• Journal of the Korea Institute of Information Security & Cryptology
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• v.14 no.4
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• pp.163-181
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• 2004

Group key agreement protocols are designed to solve the fundamental problem of securely establishing a session key among a group of parties communicating over a public channel. Although a number of protocols have been proposed to solve this problem over the years, they are not well suited for a high-delay wide area network; their communication overhead is significant in terms of the number of communication rounds or the number of exchanged messages, both of which are recognized as the dominant factors that slow down group key agreement over a networking environment with high communication latency. In this paper we present a communication-efficient group key agreement protocol and prove its security in the random oracle model under the factoring assumption. The proposed protocol provides perfect forward secrecy and requires only a constant number of communication rounds for my of group rekeying operations, while achieving optimal message complexity.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.10 no.1
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• pp.112-123
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• 2011

This study focused on developing strategies of cyber-compact city, combining compact city with information and communications technologies(ICTs), in order to enhance sustainable transportation. The cyber-compact city development is defined as a development that is able to reduce travel by ICTs and encourage people to use transit or non-motorized vehicles such as bicycles for ICT-induced travel (especially, discretionary travel) by compact and mixed land use. It can be achieved with combining cyber and compact strategies with respect to network, node, and area. For example, ICT network may use transit network facility, a transfer station may be a hub of ICTs, and transit influenced zone may work with ICT service area. We proposed three cohesive strategies for the cyber-compact city based on literature review and case studies on cyber and compact cities. The first strategy is a cohesion between public transportation and telecommunication network by centering on the two for national and urban spatial linkage structure. That is, cities or urban centers and its peripheral areas can be connected by rail network, and extra space of railway network can be used for constructing telecommunication network infrastructure. The second strategy is a cohesion between public transportation node and telecommunication node by building up regional and urban telecommunication centers near to or at main railway stations. For this strategy, telework centers and communication service centers should be established mainly at transfer stations. The third strategy is a cohesion between public transportation impact zone and telecommunication impact zone as transit oriented development.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.11
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• pp.32-40
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• 2016

IEEE 802.15.4 is the one of the protocols for radio communication in a personal area network. Because of low cost and low power communication for IoT communication, it requires the highest optimization level in the implementation. Recently, the studies of location aware algorithm based on IEEE802.15.4 standard has been achieved. Location estimation is performed basically in equal consideration of reference node information and blind node information. However, an error is not calculated in this algorithm despite the fact that the coordinates of the estimated location of the blind node include an error. In this paper, we enhanced a conventual maximum likelihood estimation using weighted coefficient and implement the hardwired location aware engine for small code size and low power consumption. On the field test using test-beds, the suggested hardware based location awareness method results better accuracy by 10 percents and reduces both calculation and memory access by 30 percents, which improves the systems power consumption.

• Journal of Satellite, Information and Communications
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• v.2 no.2
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• pp.41-47
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• 2007

The first geostationary satellite made by Korea, COMS, has the three different payload ; Meteorological sensor, Oceanographic sensor and Ka-band communication payload. There are Meteorological & Ocean Data Communication Subsystem(MODCS) and Telemetry, Command and Ranging Subsystem(TC&R) as other RF radiation sources. MODCS transmits and receives Meteo and Ocean measurement data from/to earth using L-band and TC&R using S-band. The Ka-band communication payload will provide high-speed multimedia services and communication services for natural disaster such as prediction, prevention, and recovery services in the government communications network.Ka-band beacon is for the earth antenna pointing and the experiment of rain fading. This paper gives the analysis results about the mutual radiation effect on Ka-band communication payload, Ka-band beacon, MODCS and TC&R. Up/Down link power and coupling factor including the geometrical position and distance of antenna, filter rejection and degradation factor due to the different polarization are considered. The results show MODCS and TC&R are compatible for Ka-band communication payload and Ka-band beacon does not interfere with MODCS and TC&R normal operation.

• The KIPS Transactions:PartC
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• v.10C no.4
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• pp.471-478
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• 2003

Traditionally,, analysis, simulation and measurement have all been used to evaluate the performance of network protocols and functional entities that support mobile wireless service. Simulation methods are useful for testing the complex systems which have the very complicate interactions between components. To develop a mobile call simulator which is used to examine, validate, and predict the performance of mobile wireless call procedures must have the teletraffic model, which is to describe the mobile communication environments. Mobile teletraffic model is consists of 2 sub-models, traffic source and network traffic model. In this paper, we analyzed the network traffic data which are gathered from selected Base Stations (BSs) to define the mobile teletraffic model. We defined 4 types of cell location-Residential, Commercial, Industrial, and Afforest zone. We selected some Base Stations (BSs) which are represented cell location types in Seoul city, and gathered real data from them And then, we present the call rate per hour, cail distribution pattern per day, busy hours, loose hours, the maximum number of call, and the minimum number of calls based on defined cell location types. Those parameters are very important to test the mobile communication system´s performance and reliability and are very useful for defining the mobile network traffic model or for working the existed mobile simulation programs as input parameters.

