• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.4 s.346
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• pp.58-66
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• 2006

This paper proposes an FSS(Frequency Selective Surface) design system that automatically derives design parameters minimally specified by engineers. The proposed system derives optimal design parameters through theory of electromagnetic scattering on FSS, database implemented from real data obtained from practically manufactured FSS, and GA(Genetic Algorithm) for optimizing design parameters. The system, at the first step, searches the best matching FSS within preconstructed DB with given characteristics specified by operators, and then sets initial genes from the searched FSS parameters. GA iterates the optimization process until the system finds the FSS design parameters that matches the characteristics specified by operators. The theory for the electromagnetic scattering on FSS is verified by comparing the simulation results with real data obtained by measuring system composed of horn antenna and receiver. The process for manufacturing the FSS is also included in the paper.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.2 s.105
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• pp.101-109
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• 2006

A broadband, DC to 40 GHz 5-bit MMIC digital attenuator has been developed. The ultra broadband attenuator has been achieved by adding transmission lines in the conventional Switched-T attenuator and optimizing the transmission line parameters. Momentum simulation was performed in design for accurate performance prediction at high frequencies and Monte Carlo analysis was applied to verify the performance stability against the MMIC process variation. The attenuator has been fabricated with $0.15\;{\mu}m$ GaAs pHEMT process. This attenuator has 1 dB resolution and 23 dB dynamic ranges. High attenuation accuracy has been achieved over all attenuation ranges and 40 GHz bandwidth with the reference state insertion loss of less than 6 dB at 20 GHz. The input and output return losses of the attenuator are better than 14 dB over all attenuation states and frequencies. The measured IIP3 of the attenuator is 33 dBm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.10
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• pp.1077-1083
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• 2009

To reject the Doppler frequency spectrum dispersion of clutter caused by high-speed antenna rotation of MTI radar system due to terrain characteristics, signal processing parameters(MTI filter constant, M/N detector ration, K-factor and offset of CFAR) are adjusted for the optimal elimination of the ground clutter. For this investigation, logging equipment is designed and utilized for the collection of classified ground clutter data. Test case is devised through Matlab simulation for the classified analysis and optimization of clutter rejection. Then indoor radar test and outside test in accordance with terrain characteristics are repeatedly performed for the verification of the test. This whole process is through the evolutional development model and repeated for the optimization. Final result is that ground-clutter rejection capability is 5.6 times(7.5 dB) better than that of existing radar system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.8
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• pp.624-631
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• 2018

To meet the requirements of various satellite synthetic aperture radar(SAR) system performance parameters, the characteristics of the antenna pattern should be analyzed. In this paper, we propose a method to improve the SAR system performance using an effective technique for optimizing antenna pattern synthesis in the presence of element failure. The desired antenna pattern can be synthesized by referring to the optimized antenna mask templates using the particle swarm optimization algorithm. In the simulation, the performance of the proposed method is verified by analyzing characteristics related to the SAR system performance parameters using antenna pattern regeneration.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.9
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• pp.4287-4306
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• 2016

Network resilience provides an effective way to overcome the problem of network failure and is crucial to Internet protocol (IP) network management. As one of the main challenges in network resilience, recovering from link failure is important to maintain the constancy of packets being transmitted. However, existing failure recovery approaches do not handle the traffic engineering problem (e.g., tuning the routing-protocol parameters to optimize the rerouting traffic flow), which may cause serious congestions. Moreover, as the lack of QoS (quality of service) restrictions may lead to invalid rerouting traffic, the QoS requirements (e.g., bandwidth and delay) should also be taken into account when recovering the failed links. In this paper, we first develop a probabilistically correlated failure model that can accurately reflect the correlation between link failures, with which we can choose reliable backup paths (BPs). Then we construct a mathematical model for the failure recovery problem, which takes maximum rerouting traffic as the optimizing objective and the QoS requirements as the constraints. Moreover, we propose a heuristic algorithm for link failure recovery, which adopts the improved k shortest path algorithm to splice the single BP and supplies more protection resources for the links with higher priority. We also prove the correctness of the proposed algorithm. Moreover, the time and space complexity are also analyzed. Simulation results under NS2 show that the proposed algorithm improves the link failure recovery rate and increases the QoS satisfaction rate significantly.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.9B
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• pp.832-844
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• 2008

