• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.8 no.3
• /
• pp.91-99
• /
• 2009

Development of high-speed Internet services and the increased supply of mobile devices have become the key factor for the acceleration of ubiquitous technology. WiBro system, formed with lP backbone network, is a MBWA technology which provides high-speed multimedia service in a possibly broader coverage than Wireless LAN can offer. Wireless telecommunication environment needs not only mobility support in Layer 2 but also mobility management protocol in Layer 3 and has to minimize handover latency to provide seamless mobile services. In this paper, we propose a fast cross-layer handover scheme based on signal strength prediction in WiBro environment. The signal strength is measured at regular intervals and future value of the strength is predicted by Exponential Smoothing Method. With the help of the prediction, layer-3 handover activities are able to occur prior to layer-2 handover, and therefore, total handover latency is reduced. Simulation results demonstrate that the proposed scheme predicts that future signal level accurately and reduces the total handover latency.

• Proceedings of the KIEE Conference
• /
• 2015.07a
• /
• pp.177-178
• /
• 2015

This paper proposes a power smoothing scheme of a doubly-fed induction generator. The proposed scheme aims to mitigate system frequency deviation caused by the variable wind. To achieve this, a dynamic droop loop is used and its gain changes with rate of change of frequency so that it can release a large amount of kinetic energy at the initial stage of a frequency event. The performance of the proposed scheme was investigated in a model system with high wind penetration using EMTP-RV simulator. The test results indicate that the scheme can smooth the output power by absorbing or releasing the output power under a varying wind condition.

• International Journal of Automotive Technology
• /
• v.8 no.3
• /
• pp.337-342
• /
• 2007

A multi-objective optimization technique was implemented to obtain optimal topologies of the inner reinforcement for a vehicle's hood simultaneously considering the static stiffness of bending and torsion and natural frequency. In addition, a smoothing scheme was used to suppress the checkerboard patterns in the ESO method. Two models with different curvature were chosen in order to investigate the effect of curvature on the static stiffness and natural frequency of the inner reinforcement. A scale factor was employed to properly reflect the effect of each objective function. From several combinations of weighting factors, a Pareto-optimal topology solution was obtained. As the weighting factor for the elastic strain efficiency went from 1 to 0, the optimal topologies transmitted from the optimal topology of a static stiffness problem to that of a natural frequency problem. It was also found that the higher curvature model had a larger static stiffness and natural frequency than the lower curvature model. From the results, it is concluded that the ESO method with a smoothing scheme was effectively applied to topology optimization of the inner reinforcement of a vehicle's hood.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.9 s.180
• /
• pp.2397-2405
• /
• 2000

The remeshing is a method to replace a distorted mesh by a new mesh without interrupting the finite element calculation. The remeshing procedure in this paper refers to the rezoning, for which a sm oothing process is developed to alleviate the distortions of mesh. In the paper, an automatic finite element rezoning system with tetrahedral elements for large deformation analysis has been developed. Our smoothing process is composed of two steps, a surface smoothing and a volume smoothing. In the surface smoothing, checking the dihedral angle and projection on surface patch reduced the change of shape and nodes penetrating die. The constrained Laplacian smoothing has been employed for the volume smoothing process. The state variables are mapped from old mesh to new mesh by using volume coordinates within a tetrahedral element. All these procedures have been linked to the NIKE3D program As illustrated in the examples the overall strategy ensures a robust and efficient rezoning scheme for finite element simulation of metal-forming processes.

