• 한국전자파학회논문지
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• 제17권12호
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• pp.1249-1258
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• 2006

ISAR 자동 초점(autofocus) 기법이란 움직이는 표적에 대한 2차원 레이더 영상인 ISAR 영상을 얻을 때 표적에 의한 doppler-shift 때문에 발생하는 위상 오차를 예측, 제거하는 기법이다. 이러한 자동 초점 기법이 수행되지 않은 ISAR 영상은 위상 오차(phase ewer)에 의한 왜곡이 포함되기 때문에 초점이 맞지 않는 것처럼 흐린(blurred) 영상이 된다. 이러한 영상은 추후에 구분기(classifier)를 이용하여 표적 구분 시 올바른 구분을 보장할 수 없으므로 반드시 자동 초점 기법이 수행되어야 하며, 본 논문에서는 이를 위해 영상의 엔트로피(entropy)를 최소화시키는 알고리즘을 이용한다. ISAR 자동 초점 기법은 크게 range alignment 과정과 phase adjustment 과정으로 나뉘는데, range alignment 과정에서 샘플링 포인트(sampling point)의 수와 그에 따른 영상 품질과의 관계를 분석하고, phase adjustment 과정 을 수행하기 위한 알고리즘인 SSA(Stage-by-Stage Approaching)의 계산시간 단축을 위한 방법을 분석한다.

• Journal of Korean Neurosurgical Society
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• 제60권2호
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• pp.257-261
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• 2017

Objective : This study was conducted to assess the surgical results of one-stage posterior minimal laminectomy and video-assisted thoracoscopic surgery (VATS) for the treatment of thoracic dumbbell tumor and to describe its precise technique. In addition, we investigated the technique's usefulness and limitations. Methods : Seven cases of thoracic dumbbell tumor (two men and five women, mean age, 43 years) were analyzed retrospectively. Pathological findings included schwannoma in four patients, neurofibroma in two patients, and hemangioma in one patient. The location of tumors varied from T2/3 to T12/L1. Dumbbell tumors were resected by one-stage operation using posterior laminectomy followed by VATS without instrumentation. Clinical data were reviewed. Results : The mean follow-up period was 25 months (range, 3-58 months), and the operative time ranged from 255 to 385 min (mean, 331 min), with estimated blood loss ranging from 110 to 930 mL (mean, 348 mL). The tumor was completely resected without instrumentation and postoperative instability in all cases. Postoperative complications included atelectasis and facial anhydrosis in one case each. Conclusion : One-stage posterior minimal laminectomy and VATS may be a safe and less invasive technique for removal of thoracic dumbbell tumor without instability. This method has the advantage of early ambulation and rapid recovery because it reduces blood loss and postoperative pain.

• Journal of applied mathematics & informatics
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• 제33권1_2호
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• pp.77-87
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• 2015

Parallel lines are often used to increase production rate in many manufacturing systems where the main line splits into several lines in parallel, and after some operations, they merge into a main line again. Queueing networks with finite buffers have been widely used for modeling and analyzing manufacturing systems. This paper provides an approximation technique for multi-server two-stage networks with merge configuration and blocking which will be a building block for analysis of general manufacturing systems with parallel lines and merge configuration. The main idea of the method is to decompose the original system into subsystems that have two service stations with multiple servers, two buffers and external arrivals to the second stage are allowed. The subsystems are modeled by level dependent quasi-birth-and-death (LDQBD) process.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.1206-1210
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• 2005

This paper presents performance improvement in optical CDMA system under the presence of beat noise using a cancellation technique. Optical fibers and atmospheric optical communications have been proposed the connection between base stations and central station. The optical signal beat noise is due to interference between lightwave, many optical waves are simultaneously incident on each receiver photodiode. Since the photodiode acts as a square-law detector, beat noise can occur in the receiver. While A two-stage cancellation technique is analyzed and verified via simulation employed here because of its system simplicity. By using the random ingredients of all user signals are estimated, the beat noise is rebuilt and removed from the intended signal. In addition to cancellation technique cancel the inherent multiuser interference (MUI) in CDMA system and nonlinear distortion (NLD) in optical system. It is performed at the receiver of the central station where the random ingredients of all user signals are estimated and the MUI and the NLD are rebuilt and removed from the received signal. The validity of the cancellation technique is theoretically analyzed and shown by numerical results. The increasing of capacity in two stage cancellation are obtained.

• 전자공학회논문지S
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• 제34S권1호
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• pp.80-93
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• 1997

This paper proposes a new technique of optimal codebook design in multistage gain-shape vector quantization (MS-GS VQ) for wireless image communication. An original image is divided into a smany blocks as possible in order to get strong robustness to channel transmission errors: the original image is decomposed into a number of subband images, each of which contains a sperate spatial frequency information and is obtained by the biorthogonal wavlet transform; each subband is separated into several consecutive VQ stages, where each stage has a residual information of the previous stage; one vector in each stage is divided into two components-gain and shape. But, this decomposition genrates too many blocks and it thus makes the determination of optimal codebooks difficult. We overcome this difficulty by evolving each block's codebook independently with different genetic algorithm that uses each stage's individual training vectors. Th eimpact of th eproposed VQ technique on the channel transmission errors is compared with that of other VQ techniques. Simulation results show that the proposed VQ technique (MS-GS VQ) with the optimal codebook designe dy genetic algorithms is very robust to channel transmission errors even under the bursty and high BER conditions.

