• Korean Management Science Review
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• v.12 no.2
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• pp.89-103
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• 1995

Traditionally, the scarce and expensive resources in communication networks has been the bandwidth of transmission facilities; accordingly, the techniques used for networking and switching have been chosen so as to optimize the efficient use of that resource. One of them is the packet switching for data communications, which is much different from the circuit switching. It allows multiple users to share the data network facilities and bandwidth, rather than providing specific amounts of dedicated bandwidth to each users. One main challenge therefore has been to design and build cost-effective packet switching networks. In this paper, we develop a mathematical programming medel and heuristic algorithm for designing the packet switching networks with hop-count constraints. To develop an efficient heuristic, we apply the Lagrangian relaxation method. Some valid inequalities, which have been known as the tight constraints, are considered to improve the bound for Lagrangian sub-problem. The computational experiments show that the performance of the proposed heuristic is very satisfactory in both the speed and the quality of design solutions generated.

• ETRI Journal
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• v.30 no.2
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• pp.216-226
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• 2008

This paper proposes a novel transport network architecture for the next generation network (NGN) based on the optical burst switching technology. The proposed architecture aims to provide efficient delivery of various types of network traffic by satisfying their quality-of-service constraints. To this end, we have developed a soft-state bandwidth reservation mechanism, which enables NGN transport nodes to dynamically reserve bandwidth needed for active data burst flows. The performance of the proposed mechanism is evaluated by means of numerical analysis and NS2 simulation. Our results show that the packet delay is kept within the constraint for each traffic flow and the burst loss rate is remarkably improved.

• Journal of Broadcast Engineering
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• v.13 no.1
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• pp.119-127
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• 2008

Transmission of video over Internet or wireless network requires coded stream capable of adapting to dynamic network conditions instantly. To meet this requirement, various scalable video coding schemes have been developed, among which the Scalable Video Coding (SVC) extension of the H.264/AVC is the most recent one. In comparison with the scalable profiles of previous video coding standards, the SVC achieves significant improvement on coding efficiency performance. For adapting to dynamic network bandwidth, the SVC employs inter-layer switching between different temporal, spatial or/and fidelity layers, which is currently supported with instantaneous decoding refresh (IDR) access unit. However, for real-time adaptability, the SVC has to frequently employ the IDR picture, which dramatically decreases the coding efficiency. Therefore, an extension of SP picture from the AVC to the SVC for an efficient inter-layer switching is investigated and presented in this paper. Simulations regarding the adaptability to dynamic network bandwidth are implemented. Results of experiment show that the SP picture added SVC provides an average 1.2 dB PSNR enhancement over the current SVC while providing similar adaptive functionality.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.10
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• pp.59-66
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• 2003

We propose the novel optical burst switching scheme to guarantee a minimum bandwidth for multiple classes. To date, QoS studies on OBS network are capable of differentiating two classes, but have difficulties in providing a minimum bandwidth lot several classes because of lower classes' collision with the highest class bursts in the networks. To solve that problem, in our proposed scheme we assign time zones in a data channel for each class periodically, making one burst have top priority at least its zone. Also, the new burst assembling algorithm, as well as the way of managing data channel, is necessarily proposed to coordinate with the proposed OBS scheme. Through the evaluation, we show that the worst-case end-to-end delay is small enough and the received bandwidth of the lower classes is still assured regardless of the traffic load of the highest class.

• Proceedings of the KIEE Conference
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• 1991.11a
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• pp.171-174
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• 1991

Among the various PWM methods, the hysteresis-band current control PWM method is popularly used because of its simplicity of implementation, fast response characteristics and inherent peak current limiting capability. However, the current control PWM method with a fixed hysteresis-band has the disadvantage that switching frequency decreases and current ripple is high as the increasing of back-EMF. As a result, load current contains excess harmonics. This paper describes a adaptive hysteresis-bandwidth control algorithm so as to maintain the average switching frequency constant and decrease the current ripple where the hysteresis bandwidth is derived as a relation with the switching frequency. This control algorithm is applied to the surface-type brushless DC motor with separated winding and using the computer simulation, the validity of its algorithm is proved.

