• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.8
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• pp.55-63
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• 2018

In this paper, we measured the propagation path loss by a ground to air flight communication test at UHF band and analyzed the results. The ground receiving terminal was located at 1,100m above sea level in Cheju Island and the airborne transmit terminal flew at an altitude of 3.5km from 150 to 220km from the ground terminal. In this case, the ground terminal and the airborne terminal are on the Line of Sight. Therefore loss in this communications environment can be predicted based on Free Space Loss. However, in this test, the sea level exists between two terminals, and due to the very small angle of incidence on the reflecting surface due to the long-range communication environment, it is not possible to accurately predict the loss of free space only. Therefore, considering that there are no surrounding obstacles and that a line of sight is secured between the end of two terminals, we applied a plane earth reflection model and a spherical earth reflection model to estimate the propagation path loss and compared with the actual test results. As a result of the comparison, the predicted propagation path loss by a spherical earth reflection model were quite similar to the actual test values.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.11
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• pp.1228-1238
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• 2012

In this paper, we design, fabricate and measure two kinds of high-frequency packages for K-band CMOS FMCW radar chips using RF via structures. The packages are fabricated with the conventional PCB process and LTCC process. The design centering of the packages is performed at 24 GHz and impedance variation caused by the wire bonding and RF via structure is fully evaluated using 3D electromagnetic simulation. The RF via structure with characteristic impedance of $50{\Omega}$ is used to reduce impedance mismatch loss. Two kinds of test packages with back-to-back connected RF paths are fabricated and measured for the design verification of the PCB-based package and LTCC package. Their measured results show an insertion loss of less than 0.4 dB at 24 GHz and less than 0.5 dB for 20~29 GHz. The measured return loss is less than -13 dB for the PCB-based package and less than -15 dB for the LTCC package in the frequency band, but the return loss of the package itself is predicted to be better than that of the test package by about 5 dB, because the ripples of the back-to-back connection typically degrade the return loss by 5 dB or more.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.2
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• pp.107-114
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• 2009

In this paper, high efficiency amplifier configuration is proposed using the reconfigurable power divider. In order to enhance average efficiency of linear power amplifiers for wireless communication, it is required to increase efficiency in low output power region. The proposed power divider operates in two modes, high power mode and low power mode, according to output power. In each mode, it allows impedance matches and low loss, which is made possible by employing two $\lambda/4$ coupled lines and two switches. The fabricated power divider shows the return loss ($S_{11}$) and insertion loss ($S_{21}$) of -16.49 dB and -0.83 dB, respectively, in low power mode. In high power mode, the measured return loss ($S_{11}$) and insertion loss ($S_{31}$) are -16.28 dB and -0.73 dB, respectively. This result successfully demonstrates the reconfigurability of the proposed power divider.

• Horticultural Science & Technology
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• v.16 no.4
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• pp.511-513
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• 1998

Tomato fruits(Lycopersicon esculentum $M_{ILL}$.) picked at mature (from mature green to breaker) and ripe (from pink to red) stage were packed into two layers in corrugated fiberbox and transported 200km and 400km from the harvested site. Loss (abrasion + cracking) in marketability was lowest (11.0%) from mature + 200km transport, followed by mature + 400km transport(13.5%), ripe + 200km transport(28.5%), and ripe + 400km transport (45.5%). When data were pooled by fruit maturity, firmness of mature fruit was 1.55 times higher than ripe fruit. However, vitamin C content was 1.25 times higher in ripe fruit than in mature fruit. Fruit transported longer distance and packed in bottom layer within a box exhibited lower firmness and vitamin C content in both maturity. It was concluded that it is desirable to transport relatively shorter distance for ripe tomato and longer distance for less ripe fruit.

• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.553-555
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• 2002

현재 화상 또는 음성 회의와 같은 네트워크에 기반한 응용들의 증가와 함께 멀티캐스트 서비스의 중요성이 한층 증가되었다. Xcast는 멀티캐스트 서비스를 제공하기 새롭게 제안된 방법이고, XMIF는 MIPv4와 MIPv6 환경에서 Xcast를 이용해서 멀티캐스트 서비스를 제공하기 위한 방법이다. 하지만 XMIFv4에서는 MIP가 가지는 Triangle Routing 문제를 그대로 가지고 있고 이동 중 심각한 패킷 손실이 발생 할 수 있다. 또한 QoS를 제공하기 위해 RSVP와 같은 프로토콜을 함께 사용할 때 확장성이 용이하지 않다. 따라서, 본 논문에서는 MIPv4 환경에서 XMIPv4가 가지는 문제를 해결하기 위한 방법으로 XMIPRO를 제안한다.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10e
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• pp.13-15
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• 2002

무선 네트워크 환경은 유선 네트워크 환경에 비해서 상대적으로 부족한 대역폭을 가진다. 또, 무선 네트워크 환경에서는 이동에 의해 빈번한 핸드오프가 일어나고 이는 패킷손실, 지연 증가 등으로 인한 성능 저하를 야기한다. 하나의 엔드 시스템이 여러 개의 IP 주소를 가지고, 동시에 그 경로를 이용할 수 있다면, 이러한 문제를 완화시킬 수 있을 것이다.이 논문에서는 하나의 엔드 시스템이 여러 개의 IP 주소를 가지는 경우에 그러한 여러 개의 경로상에 데이터 플로우를 분배하기 위한 알고리즘을 제안한다.

