• ETRI Journal
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• v.45 no.3
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• pp.492-504
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• 2023

Researchers have recently shown an increased interest in estimating the direction-of-arrival (DOA) of wideband noncircular sources, but existing studies have been restricted to subspace-based methods. An off-grid sparse recovery-based algorithm is proposed in this paper to improve the accuracy of existing algorithms in low signal-to-noise ratio situations. The covariance and pseudo covariance matrices can be jointly represented subject to block sparsity constraints by taking advantage of the joint sparsity between signal components and bias. Furthermore, the estimation problem is transformed into a single measurement vector problem utilizing the focused operation, resulting in a significant reduction in computational complexity. The proposed algorithm's error threshold and the Cramer-Rao bound for wideband noncircular DOA estimation are deduced in detail. The proposed algorithm's effectiveness and feasibility are demonstrated by simulation results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.11a
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• pp.97-98
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• 2008

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.121-124
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• 2003

In this paper, the non-parametric algorithm to estimate DOA(Direction Of Arrival) of signals is proposed and compared with the multidimensional MUSIC algorithm. This non-parametric algorithm with regularizing sparsity constraints achieves super-resolution and noise suppression, effectively. Also, this algorithm offers the increased resolution and significantly reduced sidelobes.

• Journal of Communications and Networks
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• v.14 no.4
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• pp.374-384
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• 2012

Utilizing artificial noise (AN) is a good means to guarantee security against eavesdropping in a multi-inputmulti-output system, where the AN is designed to lie in the null space of the legitimate receiver's channel direction information (CDI). However, imperfect CDI will lead to noise leakage at the legitimate receiver and cause significant loss in the achievable secrecy rate. In this paper, we consider a delayed feedback system, and investigate the impact of delayed CDI on security by using a transmit beamforming and AN scheme. By exploiting the Gauss-Markov fading spectrum to model the feedback delay, we derive a closed-form expression of the upper bound on the secrecy rate loss, where $N_t$ = 2. For a moderate number of antennas where $N_t$ > 2, two special cases, based on the first-order statistics of the noise leakage and large number theory, are explored to approximate the respective upper bounds. In addition, to maintain a constant signal-to-interferenceplus-noise ratio degradation, we analyze the corresponding delay constraint. Furthermore, based on the obtained closed-form expression of the lower bound on the achievable secrecy rate, we investigate an optimal power allocation strategy between the information signal and the AN. The analytical and numerical results obtained based on first-order statistics can be regarded as a good approximation of the capacity that can be achieved at the legitimate receiver with a certain number of antennas, $N_t$. In addition, for a given delay, we show that optimal power allocation is not sensitive to the number of antennas in a high signal-to-noise ratio regime. The simulation results further indicate that the achievable secrecy rate with optimal power allocation can be improved significantly as compared to that with fixed power allocation. In addition, as the delay increases, the ratio of power allocated to the AN should be decreased to reduce the secrecy rate degradation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.110-112
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• 2009

Transient acoustic pressure in the near field of an impacted plate carries information that can be utilized for recovering the impact force history. The inverse calculation approach using BEM-based NAH, which is conventionally used for time harmonic excitation, can be applied for reconstructing the transient waves using the principle of Fourier transform and spectral analysis. Then, using the recovered velocity in normal direction of the plate surface, the corresponding structural intensity can be obtained and the identification of input power can be performed. However, several manipulations should be given to overcome numerical artifacts, such as aliasing and erratic oscillation at discontinuity, and to suppress the effect of noise. Experiment using a simply supported plate is presented for demonstration purpose.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.498-501
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• 2006

When an object or objects, rigid or flexible, presents in incident sound field, the sound wave is scattered. This, we call, is scattered sound field. It, of course, depends on the amplitude and the direction of the incident sound field as well as the geometry and the surface impedance of the scatterer(object). This paper addresses the way to measure scattered sound field by using arbitrary incident sound wave. This means that the method can decompose the scattered field from measured sound field with respect to any magnitudes and directions of incident plane-waves.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.6
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• pp.98-108
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• 1994

An assessment of a mathematical method of synthesing tire tread pitch noise spectra is studied. The method is based on the summation of phasors and the calculated spectra are conveniently generated as computer printout in the form of bar graph. The technique, its usefulness, its limitations and the implications of using such a model are discussed. This paper presents a basic study on optimum pitch arrangement for prediction and control of tire tread pitch noise in constraint condition relatied with tire properties, thus enabling optimum tread pitch arrangements to be determined at the design stage, by application of old tire tread pitch simulation.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.2
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• pp.207-213
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• 2014

In this paper, we propose a modified median filter for impulse noise reduction. The proposed method based on multi-step finds noisy pixels from the corrupted image and applies filtering on the noisy pixels. Neighbor pixels for filtering are filtered by linear filter which adjusts filtering direction according to an edge. Thus, our proposed method not only preserves edge, but also reduces noise in uniform region. Experimental results show that our proposed method has better quality than those by existing modified median filtering method.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.715-721
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• 2007

On a conventional rail vehicle, passive primary suspensions stabilize wheelsets in the longitudinal and yaw direction. However, these suspensions reduce the natural curving ability due to the profile of the wheels. Stabilizing and steering of the wheelsets generate the conflict problems in design process. Therefore, most systems are designed to guarantee the stability in spite of decreased curving performance. As a result, severe wear of the wheels and rails occur on tight curves and squeal noise on curving is high. Active steering has been proposed to satisfy stabilizing and steering performance simultaneously. This paper describes the possibility investigation about the application of the active steering bogie for a urban railway vehicle. Vehicles run on an amount of tight curves at mid or low speed in urban railways. Thus, it is important to reduce the wear and squeal noise between wheels and rails. Simulations show that active steering can be reduce the wear and squeal noise significantly compared to conventional systems.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.71-77
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• 2000

An axisymmetric supersonic jet is simulated at a Mach number of 1.5 and a Reynolds number of $10^5$ to identify the mechanism of sound radiation from the jet. The present simulation is performed based on the high-order accuracy and high-resolution ENO(Essentially Non-Oscillatory) schemes to capture the time-dependent flow structure representing the sound source. In this simulation, optimum expansion jet is selected as a target, where the pressure at nozzle exit is equal to that of the ambient pressure, to see pure shear layer growth without effect of change in jet cross section due to expansion or shock wave generated at nozzle exit. Shock waves are generated near vortex rings, and discernible pressure waves called Mach wave are radiated in the downstream direction with an angle from the jet axis, which is characteristic of high speed jet noise. Furthermore, vortex roll-up phenomena are observed through the visualization of vorticity contours.