Distributed localization algorithms are necessary for large-scale wireless sensor network applications. In this paper, we introduce an efficient node distribution based localization algorithm that emphasizes simple refinement and low system load for low-cost and low-rate wireless sensors. Each node adaptively chooses neighbor nodes for sensors, update its position estimate by minimizing a local cost function and then passes this update to the neighbor nodes. The update process considers a distribution of nodes for large-scale networks which have same density in a unit area for optimizing the system performance. Neighbor nodes are selected within a range which provides the smallest received signal strength error based on the real experiments. MATLAB simulation showed that the proposed algorithm is more accurate than trilateration and les complex than multidimensional scaling. The implementation on MicaZ using TinyOS-2.x confirmed the practicality of the proposed algorithm.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.40 no.4
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• pp.264-274
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• 2003

This paper presents a direct generalized minimum-variance self tuning controller with a PID structure using neural network which adapts to the changing parameters of the nonlinear system with nonminimum phase behavior, noises and time delays. The self-tuning controller with a PID structure is a combination of the simple structure of a PID controller and the characteristics of a self-tuning controller that can adapt to changes in the environment. The self-tuning control effect is achieved through the RLS (recursive least square) algorithm at the parameter estimation stage as well as through the Robbins-Monro algorithm at the stage of optimizing the design parameter of the controller. The neural network control effect which compensates for nonlinear factor is obtained from the learning algorithm which the learning error between the filtered reference and the auxiliary output of plant becomes zero. Computer simulation has shown that the proposed method works effectively on the nonlinear nonminimum phase system with time delays and changed system parameter.

• The Journal of the Acoustical Society of Korea
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• v.22 no.7
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• pp.562-572
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• 2003

A matched-target model inversion method was developed for a passive sonar to estimate the position of moving targets. Based on the well known matched-field processing in underwater acoustics, the method finds target position by matching the measured target directions and frequencies with the corresponding values of the proposed target model. For the efficient and accurate estimations, the parameter searching was accomplished using a hybrid optimizing method, which first starts with a global optimization such as generic algorithm or simulated annealing then applies a local optimization of a simple down hill algorithm. The suggested method was testified using simulations for three different moving scenarios. The simulation results showed that the method is robust in convergence, even under the situation of over 5 times standard deviation of Gaussian distribution of measured error, and is practical in calculation time as well.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.7
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• pp.131-139
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• 2013

To overcome the limitations in performance and power consumption of traditional electrical interconnection based network-on-chips (NoCs), a hybrid optical network-on-chip (HONoC) architecture using optical interconnects is emerging. However, the HONoC architecture should use circuit-switching scheme owing to the overhead by optical devices, which worsens the latency unfairness problem caused by frequent path collisions. This resultingly exert a bad influence in overall performance of the system. In this paper, we propose a new task mapping algorithm for optimizing latency by reducing path collisions. The proposed algorithm allocates a task to a certain processing element (PE) for the purpose of minimizing path collisions and worst case latencies. Compared to the random mapping technique and the bandwidth-constrained mapping technique, simulation results show the reduction in latency by 43% and 61% in average for each $4{\times}4$ and $8{\times}8$ mesh topology, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.1
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• pp.61-68
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• 2017

In this paper, we propose an improved magnetic field shielding structure to reducing the magnetic field generated in the wireless power transfer system operating at a low frequency band. The proposed structure consists of the magnetic material and the conductive material, magnetic field cancelling effect for power transfer is minimized while improving the leakage magnetic field cancelling effect by optimizing the various design parameters in the proposed structure. We analyzed and verified the efficiency of the wireless power transfer system and the reduction effect of the leakage magnetic field through computer simulation and measurement. Analysis results show that power transfer efficiency of the wireless power transfer system utilizing the proposed structure is 77 %, which is maintained at the conventional power transfer efficiency. In addition, compared with the structure maintaining high power transfer efficiency, leakage magnetic field strength is reduced to 29~37 % at the nearest point.