• The Journal of the Acoustical Society of Korea
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• v.19 no.2
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• pp.46-53
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• 2000

In coastal bay waters, bubbles are generated by relatively heavy ship-traffic, breaking waves due to man-made structures and biological activities. Therefore, the bubble-generating mechanism as well as the bubble density distribution in the bay are quite different from the open ocean where breaking waves are major contributor for bubble density distribution. High frequency surface-backscattered signals were obtained in the coastal bay waters and they were analyzed to compare with those from the open waters in terms of the sea-surface backscattering strength at various grazing angles, the reverberation characteristics in the sub-surface layer and spectral spreading of the scattered signals. The results show that, the surface scattered signals have an irregular distribution of amplitude in time and the width of the spectral spreading is wider than that of the open sea with rough surface. Furthermore, the amplitude distribution of the reverberation signals is not following the Rayleigh distribution, that is eon to be a typical pattern for the open ocean. The results of our analysis imply that the bubble size and the bubble density in the bay are quite different from those observed in the open waters.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6B
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• pp.1004-1014
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• 1999

MAC protocols in wireless ATM has to increase and maintain the system throughput performance. To achieve these purposes, this paper proposes a dynamic control algorithm called DSPA (Dynamic Signalling Period Allocation) for wireless ATM MAC protocol. The proposed DSPA algorithm consists of the following three algorithms. First, a control slot generation algorithm which generates the control slots by utilizing static and dynamic parameters from the terminals, is proposed. Second, a dynamic signalling period allocation algorithm is proposed for a base station to dynamically determine each signalling period according to current terminal states, and thus allocates the optimal signalling periods. Finally, a dynamic slot allocation algorithm is proposed to dynamically determine priorities of the terminals whenever a slot is allocated. Simulation results indicates that DSPA algorithm decreases average packet delay of the terminals by dynamic allocation of signal periods based on the system utilization, and thus increases the limitation of allowable loads that quarantee quality of services. Also the proposed algorithm is shown to maintain stable throughput even in the case of traffic variations.

• Journal of Advanced Navigation Technology
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• v.19 no.6
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• pp.607-613
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• 2015

In order to design M/W(microwave) short backhaul above 10 GHz to meet the increase in mobile traffic demand, the rain attenuation as well as the atmospheric conditions such as Earth bulge and Fresnel zone should be considered. In this paper, the path lengths have been estimated theoretically in various frequency bands using the Korean standard rain rate, and an example of path profile has been analyzed in urban area utilizing spectrum management intelligence system (SMIS). These derived minimum path lengths in various frequency bands are compared to the foreign them, and then will be proposed to improve the Korean minimum path length unitized to 10 km. This paper will provide useful information for microwave engineers in designing a M/W access link, and be utilized to make an efficient usage of high frequency bands for the short mobile broadband backhaul.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.4
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• pp.371-377
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• 2013

Fishing boats more than 5 tons is obliged to VHF DSC by Fishing Vessels Act and Vessel Safety Act. The owner of the fishing vessel is equipped to the automatic position reporting device in accordance with the Notice of the Minister of Land, Transport and Maritime Affairs to regulations, shall be ensure to navigations safety and in order to respond quickly in the event of maritime accidents on fishing vessels. East sea set up to start in 2012, which is now underway the annual install plain to the yellow sea and the south sea for VHF coast stations. It is web-based remote operation of DSC on the remote control and monitoring in Fishery Information Communication Station for the coastal VMS construction project. All fishing vessels is VHF DSC in conjunction with the GPS that location information transmitted to the coast station. automatically by the DSC call. This paper has been studied on the communications coverage set up and traffic operation for realization a roaming service by navigation route tracking and RSSI techniques in parallel algorithm refer to VHF DSC coast stations in east sea.

• Journal of KIISE
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• v.42 no.6
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• pp.807-816
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• 2015

The Internet of Things (IoT) has recently been showered with much attention worldwide. Various kinds of devices, communicating with each other in the IoT, demand multiple communication technologies to coexist. In this environment, mobile devices may utilize the vertical handover between different wireless radio interfaces such as Wi-Fi and Bluetooth, for efficient data transfer. In this paper, an IoT broker is implemented to support the vertical handover, which can also support and manage heterogeneous devices and communication interfaces. The handover is activated based on RSSI, Link Quality values, and real time traffic. The experimental results show that the proposed handover system substantially improves QoS in Bluetooth and reduces power consumption in mobile devices as compared with a system using only Wi-Fi.

