• Journal of Korea Multimedia Society
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• v.2 no.3
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• pp.329-338
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• 1999

In this paper we propose a WATM MAC protocol called DTDD/PS (Dynamic Time Division Duplex using Poll/Select scheme). The idea of the DTDD/PS protocol is based that a radio cell is considered as queueing system. The MAC controller in base station is charged in coordinating terminals for the QoS requirement from each terminal. For that reason, terminals send it's own dynamic parameter represented its status, and controller controls the access of terminals and assigns time slots dynamically using received parameters. Therefore this system can satisfy the QoS of real-time service in wireless environments. To evaluate DTDD/PS protocol simulations are executed. In 25Mbps channel capacity, the voice and data coexist traffic situation, as the total number of terminal is increased, the delay of data terminals is increased rapidly. But the case of only increasing data terminals, the number of supported voice terminals is not varying. Therefore we can expect that DTDD/PS protocol can applied to multimedia traffic effectively.

• Journal of Korean Society of Transportation
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• v.33 no.5
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• pp.488-496
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• 2015

The main reason to install pedestrian pushbuttons is improving traffic operations. The current guideline for the installation of signal systems with pedestrian pushbuttons is car-oriented. It is difficult to clearly understand the guideline because there isn't an in-depth study to compare the pros and cons of the pedestrian- and vehicle-oriented methods in terms of waiting time. Thus, this study aims to estimate the waiting times of pedestrians and vehicles. The two delay times are compared considering the hypothetical circumstances such as geometry, pedestrian crossing time, pedestrian/vehicle counts and arrival distribution. The results show that when the pedestrian traffic volume exceeds 97 ped/h in the case of a two-lane road (one lane in each direction) the pushbutton system is effective and beneficial to pedestrians. It means that the total waiting time of pedestrians is less than the one of vehicles. Additional four scenarios are designed and tested by varying the number of lanes and design speeds. In conclusion, the pushbutton signal is more beneficial for pedestrians when the number of pedestrians is less than or equal to 85, 70, and 70 ped/h for the three-lane scenario, the four-lane with the design speed of 80km/h scenario, and the four-lane with the design speed of 100km/h, respectively.

• Journal of the Institute of Convergence Signal Processing
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• v.12 no.2
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• pp.107-112
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• 2011

Several developed countries have been developing their own satellite navigation systems, such as Europe's Galileo, China's BEIDOU, and Japan's QZSS, to cope with clock errors and signal vulnerabilities of GPS. In addition, modernization of Loran, eLoran, for GPS backup has been conducted. In Korea, a dependent navigation system has been required and for GPS backup, the need for utilization of time synchronization infrastructure through the modernization of Loran has been raised. Loran signal uses 100Khz groundwave. A significant factor limiting the ranging accuracy of the Loran signal is the ASF arising from the fact that the groundwave signal is likely to propagate over paths of varying conductivity and topography. Thus, an ASF compensation method is very important for Loran and eLoran navigation. This paper introduces the propagation delay model and then compares and analyzes the estimations from the propagation delay model and measured ASFs.

• Journal of Advanced Navigation Technology
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• v.26 no.4
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• pp.226-234
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• 2022

With advances in autonomous vehicles and networked control, there is a growing interest in the consensus control of a multi-agents system to control multi-agents with distributed control beyond the control of a single agent. Since consensus control is a distributed control, it is bound to have delay in a practical system. In addition, it is often difficult to have a very accurate mathematical model for a system. Even though a reinforcement learning (RL) method was developed to deal with these issues, it often experiences slow convergence in the presence of large uncertainties. Thus, we propose a slide RL which combines the sliding mode control with RL to be robust to the uncertainties. The structure of a sliding mode control is introduced to the action in RL while an auxiliary sliding variable is included in the state information. Numerical simulation results show that the slide RL provides comparable performance to the model-based consensus control in the presence of unknown time-varying delay and disturbance while outperforming existing state-of-the-art RL-based consensus algorithms.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.5B
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• pp.573-581
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• 2011

The underwater channel is known to offer poor communications channel. The channel medium is highly absorptive and the transmission bandwidth is limited. In addition, the channel is highly frequency selective; the degree of selectiveness depends on a detailed geometry of the channel. Furthermore, the response changes over time as the channel conditions affecting the response such as water temperature, sea surface wind and salinity are time-varying. The transceiver design to deal with the frequency and time selective channel, therefore, becomes very challenging. It has been known that deep fading at certain specific sub-carriers are detrimental to OFDM systems. To mitigate this negative effect, the proposed coded OFDM system employs an LDPC code based modulation. In this paper, we aim 1) to provide a detailed underwater channel model; 2) to design a robust LDPC coded OFDM system; 3) to test the proposed system under a variety of channel conditions enabled by the channel model.

