• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.5
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• pp.1303-1315
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• 2012

In the draft of the IEEE 802.11s standard, a tree topology is established by the proactive tree-building mode of the Hybrid Wireless Mesh Protocol (HWMP). It is used for cases in which the root station (e.g., gateway) is an end point of the majority of the data connections. In the tree topology, the root or central stations (e.g., parent stations) are connected to the other stations (e.g., leaves) that are one level lower than the central station. Such mesh stations are likely to suffer heavily from contention in bottleneck links when the network has a high traffic load. Moreover, the dependence of the network on such stations is a point of vulnerability. A failure of the central station (e.g., a crash or simply going into sleep mode to save energy) can cripple the whole network in the tree topology. This causes performance degradation for end-to-end transmissions. In a connected mesh topology where the stations having two or more radio links between them are connected in such a way that if a failure subsists in any of the links, the other link could provide the redundancy to the network. We propose a scheme to utilize this characteristic by organizing the network into concentric tiers around the root mesh station. The tier structure facilitates path recovery and congestion control. The resulting mode is referred to as Tier-based Proactive Path Selection Mode (TPPSM). The performance of TPPSM is compared with the proactive tree mode of HWMP. Simulation results show that TPPSM has better performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.4
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• pp.758-767
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• 2017

IoT paradigm which makes a information without direct intervention of a human and interworks with other objects, humans and systems is attracting attention. It will be expected the number of smart devices equipped with sensors and wireless communication capabilities is reached to about 260 billion by 2020. With the vast amount of sending data generated from rapidly increasing number of smart devices, it will bring up the traffic growth over internet and congestion in wireless networks. In this paper, we utilize the smart device as a sink node to collect and forward the sensing data periodically in IoT and propose a heuristic algorithm for a selection of sink nodes' set with each sink node satisfies the QoS its applications because a selection of optimal sink nodes' set is NP-hard problem. The complexity of proposed heuristic algorithm is $O(m^3)$ and faster than the optimal algorithm.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.2
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• pp.104-113
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• 2009

Recently, high-speed Internet users and broadband network infrastructure are increasing. However, the TCP protocol widely used in the Internet is an appropriate transport only for the legacy Internet, it is inefficient for traffic transport for network environments with large bandwidth-delay product. In order to remedy this problem, there have been many researches about improved congestion control algorithms for broadband networks. In these studies, most of performance evaluation has been done by simulations. In this paper, after we reviewed the proposed high bandwidth transport layer protocols, we implemented a real testbed, measured the performance and analyzed the problems of high-speed transport protocols through the international research network TEIN2 between three nations, Korea, China, and Germany.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.12
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• pp.2811-2817
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• 2010

In this paper we propose the QAC-MAC that supports Quality of Service(QoS) and saves energy resources of the sensor node, and hence prolonging the lifetime of the sensor network with multiple sink nodes. Generally, the nodes nearest to the sink node often experience heavy congestion since all data is forwarded toward the sink through those nodes. So this critically effects on the delay-constraint data traffics. QAC-MAC uses a hybrid mechanism that adapts scheduled scheme for medium access and scheduling and unscheduled scheme based on TDMA for no data collision transmission. Generally speaking, characteristics of the real-time traffic with higher priority tends to be bursty and has same destination. QAC-MAC adapts cross-layer concept to rearrange the data transmission order in each sensor node's queue, saves energy consumption by allowing few nodes in data transmission, and prolongs the network lifetime.