• International Journal of Highway Engineering
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• v.18 no.4
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• pp.83-92
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• 2016

PURPOSES : The purpose of this study was to develop safety performance functions (SPFs) that use zero-inflated negative binomial regression models for urban intersections in central business districts (CBDs), and to compare the statistical significance of developed models against that of regular negative binomial regression models. METHODS : To develop and analyze the SPFs of intersections in CBDs, data acquisition was conducted for dependent and independent variables in areas of study. We analyzed the SPFs using zero-inflated negative binomial regression model as well as regular negative binomial regression model. We then compared the results by analyzing the statistical significance of the models. RESULTS : SPFs were estimated for all accidents and injury accidents at intersections in CBDs in terms of variables such as AADT, Number of Lanes at Major Roads, Median Barriers, Right Turn with an Exclusive Turn Lane, Turning Guideline, and Front Signal. We also estimated the log-likelihood at convergence and the likelihood ratio of SPFs for comparing the zero-inflated model with the regular model. In he SPFs, estimated log-likelihood at convergence and the likelihood ratio of the zero-inflated model were at -836.736, 0.193 and -836.415, 0.195. Also estimated the log-likelihood at convergence and likelihood ratio of the regular model were at -843.547, 0.187 and -842.631, 0.189, respectively. These figures demonstrate that zero-inflated negative binomial regression models can better explain traffic accidents at intersections in CBDs. CONCLUSIONS : SPFs that use a zero-inflated negative binomial regression model demonstrate better statistical significance compared with those that use a regular negative binomial regression model.

• Journal of Korean Society of Transportation
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• v.22 no.2 s.73
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• pp.109-119
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• 2004

In COSMOS, an area for signal coordination is divided into subareas composed of several signalized intersections that share a common cycle time. Each subarea contains only one critical intersection having heavy traffic load. Subarea is a basic unit of control. The performance of COSMOS is highly dependent on the linkage rule between adjacent subareas. The purpose of this study is to provide an appropriate subarea linkage rule in COSMOS. This study developed a control strategy for Critical Intersection and Sub Area linkage. Critical Intersections calculate the Offset Pattern both East-West Axis and North-South Axis, and the coordination direction either East-West Axis or North-South Axis. Subarea can be combined with other one in all directions. The performance of the suggested linkage rule was evaluated on the real network in Gangnam-Gu. The result was that travel time was reduced by the suggested linkage rule.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.11 no.2
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• pp.101-106
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• 1993

This study is a efficient management techniques of road by facility database. The purpose of road ledger investigate the property of road facility, the present condition of the location, the quality of the material of the ground and underground facility. Also, this is used to make plan for construction, and investment program of the road. To build road database, photogrammetry, ground control surveying and aerial photogrammetry must be performed. After the research of the road facility, a underground facility map and the road drawings are to be made. In this study, model area is the KUMJUNG-KU in Pusan where an industrial road is located on. There are about 7,000 signal lampes and traffic safety boards. It is possible to manage scientifical and efficient road ledger though statistical handling using facility database. In this paper, authors found the database of road facility through basic circumstances in the use of SML of ARC/INFO.

• Journal of KIISE:Information Networking
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• v.27 no.1
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• pp.88-97
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• 2000

Applied with multicast transmission techniques in mobile computing environments, a mobile host will experience join and graft delay, happened when a host wants to join a multicast group in the fixed network, if there are no same multicast group member in the new cell the mobile host enters. Due to low bandwidth and higher error rate, there happens many additional traffic. In this paper, we propose a pre-join technique which new mobile support station joins the multicast group in advance based on signal strength hint in the current cell. We use the multiple level acknowledgement strategy that executes acknowledgment separately between the fixed part and the wireless transmission path. Using our strategy, it is an efficient technique in case there are more cells that has no multicast group members and less mobile host movements.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.6
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• pp.83-88
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• 2010

In this paper, to propose a valid method solving a problem relevant to grounding from actual field data, the experimental results relevant to touch and step voltages and surface potential profiles measured around the real-sized and small-sized grounding electrode models were described. The ground surface potential profiles and dangerous voltages around the concrete pedestals employed in street facilities such as street lamps, traffic signal lamp and controllers as a case study were measured and discussed. The hemispherical cell with a diameter of 1,160[mm] was employed to simulate uniform soil. As a result, the results measured with the small-sized model were in reasonably agreement with the data obtained from the real-sized installation. It was found that the small-sized model test could be employed as a useful means evaluating the dangerous voltages around grounding electrodes installed at the inaccessible areas such as mountains, underground, underwater, and so on.