• Korean Journal of Optics and Photonics
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• v.26 no.5
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• pp.269-274
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• 2015

In this paper we design the optical system for an integrated two-channel TO-type optical transmitter to apply the HDMI interface using the code V simulator. The proposed integrated two-channel optical transmitter has two VCSELs attached in parallel on an 8-pin TO-CAN package, on top of which is a lens filter block ($1mm{\times}2mm{\times}4mm$) composed of hemispherical lenses and WDM filters. Considering two-channel transmitters manufactured with wavelength combinations of 1060nm/1270nm and 1330nm/1550nm, we obtain the optimum value of the diameter of the hemispherical lens as 0.6 mm for both combinations, and the distances L between the lens filter block and ball lens as 1.7 mm and 2.0 mm for the 1060nm/1270nm and 1330nm/1550nm wavelength combinations, respectively. At this time, the focal length f0 of the lens filter blocks for wavelengths of 1060, 1270, 1330, and 1550 nm are 0.351, 0.354, 0.355, and 0.359 mm, respectively, and the focal lengths F of light passing through the lens filter block and ball lens are 0.62 mm for 1060nm/1270nm and 0.60-0.66 mm for 1330nm/1550nm wavelength combinations.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.12
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• pp.149-158
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• 2005

This paper proposes a congestion avoidance algorithm which provides stable throughput and transmission rate regardless of buffer size by limiting the TCP congestion window in fixed bandwidth networks. Additive Increase, Multiplicative Decrease (AIMD) is the most commonly used congestion control algorithm. But, the AIMD-based TCP congestion control method causes unnecessary packet losses and retransmissions from the congestion window increment for available bandwidth verification when used in fixed bandwidth networks. In addition, the saw tooth variation of TCP throughput is inappropriate to be adopted for the applications that require low bandwidth variation. We present an algorithm in which congestion window can be limited under appropriate circumstances to avoid congestion losses while still addressing fairness issues. The maximum congestion window is determined from delay information to avoid queueing at the bottleneck node, hence stabilizes the throughput and the transmission rate of the connection without buffer and window control process. Simulations have performed to verify compatibility, steady state throughput, steady state packet loss count, and the variance of congestion window. The proposed algorithm can be easily adopted to the sender and is easy to deploy avoiding changes in network routers and user programs. The proposed algorithm can be applied to enhance the performance of the high-speed access network which is one of the fixed bandwidth networks.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.7 s.349
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• pp.32-40
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• 2006

It is very important to establish a pairwise key securely in wireless sensor networks. Because sensor networks consist of devices with weak physical security, they are likely to be compromised by an attacker. However, some approaches using key pre-distribution and other approaches using one hop local keys are known to be very vulnerable to threats caused by compromised nodes, even a small number. This paper proposes a scheme where each node establishes three hop local keys and employs them for a later pairwise key establishment. When any two nodes agree a pairwise key, all nodes on the route between two nodes contribute to the agreement of the pairwise key. Here, the initial three hop local keys are employed for encrypting a secret key delivered from a node to other nodes. Therefore, the proposed scheme bothers attackers to compromise much more nodes than the scheme using one hop local keys only. The simulation results have proven that the proposed scheme provides better performance and higher security than the scheme using one hop local keys in terms of message exchange, the number of encryption and decryption, and pairwise key exposure rate.

• The Journal of Society for e-Business Studies
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• v.9 no.4
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• pp.117-136
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• 2004

As the time-to-market gets more important for competitiveness of an enterprise in manufacturing industry, it becomes important to shorten the development cycle of a product. Reuse of existing design models and e-Catalog for components are required for faster product development. To achieve this goal, an electric catalog must provide parametric CAD models since parametric information is indispensable for configuration design. There are difficulties in building up a parametric library of all the necessary combination using a CAD system, since we have too many combinations of components for a product. For example, there are at least 80 million combinations of components on one page of paper catalog of a mold base. To solve this problem, we propose the method of table parametric for the automatic generation of parametric CAD models. Any combination of mold base can be generated by mapping between a classification system of an electric catalog and the design parameters set of the table parametric. We propose how to select parametric models and to construct the design parameters set.

• Korean Journal of Materials Research
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• v.8 no.8
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• pp.751-756
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• 1998

Effects of remote hydrogen plasma cleaning process parameters on the removal of Fe impurities on Si surfaces and the Fe removal mechanism were investigated. Fe removal efficiency is enhanced with decreasing the plasma exposure time and increasing the rf-power. The optimum plasma exposure time and rf-power are 1 min and 100W. respectively, in the range below 10 min and 100W. Fe removal efficiency is better under lower pressures than higher pressures, and the optimum $\textrm{H}_2$ flow rate was found to be 20 and 60sccm, respectively, under a low and a high pressure. The post-RHP(remote hydrogen plasma) annealing enhanced metallic contaminants removal efficiency, and the highest efficiency was achieved at $600^{\circ}C$. According to the AFM analysis results Si surface roughness was improved by 30-50%, which seems to be due to the removal of particles by the plasma cleaning. Also. Fe impurities removal mechanisms by remote hydrogen plasma are discussed.

