• The Journal of the Acoustical Society of Korea
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• v.36 no.5
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• pp.300-304
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• 2017

In a cylindrical sonar, a conventional broadband energy detector has limitations in the separation of adjacent targets. In this paper, a broadband detection algorithm using cross-correlation is applied to the cylindrical sonar to improve the bearing resolution. The proposed algorithm uses split beamforming before broadband detection processing using cross-correlation to generate half beams. The time delay obtained from the peak of correlation between half beams is used to estimate the bearing of target. Simulations demonstrate the improved performance of the proposed algorithm against the conventional algorithm.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.8
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• pp.11-19
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• 2014

In recent SONAR (sound navigation and ranging) systems, wideband active SONAR systems has received more attention than narrowband SONAR systems due to the remarkable detection performance in terms of range resolution. However, the wideband SONAR systems usually requires a huge amount of computational burden in order to achieve their own superiority. To cope with this drawback of the wideband SONAR systems, this paper proposes a fast target detection and velocity estimation method using an extended replica in wideband hyperbolic frequency modulation active SONAR system. Computer simulation shows that the proposed method can be implemented by a highly reduced computational complexity with a little performance degradation in target detection and velocity estimation compared to the conventional filter bank method.

• The Journal of the Acoustical Society of Korea
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• v.32 no.6
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• pp.532-540
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• 2013

In this paper, we propose the modified SED (Subband Energy Detection) which can assign weights adapting to the receiving signal level for the broadband energy detection in the passive SONARs. SED which is one of the broadband processing mainly employed by passive SONARs to detect a target is more robust against interference like multi signals or a clutter than CED (Conventional Energy Detection), but it degrades detection performance to assign weights independent of extracted extrema level of the receiving signal. Therefore, in this paper, the weighting method which can efficiently assigns rewards or penalties adapting to extracted extrema level of the receiving signal is proposed. In order to evaluate the performance of proposed method, we conducted experiments by using simulation and real ocean acoustic signal which is acquired from Yellow Sea. From the experiments, our proposed method has shown better performance than conventional SED.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.8A
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• pp.752-759
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• 2006

In this paper, the performances of representative high resolution direction finding algorithms are evaluated and compared in wideband mobile environments. The angular spread phenomenon in mobile environments is first investigated and then a vector channel model for wideband OFDMA signals is derived. A direction finding system architecture for OFDMA smart antenna systems is proposed and finally the performances of high resolution direction finding algorithms are evaluated in wideband mobile environments by taking the WiBro system as a target system.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1467-1468
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• 2006

본 논문에서는 현재 운용되고 있는 낙뢰탐지 시스템들과는 다른 측위방식인 TDOA(Time Difference of Arrival)방법을 사용한 3차원 낙뢰 탐지 및 추적 시스템을 제안한다. TDOA방식은 낙뢰와 수신국사이의 도달시간을 측정하여 두 수신국간의 시간차가 일정한 쌍곡선을 얻고 이들 쌍곡선의 교점을 이용해 낙뢰의 위치를 결정하는 방법이다. 이 시스템을 이용하여 위치정확도가 수 미터인 3차원 낙뢰 방전 궤적을 얻을 수 있다. 시스템의 구현을 위해서 먼저 낙뢰의 신호를 저장해야 하는데, 광대역의 낙뢰신호를 저장하기 위해서는 고속의 디지타이저가 필요하다. 그러나 디지타이저와 프로세서간의 인터페이스의 한계로 연속적으로 이를 저장하는 것은 어려우며, 이러한 신호 저장의 문제점을 해결하기 위해서 낙뢰 신호 저장 시스템이 필요하다. 본 논문에서는 낙뢰의 메커니즘과 광대역 낙뢰신호 검출기법을 설명하고, 구현한 낙뢰 신호 저장 시스템을 소개한다.

• The Journal of the Acoustical Society of Korea
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• v.36 no.3
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• pp.179-185
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• 2017

The problem that occurred in the design/fabrication/testing of the wideband transmitting power amplifier for an embedded active SONAR (Sound Navigation and Ranging) system operating underwater was analyzed and the solution of the problem was proposed in this paper. Wideband acoustic SONAR systems had been developed in order to improve the underwater detection performance. The underwater acoustic transmission system had been also developed to achieve the wideband SONAR system. In this paper, the wideband acoustic transmission signal was generated using a 2 Level sawtooth type Class D PWM (Pulse Width Modulation) which was not complicated to implement. When the sonar signals having two or more frequencies were simultaneously generated, parasitic frequencies were added to the original signals by integer multiples of the frequency difference of the original signal. To cope with this problem, we proposed a way to remove the parasitic frequency from the source signal through modeling and simulation of the implemented power amplifier and PWM control hardware using MATLAB and Simulink.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.11
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• pp.2206-2212
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• 2017

When it comes to naval surface warfare, the probability of detection is an important factor in survivability and the Radar Cross Section(RCS) is a major parameter. In this paper, the RCS reduction technology of the Radar Absorbing Material(RAM) method is carried out for the general frequency range for naval warfare. We set the analysis model with the simplified ship model and the wide band metamaterial which is high-tech radar absorbing materials is selected for the RAM method. The modeling of the wide band metamaterial composed of an MIK surface which has the wide band resonant properties and flexible substance and the electromagnetic absorptions and reflections of the wide band metamaterial has been simulated to explore the performance. Also, the wide band metamaterial is compared with the paint absorber to analyze RCS reduction in terms of RCS values.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.14 no.4
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• pp.111-121
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• 2004

With rapid growth of the Internet, network intrusions have greatly increased and damage of attacks has become more serious. Recently some kinds of Internet attacks cause significant damage to overall network performance. Current Intrusion Detection Systems are not capable of performing the real-time detection on the backbone network In this paper, we propose the broadband network intrusion detection system using the exponential smoothing method. We made an experiment with real backbone traffic data for 8 days. The results show that our proposed system detects big jumps of traffic volume well.

• Journal of the Institute of Convergence Signal Processing
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• v.4 no.3
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• pp.1-6
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• 2003

It is difficult to detect and to track the moving targets like tanks and diesel vehicles due to the variety of terrain and moving of targets. It is possible to be happened the aliasing conditions as the difficulty of antenna deployment in the complex environment like the battle fields. In this paper, we study the problem of detecting and tracking of moving targets which are emitting wideband signals under severe spatial aliasing conditions because of the sparse arrays. We developed a direction of arrival(DOA) estimation algorithm based on subband MUSIC(Multiple Signal Classification) method which produces high-resolution estimation. In this algorithm, the true bearings are invariant regardless of changes of frequency bands while the aliased false bearings vary. As a result, the proposed algorithm overcomes the aliasing effects and improves the localization performance in sparse passive arrays.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.1
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• pp.155-162
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• 2020

In this paper, we present a radiation compensation method and experiment method for two-dimensional direction finding by elevation and azimuth angles of broadband GPS signal, and then produce experimental results. Previous studies have performed direction finding by only using the azimuth angle of the detected signal. So, the compensation table utilizes compensation data by azimuth angles only. However, the presented method in this study has compensation data by azimuth and elevation angles for two-dimensional direction finding. Because of direction finding systems and applications are diversified, recently. So, we present a two-dimensional radiation compensation method. For evaluation of the presented compensation method, we calculate the ideal phase differences on the antenna for two-dimensional direction finding and simulate phase differences using a FEKO EM simulator. Subsequently, we analyze experimental data by radiation compensation experiments using the presented compensation method in an anechoic chamber.