• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.12
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• pp.4600-4616
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• 2021

In cognitive radio networks where unlicensed secondary users opportunistically access to licensed spectrum unused by licensed primary users, spectrum sensing is one of the key issues in order to effectively use the frequency resource. For enhancing the sensing performance in energy detection-based spectrum sensing, spatial diversity based on multiple antennas is utilized. However, the sensing performance can be degraded when antennas are spatially correlated, resulting in inducing the harmful interference to primary users. To overcome this problem, in this paper, an advanced energy detector is proposed. In the proposed sensing method, a weight matrix based on the eigenvalues of the spatial channels without any prior information on the primary signals is defined and utilized. In numerical simulations, it is shown that the proposed detector outperforms the conventional detector with regard to false-alarm and detection probabilities when antenna are spatially correlated.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.1
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• pp.18-25
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• 2022

The cold staring issue of permanent magnet synchronous motors (PMSM) is a chronic problem in the field of PMSM sensorless drives. A traditional starting method, called the I-F method, is widely adopted because of its simple structure. However, when using this method, the pre-defined magnitude and frequency of the starting current should be changed according to the condition of the load and machine inertia. In this paper, a smart and simple algorithm for the cold starting of PMSM is proposed. In the proposed method, an integrated control angle from the estimated electrical rotor speed is used for vector control such as the indirect vector control of the induction machine. Thus, very stable cold starting is performed regardless of the machine load condition or inertia changing.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.863-868
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• 2002

Operational Modal Analysis also known as Ambient Modal Analysis has an increasing interest in mechanical engineering. Especially on big structures where the excitation and not less important the determination of the forces is most often a problem. In a structure like a wind turbine wing where the modes occur both close in frequency and hi-directional the ambient excitation has big advantages. In this paper modal parameters are identified from the wing by operational modal analysis. For the parameter identification both parametric and non-parametric techniques are used. Advantages and disadvantages are discussed and results from the different techniques are compared

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.161.6-161
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• 2001

Confocal scanning microscopy (CSM) has an important role as the three-dimensional profiler. An image distribution can be reconstructed by a correlation analysis of spots with the bandwidth of radio frequency. But it is a serious problem for the high performance to align the optical components. Especially, the parasitic motion of focus on the detector gives rise to the fatal distortion of an image profile named the extinction effect while using acousto-optical(AO) deflector. An image profile can be regenerated in CSM with many advantages of non-contact, high speed and high resolution comparatively. In addition to the axial response of the primary focus, the lateral movement of it gives a necessity of the unitary lens to the scanning system. While using the beam deflector, the pupil of beam may be fixed at the nominal position. Furthermore, the use of a deflector may result in ...

• Steel and Composite Structures
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• v.46 no.5
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• pp.659-667
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• 2023

Nonlinear forced vibration behaviors of sandwich plates having graphene platelets (GPL) based face sheets have been researched in this article. Possessing low weight together with low stiffness, square honeycomb cores are mostly constructed by aluminum. Herein, the square shaped core has been fortified by two skins of GPL-based type in such a way that the skins have uniform and linearly graded GPL dispersions. The square shaped core has the effective material specification according to the relative density concept. The whole formulation has been represented based upon classical plate theory (CPT) while harmonic balance approach is applied for solving the problem and plotting the amplitude-frequency curves. The forced vibration behaviors of such plates are influenced by square-shaped core and the relative density, skin's height and GPL fortification.

• Coupled systems mechanics
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• v.12 no.1
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• pp.21-40
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• 2023

In thisstudy, the vibration problem ofthermo elastic carbon nanotubes conveying pulsating viscous nano fluid subjected to a longitudinal magnetic field is investigated via Euler-Bernoulli beam model. The controlling partial differential equation of motion is arrived by adopting Eringen's non local theory. The instability domain and pulsation frequency of the CNT is obtained through the Galerkin's method. The numerical evaluation of thisstudy is devised by Haar wavelet method (HWM). Then, the proposed model is validated by analyzing the critical buckling load computed in presentstudy with the literature. Finally, the numerical calculation ofsystem parameters are shown as dispersion graphs and tables over non local parameter, magnetic flux, temperature difference, Knudsen number and viscous parameter.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10e
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• pp.76-78
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• 2002

Multicasting over mobile IP network becomes more important with the increasing needs of supporting multimedia services in mobile network. The IETF has suggested two approaches which are remote subscription and bidirectional tunneling for supporting mobility management in multicasting over mobile IP. But these protocols have problems - the frequent reconstruction of multicast delivery tree, packet less during handoff, convergence problem, and so on. In this paper, we propose to use preconfiguration of multicast delivery tree when mobile host enters the foreign network. It will decrease the frequency of multicast delivery tree reconstruction, and reduce the packet loss during handoff, Also the multicast delivery tree maintained by Keep Alive messages makes the signaling overload of networks diminished.

• Structural Engineering and Mechanics
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• v.85 no.1
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• pp.15-27
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• 2023

Using artificial intelligence and internet of things methods in engineering and industrial problems has become a widespread method in recent years. The low computational costs and high accuracy without the need to engage human resources in comparison to engineering demands are the main advantages of artificial intelligence. In the present paper, a deep neural network (DNN) with a specific method of optimization is utilize to predict fundamental natural frequency of a cylindrical structure. To provide data for training the DNN, a detailed numerical analysis is presented with the aid of functionally modified couple stress theory (FMCS) and first-order shear deformation theory (FSDT). The governing equations obtained using Hamilton's principle, are further solved engaging generalized differential quadrature method. The results of the numerical solution are utilized to train and test the DNN model. The results are validated at the first step and a comprehensive parametric results are presented thereafter. The results show the high accuracy of the DNN results and effects of different geometrical, modeling and material parameters in the natural frequencies of the structure.

• International Journal of Computer Science & Network Security
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• v.22 no.12
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• pp.1-12
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• 2022

Besides unexpected growth perceived by IoT's, the variety and volume of threats have increased tremendously, making it a necessity to introduce intrusion detections systems for prevention and detection of such threats. But Intrusion Detection and Prevention System (IDPS) inside the IoT network yet introduces some unique challenges due to their unique characteristics, such as privacy inference, performance, and detection rate and their frequency in the dynamic networks. Our research is focused on the privacy inferences of existing intrusion prevention and detection system approaches. We also tackle the problem of providing unified a solution to implement the open-source IDPS in the IoT architecture for assessing the performance of IDS by calculating; usage consumption and detection rate. The proposed scheme is considered to help implement the human health monitoring system in IoT networks

• The Journal of Korea Robotics Society
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• v.18 no.3
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• pp.271-280
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• 2023

FMCW (Frequency Modulated Continuous Wave) radar system is widely used in autonomous driving and navigation applications due to its high detection capabilities independent of weather conditions and environments. However, radar signals can be easily contaminated by various noises such as speckle noise, receiver saturation, and multipath reflection, which can worsen sensing performance. To handle this problem, we propose a learning-free noise removal technique for radar to enhance detection performance. The proposed method leverages adaptive thresholding to remove speckle noise and receiver saturation, and wavelet transform to detect multipath reflection. After noise removal, the radar image is reconstructed with the geometric structure of the surrounding environments. We verify that our method effectively eliminated noise and can be applied to autonomous driving by improving the accuracy of odometry and place recognition.