• Journal of Advanced Navigation Technology
• /
• v.12 no.4
• /
• pp.350-356
• /
• 2008

The recent networks are trending toward wireless networks. So wireless internet used to service of wired networks. But wireless networks can't show same performance of wired networks. Therefore, we are must concerned about Routing Protocol for improvement of a weak point of physical feature. But many researchers are not focusing on developing Routing Protocol. In this paper, we improve on AODV(Ad-hoc On-demand Distance Vector) for Wireless Mesh Networks. And it analyzed the result of simulation.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.20 no.1
• /
• pp.63-71
• /
• 2017

During the sea trial test, we discovered EMI(Electromagnetic Interference) between MIL-SATCOM parabolic antenna and ES(Electronic Warfare Support) omni antenna. Emitted side lobe of CW(Continuous Wave) from MIL-SATCOM raises the threshold level of ES omni antenna. Therefore detection rate of ES is decreased. To solve this problem, the path of side lobe of CW from MIL-SATCOM should be blocked using EMI shield. This paper presents the method how to calculate the size of EMI shield, material, and optimized deployment. The test of the EMI shield effect was performed on a surface ship. After installing EMI shield, EMI has been decreased significantly. This paper will provide a method how to design EMI shield and a way to verify the result.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.24 no.6B
• /
• pp.1048-1058
• /
• 1999

This paper compares some architectures to achieve the optimized WDM architecture for all optical transport network, the comparison is presented in terms of the number of required wavelength and LT. These architecture types are PPWDM, SHWDM, DHWDM and fully optical WDM. Topology is a static ring network where the routing pattern is fixed and traffic pattern has uniform demand. This paper also proposes an algorithm for the wavelength assignment for a folly optical WDM ring network which has full mesh traffic pattern. The algorithm is based on heuristic algorithm which assigns traffic connections according to their respective shortest path. Traffic described here that is to be passed through can be routed directly within the optical layer instead of having the higher layer to handle it.

• Tribology and Lubricants
• /
• v.30 no.1
• /
• pp.15-20
• /
• 2014

A more accurate expression for effective viscosity is obtained using a linear regression of the data from Fukui-Kaneko's model, which are obtained through numerical calculations based on the linearized Boltzmann equation. Veijola and Turowski's expression is adopted as a base function for effective viscosity. The four coefficients in that equation are optimized, and sensitivity analysis is conducted for these coefficients. The results show that the coefficient for the first-order Knudsen number is the most accurate, whereas the coefficient in the exponential of the Knudsen number is the least accurate compared with Fukui-Kaneko's results. The expression for effective viscosity is accurate within 0.02% rms of Fukui-Kaneko's results for the inverse Knudsen numbers from 0.01 to 100 and surface accommodation coefficients ranging from 0.7 to 1.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.11 no.3
• /
• pp.1373-1392
• /
• 2017

WiFi Direct (WD) is a state of the art technology for a Device-to-Device (D2D) communication in 802.11 networks. The performance of the WD system can be significantly affected by some key factors such as the type of application, specifications of MAC and PHY layer parameters, and surrounding environment etc. It is, therefore, important to develop a system model that takes these factors into account. In this paper, we focus on investigating the design parameters of the PHY layer that could maximize the efficiency of the WD 802.11 system. For this purpose, a basic theoretical model is formulated for a WD network under a 2x2 Multiple In Multiple Out (MIMO) TGn channel B model. The design level parameters such as input symbol rate and antenna spacing, as well as the effects of the environment, are thoroughly examined in terms of path gain, spectral density, outage probability and Packet Error Rate (PER). Thereafter, a novel adaptive algorithm is proposed to choose optimal parameters in accordance with the Quality of Experience (QoE) for a targeted application. The simulation results show that the proposed method outperforms the standard method thereby achieving an optimal performance in an adaptive manner.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.11 no.3
• /
• pp.1477-1491
• /
• 2017

