• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.3A
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• pp.261-270
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• 2007

The Delay Threshold-based Priority Queueing (DTPQ) scheme has been shown useful for scheduling both real-time (RT) and non-real-time (NRT) service traffic in mobile broadband wireless access (MBWA) systems. The overall system capacity can be maximized subject to their QoS requirement by the DTPQ scheme, which takes the urgency of the RT service into account only when their head-of-line (HOL) packet delays exceed a given delay threshold. In practice, the optimum delay threshold must be configured under the varying service scenarios and a corresponding traffic load, e.g., the number of RT and NRTusers in the system. In this paper, we propose an adaptive version of DTPQ scheme, which updates the delay threshold by taking the urgency and channel conditions of RT service users into account. By evaluating the proposed approach in an orthogonal frequency division multiple access/time division duplex (OFDM/TDD)-based broadband mobile access system, it has been found that our adaptive scheme significantly improves the system capacity as compared to the existing DTPQ scheme with a fixed delay threshold.

• Journal of Korean Society of Transportation
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• v.31 no.4
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• pp.58-66
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• 2013

Due to the characteristics of urban freeways such as heavy traffic and high speed, work zone on urban freeways causes the increase of not only the likelihood of crash occurrence but also traffic congestion caused by lane drop, lane change, acceleration/deceleration, and etc. This paper aims to determine the proper length of transition area that satisfies two criteria, mobility and safety, to make the operation of work zone more efficient. For the analysis, three different scenarios were developed by the number of lanes and the proper length of transition area were determined by changing the length from 100m to 500m in 100m increments. The results showed that the proper length of transition area for 3- and 4-lane freeways is 300m, whereas the proper length of 2-lane freeways is 200m. The results indicated that the different length of transition area based on the number of lanes is more desirable and efficient.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.10
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• pp.2085-2094
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• 2012

In this paper, we propose a wireless access network virtualization algorithm based on a digital unit (DU)-radio unit (RU) separated network structure in a cellular network with multiple radio access technologies (RATs). The proposed wireless access network virtualization algorithm consists of a baseline access network virtualization, RAT virtualization, and access path migration algorithms. Final wireless access network virtualization is performed by sequentially performing these procedures. Through system-level simulations which assume 3GPP LTE and WiMAX systems, the performance of the proposed wireless access network virtualization is evaluated in terms of system throughput for two scenarios according to asymmetry of network traffic load. Numerical results show that our proposed wireless access network virtualization algorithm achieves significant system throughput gain even in asymmetric traffic load and user distribution situations.

• Journal of Auto-vehicle Safety Association
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• v.9 no.4
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• pp.38-47
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• 2017

With automobiles sharply increasing worldwide, we are faced with serious social problems such as traffic accidents, traffic jams, environmental pollution, and economic inefficiency. In response, research on ITS is promoted mainly by regions with advanced automotive industry such as the US, Europe, and Japan. While Korea is working to get ahead to take global market through developing and turning into global standards systems related to ASV(Advanced Safety Vehicle), the country is not excellently prepared for such projects. The purpose of ACC is to control the vehicle's longitudinal speed and distance and minimize driver workload. Such a system should be useful in preventing accidents, as it reduces driver workload in the 21st-century world of telematics created by the development of automobile culture industry. In this light, the thesis presents a method to test and evaluate ACC system and a mathematical method to assess distance. Furthermore, for the proposed test and evaluation, theoretical values are tested with vehicle test and a database is acquired, by using vehicles equipped with an ACC system. We proposed the scenarios suitable for the domestic environment and conducted the actual road test. Theoretical evaluation criteria for developing ACC system may be employed and scenario-specific evaluation methods may find their useful application through testing the formula proposed by comparing the database and the mathematical method. and, many companies are expected to utilize the scenario in the developing stage of ACC, and be able to employ as a verification method by harnessing theoretical formula before a road test.

• International Journal of Highway Engineering
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• v.14 no.5
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• pp.165-177
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• 2012

PURPOSES: The number of traffic accidents in 2010 was 226,978 in Korea, a high percentage of which up to 12.61% was due to drunk driving. As it is expected that the number of traffic accidents will increase because of the drastic increase of the number of vehicle registrations and the prevalent drinking cultures, it is necessary to understand the driving characteristics of drunken drivers to lower the increasing rate. METHODS: This study, therefore, comparatively analyzes the two groups - one group before drinking and the other after drinking - based on the graph, and implements the correlation in each scenario(1,2,3). scenario 1. appearance of jaywalkers; scenario 2. appearance of an illegal left-turning car; and scenario 3. appearance of a vehicle and a person as obstacles to the driver after an accident. RESULTS: The comparative analysis of speed shows that the group after drinking was 50km/h faster than the group before drinking in Scenario 1, 20km/h in Scenario 2, and 15km/h in Scenario 3 respectively. In the comparative analysis of acceleration, the average level of the group after drinking was 0.15 higher than that of the group before drinking in Scenario 1, 0.30 in Scenario 2, and 0.15 in Scenario 3. In the comparative analysis of deceleration, the average level of the group after drinking was about 0.4 lower than that of the group before drinking in Scenario 1, 0.35 in Scenario 2, and 0.2 in Scenario 3 respectively. In the comparative analyses, the item of speed, acceleration and deceleration was of significance for each group in Scenarios. CONCLUSIONS: The comparative analysis demonstrated that there is a difference between the group before drinking and the group after drinking. In the analysis of correlation in each group, it was proved that the drunken group was of significance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.5
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• pp.440-451
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• 2013

