• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.2
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• pp.17-23
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• 2000

Wireless link has high bit error rate compared with wired link and many users share this limited bandwidth. So it needs more powerful error control code and efficient media access control(MAC) to provide multimedia service reliably. In this paper we proposed efficient MAC frame format based on TDMA using mini-slot for request access. The number of mini-slots is variable based on the result of collision in the previous frame. This dynamic allocation of request mini-slots helps resolve the contention situation quickly and avoids the waste of bandwidth that may occur when there are several unneeded request mini-slots. The simulation results are also presented in terms of channel utilization, call blocking probability and cell transmission delay for mixed traffic environment.

• Journal of Korean Academy of Nursing Administration
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• v.16 no.4
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• pp.475-487
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• 2010

연구목적: 노인을 위한 건강정보 웹사이트들이 사용성과 접근성을 높이기 위해 지켜야 할 디자인 요소를 어떻게 반영하고 있는지 평가·비교함으로써 개선 방향을 제언하고자 하였다. 연구방법: 국내 및 미국에서 개발된 노인 대상의 건강정보 웹사이트를 각각 9개씩 선정하였다. 근거 기반의 웹디자인 지침서인 Make Your Website Senior Friendly: Checklist와 Research-based Web Design & Usability Guideline을 통합 수정하여 얻은 4개 영역의 평가 항목 48개를 적용해 두 명의 평가자가 선정된 총 18개 웹사이트를 평가하였다. 연구결과: '가독성' 영역 중 서체 선택, 줄 간격, 배경색과 글자색 선택 등은 양호하였으나 국내 웹사이트들 중에는 글자 크기가 조절되지 않는 경우가 빈번하였다. '정보의 표현과 구성' 영역에서 다수의 웹사이트들은 정보 배치 등이 우수하고 소비자 용어를 사용하는 노력을 보였다. 그러나 일부 국내 웹사이트들은 프린트 기능을 제공하지 않거나, 노인들의 저하된 인지 능력을 배려하려는 노력이 부족하였다. '미디어 사용' 영역에서 국내 웹사이트들은 글자 외에 다른 매체를 사용하는 빈도가 미국 웹사이트들에 비해 낮았고, 시청각 매체를 사용할 때는 동일한 내용을 문자로도 볼 수 있도록 하라는 권고안을 준수하지 않았다. '내비게이션과 검색의 용이성'에서는 메뉴나 링크의 명칭이 명확하며, 이용 중에도 쉽게 홈페이지로 돌아갈 수 있도록 구성되었다. 그러나 다수의 국내 사이트들이 사이트맵을 제공하지 않거나, 검색어의 철자오류 등에 대한 배려가 부족하였다. 결론: 국내 웹사이트들은 미국 웹사이트들에 비해 노인들의 사용성과 접근성을 높이는 것으로 밝혀진 연구 근거들을 제대로 반영하지 못하고 있었다. 노인 대상의 인터넷과 웹을 활용한 교육이 지속적으로 증가할 것이므로, 그 효과성을 높이기 위해 간호사들은 정보의 질 뿐만 아니라 디자인 측면의 중요성을 인식하고 실천할 수 있어야겠다.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.5
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• pp.58-69
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• 2014

To cope with sever accident like Fukushima accident, the emergency response system is needed. It consist of the hardened I&C system and the mobile control station. The hardened I&C system monitors the state in the nuclear power plant and controls the emergency equipment such as valves, pumps and the mobile control station placed at 30km away from nuclear power plant receives the status information from the hardened I&C system and transmits the control data to the hardened I&C system. In this paper, we design the emergency communication system connecting the hardened I&C system to the mobile control station and analyze the performance of the system. This system consists of the terrestrial communication system and the satellite communication. The performance such as a communication link budget, throughput and delay time is analyzed for each system.

• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.2
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• pp.175-181
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• 2009

All of the military aircrafts in Korea Air Force are administered and operated together in the same system regardless of whether they are equipped with the data communication capability or not. The absence of the data communication capability in some of the aircrafts might increase whole kill chain hour at the point of the Network Centric Warfare achievement. Network synergy effects cannot also be desired if the section which is not connected to the network influences to the whole tactical network. Equipping aircrafts with the data communication capability could be done by upgrading the aircrafts, but resulting in high costs and long updating time. This paper is a research about the design and implementation of the UMPC based Data Link System to aircrafts that do not have the data communication capability. The proposed system grafts the UHF-based wireless modem technology and the aircraft flight mission support software onto the off-the-shelf UMPC and GPS system. The employed UHF radio equipment allows communicating tactic data with another aircrafts on the air, the ground control point, and even the Tactical Air Control Party(TACP) control vehicle that achieve missions with aircrafts. It thereby increases such capabilities as navigation aid, situation awareness, quick target identification and attack. We also applied Closed Air Support(CAS) scenarios, which is very close to the real environment, to the experiments of the proposed system. The experimental results show that the proposed system could support the data communication capability effectively and the flight mission at low costs of money and time.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.5
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• pp.113-118
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• 2015

