• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.7A
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• pp.628-638
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• 2005

The analysis of maximum diversity order and coding gain for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems over time-and frequency-selective (or doubly-selective) channels is addressed in this paper. A novel channel time-space correlation function is developed given the spatially correlated doubly-selective Rayleigh fading channel model. Based on this channel-model assumption, the upper-bound of pairwise error probability (PEP) for MIMO-OFDM systems is derived under the maximum likelihood (ML) detection. For a certain space-frequency code, we quantify the maximum diversity order and deduce the expression of coding gain. In this wort the impact of channel time selectivity is especially studied and a new definition of time diversity is illustrated correspondingly

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.71-74
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• 2002

A higher-order zig-zag theory is developed to refine the predictions of natural frequency and mode shape of laminated composite plates with multiple delaminations. By imposing top and bottom surface transverse shear stress-free and interface continuity conditions of transverse shear stresses including delaminated interfaces, the displacement field with minimal degree-of-freedoms are obtained. This displacement field can systematically handle the number, shape, size, and locations of delaminations. Through the dynamic version of variational approach, the dynamic equilibriums and variationally consistent boundary conditions are obtained. Through the numerical example of natural frequency analysis, the accuracy and efficiency of present theory are demonstrated. The present theory is suitable as an efficient tool to analyze the static and dynamic behavior of the composite plates with multiple delaminations.

• Smart Structures and Systems
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• v.26 no.2
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• pp.185-193
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• 2020

Nonlinear vibration of sandwich plate with functionally graded material (FGM) core and carbon nano tubes reinforced (CNTs) nano-composite layers by considering temperature-dependent material properties are studied in this paper. Base on Classical plate theory (CPT), the governing partial differential equations of motion for sandwich plate are derived using Hamilton principle. The Galerkin procedure and multiple scales perturbation method are used to find relation between nonlinear frequency and amplitude of vibration response. The dynamic responses of the sandwich plate are also investigated in both time and frequency domains. Then, the effects of nonlinearity, excitation, power law index of FG core, volume fraction of carbon nanotube, the function of material variations of FG core, temperature changes, scale transformation parameter and damping factor on the frequency responses are investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.3
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• pp.318-324
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• 2004

The stability of a simply supported straight pipe is investigated. The time dependent flow is assumed to vary harmonically about a constant mean velocity. Stability conditions and dynamic reponses of a governing equation are conducted by use of multiple scale mettled. Parametric resonances and combination resonances are investigated. Stability boundaries are analytically determined. The resulted stability conditions show that instabilities exist when the frequency of flow fluctuation is close to two times the natural frequency or to the sum of any two natural frequencies. In case that the fluctuated flow frequency is close to zero or to the difference of two natural frequencies, however, instabilities are not found up to the first order of perturbation. Stability charts are numerically Presented fir the first two vibration modes.

• Journal of Information Processing Systems
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• v.11 no.3
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• pp.342-353
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• 2015

It is widely accepted that single carrier frequency division multiple access (SC-FDMA) is an excellent candidate for broadband wireless systems. Channel estimation is one of the key challenges in SC-FDMA, since accurate channel estimation can significantly improve equalization at the receiver and, consequently, enhance the communication performances. In this paper, we study the application of compressive sensing for sparse channel estimation in a SC-FDMA system. By skillfully designing pilots, their patterns, and taking advantages of the sparsity of the channel impulse response, the proposed system realizes channel estimation at a low cost. Simulation results show that it can achieve significantly improved performance in a frequency selective fading sparse channel with fewer pilots.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.535-539
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• 2008

Recently mobile devices can transmit mass data contained multi-media contents. According these flow, a demand for fast data transmission is being risen, so we acutely require remarkable technology that overcome mobile communication's poor environment and rise data transmission volume. Because it can be satisfied these needs, the OFDM(Orthogonal Frequency Division Multiplexing) that rise data transmission volume using efficient frequency, and MIMO(Multiple Input Multiple Output) that rise transmission confidence and data transmission volume using numbers of antenna is attended. Before design of MIMO-OFDM System we want to make an analysis for theory of its systems, and we want to design MIMO-OFDM simulator for verify an ability of modulation, data volume and numbers of antenna.

• Proceedings of the Korea Information Processing Society Conference
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• 2002.04b
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• pp.1239-1242
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• 2002

In this paper, the implementation of MAI(multiple access interference)-cancelled SSMA(spread spectrum multiple access) system using orthogonal carriers was presented. Employing the pseudo periodic spreading codes and orthogonal carriers frequency offset, proposed system have the features no MAI during a certain local time-duration. Spreading signals designed by pseudo periodic method and repetition, have zero correlation duration(ZCD) by orthogonal frequency shift method. The SSMA modem has been designed and implemented using surface-acoustic-wave(SAW) device as the matched filter of receiver. The effects of frequency offset on stability have been evaluated using computer simulation.

• Fisheries and Aquatic Sciences
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• v.27 no.4
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• pp.225-230
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• 2024

We examined the dB difference in target strength at multiple frequencies (ΔTS) for the identification of Antarctic krill (Euphausia superba) and ice krill (Euphausia crystallorophias) using a stochastic distorted-wave Born approximation model. Our investigation focused on ΔTS patterns at multiple frequencies in relation to size, along with key acoustic properties influencing TS, including density and sound speed contrast, fatness, and orientation. The findings revealed that the orientation and fatness significantly affect the ΔTS patterns. The results provide insight into the importance of the multi-frequency technique for estimating krill biomass and their ecological interactions with environmental features in the Southern Ocean.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.148-148
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• 2000

In this paper the IMM(Interacting Multiple model) algorithm using the MGEKF(Modified Gain Extended Kalman Filter) which modes are variances of the process noises is proposed to enhance the performance of maneuvering target tracking with bearing and frequency measurements. The state are composed of relative position, relative velocity, relative acceleration and doppler frequency. The mode probability is calculated from the bearing and frequency measurements. The proposed algorithm is tested a series of computer simulation runs.

• Journal of electromagnetic engineering and science
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• v.12 no.3
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• pp.223-225
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• 2012

In this paper, we develop a symbol/frame time and carrier frequency synchronization scheme for multi-carrier signaling in wireless mobile channels. The proposed scheme achieves simultaneous time synchronization and carrier frequency offset estimation. Simulation results show that the frequency offset of multiple sub-carrier spacings can be estimated and that performance is improved with robustness regardless of the cyclic prefix length.