• Journal of the Korean Institute of Navigation
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• v.10 no.1
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• pp.101-127
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• 1986

Transportation provides an infrastructure vital to economic growth, and it is an integral part of production . As a port is the interface between the maritime transport and domestic transport sectors, it certainly plays a key role in any economic development. Therefore, it is doubtless that inadequacy of a nation's port will depress the level of throughput, to the level where it fails to meet the target set by the national economic planning schemes. Korea is surrounded by the seas and the economic structure of Korea consists of processing trades, so that it cannot be overstated that substantial economy in maritime transport coasts can be achieved through the improvement of the port transport system. This paper treats the transportation process in Pusan Port by Queueing Simulation method, and the reasonable size of Pusan Port is suggested from the point of view of efficiency maximization. The results of the analysis are summarized as follows; 1) the utility rate is 47.91 percents in general piers, 85-52 percents in container piers, and waiting time 5.2hrs, in general piers, 0.8 hrs, in container piers, and the probability of maximum queue length 12 ships in general piers, 2 ships in container piers, and the probability of waiting is 44 percents in general piers, 8 percents in container pier. 2) in general piers, the improvement of app. 30 percents in port capacity is desirable for operating effectively concerning the current arrival rate. By introducing the traffic control ion container piers, there is no apparent necessity of port investment, but I is expected to reduce invisible congestion occurred along the waiting line. 3) On Pusan Port, the optimal utility rate and the optimal arrival rate for reducing waiting time are 3.5 to 4.0(hrs./ship) in general piers, 5.1 to 6.0(hrs./ship) in container piers.

• Journal of the Korean Institute of Landscape Architecture
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• v.31 no.3
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• pp.74-82
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• 2003

Under the assumption that the temperature of one location is closely related to land use characteristics around that location, this study is carried out to assess the impact of urban land use patterns on air temperature. In order to investigate the relationship, GIS techniques and statistical analyses are utilized, after spatially connecting urban land use data in Seoul Metropolitan Area with atmospheric data observed at Automatic Weather Stations (AWS). The research method is as follows: (1) To find out important land use factors on temperature, simple linear regressions for a specific time period (pilot study) are conducted with urban land use characteristics, (2) To make a final model, multiple regressions are carried out with those factors and, (3) To verify that the final model could be appled to explain temperature variations beyond the period, the model is extensively used for 5 different time periods: 1999 as a whole; summer in 1999; 1998 as a whole; summer in 1998; August in 1998. The results of simple linear regression models in the pilot study show that transportation facilities and open space area are very influential on urban air temperature variations, which explain 66 and 61 percent of the variations, respectively. However, the other land use variables (residential, commercial, and mixed land use) are found to have weak or insignificant relationship to the air temperatures. Multiple linear regression with the two important variables in the pilot study is estimated, which shows that the model explains 75 percent of the variability in air temperatures with correct signs of regression coefficients. Thus, it is empirically shown that an increase in open space and a decrease in transportation facilities area can leads to the decrease in air temperature. After the final model is extensively applied to the 5 different time periods, the estimated models explain 68 ∼ 75 percent of the variations in the temperatures is significant regression coefficients for all explanatory variables. This result provides a possibility that one air temperature model for a specific time period could be a good model for other time periods near to the period. The important implications of this result to lessen high air temperature we: (1) to expand and to conserve open space and (2) to control transportation-related factors such as transportation facilities area, road pavement and traffic congestion.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.6
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• pp.749-762
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• 2019

In recent years, in urban areas, underground of roads are being promoted in order to resolve traffic congestion and to secure green spaces, and due to the low ratio of large vehicles, they are planned or constructed as road tunnels for small cars only. In addition, the tunnels being built in the city is a tendency to be enlarged to play the role of main roads. Accordingly, the capacity of the ventilation system is increasing and various ventilation methods are required, and the importance of maintenance after the completion of the tunnel such as the operating cost of the ventilation system is emphasized. Therefore, the need for optimization of the operation stage for reducing the power consumption of the ventilation system and the study of the ventilation system operation control logic is increasing. In this study, the study on the necessity of the optimization of operation stage and control logic of the ventilation system was carried out to realize the energy-saving operation for the small car only passing through tunnels which is applied of ① jet fan and combination ventilation system (② jet fan + air purifying equipment, ③ jet fan + vertical shaft, ④ jet fan + supply air semi-transverse). As a result of this study, there can be various operating combinations in the case of the combined ventilation system, and even though the amount of ventilation air is the same, the operating power varies greatly according to the operating combinations. It was found that operating the axial fan first rather than the jet fan first operation method has an effect on power saving.