Mobile wireless networks have received a lot of attention as a future wireless network due to its rapid deployment without communication infrastructure. In these networks communication path between two arbitrary nodes break down because some links in the path are beyond transmission range($r_0$) due to the mobility of the nodes. The set of total path break down time(${\bigcup}T_i$), which is the union of path break down time of every node pair, can be a good measure of the connectivity of the dynamic mobile wireless network. In this paper we show that the distribution of the total path break down time can be approximated as a exponential probability density function and confirms it through experimental data. Statistical knowledge of break down time enables quantitative prediction of delay, packet loss between two nodes, thus provides confidence in the simulation results of mobile wireless networks.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.11
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• pp.2563-2568
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• 2013

Recently, various solutions to support explosively growing mobile data traffic have attracted intensive attentions. However, the range of spectrum which can be exploited for mobile communications is very limited. Small cell networks are actively investigated because they can efficiently offload mobile data traffic from macro cells without using additional spectrum. In this paper, we developed a system-level simulator considering small cell networks in the indoor environments. We compare the performance of outage probability when a load-balancing algorithm is utilized or not. We can reduce the outage probability of congested BS with the load-balancing algorithm. In addition, overall outage probability of whole wireless systems can be reduced by using the proposed load-balancing algorithm.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.11
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• pp.2533-2540
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• 2013

In multihop cellular network environments, the mobility of nodes is a major obstacle to find a reliable routing path between a mobile node (MN) and the access node (AN). Therefore, in this paper, we propose a fast and reliable neighbor discovery protocol that enables the fast and reliable neighbor discovery by considering the node mobility in the multihop cellular network. The proposed neighbor discovery protocol inhibits the transmission of unnecessary control messages to quickly find a suitable neighbor node (NN) and performs a priority-based access control to transmit control messages without collision in the order of NN desirable to be selected. Simulation results show that the proposed neighbor discovery protocol can discover the NNs faster than the conventional scheme and select a more reliable relay node although the number of neighbor nodes increases and the node mobility increases.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.1
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• pp.35-41
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• 2017

To solve the shortage of radio spectrum and utilize spectrum resource more efficiently, cognitive radio technologies are proposed, and many studies on cognitive radio have been conducted. Multi-hop routing is one of the important technologies to enable the nodes to transmit data further with lower power in ad-hoc cognitive radio networks. In a multi-channel cognitive radio networks, each channel should be allocated to minimize interference to primary users. In the multi-hop routing, channel allocation should consider the inter-channel interference to maximize network throughput. In this paper, we propose multi-channel scheduling scheme which minimizes inter-channel interferences and avoids collision with primary users for the multi-hop multi-channel cognitive radio networks. The proposed scheduling is designed to determine both of routing path and channel selection. The performance of proposed channel allocation scheme is evaluated by the computer simulation in the aspect of capacity and collision rate.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.4
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• pp.724-730
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• 2017

SpaceWire invented for spacecrafts has Time-Code defined for time synchronization over SpaceWire network. A Time-Code suffers transmission delay of 14[bit-period] and jitter up to 10[bit-period] whenever it passes through a SpaceWire link, which is the primary cause of time synchronization error. This work presents a simple method to improve the time synchronization which uses two extended Time-Codes. Nodes on a SpaceWire network can find how much delay and jitter a received Time-Code has suffered while it passes through the network, and they can correct time synchronization error with this information. The proposed method was validated in a simulation environment developed based on OMNeT++. The simulation result showed that time synchronization error less than a few bit-periods can be achieved. The proposed method is cost effective and suitable for small-scale SpaceWire network systems.

• Journal of Broadcast Engineering
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• v.20 no.5
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• pp.748-755
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• 2015

In this paper, sharing based admission control scheme is suggested for both service differentiation and improvement of wavelength utilization efficiency in burst switching networks. To provide service differentiation and high wavelength utilization efficiency, some of the wavelengths on a output link are shared with all classes and the others are used for the highest class exclusively. Markov based analysis is applied to the suggested scheme for the performance analysis and the numerical results are derived. The results are: The performance of lower traffic is more improved by the more number of shared wavelengths in case that the higher traffic or lower traffic is arrived equally or that the input rate of lower traffic is low. Another result is that the sharing effect of wavelengths is a little bit lowered when lower traffic passes the threshold.