• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.9
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• pp.714-723
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• 2003

An effective technique to increase the signal swing and reduce noise is to use fully-differential -circuits. However, design of a common-mode feedback (CMFB) circuit that stabilizes the common-mode output level is essential. In this paper, a general description is given to fully-differential amplifiers with their CMFB loops, then a new error amplifier that is just composed of transistors and stabilizes the DC output level is proposed. We designed a simple and efficient bias circuit that allows the stability and maximum input swing. Simulation result shows the enhanced phase margin and increased differential-mode input swing with a proposed error amplifier.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.1
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• pp.138-145
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• 2007

Wireless transmission system using the multipath channel is affected ISI due to the delay spread. So we use a decision feedback equalizer which consist of decision part and feedback filter for remove the ISI effectively. In this paper, we propose a improved adaptive decision feedback equalizer to mitigate ISI effectively. The proposed adaptive decision feedback equalizer is construct by using soft decision device and hierarchical feedback filter based on MMSE sub-optimal equalizer using the LMS algorithm. Soft decision device mitigate the error propagation in feedback filter by incorrectly detected decision symbol and feedback filter which is divided two step independently mitigate the ISI by using a adaptive algorithm. As a result this structure shows better performance than conventional decision feedback equalizer by mitigating the error propagation in filter cause incorrectly detecting symbol. and we get the MSE more rapidly by using larger step-size due to reduce the number of feedback filter tap. In computer simulation, we compare the bit error rate performance of proposed decision feedback equalizer with conventional one on the S-V channel model for UWB system.

• English Language & Literature Teaching
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• v.16 no.4
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• pp.133-152
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• 2010

There is disagreement, among researchers, on the benefits of corrective feedback on L2 learners' written output. Some scholars advocate the usefulness of corrective feedback while some claim that error correction is ineffective and even harmful. So far, however, research outcomes cannot settle this debate. Based on this debate, this study examines whether there is a difference among diverse types of feedback on the effects of L2 learners' writing improvement. This study found that teacher's direct feedback was more effective than any other types of feedback on the effect of participants' writing improvement. In particular, teacher's direct feedback helped their improvement on grammar, mechanics, and form. Among the types of peer feedback, self-correction was the most effective. In teacher feedback, form-focused feedback had more effects than content-focused feedback, but no difference with regard to peer feedback. In addition, teacher's content-focused feedback was more effective than peer's content-focused feedback. Overall, in all types of feedback, teacher feedback was more effective than peer feedback. However, direct (form-focused) feedback was the most effective in teacher feedback, and self-correction in peer feedback. The least effective feedback in both teacher and peer feedback was indirect (form-focused) feedback, which is simple underlining of errors.

• Journal of Sensor Science and Technology
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• v.23 no.1
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• pp.1-6
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• 2014

In many medical image devices, dc noise often prevents normal diagnosis. In wireless capsule endoscopy systems, multipath fading through indoor wireless links induces inter-symbol interference (ISI) and indoor electric devices generate impulsive noise in the received signal. Moreover, dc noise, ISI, and impulsive noise are also found in optical fiber communication that can be used in remote medical diagnosis. In this paper, a blind signal processing method based on the biased probability density functions of constant modulus error that is robust to those problems that can cause error propagation in decision feedback (DF) methods is presented. Based on this property of robustness to error propagation, a DF version of the method is proposed. In the simulation for the impulse response of optical fiber channels having slowly varying dc noise and impulsive noise, the proposed DF method yields a performance enhancement of approximately 10 dB in mean squared error over its linear counterpart.