• Korean Security Journal
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• no.10
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• pp.189-213
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• 2005

Risk management should be controlled systematically by effectively evaluating and suggesting countermeasures against the various risks which are followed by the change of the society and environment. These days, enterprise risk management became a new trend in the field. The first step in risk analysis is to recognize the risk factors, that is to verify the vulnerabilities of loss in the security facilities. The second step is to consider the probability of loss in assessing the risk factors. And the third step is to evaluate the criticality of loss. The security manager will determine the assessment grades and then the risk levels of each risk factor, on the basis of the result of risk analysis which includes the assessment of vulnerability, the provability of loss and the criticality. It is of great importance to put the result of risk analysis in mathematical statement for a scientific approach to risk management. Using the risk levels gained from the risk analysis, the security manager can develop a comprehensive and supplementary security plan. In planning the risk management measures to prepare against and minimize the loss, insurance is one of the best loss-prevention programs. However, insurance in and of itself is no longer able to meet the security challenges faced by major corporations. The security manager have to consider the cost-effectiveness, to suggest the productive risk management alternatives by using the security files which contains every information about the security matters. Also he/she have to reinforce the company regulations on security and safety, and to execute education repeatedly on security and risk management. Risk management makes the most efficient before-the-loss arrangement for and after-the-loss continuation of a business. So it is very much important to suggest a best cost-effective and realistic alternatives for optimizing risk management above all, and this function should by maintained and developed continuously and repeatedly.

• Proceedings of the Korea Information Processing Society Conference
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• 2010.04a
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• pp.635-636
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• 2010

기반 망 없이 네트워크 구축이 이루어지는 애드 혹 네트워크 기술이 다양한 방면에서 활용되고 있다. 애드 혹 네트워크에서 널리 사용하는 AODV(Ad-hoc On Demand Distance Vector)라우팅 알고리즘을 사용한다. 하지만 빈번하게 경로가 변경될 수 있는 상황에서 이러한 라우팅 알고리즘을 사용하게 되면 경로를 생성 및 복구에 사용되는 제어 메시지의 과도한 사용으로 인해 메시지간의 충돌과 손실될 문제가 발생하게 된다. 이 논문에서는 기존의 AODV 라우팅 프로토콜의 경로 생성에 필요한 RREQ, RREP 메시지를 하나의 메시지로 통합하는 라우팅 알고리즘을 제안한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.8A
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• pp.858-870
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• 2007

TCP is popular protocol for reliable data delivery in the Internet. In recent years, wireless environments with transmission errors are becoming more common. Therefore, there is significant interest in using TCP over wireless links. Previous works have shown that, unless the protocol is modified, TCP may perform poorly on paths that include a wireless link subject to transmission errors. The reason for this is the implicit assumption in TCP that all packet losses are due to congestion which causes unnecessary reduction of transmission rate when the cause of packet losses are wireless transmission errors. In this paper, we propose a new LDA that monitors the network congestion level using ROTT. And we evaluate the performance of our scheme and compare with TCP Veno, Spike scheme with NS2(Network Simulator 2). In the result of our experiment, our scheme reduces the packet loss misclassification to maximum 55% of other schemes. And the results of another simulation show that our scheme raise its transmission rate with the fairness preserved.

• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.550-552
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• 2002

표준 비디오 압축 기법은 프레임 간의 시간적, 공간적 중복성을 이용하여 데이터를 압축한다. 압축된 프레임이 인터넷을 통하여 전송되는 중에 네트워크의 상태에 따라 패킷의 손실이 발생할 수 있다. 이러한 오류가 발생하면 손실된 블록을 포함하는 프레임의 화질 뿐 아니라, 이 프레임을 참조하여 압축된 이후의 프레임에도 영향을 미친다. 본 논문에서는 전송오류가 발생한 경우, 디코더에서의 오류전파를 최소화하기 위해 보조 모션벡터를 이용한 압축 기법을 제안한다. 즉, 여러 개의 후보 프레임 중 현재 압축하려는 매크로블록과 가장 가까운 값을 가진 두 개의 매크로 블록을 선택하여 그 위치를 기본 모션벡터와 보조 모션벡터로 지정한다. 이때, 두 모션벡터는 서로 다른 프레임에 속한다. 디코더에서 압축해제를 위해 참조하는 기본 모션벡터의 프레임이 손실된 경우, 보조모션 벡터를 이용하여 원래의 화질에 가깝게 디코딩 할 수 있다. 이 기법은 오류제어를 위한 피드백 채널이 필요하지 않으며, 네트워크상의 전송오류 발생시 표준 H.263 압축보다 높은 성능을 보인다.