• The Journal of the Korea Contents Association
• /
• v.14 no.9
• /
• pp.589-597
• /
• 2014

The increasing demand for various mobile telecommunication services calls for more spectrum resource. Considering the scarcity of spectrum resource and the difficulties of development of higher frequency band, the unique way to meet the increasing demand is to maximize the utilization efficiency of the current spectrum resource. Under the circumstances, various spectrum sharing plans have been in recent studies to dissolve the excess spectrum demand. In addition, spectrum efficiency measurement methods become more important to verify the effectiveness of spectrum sharing and estimate the performance of various wireless systems. Our research addresses measurement methods to estimate spectrum utilization efficiency in a rational manner. Based on ITU-R recommendations, various measuring methods for spectrum utilization efficiency are reviewed. Then a queueing based approach is newly presented as alternatives to the current models. By using the proposed model, the spectrum efficiency increment with the adoption of spectrum sharing plans can be estimated more properly.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.21 no.1
• /
• pp.17-34
• /
• 2022

This paper develops a model for dynamic station assignment to optimize the Demand Responsive Transit (DRT) operation. In the process of optimization, we use the bus travel time as a variable for DRT management. In addition, walking time, waiting time, and delay due to detour to take other passengers (detour time) are added as optimization variables and entered for each DRT passenger. Based on a network around Anaheim, California, reserved origins and destinations of passengers are assigned to each demand responsive bus, using K-means clustering. We create a model for selecting the dynamic station and bus route and use Non-dominated Sorting Genetic Algorithm-III to analyze seven scenarios composed combination of the variables. The result of the study concluded that if the DRT operation is optimized for the DRT management, then the bus travel time and waiting time should be considered in the optimization. Moreover, it was concluded that the bus travel time, walking time, and detour time are required for the passenger.

• Journal of Korea Port Economic Association
• /
• v.34 no.2
• /
• pp.69-82
• /
• 2018

The number of ships serviced at the container terminals in Busan is increasing by 2.9% per year. In spite of the increase in calling ships, there are no official records of waiting rate by the port authority. This study attempts to compare the theoretical ship waiting ratio and actual ship waiting ratio. The actual ship waiting ratio of container terminals is acquired from the 2014 to 2016 data of PORT-MIS and Terminal Operating System (TOS). Furthermore, methods and procedures to measure the actual ship's waiting rate of container terminal are proposed for ongoing measurement. In drawing the theoretical ship waiting ratio, the queuing theory is applied after deploying the ship arrival probability distribution and ship service probability distribution by the Chi Square method. As a result, the total number of ships waiting in a terminal for three years was 587, the average monthly service time and the average waiting time was 13.8 hours and 17.1 hours, respectively, and the monthly number of waiting ships was 16.3. Meanwhile, according to the queuing theory with multi servers, the ship waiting ratio is 31.1% on a 70% berth occupancy ratio. The reason behind the huge gap is the congested sailing in the peak days of the week, such as Sunday, Tuesday, and Wednesday. In addition, the number of waiting ships recorded on Sundays was twice as much as the average number of waiting ships.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.12
• /
• pp.816-821
• /
• 2019

This study shows that it is reasonable for an R&D Information and Evaluation Center to have a building with the fifth floor above the ground and the second floor below the ground. A survey was conducted with 22,655 researchers who are registered in the NRF database. The researchers provided 883 responses. The results indicate that about 56% of the respondents positively support the construction of the NFR R&D Information and Evaluation Center. The survey results show that many respondents recognize that both evaluation and information integration functions among the NRF's roles are very important compared to other roles. The findings of the economic validity analysis support this statement. Based on the current demand for the construction of the R&D Information and Evaluation Center, this study investigates whether it is reasonable to build a new center in the available space while examining an environment focused on a physical work space and looking at significant results obtained through a cost-benefit analysis.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.39 no.2
• /
• pp.361-367
• /
• 2019

Ramp metering is a traffic management technique that reduces the congestion of Expressway by controlling vehicles entering the highway. It is widely used outside the country, and Korea is also operating in seven sites (Seoul Ring Expressway). Ramp metering has the advantage of reducing congestion of Expressway, but there are disadvantages, as queuing occurs because vehicles are waiting for ramp, and the ramp queue affects adjacent roads at rush hour. To solve this problem, we improved the ramp metering algorithm to reduce the metering rate more spaces on ramp and to increase the metering rate less spaces. In order to evaluate this, the combined evaluation index was used and it was found that the result satisfied the equity and efficiency at the same time.

