• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.2
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• pp.235-243
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• 2012

In this paper, we propose a method to improve performance of pilot symbol assisted modulation(PSAM) channel estimation method for OFDM systems over frequency selective channel. When channel values are estimated, the low pilot density used for channel estimation increases not only the effective data rate but also power efficiency. Thus, the lower pilot density which is used for channel estimation is better for OFDM system. At first, we estimate the channel values which are located at the middle of adjacent pilots, and then all of the possible channel values are estiamted by using original pilot values and previously estimated pilot values. Furthermore, the error of estimated channel values is reduced by introducing guard interval which is designed acccording to maximum channel delay. Performance achieved with the proposed method is illustrated by simulation experiments in comparison with the existing methods in terms of mean squared error(MSE).

• Journal of Convergence for Information Technology
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• v.9 no.2
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• pp.17-22
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• 2019

Cache is a technique that improves the client's response time, thereby reducing the bandwidth and showing an effective side. However, there are vulnerabilities in the cache technique as well as in some techniques. Web caching is convenient, but it can be exploited by hacking and cause problems. Web cache problems are mainly caused by cache misses and excessive cache line fetch. If the cache miss is high and excessive, the cache will become a vulnerability, causing errors such as transforming the secure data and causing problems for both the client and the system of the user. If the user is aware of the cache infection and the countermeasure against the error, the user will no longer feel the cache error or the problem of the infection occurrence. Therefore, this study proposed countermeasures against four kinds of cache infections and errors, and suggested countermeasures against web cache infections.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.6
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• pp.154-163
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• 2006

This paper presents a nonlinear analysis method for the reinforced concrete beams strengthened by the external bonding of high strength, lightweight fiber sheets on the tension face of the beams. The method is based on the results of experimental studies. The experimental study involved tensile tests of 120 specimens to evaluate the tensile properties of fiber sheets(carbon, glass, and aramid fiber) and bending tests of 75 beams strengthened with various types of fiber sheets to evaluate the flexural capacities. Based on these experimental results, reasonable rupture strains of the fiber sheets were estimated. The nonlinear flexural analysis considered nonlinear flexural stresses as compressive and tensile stresses of concrete, load-deflection curves, and rupture strains of fiber sheets. The nonlinear flexural analysis accurately predicts the load-deflection response and the flexural behavior of the retrofitted beams.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.3
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• pp.31-40
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• 2002

The purpose of this study is to investigate the seismic behavior of RC bridge piers and to provide the data for developing improved seismic design criteria. The accuracy and objectivity of the assessment process may be enhanced by the use of sophisticated nonlinear finite element analysis program. A computer program, named RCAHEST(reinforced concrete analysis in higher evaluation system technology), for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. n boundary plane at which each member with different thickness is connected, local discontinuity in deformation due to the abrupt change in their stiffness can be taken into account by introducing interface element. The effect of number of load reversals with the same displacement amplitude has been also taken into account to model the reinforcing steel and concrete. In the companion paper, the proposed numerical method for seismic damage evaluation of RC bridge piers is verified by comparison with the reliable experimental results.

• Land and Housing Review
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• v.3 no.4
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• pp.451-456
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• 2012

In this study, a numerical analysis to evaluate the reduction of seismic load due to pile group was performed and compared the peak ground acceleration(PGA) measured at free-field and foundation. The special attention was given to the amplification of seismic acceleration on the foundation due to the pile effects. The analysis considering pile effects was carried out for 4, 8 and 12 piles with same condition by PLAXIS 2D Dynamics. Based on the analysis results, it is found that the overall reduction in seismic load due to foundation and reduction rates are similar irrespective of pile numbers. This study gives a possibility for effective design of piled foundation by reducing seismic load about 20~25%.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.190-197
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• 2004

In order to consider statistical properties of probability variables used in the structural analysis, the conventional approach using the safety factor based on past experience usually estimated the safety of a structure. Also, the real structures could only be analyzed with the error in estimation of loads, material characters and the dimensions of the members. But the errors should be considered systematically in the structural analysis. In this paper, we estimated the probability of failure of the pressure vessel. And also, this paper presents sensitivity values of the random variable. Finally, we show that reliability index and probability of failure can present the tolerance limit of dimension of randam variables.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.2
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• pp.407-416
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• 2000

Adaptive digital filtering and noise cancelling technique using a tree structured filter bank are presented to reduce a undesirable aliasing due to the decimation of filtered output and improve the performance in terms of mean-square error and the convergence speed using a aliasing canceller. A signal is split into two subband by analysis filter bank and decimated by decimator and reconstructed by interpolation technique and synthesis filter bank. A variable step-size LMS algorithm is used to improve the convergence speed in case of existing the measurement noise in desired input of filter. It is shown by computer simulation that the proposed subband structure in this paper is superior to conventional subband filter structure in terms of mean-square error and convergence speed.

• Journal of Ocean Engineering and Technology
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• v.19 no.2 s.63
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• pp.40-46
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• 2005

In order to consider the statistical properties of probability variables which are used in structural analysis, the conventional approach of using safety factors based on past experience, are usually used to estimate the safety of a structure. The real structures could only be analyzed with the error in estimation of loads, materials and dimensional characteristics. Errors should be considered systematically in the structural analysis. In this paper, we estimated the probability of failure of two pressure vessels, simultaneously, using computational analysis. One pressure vessel, theoretically, had no stiffener whereas the other had. This paper also discusses sensitivity values of random variables in the rounded parts of the pressure vessel which had ring-style stiffener in the center of the external area which had ring-style stiffener. Finally, we show that the reliability index, and the probability of failure, can be calculated to particular tolerance limits.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.295-300
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• 2007

Probabilistic Risk Assessment considering statistically random variables is performed for the preliminary design of a Arch Bridge. Component reliabilities of girders have been evaluated using the response surfaces of the design variables at the selected critical sections based on the maximum shear and negative moment locations. Response Surface Method (RSM) is successfully applied for reliability analyses for this relatively small probability of failure of the complex structure, which is hard to be obtained by Monte-Carlo Simulations or by First Order Second Moment Method that can not easily calculate the derivative terms of implicit limit state functions. For the analysis of system reliability, parallel resistance system composed of girders is changed into parallel series connection system. The upper and lower probabilities of failure for the structural system have been evaluated and compared with the suggested prediction method for the combination of failure modes. The suggested prediction method for the combination of failure modes reveals the unexpected combinations of element failures in significant]y reduced time and efforts compared with the previous permutation method or system reliability analysis method.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2003.05a
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• pp.311-315
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• 2003

Recently, there is asymmetrical transmission in Internet data stream. The asymmetrical transmission has much more downstream than upstream. Owing to this point, it needs to reduce the acknowledgement as element of the obsrtuction in downstream. In this paper, according to simulation's result, we know that Sack has good performance than New Reno in bottleneck environment Comparing two protocols in packet loss rate, NewReno is lower than Sack. And also comparing two protocols in throughput of ack packet, not only NewReno processes ack packet more quickly than Sack, but also NewReno processes more ack packet than Sack protocol during ten seconds in simulation. As a result, NewReno is batter than Sack in throughput of asymmetrical link.