• Journal of IKEEE
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• v.3 no.1 s.4
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• pp.141-149
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• 1999

If signal time duration of MC-CDMA method which has studied for next-generation high-speed data transmission is not sufficiently large compared to delay spread of channel, the performance is degraded by generation of intersymbol interference. In this paper, this problem will solve through serial to parallel convertor and make large sufficiently time duration of signal compared to delay spread of channel and rise variable spectral efficiency through the number of serial to parallel convertor subchannel we will add to parallel frequency diversity block for improve the performance in mobile Communication. Spectral efficiency of the proposed system is counted and compared to spectral efficiency of MC-CDMA and investigated through computer simulations by using multipath Rayleigh fading channel.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.12
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• pp.48-58
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• 2006

The spray and combustion characteristics of liquid jet in cross flow with variation of injection angle are numerically studied. Numerical analysis was carried out using KIVA code, which may be used to generate numerical solutions to spray and chemical reactive fluid problem in three space dimensions and modified to be suitable for simulating liquid jet ejected into the cross flow. Wave model and Kelvin- Helmholtz(KH) /Rayleigh-Taylor(RT) hybrid model were used for the purpose of analyzing liquid column, ligament, and the breakup of droplet. Penetration length increases as flow velocity decreases and injection velocity increases. Numerical error increases as inflow velocity increases. The results of flame propagation contour in combustion chamber and local temperature distribution, combustion emissions were obtained.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10B
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• pp.2004-2010
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• 1999

This paper presents the blind multiuser detector using the constant modulus algorithm(CMA) to solve the near-far problem in DS-CDMA systems. The convergence property of the detector is compared with the conventional MOE(minimum output energy) detector by means of SIR(signal-to-interference ratio). The MOE detector needs both the spreading code of the users and the timing information, while proposed methods needs only information about the spreading code of users Simulation results show that the CMA-based detector is superior to the conventional blind MOE multiuser detector. For this, the BER performance was tested using different values of SNR and near-far ratio. The SIR is also investigated for different number of users in AWGN and Rayleigh fading channels. We have observed that the proposed blind multiuser detector performs better than conventional MOE multiuser detector.

• Steel and Composite Structures
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• v.35 no.1
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• pp.77-92
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• 2020

The present paper outlined a procedure for geometrically nonlinear dynamic analysis of functionally graded graphene platelets-reinforced (GPLR-FG) nanocomposite cylinder subjected to mechanical shock loading. The governing equation of motion for large deformation problems is derived using meshless local Petrov-Galerkin (MLPG) method based on total lagrangian approach. In the MLPG method, the radial point interpolation technique is employed to construct the shape functions. A micromechanical model based on the Halpin-Tsai model and rule of mixture is used for formulation the nonlinear functionally graded distribution of GPLs in polymer matrix of composites. Energy dissipation in analyses of the structure responding to dynamic loads is considered using the Rayleigh damping. The Newmark-Newton/Raphson method which is an incremental-iterative approach is implemented to solve the nonlinear dynamic equations. The results of the proposed method for homogenous material are compared with the finite element ones. A very good agreement is achieved between the MLPG and FEM with very fine meshing. In addition, the results have demonstrated that the MLPG method is more effective method compared with the FEM for very large deformation problems due to avoiding mesh distortion issues. Finally, the effect of GPLs distribution on strength, stiffness and dynamic characteristics of the cylinder are discussed in details. The obtained results show that the distribution of GPLs changed the mechanical properties, so a classification of different types and volume fraction exponent is established. Indeed by comparing the obtained results, the best compromise of nanocomposite cylinder is determined in terms of mechanical and dynamic properties for different load patterns. All these applications have shown that the present MLPG method is very effective for geometrically nonlinear analyses of GPLR-FG nanocomposite cylinder because of vanishing mesh distortion issue in large deformation problems. In addition, since in proposed method the distributed nodes are used for discretization the problem domain (rather than the meshing), modeling the functionally graded media yields to more accurate results.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.3
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• pp.7-12
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• 2014

The data forwarding transmission is an important function of the relay in cooperative communication in wireless communication systems. However, additional relay cause the waste of power consumption and cost. Therefore, in this paper, we consider how to use the user mobile devices in stead of relays to deal with this problem. In this paper, we proposed the protocol that divide each relay into two states of idle and non-idle. The receiver has two functions of base station and user mobile device. In this case, it is possible that no additional cost, and improve the spectral efficiency and network capacity. We verified BER performance for the proposed protocol over Rayleigh fading through Monte-Carlo simulation.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.1
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• pp.88-95
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• 2015

For the frequency-domain spectral fatigue analysis, the probability density function of stress range needs to be estimated based on the stress spectrum only, which is a frequency domain representation of the response. The probability distribution of the stress range of the narrow-band spectrum is known to follow the Rayleigh distribution, however the PDF of wide-band spectrum is difficult to define with clarity due to the complicated fluctuation pattern of spectrum. In this paper, efforts have been made to figure out the links between the probability density function of stress range to the structural response of wide-band Gaussian random process. An artificial neural network scheme, known as one of the most powerful system identification methods, was used to identify the multivariate functional relationship between the idealized wide-band spectrums and resulting probability density functions. To achieve this, the spectrums were idealized as a superposition of two triangles with arbitrary location, height and width, targeting to comprise wide-band spectrum, and the probability density functions were represented by the linear combination of equally spaced Gaussian basis functions. To train the network under supervision, varieties of different wide-band spectrums were assumed and the converged probability density function of the stress range was derived using the rainflow counting method and all these data sets were fed into the three layer perceptron model. This nonlinear least square problem was solved using Levenberg-Marquardt algorithm with regularization term included. It was proven that the network trained using the given data set could reproduce the probability density function of arbitrary wide-band spectrum of two triangles with great success.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.39 no.3
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• pp.51-58
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• 2002