• The KIPS Transactions:PartC
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• v.10C no.2
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• pp.155-162
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• 2003

Fast restoration time and service guarantee are the important goals to achieve the network reliability. In the protection switching scheme, one way to guarantee service fro an application session if a network happens to fail is to establish the restoration path that amounts to the same bandwidth of the working path of the session at the same time. When we setup the restoration path, we can reduce the bandwidth consumption by the restoration path if the path can share the bandwidth required by the other paths. This paper explains the methods how to determine the shared bandwidth of the restoration path in the protection switching scheme, given the maximum bandwidth assigned to a link along the working path. We point out that such sharing algorithm can not reduce the bandwidth consumption by the restoration paths in some cases, which contradict the general conception. We explain why this can happen, and show the simulation results in real network topologies to prove our arguments. We explain the reason of the failure of the sharing effect by the simple sharing algorithm. Finally we propose the way of how we can overcome the failure of the sharing effect, using the complete sharing algorithm based on the link database and showing the results.

• Journal of Power Electronics
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• v.11 no.2
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• pp.156-162
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• 2011

The control loop time delay caused by sampling, the zero-order-holder effect and calculations is inevitable in the digital control of dc-dc switching converters. The time delay will limit the bandwidth of the control loop and therefore degrade the transient performance of digital systems. In this paper, the quantization time delay effects with different time delay values based on a generic second-order system are analyzed. The conclusion that the bandwidth of digital control is reduced by about 20% with a one cycle delay and by 50% with two cycles of delay in comparison with no time delay is obtained. To compensate the time delay and to increase the control loop bandwidth, a duty ratio predictive control scheme based on linear extrapolation is proposed. The compensation effect and a comparison of the load variation transient response characteristics with analogy control, conventional digital control and duty ratio predictive control with different time delay values are performed on a point-of-load Buck converter by simulations and experiments. It is shown that, using the proposed technique, the control loop bandwidth can be increased by 50% for a one cycle delay and 48.2% for two cycles of delay when compared to conventional digital control. Simulations and experimental results prove the validity of the conclusion of the quantization effects of the time delay and the proposed control scheme.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.4
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• pp.72-78
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• 2004

In this paper, a development of an inductive position sensor is described. The sensor is similar to a radial magnetic bearing in that the sensor stator is shaped like a heteropolar magnetic bearing and is driven by a switching amplifier. A demodulation filter extracts the gap information from the switching current ripples. A prototype sensor exhibits the resolution of $0.43\mum$ and the dynamic bandwidth of about 800Hz. The dynamic performance can be improved by increasing the switching frequency. However, the eddy current effects become noticeable at high switching frequency, thus limiting the improvement of the bandwidth.

• Proceedings of the KIEE Conference
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• 1998.07f
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• pp.2145-2147
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• 1998

This paper presents a Class-D type switched mode audio power amplifier employing ZVT(Zero-Voltage-Transition) soft switching technique. In order to obtain a wide bandwidth and lower distortion for an audio amplifier a high switching frequency is essential. The ZVT switching scheme enables a high frequency switching without sacrificing the efficiency much as in a hard switching. A prototype amplifier is built to demonstrate the feasibility of this technique for the audio power amplifier.

• ETRI Journal
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• v.44 no.2
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• pp.274-285
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• 2022

Retransmission in optical burst switching networks is a solution to recover data loss by retransmitting the dropped burst. The ingress node temporarily stores a copy of the complete burst and sends it each time it receives a retransmission request from the core node. Some retransmission schemes have been suggested, but uncontrolled retransmission often increases the network load, consumes more bandwidth, and consequently, increases the probability of contention. Controlled retransmission is therefore essential. This paper proposes a new controlled retransmission scheme for loss recovery, where the available bandwidth of wavelength channels and the burst lifetime are referred to as network conditions to determine whether to transmit a dropped burst. A retrial queue-based analysis model is also constructed to validate the proposed retransmission scheme. The simulation and analysis results show that the controlled retransmission scheme is more efficient than the previously suggested schemes regarding byte loss probability, successful retransmission rate, and network throughput.