• Journal of the Korea Computer Graphics Society
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• v.16 no.3
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• pp.1-10
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• 2010

In this paper, we propose a novel noiseless method of BRDF rendering on a GPU in real-time. Illumination at a surface point is formulated as an integral of BRDF producted with incident radiance over the hemi-sphere domain. The most popular method to compute the integral is the Monte Carlo method, which needs a large number of samples to achieve good image quality. But, it leads to increase of rendering time. Otherwise, a small number of sample points cause serious image noise. The main contribution of our work is a new importance sampling scheme producing a set of incoming ray samples varying continuously with respect to the eye ray. An incoming ray is importance-based sampled at different latitude angles of the eye ray, and then the ray samples are linearly connected to form a curve, called a thread. These threads give continuously moving incident rays for eye ray change, so they do not make image noise. Since even a small number of threads can achieve a plausible quality and also can be precomputed before rendering, they enable real-time BRDF rendering on the GPU.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.2B
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• pp.100-107
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• 2007

Recently, a study of BcN(Broadband convergence Network) is progressing continuously, and it is important to improve the quality of the service according to subscribers because a scale of network is about to be larger. It is more important to manage QoS(Quality of Service) of all subscribers in layer 2 than layer 3 network since managing it in layer 3 network cost both additional processes and large hardware. Moreover, QoS based on Best-Effort service has been developed because tots of subscribers should use limited resource in BcN. However, they want to be supplied with different service even though they pay more charge. Therefore, it is essential to assign the different bandwidth to subscribers depending on their level of charge. The method of current Rate Limiter limits the bandwidth of each port that does not offer fair service to subscribers. The Rate Limiter proposed in this paper limits bandwidth according to each subscriber. Therefore, subscribers can get fair service regardless of switch structure. This new Rate Limiter controls the bandwidth of subscribers according to the information of learning subscriber and manages maximum performance of Ethernet switch and QoS.

• Journal of Biomedical Engineering Research
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• v.25 no.6
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• pp.431-438
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• 2004

Medical ultrasonic imaging is a useful imaging facility known to be most safe and easy. It enables physicians to observe the inside structures of the bodies, blood flow, and motions of internal organs. Some physical properties of biologic tissues can also be estimated from backscattered sounds. However, the ultrasonic pulses interrogating the living organisms leave their footprints in the returning signals during imaging. Some significant details are buried in the footprints and their overlaps from adjacent particles. These distortions also decrease the quality of the images. Many research efforts have been made to enhance the image quality and to recover the acoustic information in various ways. In this study, a new interrogation method based on the wavelet and subband filter bank is proposed. It adopts the subband wavelet filters satisfying the perfect-reconstruction (PR) conditions as the interrogating pulses to restore the details useful in tissue characterization and to enhance the image quality. The proposed method was applied to two types of simulations of ultrasonic imaging. The results showed its ability to restore the detailsin the simulated interrogation of biologic tissues, and verified the improved image quality in the simulated imaging of general ultrasonic phantom compared with the conventional method.

• Journal of Broadcast Engineering
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• v.17 no.1
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• pp.108-121
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• 2012

As Scalable Video Coding (SVC) is a video compression standard extended from H.264/AVC, it is a way to provide scalability in terms of temporal, spatial and quality. Although the compression efficiency of SVC is increased due to the scalability in many aspect, it is essential to reduce the complexity in order to efficiently use because the complexity is relatively increased. To reduce the complexity of SVC in the paper, we propose fast mode decision algorithm to reduce the complexity of encoding process using direction information of B-picture by efficiently performing inter-layer prediction. The proposed algorithm is a fast mode decision algorithm that makes different from detection mode number of forward and backward, bi-direction in the way using best mode of base-layer up-sampled after simply SKIP mode detection using the direction information of best mode of base-layer up-sampled. The experimental results show that the proposed algorithm approach can achieve the maximum computational time saving about 53% with almost no loss of rate distortion (RD) performance in the enhancement layer.

• Journal of Broadcast Engineering
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• v.24 no.6
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• pp.928-938
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• 2019

Republic of Korea has established 'Transmission and Reception for Terrestrial UHDTV Broadcasting Service' standard based on ATSC 3.0, the next-generation broadcasting standard in North America and is now providing commercial services. Republic of Korea has been studying terrestrial UHDTV based disaster broadcasting service using the ATSC 3.0 AEA system's technology since 2018. ATSC 3.0 has established a standard for expanding disaster broadcasting services, which were used to be simple push-type text message broadcasting, by introducing bidirectional and rich-media transporting mechanisms. However, the disaster information is still focused on the general public, and disaster broadcasting service including detailed information for the vulnerable are still insufficient. In this paper, we proposed the optimized disaster broadcasting service for vulnerable populations based on ATSC 3.0 after defined the disaster vulnerable populations as the target of the service. And we defined the extension element of disaster broadcasting message for service provision. The proposed service can be an effective means to increase the possibility of disaster information reception and evacuation to vulnerable populations. In addition, it is expected to be used as a basic research for development of diverse and effective advanced services for vulnerable populations through linkage with existing disaster alerting and countermeasures studies.