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

• Journal of Advanced Technology Convergence
• /
• v.2 no.1
• /
• pp.1-7
• /
• 2023

Recently, there have been increasing interests in researches to apply wireless communication technologies for smart farm. This paper introduces the problems in the smart farm for the outdoor culture and technical considerations to solve the problems. As candidate technologies, this paper selects LoRa, Sigfox, NB-IoT, and Wi-Fi and then determines that LoRa is a suitable technology based on the CAPEX, coverage, transmission rate, battery, and the price. To provide technical analysis, this paper introduces technologies related to the physical and medium access control (MAC) layers as well as the security. Specifically, this paper includes the modulation technology in the physical layer, Class (Class A, B, and C) based protocol operations in MAC layer, and security architecture based on the LoRa version.

• Korean Security Journal
• /
• no.62
• /
• pp.321-346
• /
• 2020

The purpose of this study is to identify the relationship among customer access service, internal response, and consumption behavior of security agency users through a structural model. The research will be meaningful in that it can contribute to the development of the security industry by identifying the importance of customer access service, which is an empirical face of buyers using security agency, and thus establishing the relationship between consumer reaction and consumption behavior. The study subject is a store that uses security agency in areas with dense shopping districts in Cheonan and Asan of South Chungcheong Province, where 375 store representatives and employees were selected to conduct the research. Research tools were modified and used to suit the purpose of the research based on domestic and foreign prior research. Using two statistical programs, SPSS 25.0 and AMOS 25.0, data processing was performed: frequency analysis, exploratory factor analysis, reliability analysis, confirmed factor analysis, and structural model analysis. The statistical significance level was analyzed by setting a value of .05 and the following conclusions were obtained. First, the customer access service of security agency users has a positive impact on consumption behavior. Second, the customer access service of security agency users has a positive effect on the internal response. Third, the internal response of security agnecy users has a positive effect on consumption behavior. Fourth, the internal response has a positive effect as a medium effect between customer access service and consumption behavior of security agency users.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.3B
• /
• pp.183-198
• /
• 2006

We define the incomplete medium sharing system as a multi-channel shared medium communication system where constraints are imposed to the set of channels that may be allocated to some transmitter-receiver node pairs. To derive a centralized MAC scheme of a incomplete medium sharing system, we address the problem of optimal channel allocation The optimal channel allocation problem is then translated into a max-flow problem in a multi-commodity flow graph, and it is shown that the optimal solution can then be obtained by solving a linear programming problem. In addition, two suboptimal channel allocation schemes are proposed to bring down the computational complexity to a practical/feasible level; (1) one is a modified iSLIP channel allocation scheme, (2) the other is sequential channel allocation scheme. From the results of a extensive set of numerical experiments, it is found that the suboptimal schemes evaluate channel utilization close to that of the optimal schemes while requiring much less amount of computation than the optimal scheme. In particular, the sequential channel allocation scheme is shown to achieve higher channel utilization with less computational complexity than . the modified iSLIP channel allocation scheme.

• Proceedings of the Korean Institute Of Construction Engineering and Management
• /
• 2007.11a
• /
• pp.899-904
• /
• 2007

Process management techniques are highly important in the construction industry. However, indicators or details of assessment which will show process management and its performance are still very insufficient. In particular, it is true that local corporations or small and medium sized companies suffer more difficulties than ones in metropolitan areas. Therefore, it is necessary to prepare a flexible process management and performance assessment system suited to field situations. This study identified problems of local small and medium sized companies, implemented a process and performance management system using the Lean concept, and systemized a web-based system. Also, the study proposed operational strategies so that small and medium construction companies may access and use the system easily. This will ensure the competitiveness of local small and medium sized companies, will pursue visible outcomes such as construction period reduction and construction cost reduction, and will be utilized as data related to performance assessment both during construction progress and after construction.

