• 제어로봇시스템학회논문지
• /
• 제15권5호
• /
• pp.548-554
• /
• 2009

We propose an automatic inspection system for hologram with multiple patterns. The system hardware consists of illuminations, camera, and vision processor. Multiple illuminations using LEDs are arranged in different directions to acquire each image of patterns. The system software consists of pre-processing, pattern generation, and pattern matching. The acquired images of input hologram are compared with their reference patterns by developed matching algorithm. To compensate for the positioning error of input hologram, reference patterns of hologram for different position should be generated in on-line. We apply a frequency transformation based CGH(computer-generated hologram) method to generate reference images. For the fast pattern matching, we also apply the matching method in the frequency domain. Experimental results for hologram of Korean currency are then presented to verify the usefulness of proposed system.

• 융합신호처리학회논문지
• /
• 제2권3호
• /
• pp.45-49
• /
• 2001

광대역 코드분할다중 접속은 가장 광범위하게 채택되고 있는 3세대 무선접속이다. 무선접속의 물리계층은 표준화 과정에서 주요 토의 주제이다. 본 논문은 실제적인 환경에서 많은 고려가능한 전송 시나리오상에서 상향 WCDMA 성능을 조사하는 것이 목적이다. 본 논문의 초점은 주파수 선택적 페이딩 채널조건에서 다중 접속 간섭 및 혼합 서비스 환경 경우의 성능분석에 있다. 본 조사를 위해 시뮬레이터를 개발하였으며 다양한 WCDMA 의 무선접속 특징을 포함하고 있다. 시뮬레이션 결과에 의하면 성능은 다중접속 간섭에 의해 크게 영향을 받으며 또한 주파수 선택적 페이딩 조건에 의해 성능열화 현상을 초래하게 되어 적절한 보상기술 적응이 요구된다.

• 전자공학회논문지
• /
• 제51권2호
• /
• pp.46-52
• /
• 2014

본 논문은 다중 이득 제어를 통하여 빠른 lock-time을 갖는 디지털 위상 주파수 검출기 회로를 제안한다. 기준신호와 피드백 신호의 위상 차이가 클 때, 위상 차이가 적으면서 lock에 근접했을 때, lock 이후의 세 경우에 따라 디지털 위상 동기 루프의 이득을 다르게 설정하여 lock-time을 효과적으로 줄일 수 있다. 시뮬레이션 결과를 통해 제안된 기법을 적용함으로써 기존의 단일 이득 제어 구조보다 lock-time을 약 100배 개선시킬 수 있음을 확인하였다.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2009년도 춘계학술대회 논문집
• /
• pp.490-495
• /
• 2009

An approach to 3D visualization of multiple sound sources has been developed with the application of a moving array technique. Frequency-domain beamforming algorithm is used to generate a beam power map and the sound source is modeled as a point source. When a conventional delay and sum beamformer is used, it is considered that 2D distribution of sensors leads to have deficiency in spatial resolution along a measurement distance. The goal of moving an array in this study is to form 3D array aperture surrounding multiple sound sources so that the improved spatial resolution in a virtual space can be expected. Numerical simulation was made to examine source localization capabilities of various shapes of array. The 3D beam power maps of hemispherical and spherical distribution are found to have very sharp resolution. For experiments, two sound sources were placed in the middle of defined virtual space and arc-shaped line array was rotated around the sources. It is observed that spherical array show the most accurate determination of multiple sources' positions.

• 한국소음진동공학회논문집
• /
• 제19권9호
• /
• pp.907-914
• /
• 2009

An approach to 3D visualization of multiple sound sources has been developed with the application of a moving array technique. Frequency domain beamforming algorithm is used to generate a beam power map and the sound source is modeled as a point source. When a conventional delay and sum beamformer is used, it is considered that 2D distribution of sensors leads to have deficiency in spatial resolution along a measurement distance. The goal of moving an array in this study is to form 3D array aperture surrounding multiple sound sources so that the improved spatial resolution in a virtual space can be expected. Numerical simulation was made to examine source localization capabilities of various shapes of array. The 3D beam power maps of hemispherical and spherical distribution are found to have very sharp resolution. For experiments, several sound sources were placed in the middle of defined virtual space and arc-shaped line array was rotated around the sources. It is observed that spherical array shows the most accurate determination of multiple sources' positions.