• Journal of KIISE:Computer Systems and Theory
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• v.27 no.3
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• pp.277-286
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• 2000

Switch-based network is suitable for the environment of demanding high performance network. Traditional shared-medium Local Area Networks(LANs) do not provide sufficient throughput and latency. Specially, communication performance is more important with multimedia application. In these environments, switch-based network results in high performance. A kind of switch-based network provides higher bandwidth and low latency. Thus high-speed switch is essential to build switch-based LANs. An effective switch design is the most important factor of the switch-based network performance, and is required for the multicast message processing. In the previous cut-through switching technique, switch element reconfiguration has the capability of multicasting and deadlock-free. However, it has problems of low throughput as well as large scale of switch. Therfore, effective multicating can be implemented by using divided hardware unicast and multicast. The objective of this thesis is to suggest switch configuration with these features.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.12B
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• pp.719-727
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• 2007

The Wireless Mesh Network technology is able to provide an infrastructure for isolated islands, in which it is difficult to install cables or wide area such as battlefield of armed forces. Therefore, Wireless Mesh Network is frequently used to satisfy needs for internet connection and active studies and research on them are in progress However, as a result of increase in number of hops under hop-by-hop communication environment has caused a significant decrease in throughput and an increase in delay. Considering the heavy traffic of real-time data, such as voice or moving pictures to adaptive WMN, in a military environment, it is restricted for remote units to have their Mesh Node to get real-time services. Such phenomenon might cause an issue in fairness. In order to resolve this issue, the Location-based Packet Scheduling Scheme, which can provide an fair QoS to each mesh node that is connected to each echelon's AP and operates based on WRR method that gives a priority to emergency message and control packet. The performance of this scheme is validated.

• Journal of Digital Convergence
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• v.14 no.2
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• pp.31-39
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• 2016

In recent university classes, consistent effort to improve co-operative interaction and communication between student and professor utilizing SNS(Social Network Service) is being made. This research conducted survey study with 137 pre-teachers in Daejeon & Chungnam area in order to find the relationship between pre-teachers' ego resilience, level of social support and awareness of the instructional outcome in classes that incorporate SNS. According to the result, it has been found that male's class satisfaction is higher than female's class satisfaction, while significant correlations have been found between ego resilience-social support, social support-class satisfaction, social support-semester satisfaction, and class satisfaction-semester satisfaction. Also, ego resilience and social support have significant effect on awareness of the instructional outcome. From these results, a rather close attention towards students' characteristics and their adaptation in class is needed in order to successfully carry out classes that incorporate various new media.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.11
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• pp.2640-2644
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• 2014

With the development of technology, wireless sensor networks (WSN) are wireless networks of consisting a large number of small and low-cost sensors. Wireless sensor networks facilitate collaboration to achieve the perception of information collection, processing and transmission tasks in deployment area. They have various purposes such as military, disaster relief, medical rescue, environmental monitoring, precision farming and manufacturing industry etc. Therefore, technologies for data maintaining technologies in sensor network environment is one of essential parts of sensor networks. In this paper, we present the essential particulars about data management technology at wireless sensor network environments and propound the issues. Further, we could organize and develop a systematic approach in solving the issues.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.6
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• pp.809-817
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• 2020

In the design and development process of Small-Sat power distribution and transmission module, the stability of dynamic resources was evaluated by a deep learning algorithm. The requirements for the stability evaluation consisted of the power distribution function of the power distribution module and demand module to the SAR radar in Small-Sat. To verify the performance of the switching power components constituting the power module PDM, the reliability was verified using a dynamic neural network. The adoption material of deep learning for reliability verification is the power distribution function of the payload to the power supplied from the small satellite main body. Modeling targets for verifying the performance of this function are output voltage (slew rate control), voltage error, and load power characteristics. First, to this end, the Coefficient Structure area was defined by modeling, and PCB modules were fabricated to compare stability and reliability. Second, Levenberg-Marquare based Two-Way NARX neural network Sigmoid Transfer was used as a deep learning algorithm.