• Structural Engineering and Mechanics
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• 제50권4호
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• pp.563-573
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• 2014

In hydroforming, the general technique employed to overcome the problem of die corner filling consist in increasing the maximum fluid pressure during the forming process. This technique, in other hand, leads to other difficulties such as thinning and rupturing of the final work piece. In this paper, a new technique has been suggested in order to produce a part with complete filled corners. In this approach, two moveable bushes have been used. So, the workpiece moves driven by both bushes simultaneously. In the first stage, system pressure increases until a maximum of 15 MPa, providing aninitial tube bulge. The results showed that the pressure in this stage have to be limited to 17 MPa to avoid fracture. In a second stage, bushes are moved keeping the constant initial pressure. The punches act simultaneously at the die extremities. Results show that the friction between part and die decreases during the forming process significantly. Also, by using this technique it is possible to produce a part with reasonable uniform thickness distribution. Other outcomes of applying this method are the lower pressures required to manufacture a workpiece with complete filled corners with no wrinkling.

• 한국통신학회논문지
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• 제21권4호
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• pp.972-983
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• 1996

This paper proposes a new technique for frequency offset correction for OFDM systems on a frequency selective fading channel. Frequency offset in OFDM introduces interchannel interference among the multiple subcarriers of OFDM signal. To compensate the interference, this paper describes an algorithm with two stages:acquisition and tracking. At both stages, the proposed algorithm oversamples the received OFDM signal to obtain a couple of demodulated symbol sets. At acquisition stage the frequency offset is reduced to half or less of the intercarrier spacings by matching the sign pattern of each element of the sets. Next, at tracking stage the frequency offset is corrected with a frequency detector which is controlled by the correlation of the two sets. It is shown that the proposed algorithm can correct the frequency offset in the event of uncertainty in the initial offset that exceeds one half of the intercarrier spacing. In addition, the proposed algorithm is robust to transmitted symbols and channel characteristics by using oversampled symbol sets.

• 한국경영과학회지
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• 제22권1호
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• pp.123-140
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• 1997

In this paper we consider closed flow line systems with samploing inspections. The total number of parts in the system is assumed to be N. The processings carried out of each station do not always meet the requirement of quality. Therefore, upon completion of its processing at each station, a part is inspected to determine whether the processings meet the requirement of quality or not. We assume that inspection are done on a random basis. If a part is found to be defective by an inspection, it is fed back to the apropriate station. Two different cases will be considered in this study : a three-station flow line system with infinite buffers and a two-station flow line system with finite buffers. For each case, we will develop an exact method to obtain the performance measures such as throughput, machinen utilization, average outgoing quality and manufacturing lead time. For the case of the two-station flow line system ith finite buffers, we will also develop an approximation method using a stage-aggregation technique. Then using buffers, we will also develop an approximation method using a stage-aggregation technique. Then using these results, we will try to find an optimal inspection policy which maximizes the expected net profit under a certain cost structure. Although we present the results only for the two or three station flow line system in this paper, the results obtained in this paper can be extended easily to the system which consists of more than two or three stations.

• 한국정보통신학회논문지
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• 제10권1호
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• pp.42-48
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• 2006

본 논문에서는 차세대 복합 시분할 부호분할 다중접속 이동통신 시스템에서 타 셀 사용자 간섭 제거를 위한 결합검출 방안을 제안한다. 결합검출 기술은 차세대 복합 시분할 부호분할 다중접속 이동통신 시스템 TD-CDMA 시스템에서의 가장 큰 특징이라 할 수 있는 기술로서 셀 내의 서로 다른 사용자의 신호 간섭을 제거하여 동시에 사용자 데이터를 복원할 수 있다. 종래의 연구에서는 2단계 결합 검출 방식을 이용하여 목적 셀의 사용자 간섭 뿐 아니라 타 셀 간섭을 제거해 줄 수 있는 방안이 제안되었으나 이 방안에서는 타 셀 간섭 제거를 위한 구체적인 사용자 인식에 대한 방안이 없다. 따라서 주변 타 셀 내의 사용자의 간섭의 크기에 상관없이 모든 사용자에 대하여 결합검출을 수행해야 하며 2단계 결합검출의 복잡도가 매우 높다. 본 논문에서는 타 셀 사용자의 간섭의 크기에 따라서 선택적으로 2단계 결합 검출을 수행하는 방안을 제안한다. 제안된 방식은 모의실험을 통하여 성능을 조사하였으며 종래의 결합검출 방식에 비하여 성능의 열화가 없는 동시에 2 단계 결합검출의 복잡도를 크게 줄일 수 있다.

• 전자공학회논문지B
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• 제30B권9호
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• pp.76-83
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• 1993

A morphological filtering algorithm using directional information is presented. Directional filtering technique is effective in reducing noises and preserving edges. The proposed directional filtering is composed of two stage filtering processes. The opening and closing operations in the lst stage are performed for the pixels is aligned to the vertical, horizontal, and two diagonal directions, respectively. The opening operation supresses the positive impulse noises, while the closing operation the negative ones. Then, each directional result and their average value are filtered by the opening or closing operations in the 2nd stage. The averaging operation diminishes the effects of Gaussian noises in the homogeneous regions. Thus, the morphological operation in the 1 st stageremoves the impulse noises and in 2nd stage reduces. Gaussian ones. The experimental results show that the proposed filtering is superior to the existing nonlinear filtering in the aspects of the subjective quality. Also, the morphological filtering method reduces the computational loads.