• Wind and Structures
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• v.27 no.6
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• pp.381-397
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• 2018

Nonlinear behavior in fluid-structure interaction (FSI) of bridge decks becomes increasingly significant for modern bridges with increasing spans, larger flexibility and new aerodynamic deck configurations. Better understanding of the nonlinear aeroelasticity of bridge decks and further development of reduced-order nonlinear models for the aeroelastic forces become necessary. In this paper, the amplitude-dependent and neutral angle dependent nonlinearities of the motion-induced loads are further highlighted by series of computational fluid dynamics (CFD) simulations. An effort has been made to investigate a semi-analytical time-domain model of the nonlinear motion induced loads on the deck, which enables nonlinear time domain simulations of the aeroelastic responses of the bridge deck. First, the computational schemes used here are validated through theoretically well-known cases. Then, static aerodynamic coefficients of the Great Belt East Bridge (GBEB) cross section are evaluated at various angles of attack, leading to the so-called nonlinear backbone curves. Flutter derivatives of the bridge are identified by CFD simulations using forced harmonic motion of the cross-section with various frequencies. By varying the amplitude of the forced motion, it is observed that the identified flutter derivatives are amplitude-dependent, especially for $A^*_2$ and $H^*_2$ parameters. Another nonlinear feature is observed from the change of hysteresis loop (between angle of attack and lift/moment) when the neutral angles of the cross-section are changed. Based on the CFD results, a semi-analytical time-domain model for describing the nonlinear motion-induced loads is proposed and calibrated. This model is based on accounting for the delay effect with respect to the nonlinear backbone curve and is established in the state-space form. Reasonable agreement between the results from the semi-analytical model and CFD demonstrates the potential application of the proposed model for nonlinear aeroelastic analysis of bridge decks.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.868-876
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• 2014

The objective of this study is focused on the analyzing combustion, carbon monoxide and hydrocarbon emission characteristics of marine diesel oil, utilized for naval propulsion engine, with varying pre-post injection timing of an optically accessible single cylinder engine. And also the combustion process is analyzed by means of a high speed camera visualization. On the result of retarding pre-injection timing toward main injection timing, the mean effective pressure and maximum pressure of combustion chamber are increased; however, the heat release rate is decreased. Furthermore, the emission rates of carbon monoxide and hydrocarbon are reduced in this case. In hence, when a post-injection timing is advanced, the mean effective pressure and maximum pressure are increased, because the combustion has been performed under the high temperature and high pressurized environment during main injection time, and the emission rates of carbon monoxide and hydrocarbon are increased. From the experimental results, it considered that retarding of pre-injection timing affects to shorten the ignition delay of main injection clearly, and to raise the flame intensity comparing to the advanced state. The ignition delay during post-injection is not appeared at any post-injection time, but the flame intensity has been weakened gradually according to the retarding of post-injection timing.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1996.04a
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• pp.141-146
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• 1996

Hand posture and force, which define aspects of the way an object is grasped, are features of robotics manipulation. A means for specifying these grasping "flavors" has been developed that uses an instrumented glove equipped with joint and force sensors. The new grasp specification system is being used at the Pennsylvania State University (Penn State) in a Virtual Reality based Point-and-Direct(VR-PAD) robotics implementation. In the Computer Integrated Manufacturing (CIM) Laboratory at Penn State, hand posture and force data were collected for manipulating bricks and other items that require varying amounts of force at multiple pressure points. The feasibility of measuring desired grasp characteristics was demonstrated for a modified Cyberglove impregnated with FSR (Force Sensitive Resistor) pressure sensors in the fingertips. A joint/force model relating the parameters of finger articulation and pressure to various lifting tasks was validated for the instrumented "wired" glove. Operators using such a modified glove may ultimately be able to configure robot grasping tasks in environments involving hazardous waste remediation, flexible manufacturing, space operations and other flexible robotics applications. In each case, the VR-PAD approach improved the computational and delay problems of real-time multiple-degree-of-freedom force feedback telemanipulation.ck telemanipulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.7A
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• pp.587-596
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• 2005

In this paper, we propose an OFDMA/CDM-based cellular system, which accommodates multiple users in frequency-domain and multiplexes user data with frequency-domain spreading. The proposed system utilizes random codes to discriminate cells and adopts the pre-equalization to enhance the performance. For cellular applications, a number of pre-equalization techniques are compared and an efficient power allocation scheme is suggested with a transmit power constraint. Especially, the validity of OFDMA/CDM based cellular system is investigated, by comparing the performance for varying the number of multiplexed data symbols at different locations. Finally the pre/post-equalization is proposed to reduce the performance degradation caused by time delay.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1364-1366
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• 1998

An active-matrix LCD using thin film transistors (TFT) has been widely recognized as having potential for high-quality color flat-panel displays. Pixel-Design Array Simulation Tool (PDAST) was used to profoundly understand the gate signal distortion and pixel charging capability, which are the most critical limiting factors for high-quality TFT-LCDs. Since PDAST can simulate the gate, data and pixel voltages of a certain pixel on TFT array at any time and at any location on an array, the effect of the resistivity of gate line material on the pixel operations can be effectively analyzed. The gate signal delay. pixel charging ratio, level-shift of the pixel voltage were simulated with varying the parameters. The information obtained from this study could be utilized to design the larger area and finer image quality panel.