• Journal of Energy Engineering
• /
• v.10 no.3
• /
• pp.233-242
• /
• 2001

This paper attempts to analyze the effects of promotion of natural gas vehicles (NGVs) on LNG storage facilities and load patterns, and to verify economic feasibilities of NGVs as a DSM (Demand-Side Management) strategy. For these purpose, we have established an econometric mode. Results from the model indicate that natural gas demand in transportation sector will increase continuously, having a 7.84% share in total natural gas demand in 2014. By this analysis, the increased use of NGVs can result in a decreased requirement on the volume of around 1.3 LNG tanks lower in 2014. Also, it shows that TDRs can be reduced by 0.4 for the city gas and by 0.15 for the total LNG in 2014. As a conclusion, we suggest that the promotion of NGVs may play an efficient role as a DSM strategy, and should be considered as a promising strategy to optimize the investment needs in LNG sector as well as an environmental protection measures. Lastly, we acknowledge that a transportation module in our model is based on a Korean government's NGVs promotion plan, not on a market function.

• Journal of Korean Society of Transportation
• /
• v.35 no.1
• /
• pp.37-49
• /
• 2017

This study proposes an analysis methodology for air quality improvement effect of transport and environment policy that are used for mobile pollution sources. The methodology considers the changes of traffic of road transport sources and air pollutant emission, the changes of atmospheric dispersion of air pollutants and the effects on the health of local residents in response to policy implementation. Especially, the changes to traffic flow must be considered in evaluating the effects on atmospheric environment as it has a direct connection to the effects of the policy in this study. We used bottom-up approach (BUA) based on the travel demand model to reflect the changes of travel behavior in detail in response to the policy implementation compared to the top-down approach (TDA) when calculating the changes of emission level of road transport. We showed the applicability of the proposed analysis methodology through a policy scenario analysis, and the analysis method can be effectively applied to the cases in which travelers' behavior changes are expected.

• Journal of Korean Society of Transportation
• /
• v.26 no.5
• /
• pp.227-235
• /
• 2008

This study analyzed the efficiency of a trunk with branches and a trunk with feeders route system comparing the user cost and operator cost of those route systems. Basically, a trunk with branches is more efficient than a trunk with feeders in the passengers' perspective if the transit system of a trunk and feeders are the same. In the case that the trunk system is hierarchically higher than the feeder system, a trunk with feeders has the competitive edge over a trunk with branches if the saving of travel cost induced by using the trunk line is larger than the increasing waiting and transfer cost. This result is consistent with the previous research by Park et al.(2007c), which analyzed the efficiency of hierarchical structure in a grid transit network. If the travel demand of each origins and destinations is low, increasing headway according to the travel demand can increase passenger load or operating efficiency in a trunk with feeders route system. In this case, a trunk with feeders route system is more prevalent as the operating cost, route length, and number of destinations increases, while it is less prevalent as the transfer cost and passengers' time value of the waiting time increases. In cases that central business district, which is located in the middle of a trunk line, generates travel demand, a trunk with feeders is more efficient than a trunk with branches with the increasing travel demand from and to the CBD. Therefore it can be concluded that to have a dual operating system between CBD and suburban is more efficient than one type transit system. The efficiency of that system can be increased through an efficient transfer system that can reduce the transfer cost.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.34 no.5
• /
• pp.1525-1534
• /
• 2014

In recent years, the passengers are likely to decide their route on impulse due to the development of the integrated public transport system, and real-time information system. Especially, public transport fare integration in Seoul Metropolitan area, 2004 makes them not to have resistance about changing the modes or routes and their route choice is most effected by the degree of congestion. Assignment model have limitations to describe route changes by congestion. In this study, the concept of a link cost function used in road assignment and Effective frequency is introduced to describe the passengers' behavior when the capacity of public transport is over and the waiting time variation. Two situations, new transit line operation and accident, are set up to validate the model, as a result of the transit assignment by this model, the traffic on networks is not over the capacity. It is expected that this study will be of help to reflect the various behaviors in transit assignments.

• 해운
• /
• s.100
• /
• pp.19-30
• /
• 2013

하반기 산업경기는 현재 활주로에 이륙 대기 중인 비행기의 모습으로 묘사할 수 있다. 대부분의 산업경기가 저점을 형성하거나 회복국면에 진입할 전망이며 특히, IT산업은 빠른 성장세를 보이면서 가장 앞선 회복세를 보일 것으로 기대된다. 2013년 하반기 주요 산업별 경기 국면으로는 IT제조업은 반도체와 스마트 기기 중심의 수출 호조로 가장 빠른 회복 속도를 보일 것으로 전망된다. 또한, 석유화학산업은 상반기의 회복 추세가 하반기에도 이어질 것으로 보이며, 해운업은 제한적이나마 경기 회복 조짐이 나타날 것으로 예상된다. 한편, 하반기 중 건설업과 조선업의 업황 모두 경기 저점을 지날 것이라는 기대감이 존재하는 가운데, 자동차산업과 기계산업은 제한적인 수요 확대에 힘입어 경기 저점 형성 후 미약하나마 회복 국면으로 진입할 가능성도 있다. 하지만, 철강산업은 국내외 철강 제품의 수요 회복 지연, 시장 공급과잉 문제가 지속되면서 침체 국면에 위치할 것으로 전망된다. 다음은 현대경제연구원에서 최근 발표한 '하반기 산업경기의 5대 특징과 산업전망'의 주요 내용을 요약 정리한 것이다.