30
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• 2004

A micro-fluidic oscillator is used to control a linear actuator in a dynamic microsystem. The pressure difference at its two output ports causes the linear actuator to move, and it is a standard of judging the performance of the oscillator. The performance can be improved by optimizing the geometry of the oscillator, which has to enable fluid jet to switch at low inlet velocity. For this, in this study the relationship between the pressure coefficient (difference) and geometric parameters is obtained through the analysis using the software FLUENT. From the results the optimized model that maximize the output pressure difference is obtained by using a cyclic coordinate method that is one of optimization methods. As a result not only the performance is improved, but also the working range is more widen.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.1 no.1
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• pp.61-66
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• 2008

In this paper the effect of instability and chaos in optical fiber networks based on the Internet is described. Nonlinear optical fiber effect especially Brillouin scattering in networks has emerged as the essential means for the construction of active optical devices used for all-optic in-line switching, channel selection, amplification, oscillation in optical communications and a host of other applications. The inherent optical feedback by the back-scattered Stokes wave in optical networks also leads to instabilities in the form of optical chaos. This paradigm of optical chaos in fiber Internet serves as a test for fundamental study of chaos and its suppression and exploitation in practical application in optical fiber communication. This paper attempts to present a survey and some of our research findings on the nature of Brillouin chaotic effect on Internet based optical communication.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.07a
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• pp.287-290
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• 2011

분산 동영상 부호화 시스템에서는 복호기에서 움직임 보상 보간 기법을 이용하여 부가정보를 생성한다. 생성된 부가정보와 원 Wyner-Ziv 프레임간의 차이를 채널 부호로 오류 정정하게 되는데 이때 부호기에서는 복호기에서의 오류 정정을 위하여 패리티 비트인 Wyner-Ziv 비트를 복호기로 보내게 되고 복호기에서는 이 Wyner-Ziv 비트를 이용하여 Wyner-Ziv 프레임을 복원하는데 더 많은 Wyner-Ziv 비트가 필요할 경우 피드백 채널을 통해 Wyner-Ziv 비트를 요청하게 된다. 이때 부호기에서 조건부 엔트로피를 구할 수 있다면 이를 이용하여 Wyner-Ziv 비트 전송량을 제어함으로써 피드백 채널을 제거 할 수 있다. 이를 위해 부호기에서도 부가정보를 알아야하는데 복호기에서 사용하는 부가정보 생성 기법은 복잡도가 높기 때문에 사용할 수 없다. 본 논문에서는 부호기에서 간단한 부가정보를 생성하는 방법을 제안하고 분산 동영상 부호화 시스템에 적용하여 피드백 채널을 제거하였을 때의 성능을 분석하였다.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.226-228
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• 2005

This paper deals with power system stabilization problem using a network control system in which the control is applied through a communication channel in feedback form. Analysis and synthesis issues are investigated by modeling the packet delivery characteristics of the network as a Bernoulli random variable, which is described by a two state Markov chain. This model assumption yields an overall system which is described by a discrete-time Markov jump linear system. These employ the norm to measure the performance of the system, and they compute the norm via a necessary and sufficient matrix inequality condition.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.7A
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• pp.731-742
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• 2010

We propose an incremental relaying protocol in conjunction with opportunistic communication for differential modulation with an aim to make efficient use of the degrees of freedom of the channels by exploiting a imited feedback signal from the destination. In particular, whenever the direct link from the source to the destination is not favorable to decoding, the destination will request the help from the opportunistic relay (if any). The performance of the proposed system is derived in terms of average bit error probability and achievable spectral efficiency. The analytic results show that the system assisted by the opportunistic relaying can achieve full diversity at low SNR regime and exhibits a 30㏈ gain relative to direct transmission, assuming single-antenna terminals. We also determine the effect of power allocation on the bit error probability BEP) performance of our relaying scheme. We conclude with a discussion on the relationship between the given thresholds and channel resource savings. Monte-Carlo simulations are performed to verify the analysis.

• Proceedings of the KIEE Conference
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• 2005.10b
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• pp.23-25
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• 2005

This paper is devoted to the passivity based control in bilateral teleoperation for varying time delay. Toimprove the stability and task performance, master and slave in bilateral teleoperation must be coupled via the network through which the force and velocity are communicated. However, time delay existing in the transmission channel is a long standing impediment to bilateral control and can destabilize the system, even if the system is stable without time delay, In this paper, we investigate how the varying time delay affects the advanced teleoperation stability and results in an out-of-control status. A new approach based on passivity control has been bilaterally designed for both the master and slave sites and the simulation result will verify that our approach is better and effective for passive bilateral teleoperation.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.166.5-166
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• 2001

In the teleoperation system, force, position and velocity signals are communicated between master and slave arm. The addition of force feedback for the teleoperation system benefits the operator by providing more information to perform given tasks especially for tasks requiring contact with environment. When the master and slave arms are located in different places, time delay is unavoidable. Also it is well known that the system can become unstable when a time delay exists in the communication channel. The proposed control strategy is to use predictive control method(MBPC). The predictive controller is used to control teleoperation´s position and force control. Also it is used to overcome time delay.

• Journal of Institute of Control, Robotics and Systems
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• v.6 no.4
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• pp.295-304
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• 2000

In the teleoperation system, force and velocity signals are communicated between a master and a slave robot. The addition of force feedback to a teleoperation system benefits the operator by providing more information to perform given tasks especially for tasks requiring contact with environment. When the master and slave arms are located in different places, time delay is unavoidable and it is well known that the system can become unstable when even a small time delay exists in the communication channel. The control scheme proposed in this paper is based on the estimator with virtual master model. Delayed signal from the master robot can be replaced by the estimated signal with the virtual master model. This control scheme makes the teleoperation system stable for the given time delay while the conventional scheme is not. This new control scheme is verified through numerical simulations and an experiments using the dual axis testbed of the teleoperation system.

• Proceedings of the KOSOMBE Conference
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• v.1998 no.11
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• pp.171-172
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• 1998

Recent development of digital technology has offered new possibilities for noticeable advances of hearing aids. Using the digital technology, it is possible to equip hearing aids with powerful features such as multi-channel nonlinear compression amplification and the feedback cancellation, these are often difficult to implement with analog circuits. Still, speech in noise is one of the major complaints of not only hearing impaired persons but also normal listeners. This paper describes speech intelligibility in background noise for both normal and hearing impaired listeners. Speech enhancement algorithms were implemented and compared for normal and sensorineural hearing impairment listeners.