• Journal of Environmental Health Sciences
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• v.37 no.3
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• pp.182-192
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• 2011

Objectives: This study aims to identify the influential factors on the pulmonary function of targeted general residents in the areas surrounding Gwangyang Steel Mill. Methods: An PFT (Pulmonary Function Test) was conducted from May 2007 to November 2007 on 974 target residents (438 male, 536 female), including an exposed group (674 people) who resided within a radius of 5 km from Gwangyang Steel Mill in Gwangyang-si, Jeollanam-do and a control group (300 people) who resided outside a radius of 15 km. A survey related to personal characteristics, life habits, respiratory diseases and allergic symptoms, medical histories and living environments of the residents was also conducted to identify influential factors on pulmonary function. Results: As %$FEV_1$ and %FVC of the exposed group are 99.17% and 96.98%, respectively, and those of the control group are 105.47% and 101.91%, respectively, with the PFT values of the exposed group being lower than those of the control group (p<0.001), it turns out that the pollution in the industrial complex is likely to trigger a reduction in the pulmonary function of local residents. The odds ratio analysis result for asthma diagnosis history indicates that the odds ratios tend to be higher among surveyed residents who are living near above-average traffic volumes and are using beds, where it is statistically meaningful that especially the odds ratios are higher if the residences are closer to roads (p<0.01, CI=1.12-4.52). The factors that affect the FEV1 are identified as smoking, passive smoking, asthma diagnosis history, nasal congestion symptoms and allergic eye disease ($R^2$=0.154, p<0.001). The factors that affect the FVC are identified as smoking, passive smoking, asthma diagnosis history and allergic coryza ($R^2$=0.158, p<0.001). In addition, the analysis result for the relevance of air pollution levels to pulmonary function ($FEV_1$, FVC) shows that FEV1 and FVC tend to decrease as the concentration of $O_3$ increases. Conclusions: We believe that this study may provide preliminary data for the development of preventive measures for health effects on the residents and environmental health control measures for environmental pollution in the industrial complex area.

• Journal of Korean Society of Transportation
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• v.35 no.1
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• pp.50-62
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• 2017

As the use of private cars increases along with the technological advancement in the automobile industries and their capabilities to supply, a wide range of issues are followed including the increase in traffic congestion costs, pavement damages and more. In spite of consistent effort to resolve such urban traffic problems, the modal share rate of private cars continuously increases, thus it is becoming more important to explore the ways to enable drivers to take reasonable measures, in self-motivated manner, by taking part of the transportation demand management policy rather than to rely on the strict enforcement of control policy. Considering that the urban transportation infrastructures are in much better shape than before, it is necessary to implement Mobility Management (MM) that induces reasonable usage of private cars by promoting the change in one's consciousness and behavior through communication. Hence, the research studies the factors that influence the mobility through the survey targeting the citizens of Busan on their awareness on the former transportation demand management policy, to explore the ways to motivate the citizens' involvement in reducing the use of private cars as a measure of Mobility Management.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.9
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• pp.73-80
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• 2004

In this paper, we present the cell resequencing buffer to solve the cell sequence integrity problem of the Cyclic banyan network that is a high-performance fault-tolerant cell switch. By offering multiple paths between input ports and output ports, using the deflection self-routing, the Cyclic banyan switch offer high reliability, and it also solves congestion problem for the internal links of the switch. By the way, these multiple paths can be different lengths for each other. Therefore, the cells departing from an identical source port and arriving at an identical destination port can reach to the output port as the order that is different from the order arriving at input port. The proposed cell resequencing buffer is a hardware sliding window mechanism. to solve such cell sequence integrity problem. To calculate the size of sliding window that cause the prime cost of the presented device, we analyzed the distribution of the cell delay through the simulation analyses under traffic load that have a nonuniform address distribution that express tile Property of traffic of the Internet. Through these analyses, we found out that we can make a cell resequencing buffer by which the cell sequence integrity is to be secured, by using a, few of ordinary memory and control logic. The cell resequencing buffer presented in this paper can be used for other multiple paths switching networks.