• Journal of Microbiology and Biotechnology
• /
• v.17 no.12
• /
• pp.2076-2080
• /
• 2007

The endoxylanase (GenBank Access No. U51675) of Bacillus spp. and endoglucanase (GenBank Access No. AY466436) of Trichoderma spp. were separately inserted downstream of the yeast constitutive ADHI promoter, resulting in three different plasmids (pAGX1, pAGX2, and pAGX3) according to the transcription direction of two genes. When the yeast transformants, S. cerevisiae SEY2102 harboring each expression plasmid, were grown on YPD medium, the total activities of the enzymes were approximately 3.01 unit/ml, 3.24 unit/ml, and 7.56 unit/ml for endoxylanase and 0.60 unit/ml, 0.54 unit/ml, and 0.39 unit/ ml for endoglucanase, in the following order: the pAGX1, pAGX2, and pAGX3. More than 70% of the endoxylanase and endoglucanase activities was found in the extracellular media.

• The Journal of the Korea Contents Association
• /
• v.5 no.4
• /
• pp.160-168
• /
• 2005

Today, home networking security shows the complicated and various characteristics of requirements for consideration because of the variety of information appliances and share of resources among them. Therefore, security framework to satisfy with security functions is arranged ,regardless of the variety of communication medium and protocols. Thus, we construct security framework for mobile host(or user) to securely control devices in home-network through the variety of suggested mechanism, with security mechanism to be available for future home networking model, and verified the performance of our model.

• The Journal of Sustainable Design and Educational Environment Research
• /
• v.12 no.3
• /
• pp.58-67
• /
• 2013

This study is to analyze the satisfaction and the image evaluation of landscape elements in outdoor space by types of the university campus. The results are as follows. 1) Out of outdoor elements at university campus, planting area, resting area, access road, and water feature are recognized as major landscape elements. Among them, planting area and access roads are evaluated low in terms of satisfaction levels, therefore, improvement on these elements are required. 2) In outdoor space image evaluation, university campus has image such as 'simple', 'clear', and 'safe'. By scale of universities, both 'A' university, which is the biggest in terms of size of campus, and 'B' university, which has a medium sized campus, have a positive image. However, 'C' university, which is the smallest in terms of size of campus, has a passive and negative image. 3) 6 factors are extracted through Factor Analysis for image evaluation. All of the universities show positive image in the categories of 'clarity' and 'familiarity', however, 'B' university and 'C' university show negative image in the category of 'scale'. 4) In Correlation Analysis between landscape elements satisfaction level and image evaluation, it is showed that the group of landscape facility becomes a relation factor of overall image evaluation. As a result, the higher satisfaction level goes, the better image evaluation of overall outdoor space at university campus is.

• Journal of the Korea Computer Industry Society
• /
• v.2 no.2
• /
• pp.165-180
• /
• 2001

This study is on the design and performance evaluation of a multi medium access control(MAC) protocol for multimedia access in the wireless ATM network. In general, MAC protocols for multimedia data transmission are classified into the fixed slot allocation algorithm that allocates base-station slots equally over terminals, and the dynamic slot allocation algorithm that with flexible penetration. The conventional slot allocation algorithms assign slots based on the average bandwidths required for various services types. Although the algorithms have a wide bandwidth for real-time-variant services, the slots are being wasted due the service types. To improve the slot waste problem, this thesis proposes a method that minimizes the waste by assigning variable slots based on the most appropriate bandwidth after a base-station analyzes the service type requested from terminals.

• The Journal of Asian Finance, Economics and Business
• /
• v.7 no.3
• /
• pp.9-15
• /
• 2020

This paper investigates how economic freedom affected firm investment in Vietnam. In the globalization decade, economic freedom has been an important policy to support economic development in Vietnam. Improvements in economic freedom, such as capital freedom and domestic credit freedom, allow firms to access external finance more easily, so that the firm's investment depends less on internal cash flow. In a developing country, on the drawbacks, many small and medium firms likely have more challenges if the government would not give any subsidies. The higher level of freedom may exacerbate the financing constraints of less competitive firms. We analyze unique firm-level data from 2006 to 2016, which includes listed firms on two major stock exchanges and unlisted firms in the Unlisted Public Company Market. The article also considers how economic freedom affects small firms and large firms differently. Our results show that capital freedom and domestic credit freedom played an important role in investments for Vietnamese firms. However, we cannot find evidence that overall economic freedom relaxed the financial constraints on firms. Additionally, we suggest that small firms likely gain more advantage in access to external finance than do larger firms when the government removes restrictions from capital movement and the domestic credit market.