• Journal of information and communication convergence engineering
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• v.9 no.3
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• pp.341-346
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• 2011

Wireless sensor networks (WSNs) are formed by a great quantity of sensor nodes, which are consisted of battery-powered and some tiny devices. In WSN, both efficient energy management and Quality of Service (QoS) are important issues for some applications. Real-time services are usually employed to satisfy QoS requirements in critical environment. This paper proposes a real-time MAC (Medium Access Control) protocol with extended backoff scheme for wireless sensor networks. The basic idea of the proposed protocol employs (m,k)-firm constraint scheduling which is to adjust the contention window (CW) around the optimal value for decreasing the dynamic failure and reducing collisions DBP (Distant Based Priority). In the proposed protocol, the scheduling algorithm dynamically assigns uniform transmitting opportunities to each node. Numerical results reveal the effect of the proposed backoff mechanism.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.341-348
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• 2001

In this study, a method is presented to find out a relationship between modes of a substructure and those of the system structure. Superelement analysis is performed for a full vehicle system, where the bus is partitioned by six parts. In this study, Modal Assurance Criteria(MAC) which is to represent the correlation between two mode shapes is used to investigate the contribution factor of each substructure for the full system. The proposed participation factor can be used for design of substructures to meet the design target of the total structural system.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.2 no.1
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• pp.11-17
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• 1990

Dirichlet boundary value problems originated from unsteady deep water wave propagation are transformed to Boundary Intergral Equation Methods by use of a free surface Green's function and the integral equations are discretized by a cubic spline element method. In order to enhance the stability of the numerical model based on the derived Fredholm integral equation of 1 st kind, the method by Hsiao and MacCamy (1973) is employed. The numerical model is tested against exact solutions for two cases and the model shows very good accuracy.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.3B
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• pp.114-129
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• 2005

In this paper, we examine Interleaved Polling with Adaptive Cycle Time (IPACT) algorithm which was proposed to control upstream traffic for Gigabit Ethernet-PONs, and we analyze the performance of the gated service and the limited service of the IPACT mathematically. For the mathematical performance analysis, we model IPACT algorithm as a polling system and use mean-value analysis. We divide arrival rate λ value into three regions and analyze each region accordingly. We obtain average packet delay, average queue size and average cycle time of both the gated and the limited service. We compare analytical results with simulation to verify the accuracy of the mathematical analysis. Upon now, simulation analysis have been used to evaluate the performance of EPONs, which require much time sud effort. Mathematical analysis can be widely used in the design of EPON systems since system designers can obtain various performance results rapidly.

• Journal of Internet of Things and Convergence
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• v.6 no.4
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• pp.15-19
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• 2020

In this paper, we propose a optimal CW(Conention Window) synchronization scheme in IEEE 802.11 WLANs. IEEE 802.11 WLANs support DCF(Distributed Coordination Function) mode for the MAC(Medium Access Control) operation. In DCF, the CW increases exponentially according to the collisions and becomes minimum CW according to the success of data transmissions. However, since the base minimum CW value is hardware or standard specific, the number of active stations and network status are not considered to determine the CW value. Even though the researches on optimal CW have beend conducted, they do not consider the optimal CW synchronization among mobile stations which occur network performance degradation. Therefore, this paper calculates the optimal CW value and shares it with mobile stations in the network.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.12 s.117
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• pp.1244-1251
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• 2006

The objective of this paper is to get excitation forces of the engine at each of the brackets for the prediction of the vehicle interior noise by the powertrain. A powertrain geometry model is produced by CATIA and its FE model is made by MSC/Patran. A vibration mode analysis and a running mode analysis are experimentally implemented. After getting a satisfied MAC value by doing a correlation about a measured mode analysis value and analyzed value through MSC/Nastran software, all components are assembled through MSC/ADAMS software which is a dynamic analysis tool. We can predict the vibration of brackets which is the last points to occur the force of the engine combustion by analyzing the combustion force produced by engine mechanism.

• Magazine of the Korea Concrete Institute
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• v.2 no.3
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• pp.81-88
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• 1990

For the protectioon of radioactive leakage, the quality control of main concrete structure in nuclear power plants is very important. So, this studey is designed to analyze the influence of kind of cement and aggregate on the mechanical properties of high density concrete. Test results of this study are as follows; 1)The slump of magnetite aggregate concrete(MAC) is found half value of nat.ural aggregate concrete (NAC). 2)As the effect of cement, the compressive strength of concrete using moderate heat cement is found higher 5-19 % than that of ordinary portland cement. 3)As the effect of fine aggregate, t.he compressive strength of MAC is found higher than that. of NAC below 340kg/$cm^2$ and lower t.han NAC above 340kg/$cm^2$. 4)As the effect of coarse aggregate, the compressive strength of MAC is found higher 17-22% than that of NAC.

• Journal of Digital Convergence
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• v.11 no.12
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• pp.453-458
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• 2013

In a wireless LAN environment, security is the most important. Security of 802.11 standard has many vulnerabilities of the network attack. IEEE has created mechanisms to security for this vulnerability. But the vulnerabilities is characteristic of broadcast in the air in wireless LAN, it is more disclosure then other network environments. In a wireless LAN environment, it can be accessed to the wireless LAN after authentication. Authentication process is one of most important because of the first security step. However, in the authentication process is not mentioned in the method of reducing the disclosure maximum fundamental. Therefore, in this research, the vulnerability of 802.11 are presented and how to do de-authentication in 802.11.

• Korean System Dynamics Review
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• v.12 no.4
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• pp.125-156
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• 2011

The information service management models developed thus far have put their focuses mostly on technical dimensions of information systems (IS), finding their rationale from the goods-dominant logic (GDL) that IS as goods has value in itself. Information systems, however, is nothing more than a mechanism by which value is delivered to the users. According to the service-dominant logic (SDL), value is created and determined not at the time serve is made by the providers but at the time it is consumed by the users. The users therefore should be regarded as active value creators not as passive consumers of the value delivered by the providers. Based on the service-dominant logic, DISQM (Dynamic Information Service Quality Model) is developed. DISQM's backbone is designed in causal loop diagrams referring to and reinterpreting in systems thinking the 'Parasuraman, Zeithaml & Berry's GAP Model' and 'SERVQUAL' as an operational tool for the GAP Model, and the main IS success constructs are mapped onto the model exploiting the 'DeLone & MacLean's IS Success Model'. With VENSIM simulation software, this paper also shows how DISQM works in computer-simulation settings. After confirming DISQM's validity with the base simulation run, two scenarios are developed for the exemplary purpose and tested in terms of IS quality, service quality, and net benefits from the service for the public information service. Implications from the simulation runs are also discussed.

• Journal of Korea Multimedia Society
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• v.14 no.11
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• pp.1420-1430
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• 2011

This paper proposes a new method to optimize energy consumption in a wireless modem by setting up a transmission power value according to the distance between nodes and circumstance in the MAC layer of IEEE 802.15.4. The proposed method can dynamically find an optimal transmission power range using the binary search scheme and minimize overhead caused by multiple message transmissions when determining the optimal transmission power. The determined transmission power is used for transmitting data packets and can be modified dynamically depending on the changes in a network environment when exchanging data packets and acknowledgement signals. The results of the simulations show 30% reduction in energy consumption while 2.5 times increase in data transmission rate per unit of energy comparing with IEEE 802.15.4 standard.