Recently, researches of technology and standardization for maritime safety are proceeding internationally. In particular, some technologies and strategies for e-Navigation have been developed and the necessity of development of next generation VTS (Vessel Traffic Service) has been raised in Korea. In order to construct user oriented VTS system for domestic environment, VTS operators are asked for their requirements related to developing VTS and the opinions should be reflected in the VTS. So in this paper, we collect the requirements from fifteen VTS centers in the country and we also analyze them. Furthermore, we propose an ASM (Application Specific Messages) service, which was not supported by current VTS, and we verify the proposed ASM through AIS (Automatic Identification System) system and simulation terminal for maritime safety.

• International Journal of Highway Engineering
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• v.14 no.2
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• pp.83-91
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• 2012

This study deals with the operational efficiency of roundabout. The roundabouts generally have such the merits as high capacity, delay reduction, safety improvement, and others. Circular intersection can be divided into the rotary and roundabout according to travelling priority. The objective of this study is to comparatively analyze the operational efficiency of rotary and roundabout by scenario. In pursuing the above, this study gives the particular attentions to developing 256 scenarios according to the directional and entering traffic volume and analyzing the delay using VISSIM. The main results are as follows. First, the average delay of rotary was analyzed to be 1.56-8.74 times of roundabout. Second, the operational efficiencies of rotary and roundabout were analyzed to be better in the case of bigger differences in the traffic volumes between the main and minor roads. Third, the average delay of the 4-legged was evaluated to be 1.77-11.70 times of 3-legged intersection. Finally, 2-lane intersection (3-legged & 4-legged) was analyzed to be 2.02-2.23 times of 1-lane intersection.

• International Journal of Highway Engineering
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• v.14 no.1
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• pp.73-83
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• 2012

Effective use of traffic marking can lead to driver's safer driving by speed management and visibility enhancement. One of the critical factors in designing traffic marking is how to incorporate human factor issues into the design process. This study presented a methodology for evaluating the effectiveness of Hi-pass marking on Korean freeways based on kansei engineering. Hi-pass marking scenarios made by a virtual reality tool were used to evaluate the user's perceptions. Various combination of chevron angles and peripheral transverse(PT) bars were used for the evaluation. The results show that the most effective scenario is a combination of 60 degree chevron angle and an askew parallelogramshaped PT bar shaped. It is expected that the proposed method and outcome will be useful for making safer driving maneuvers.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.2
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• pp.709-730
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• 2017

To address the challenge of unprecedented growth in mobile data traffic, ultra-dense network deployment is a cost efficient solution to offload the traffic over some small cells. The overlapped coverage areas of small cells create more than one candidate access points for one mobile user. Signal strength based user association in IEEE 802.11 results in a significantly unbalanced load distribution among access points. However, the effective bandwidth demand of each user actually differs vastly due to their different preferences for mobile applications. In this paper, we formulate a set of non-linear integer programming models for joint user association control and user demand guarantee problem. In this model, we are trying to maximize the system capacity and guarantee the effective bandwidth demand for each user by soft-association control with a software defined network controller. With the fact of NP-hard complexity of non-linear integer programming solver, we propose a Kernighan Lin Algorithm based graph-partitioning method for a large-scale network. Finally, we evaluated the performance of the proposed algorithm for the edge users with heterogeneous bandwidth demands and mobility scenarios. Simulation results show that the proposed adaptive soft-association control can achieve a better performance than the other two and improves the individual quality of user experience with a little price on system throughput.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.16 no.3
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• pp.83-94
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• 2017

There is a two lane ECTS(Electronic Toll Collection System) that users can pass with 80kph high speed in SeoBusan Tall Gate. This system to be combined two hi-pass lanes for removing meddle-island have been operated successfully. But, the appearance of two Lane ETCS makes toll gate more complicated, so it is very important how to arrange effectively various tolling lanes. This study was trying to evaluate lane configuration for minimizing speed and speed deviation among all kinds of lanes including two Lane ETCS in seoul toll gate. That is, we selected all scenarios to be happened actually, and evaluated them using micro traffic simulation model (VISSIM). The results of this study showed that each alternative had a very different speed and speed deviation by lane each other, so we will be able to achieve effective operation and configuration of lanes in toll gate using scenario methodology.