• Journal of Power Electronics
• /
• 제9권2호
• /
• pp.320-333
• /
• 2009

A Photovoltaic (PV) system's power output varies with the change of climate. Frequency deviations, tie line voltage swings are caused by the varying PV power when large PV power from several PV systems is fed in the utility. In this paper, to overcome these problems, a simple coordinated control method for smoothing the variations of combined PV power from multiple PV systems is proposed. Here, output power command is formed in two steps: central and local. Fuzzy control is used to produce the central smoothing output power command considering insolation, variance of insolation and absolute average of frequency deviation. In local step, a simple coordination is kept between the central power command and the local power commands by producing a common tuning factor. Power converters are used to achieve the same output power as local command power employing PI control law for each of the PV generation systems. The proposed method is compared with the method where conventional Maximum Power Point Tracking (MPPT) control is used for each of the PV systems. Simulation results show that the proposed method is effective for smoothing the output power variations and feasible to reduce the frequency deviations of the power utility.

• Journal of Power Electronics
• /
• 제16권6호
• /
• pp.2338-2349
• /
• 2016

This paper presents an impedance-matching-based control scheme for the harmonic resonance damping of multiple grid-connected-converters (GCCs) with LCL filters. As indicated in this paper, harmonic resonance occurs if a GCC possesses an output impedance that is not matched with the rest of the network in some specific frequency bands. It is also revealed that the resonance frequency is associated with the number of GCCs, the grid impedance and even the capacitive loads. By controlling the grid-side current instead of the converter-side current, the critical LCL filter is restricted as an internal component. Thus, the closed-loop output impedance of the GCC within the filter can be configured. The proposed scheme actively regulates the output impedance of the GCC to match the impedance of the external network, based on the detected resonance frequency. As a result, the resonance risk of multiple GCCs can be avoided, which is beneficial for the plug-and-play property of the GCCs in microgrids. Simulation and experimental results validate the effectiveness of the proposed method.

• Journal of Communications and Networks
• /
• 제9권2호
• /
• pp.159-166
• /
• 2007

In this paper, we propose an efficient and robust interference mitigation technique based on a nullsteering multi-user multiple-input multiple-output (MU-MIMO) spatial division multiple access (SDMA) scheme for frequency sharing between IMT-advanced and fixed satellite service (FSS) in the 3400-4200 and 4500-4800 MHz bands. In the proposed scheme, the pre-existing precoding matrix for SDMA unitary precoded (UPC) MIMO proposed by the authors is modified to construct nulls in the spatial spectrum corresponding to the direction angles of the victim FSS earth station (ES). Furthermore, a numerical formula to calculate the power of the interference signal received at the FSS ES when IMT-Advanced base stations (BS) are operated with the interference mitigation technique is presented. This formula can be derived in closed form and is simply implemented with the help of simulation, resulting in significantly reduced time to obtain the solution. Finally, the frequency sharing results are analyzed in the co-channel and adjacent channel with respect to minimum separation distance and direction of FSS earth station (DOE). Simulation results indicate that the proposed mitigation scheme is highly efficient in terms of reducing the separation distance as well as robust against DOE estimation errors.

• 대한조선학회논문집
• /
• 제42권5호
• /
• pp.528-533
• /
• 2005

A mono-static high frequency acoustic target strength analysis scheme was developed for underwater targets, based on the far-field Kirchhoff approximation. Au adaptive triangular beam method and a concept of virtual surface were adopted for considering the effect of hidden surfaces and multiple reflections of an underwater target, respectively. A test of a simple target showed that the suggested hidden surface removal scheme is valid. Then some numerical analyses, for several underwater targets, were carried out; (1) for several simple underwater targets, like sphere, square plate, cylinder, trihedral corner reflector, and (2) for a generic submarine model, The former was exactly coincident with the theoretical results including beam patterns versus azimuth angles, and the latter suggested that multiple reflections have to be considered to estimate more accurate target strength of underwater targets.

• Journal of Communications and Networks
• /
• 제18권3호
• /
• pp.439-445
• /
• 2016

In this paper, we consider subcarrier-index modulation (SIM) for precoded orthogonal frequency division multiplexing (OFDM) with a few activated subcarriers per user and its generalization to multi-carrier multiple access systems. The resulting multiple access is called sparse index multiple access (SIMA). SIMA can be considered as a combination of multi-carrier code division multiple access (MC-CDMA) and SIM. Thus, SIMA is able to exploit a path diversity gain by (random) spreading over multiple carriers as MC-CDMA. To detect multiple users' signals, a low-complexity detection method is proposed by exploiting the notion of compressive sensing (CS). The derived low-complexity detection method is based on the orthogonal matching pursuit (OMP) algorithm, which is one of greedy algorithms used to estimate sparse signals in CS. From simulation results, we can observe that SIMA can perform better than MC-CDMA when the ratio of the number of users to the number of multi-carrier is low.