• Journal of Electrical Engineering and Technology
• /
• v.12 no.6
• /
• pp.2099-2105
• /
• 2017

In a power system that has a high wind penetration, the output power fluctuation of a large-scale wind turbine generator (WTG) caused by the varying wind speed increases the maximum frequency deviation, which is an important metric to assess the quality of electricity, because of the reduced system inertia. This paper proposes a stable power-smoothing scheme of a doubly-fed induction generator (DFIG) that can suppress the maximum frequency deviation, particularly for a power system with a high wind penetration. To do this, the proposed scheme employs an additional control loop relying on the system frequency deviation that operates in combination with the maximum power point tracking control loop. To improve the power-smoothing capability while guaranteeing the stable operation of a DFIG, the gain of the additional loop is modified with the rotor speed and frequency deviation. The gain is set to be high if the rotor speed and/or frequency deviation is large. The simulation results based on the IEEE 14-bus system demonstrate that the proposed scheme significantly lessens the output power fluctuation of a WTG under various scenarios by modifying the gain with the rotor speed and frequency deviation, and thereby it can regulate the frequency deviation within a narrow range.

• Journal of the Korean Institute of Telematics and Electronics B
• /
• v.31B no.5
• /
• pp.108-116
• /
• 1994

In this paper, we propose a new motion vector smoothing scheme which has high reliability and coding efficiency of motion vectors. In motion vector filed, groupings are made using angle and magnitude of the motion vectors. In each group, the unreliable motion vectors are corrected by the motion vector smoothing. In 3$\times$3 window, motion vector of the current block is made to group, and the motion vector smoothing is performed only in that group. Result of computer simulation shows much improvement of the reliability of motion vectors. Moreover, coding bits of the motion vector are diminished from 0.967 to 6.773 bits per block.

• Transactions of Materials Processing
• /
• v.12 no.4
• /
• pp.340-347
• /
• 2003

In the rigid-plastic finite element simulation of hot forging processes using hexahedral mesh, remeshing of a flash is important for design and control of the process to obtain desirable defect-free products. The mesh compression method is a remeshing technique which enables the construction of an effective hexahedral mesh in the flash. However, because the mesh is distorted during the compression procedure of the mesh compression method, when it is used in resuming the analysis, it causes discretization error and decreases the conversance rate. Therefore, mesh smoothing is necessary to improve the mesh quality. In this study, several geometric mesh smoothing techniques and optimization techniques are introduced and modified to improve mesh quality. Then, the most adaptive technique is recommended for the mesh compression method.

• Journal of Information Processing Systems
• /
• v.7 no.1
• /
• pp.103-110
• /
• 2011

In this paper, an adaptive motion vector smoothing scheme based on weighted vector median filtering is proposed in order to eliminate the motion outliers more effectively for improving the quality of side information in frame-based distributed video coding. We use a simple motion vector outlier reliability measure for each block in a motion compensated interpolated frame and apply weighted vector median filtering only to the blocks with unreliable motion vectors. Simulation results show that the proposed adaptive motion vector smoothing algorithm improves the quality of the side information significantly while maintaining low complexity at the encoder in frame-based distributed video coding.

• Proceedings of the KIEE Conference
• /
• 2015.07a
• /
• pp.181-182
• /
• 2015

In a power system with a high wind power penetration level, the output power of a wind power plant (WPP) might give negative impacts on the frequency control of a power system. This paper proposes a power smoothing scheme of a wind turbine generator (WTG) to reduce the frequency deviation. To do this, an additional control loop is used, the output of which depends on the frequency deviation. The gain of the additional loop is determined depending on the kinetic energy (KE) of a WTG; in the under frequency condition, the gain is set to be proportional to the releasable KE of a WTG; otherwise, it is set to the maximum value. The performance of the proposed scheme is investigated for 100-MW doubly-fed induction generator based WPP using an EMTP-RV simulator under various wind conditions. The results show that the proposed scheme successfully reduces the frequency deviation.

• Proceedings of the IEEK Conference
• /
• 2002.06b
• /
• pp.149-152
• /
• 2002

The performance of a 1-bit DAC depends on that of the analog circuits. The mixed SC-CT (switched capacitor-continuous time) architecture is an effective design methodology for the analog circuits. This paper Proposes a new buffer scheme for the 1-bit digital-to-analog subconverter and a new SF-DSC(smoothing filter and differential-to-sig le converter) which performs both the smoothing filter and the differential-to-single convertor simultaneously.