• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.5B
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• pp.456-477
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• 2006

Due to advances in wireless communication technology and increasing demand for various types of wireless access, cellular, WLAN, and portable internet(such as WiBro and IEEE 802.16) systems are likely to be integrated into a unified wireless access system. This expectation premises the availability of multi-mode handsets and cooperative interworking of heterogenous wireless access networks allied by roaming contracts. Under such environments, a user may lie in the situation where more than one wireless accesses are available at his/her location, and he/she will want to choose the 'best' access among them. In this paper, we define the 'best' access(es) as the access(es) that charges minimum cost while fulfilling the required QoS of wireless access, and address the problem of choosing the optimal set of accesses theoretically by introducing a graph representation of service environment. Two optimal selection algorithms are proposed, which individually consider cases where single or multiple wireless access can be supported by multi-mode handsets.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.1
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• pp.69-74
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• 2003

In this paper, we propose the synchronization recovery algorithm which is suitable to wireless Multimedia of wireless channel situation which is being used OFDM signaling method. The basic of the suggested clock synchronization. restoration Algorithm is to getting the shock response of channel or getting the multipath strength profile through IFTT after the getting the frequency, response of deducted channel from channel deducted of receiver and to trace the location in the channel energy concentrated area of timing area. And it also analysis the start point of 64-QAM and 16-QAM if the sampling clock offset has the sample of ${\pm}$ 1-3, and we identified the occurance of performance deterioration when occures more than 2 samples of offset to compare with star point and BER performance in optimum sampling point result of BER performance checking, and we know that the recovery algorithm proposed algorithm also provide excellent synchronization characteries under frequency, selecting fading channel as result of simulation.

• The Journal of Korean Institute for Practical Engineering Education
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• v.1 no.1
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• pp.19-24
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• 2009

It is necessary that the industry has to develop various automated control technology for efficient creation of manufacture automation system according to rapid market situation. One of the technologies is the fused complex control based on PLC-based controlled system. According to rapid growth and distribution of various automated control technologies using PLC, the engineers in automation, Production and manufacturing technologies fields have difficulties in systematic studying on the technologies by choosing an optimal route due to various industry-applied examples and ranges, in spite that the technology is essential. Therefore, the researchers indicate applied outputs and effects extracted by systematically developing systematic company-specified training program by analyzing education procedure drawbacks for S-company engineers.

• Journal of Korean Society of Transportation
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• v.30 no.1
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• pp.125-133
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• 2012

This paper deals with the passenger transfer trips counted from smart bus-card data from Seoul transit network to understand the current operational condition of the system. Objective of this study is to relocate the location of the transit transfer centers. It delivers a bi-level programing model. The upper model is a linear 0-1 binary integer program having the objective of total travel cost minimization constrained by the number of transfer centers and the total construction budget. The lower model is an user equilibrium assignment model determining the passengers' route choice according to the transfer center locations. The proposed bi-level programming model was tested in an example network. The result showed that the proposed was able to find the optimal solution.

• Journal of Digital Convergence
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• v.10 no.9
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• pp.325-332
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• 2012

VANET(Vehicular Ad-hoc Network), which is a technology to create a network among vehicles, decides the route to the destination using information of neighbors within the transmission range as transmission nodes. The existing routing protocol which uses geographical information can cause delay and disconnection of the network when the density of nodes is not high enough to communicate because it only considers the distance of the relay nodes or destination nodes from the source nodes. To solve the problem, this dissertation suggests a routing algorithm based on zones for stable communications among vehicles in the environment of VANET. I minimize the packet loss rate by dividing the city environment into zones and taking into account not only the distance of the destination but also the density of vehicles to choose the best communications environment. This results in a better performance than the established research when the performance evaluation is implemented.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.4
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• pp.60-68
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• 2003

In this study, a steady state performance analysis program was developed for a turbofan engine, and its performance was analyzed at installed conditions. For the purpose of evaluation, the developed program was compared with the performance data provided by the engine manufacturer. It was confirmed that the developed program was reliable because the results by the developed program were well agreed with those by the engine manufacturer within 3.5%. The non-linear GPA(Gas Path Analysis) program for performance diagnostics were developed, and selection of optimal measurement variables was studied. Furthermore, in order to investigate effects of the number and the kind of measurement variables, the non-linear GPA was analyzed with various measurement sets. Finally, the measurement parameters selected in the previous step were applied to the fault detection analysis of the 2-spool separate flow type turbofan engine.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.3A
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• pp.168-177
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• 2005

In this paper, we numerically investigated the optimum pump light power resulting best compensation of pulse distortion due to both chromatic dispersion and self phase modulation (SPM) in long-haul 3×40 Gbps wavelength division multiplexing (WDM) systems. We used mid-span spectral inversion (MSSI) method with path-averaged intensity approximation (PAIA) as compensation approach, which have highly nonlinear dispersion shifted fiber (HNL-DSF) as nonlinear medium of optical phase conjugator (OPC) in the mid-way of total transmission line. We confirmed that HNL-DSF is an useful nonlinear medium in OPC for wideband WDM transmission, and in order to achieve the excellent compensation the pump light power is selected to equal the conjugated light power into the latter half fiber section with the input light power of WDM channel depending on total transmission length. Also we confirmed that compensation degree of WDM channel with small conversion efficiency is improved by using pump light power increasing power conversion ratio upper than 1.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.6
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• pp.473-480
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• 2013

Researches for various lunar landing technologies are in progress for the lunar exploration program planned for early 2020s in Korea. This paper shows the integrated simulation for safe lunar landing guidance/control system in powered descent phase. Generally, the lunar lander uses on/off(bang-bang) controller to control the RCS jet thrusters instead of proportional controller. In this paper, the on/off controller using phase-plane switching function, and thruster selection algorithm to control sixteen thrusters are applied. Also additional guidance commands are calculated by a proposed fuzzy logic guidance algorithm. The simulation results show that lunar lander can follow a reference trajectory which is generated by optimization method, then land on the surface safely.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.12
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• pp.68-74
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• 2010

A sub-${\mu}$W CMOS Wien-Bridge oscillator for ultra low power (ULP) radio applications is presented. The Wien-Bridge oscillator is based on an non-inverting opamp amplifier with a closed-loop gain $1+R_2/R_1$ as a means of providing necessary loop gain. An additional RC network provides appropriate phase shift for satisfying the Barkhausen oscillation condition at the given frequency of 1/($2{\pi}RC$). In this design, we propose a novel loop gain control method based on a variable capacitor network instead of a rather conventional variable resistor network. Implemented in $0.18{\mu}m$ CMOS, the oscillator consumes only 560 nA at the oscillation frequency of 22 kHz.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.2 no.1 s.2
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• pp.85-92
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• 2003

Due to the expansion of freeway networks in Korea, drivers have more routes to choose. Traffic information on various alternative roadway sections and routes may help drivers choose the optimal route that minimizes travel time or cost. Traffic information on roadways is, therefore, invaluable in sense that individual drivers could reduce their travel time or cost by selecting optimal routes, and furthermore total travel cost of the system could be lowered. However, consensus about the price of traffic information that drivers are willing to pay is not made yet. Current price of traffic information is decided according to the price of similar information such as stock, weather and so on. To investigate the value of traffic information, a survey was conducted at freeway rest areas near Seoul Megalopolis area including Kyunggi Province. Eight hundred drivers who had travelled on freeway within a year were randomly selected. Purposive Quota Sampling was used. A price-response function, a relationship between price and sales, was obtained based on the survey, followed by sensitivity analysis