• The Journal of the Acoustical Society of Korea
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• v.31 no.1
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• pp.1-10
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• 2012

The linear and decision-feedback equalization can mitigate time-varying intersymbol interference (ISI) caused by time-varying multipath propagation for underwater acoustic channels. The perfect elimination of interference components, however, is difficult using the linear equalization and the decision feedback equalizer has an error propagation problem. To overcome these shortcomings, this paper proposes an equalizer mode selection method using training sequences. The proposed method selects an equalization mode corresponding to the signal-to-noise ratio (SNR). If the SNR is low, the proposed system operates the linear equalizer for preventing the error propagation and if the SNR is high, the decision feedback equalizer for eliminating the residual ISI. Therefore, the proposed method can improve the error performance compared to the conventional equalizers. The computer simulation shows the proposed method improves the bit error performance using practical underwater channels responses acquired from the sea experiment.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.7
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• pp.9-19
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• 2004

WLAN (Wireless Local Area Networks) needs error recovery and flow control schemes to support reliable multicast protocol. Limited wireless bandwidth, as well as queuing losses caused by the asymmetric wired/wireless interactions, demands more effective approaches for reducing packet losses. Moreover, since the wireless channel is a shared broadcast medium, if sender receives feedback information simultaneously from several receivers, the feedback delays data frame transmission of forward direction by introducing channel congestion and burden at the sender. Therefore, it is important to minimize the amount of feedback information from receivers. In this paper, we propose an ARS(Adaptive Redundancy Scheme) that combines FEC(Forward Error Correction) using channel state estimation and ARQ(Automatic Repeat Request) both to reduce the amount of feedback information and the number of retransmissions and to guarantee high data reliability in a WLAN multicast environment. Performance of the proposed scheme is evaluated by means of analysis and simulations in AWGN and Rayleigh fading channels. The results show that the proposed scheme reduces the amount of feedback information and the number of retransmissions and guarantees high data reliability, while keeping throughput efficiency similarly with the conventional FEC and ARQ scheme.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.5
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• pp.410-415
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• 2013

This paper proposes a bidirectional platoon control law using a coupled distance error based on the backstepping-like feedback linearization control method for an interconnected mobile agent system with a string structure. Unlike the previous results where the single agent was controlled using the only own information without other agents, the proposed control law cannot show the only distance error convergence of each agent, but also the string stability of the whole system. Also, the control performances are improved by the proposed control law in spite of low performance of bidirectional control strategy in the previous results. The proposed bidirectional platoon control algorithm is based on the backstepping-like feedback linearization control method. The position errors between each agent and the preceding and the behind agents are coupled by weighted summation. By the proposed control law, the distance error of each agent can converge to zero while the string stability is guaranteed when the coupled errors can converge to zero. To this end, the back-stepping control method is employed. The pseudo velocity input is determined considering the kinematic relationship between agents and the string stability. Then, the actual dynamic control input is determined to make the actual velocity converge to the pseudo velocity input. The stability analysis and the simulation results of the proposed method are included in order to demonstrate the practical application of the proposed algorithm.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.8
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• pp.661-666
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• 2013

A state feedback controller with integration of output error is proposed for way-point tracking of an AUV (Autonomous Underwater Vehicle). For the steering control on the XY plane, the proposed controller uses three state variables (sway velocity, yaw rate, heading angle) and the integral of the steering error, and for the depth control on the XZ plane, it uses four state variables (pitch rate, depth, pitch angle) and the integral of the depth error. From the simulation using Matlab/Simulink, we verify that the performance of the proposed controller is satisfactory within an error range of 1m from the target way-point for arbitrarily chosen sets of consecutive way-points.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.1
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• pp.12-17
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• 2014

In this paper, we propose a controller capable of reducing the effect of measurement errors under AC and DC noise. Typically, the control system measures data through a sensor. If sensor noise is included in a controller via the feedback channel, the signal is distorted and the entire system cannot work normally. Therefore, some appropriate action to counter the measurement error effect is essential in the controller design. Our controller is equipped with a gain-scaling factor and a compensator to reduce the effect of measurement error in the feedback signal. Also, we use a switching control strategy to enhance the performance of the controller regarding convergence speed. Our proposed controller can therefore effectively reduce the AC and DC noise of the sensor. We analyze the proposed controller by Laplace transform technique and our control method is verified via MATLAB simulation.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.437-440
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• 1988

This paper discuss which new dynamic control method for robot arm. It is basedon nonlinear feedback and T transformation which externally linearizes the whole system and provides simultaneous output decoupling. The nonlinear feedback augmented with optimal error correcting controller, which operates on the task error level. Computer simulation were appled to evaluate the performance of new dynamic control method. The simulation results are discussed in detail.