The conventional code division multiple access(CDMA) detector shows severe degradation in communication quality as the number of users increases due to multiple access interferences(MAI). This problem thus restricts the user capacity. Various multiuser detection algorithms have been proposed to overcome the MAI problem. The existing detectors can be generally classified into one of the two categories : linear multiuser detection and subtractive interference cancellation detectors. In the linear multiuser detection, a linear transform is applied to the soft outputs of the conventional detector. In the subtractive interference cancellation detection, estimates of the interference are generated and subtracted out from the received signal. There has been great interest in the family of the subtractive interference cancellation detection because the linear multiuser detection exhibits the disadvantage of taking matrix inversion operations. The successive interference cancellation (SIC) and the parallel interference cancellation (PIC) are the two most popular structures in the subtractive interference cancellation detector. The SIC structure is very simple in hardware complexity, but has the disadvantage of increased processing delay time, while the PIC structure is good in performance, but shows the disadvantage of increased hardware complexity. In this paper we propose a mixed structure form of SIC and PIC in order to achieve good performance as well as simple hardware complexity. A performance analysis of the proposed scheme has been made, and the superior characteristics of the mixed structure are demonstrated by extensive computer simulations. 

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.10
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• pp.1517-1524
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• 2022

In this paper, we consider a heterogeneous network (HetNet) consisting of one macro base station and multiple small base stations, and assume the coordinated multi-point transmission between the base stations. In addition, we assume that the channel between the base station and the user consists of path loss and Rayleigh fading. Under these assumptions, we present the energy efficiency (EE) achievable by the user for a given base station and we formulate an optimization problem of dynamic cell selection and transmit power allocation to maximize the total EE of the HetNet. In this paper, we propose an unsupervised deep learning method to solve the optimization problem. The proposed deep learning-based scheme can provide high EE while having low complexity compared to the conventional iterative convergence methods. Through the simulation, we show that the proposed dynamic cell selection scheme provides higher EE performance than the maximum signal-to-interference-plus-noise ratio scheme and the Lagrangian dual decomposition scheme, and the proposed transmit power allocation scheme provides the similar performance to the trust region interior point method which can achieve the maximum EE.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.95-109
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• 1993

In this study, the optimal configuration of arch structure has been tested by a decomposition technique. The object of this study is to provide the method of optimizing the shapes of both two hinged and fixed arches. The problem of optimal configuration of arch structures includes the interaction formulas, the working stress, and the buckling stress constraints on the assumption that arch ribs can be approximated by a finite number of straight members. On the first level, buckling loads are calculated from the relation of the stiffness matrix and the geometric stiffness matrix by using Rayleigh-Ritz method, and the number of the structural analyses can be decreased by approximating member forces through sensitivity analysis using the design space approach. The objective function is formulated as the total weight of the structures, and the constraints are derived by including the working stress, the buckling stress, and the side limit. On the second level, the nodal point coordinates of the arch structures are used as design variables and the objective function has been taken as the weight function. By treating the nodal point coordinates as design variable, the problem of optimization can be reduced to unconstrained optimal design problem which is easy to solve. Numerical comparisons with results which are obtained from numerical tests for several arch structures with various shapes and constraints show that convergence rate is very fast regardless of constraint types and configuration of arch structures. And the optimal configuration or the arch structures obtained in this study is almost the identical one from other results. The total weight could be decreased by 17.7%-91.7% when an optimal configuration is accomplished.

• Journal of the Korean earth science society
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• v.37 no.1
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• pp.40-51
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• 2016

The problem has been pointed out that the domestic design response spectrum does not reflect site amplification, particularly in the high frequency bands, including the fact that site specific response spectrum from the observed ground motions appears relatively higher than design response spectrum. Among various methods, this study applied H/V spectral ratio of ground motion for estimating site amplification. This method, originated from S waves and Rayleigh waves, recently has been extended to Coda waves and background noise for estimating site amplification. For limited time of periods, 4 electric substation sites had operated seismic stations at two separate locations (bedrock and borehole) within each substation site. H/V spectral ratio of S wave, Coda wave, and background noise, was applied to 36 accelerations of 3 macro earthquakes (Odaesan, Jeju and Gongju earthquakes), larger than magnitude 3.4. observed simultaneously at each bedrock location within 4 electric substation sites. Site amplifications at the bedrock location of 4 sites were compared among S wave, Coda wave energy, and background noise, and then compared to the previous results from the borehole location data. The site classification was also tried using resonancy frequency information at each site and location. The results suggested that all the electric substation sites showed similar site amplification patterns among S wave, Coda wave, and background noise. Each station showed its own characteristics of site amplification property in low, high and specific resonance frequency ranges. Comparison of this study to other results using different method can give us much more information about dynamic amplification of domestic sites characteristics and site classification.