Inspired by the multi-scale nature of hippocampal place cells, a biologically inspired model based on a multi-scale spatial representation for goal-directed navigation is proposed in order to achieve robotic spatial cognition and autonomous navigation. First, a map of the place cells is constructed in different scales, which is used for encoding the spatial environment. Then, the firing rate of the place cells in each layer is calculated by the Gaussian function as the input of the Q-learning process. The robot decides on its next direction for movement through several candidate actions according to the rules of action selection. After several training trials, the robot can accumulate experiential knowledge and thus learn an appropriate navigation policy to find its goal. The results in simulation show that, in contrast to the other two methods(G-Q, S-Q), the multi-scale model presented in this paper is not only in line with the multi-scale nature of place cells, but also has a faster learning potential to find the optimized path to the goal. Additionally, this method also has a good ability to complete the goal-directed navigation task in large space and in the environments with obstacles.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.11 no.7
• /
• pp.603-610
• /
• 2001

Industrial processes are normally operated by skilled humans who have the cumulative and logical information about the system. Fuzzy control has been investigated for many application. Intelligent control approaches based on fuzzy logic have a chance to include human thinking. This paper represents modeling approach based upon operators knowledge without mathematical model of the system and optimize the controller. The experimented system is constructed for sending a ball to the goal position using wind of two DC motors in the predefined path. A vision camera to mimic human eyes detects the ball position. The system used in this experiment could be hardly modeled by mathematical methods and ould not be easily controlled by conventional manners. The controller is designed based on the input-output data and experimental knowledge obtained by trials, and optimized under the predefined performance criterion. And this paper shows the data adaptation for changeable operating condition. When the system is driven in the abnormal condition with unconsidered noise, the new optimal operating parameters could be defined by adjusting membership functions. Thus, this technique could be applied in industrial fields.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.12 no.4
• /
• pp.452-459
• /
• 2009

A 6-bit MMIC digital attenuator applicable to X-band TR module has been developed by using $0.5{\mu}m$GaAs pHEMT processes. The Switched-T attenuator scheme and the switched-path attenuator scheme were adopted to obtain low insertion loss and small phase variation, respectively. Resistors and transmission lines are optimized to achieve the digital attenuator with high attenuation accuracy and small phase variation. The digital attenuator has RMS error of 0.4dB, resolution of 0.5dB and dynamic range of 31.5dB. The measurement results show that in-out VSWRs are less than 1.5, phase variation is from -7 to +2 degrees and IIP3 is 36.5dBm.

• Bulletin of the Korean Chemical Society
• /
• v.26 no.2
• /
• pp.303-308
• /
• 2005

A miniaturized time-of-flight mass spectrometer with an electron impact ionization source and sheet membrane introduction has been developed. The advantages and features of this mass spectrometer include high sensitivity, simple structure, low cost, compact volume with field portability, and ease of operation. A mass resolution of 400 at m/z 78 has been obtained with a 25 cm flight path length. Under optimized conditions, the detection limits for the volatile organic compounds (VOCs) studied were 0.2-10 ppm by volume with linear dynamic ranges greater than three orders of magnitude. The response times for various VOCs using a silicone membrane of 127 $\mu$m thickness were in the range 4.5-20 s, which provides a sample analysis time of less than 1 minute. These results indicate that the membrane introduction/time-of-flight mass spectrometer will be useful for a wide range of field applications, particularly for environmental monitoring.

• Journal of Sensor Science and Technology
• /
• v.27 no.4
• /
• pp.269-274
• /
• 2018

High-sensitivity signal-to-noise ratio (SNR) microphones are essentially required for a broad range of automatic speech recognition applications. Piezoelectric microphones have several advantages compared to conventional capacitor microphones including high stiffness and high SNR. In this study, we designed a new piezoelectric membrane structure by using the finite elements method (FEM) and an optimization technique to improve the sensitivity of the transducer, which has a high-quality AlN piezoelectric thin film. The simulation demonstrated that the sensitivity critically depends on the inner radius of the top electrode, the outer radius of the membrane, and the thickness of the piezoelectric film in the microphone. The optimized piezoelectric transducer structure showed a much higher sensitivity than that of the conventional piezoelectric transducer structure. This study provides a visible path to realize micro-scale high-sensitivity piezoelectric microphones that have a simple manufacturing process, wide range of frequency and low DC bias voltage.