• 해양환경안전학회지
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• 제20권3호
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• pp.285-291
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• 2014

This study applied regression analysis to evaluate the impact of hourly average congestion calculated by bumper model in the congested area of each passage of each port on the peak time congestion, to suggest the model formula that can predict the peak time congestion. This study conducted regression analysis of hourly average congestion and peak time congestion based on the AIS survey study of 20 ports in Korea. As a result of analysis, it was found that the hourly average congestion has a significant impact on the peak time congestion and the prediction model formula was derived. This formula($C_p=4.457C_a+29.202$) can be used to calculate the peak time congestion based on the predicted hourly average congestion.

• 해양환경안전학회지
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• 제19권5호
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• pp.483-490
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• 2013

본 연구는 우리나라 전국 무역항 중 입항 선박이 많은 주요 4개 항만을 선정하여 10일간의 AIS 실측 자료를 분석하였다. 실측 조사로 산출한 주요항만의 피크시간 혼잡도는 시간당 평균혼잡도 보다 약 3.8~5.7배 높게 나타났다. 이는 기존의 Port-MIS 통계자료로 울산항 본항의 해상교통혼잡도를 평가한 선행연구 사례에서 피크시간 혼잡도가 시간당 평균혼잡도 보다 약 1.7배 높은 것과는 많은 차이가 있어 현 항로의 교통특성을 왜곡하는 문제를 확인할 수 있다. 따라서 해상교통혼잡도를 평가할 때에는 Port-MIS 통계자료보다 실측조사를 기반으로 해상교통혼잡도를 산출하는 것이 타당하다고 본다.

• International Journal of Internet, Broadcasting and Communication
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• 제11권1호
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• pp.17-26
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• 2019

The Constrained Application Protocol (CoAP) is a specialized web transfer protocol proposed by the IETF for use in IoT environments. CoAP was designed as a lightweight machine-to-machine protocol for resource constrained environments. Due to the strength of low overhead, the number of CoAP devices is expected to rise rapidly. When CoAP runs over UDP for wireless sensor networks, CoAP needs to support congestion control mechanisms. Since the default CoAP defines a minimal mechanism for congestion control, several schemes to improve the mechanism have been proposed. To keep CoAP lightweight, the majority of the schemes have been focused mainly on how to measure RTT accurately and how to set RTO adaptively according to network conditions, but other approaches such as rate-based congestion control were proposed more recently. In this paper, we survey the literature on congestion control for CoAP and discuss the future research directions.

• STI Policy Review
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• 제1권3호
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• pp.53-68
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• 2010

This paper empirically evaluates the effects of regional and industrial R&D on the performances of individual firms in two separated stages: (1) the stage of technological outcome from R&D and (2) the stage of economic outcome from technological outcome. Technological spillovers are separated from negative congestion effects through the stage-specific estimation. The firm-level Korean Innovation Survey data merit in coping with the endogeneity problem inherent in the estimation of spillovers. The estimation results show that: (1) there exist significant R&D spillovers both in regional and industrial dimensions, (2) the hypothesized technological spillovers and economic congestion effects are both in effect, and (3) firms with smaller individual R&D investments show greater spillovers.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권1호
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• pp.241-269
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• 2012

Wireless networks composed of multimedia-enabled resource-constrained sensor nodes have enriched a large set of monitoring sensing applications. In such communication scenario, however, new challenges in data transmission and energy-efficiency have arisen due to the stringent requirements of those sensor networks. Generally, congested nodes may deplete the energy of the active congested paths toward the sink and incur in undesired communication delay and packet dropping, while bit errors during transmission may negatively impact the end-to-end quality of the received data. Many approaches have been proposed to face congestion and provide reliable communications in wireless sensor networks, usually employing some transport protocol that address one or both of these issues. Nevertheless, due to the unique characteristics of multimedia-based wireless sensor networks, notably minimum bandwidth demand, bounded delay and reduced energy consumption requirement, communication protocols from traditional scalar wireless sensor networks are not suitable for multimedia sensor networks. In the last decade, such requirements have fostered research in adapting existing protocols or proposing new protocols from scratch. We survey the state of the art of transport protocols for wireless multimedia sensor networks, addressing the recent developments and proposed strategies for congestion control and loss recovery. Future research directions are also discussed, outlining the remaining challenges and promising investigation areas.

• 한국ITS학회 논문지
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• 제19권5호
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• pp.40-51
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• 2020

2011년에 고속도로 정체 기준 속도가 개정된 후 많은 시간이 경과함에 따라 차량의 성능 개선, 경쟁 관계에 있는 고속열차 운행 확대, 고속도로 일부 구간의 제한속도 상향 등 다양한 고속도로 주행환경 변화가 발생하였고 고속도로 이용자의 이동 신속성에 대한 기대수준 또한 증가하는 추세이다. 따라서 본 연구에서는 설문조사를 통해 고속도로 이용자의 정체에 대한 인식을 조사하고, 고속도로 교통류 분석을 통해 고속도로 정체 기준 속도의 재설정을 검토하고자 한다. 설문조사 결과, 고속도로 이용자들이 인식하는 정체 기준 속도가 다소 높아진 것을 확인하였다. K-means 알고리즘을 통해 교통량 및 속도 자료를 분석한 결과, 서행과 정체의 분류 기준은 60km/h 수준인 것으로 나타났다. 또한 정체 기준 속도를 50km/h와 60km/h로 상향하는 것을 가정하여 고속도로 정체잦은구간을 산정해본 결과, 50km/h가 고속도로 이동성 관리를 위한 정체 기준 속도로 적절한 것으로 판단된다.

• 한국철도학회논문집
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• 제18권3호
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• pp.270-277
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• 2015

수도권 도시철도 일부 구간에서는 이용객의 집중화에 따라 극심한 혼잡이 발생하고 있다. 도시철도 운영회사들은 정기 및 분기별 혼잡조사를 실시하여, 혼잡개선 대책을 수립하고 있다. 하지만, 이러한 조사는 열차혼잡도에 국한되어 있으며, 이벤트 발생에 따른 비반복 혼잡에 대한 조사가 어려운 실정이다. 본 연구에서는 교통카드자료를 활용한 시간대별 승강장 혼잡도를 추정하는 알고리즘을 개발하도록 한다. 알고리즘 검증을 위하여 2호선 잠실~신도림 구간의 비환승역을 대상으로 혼잡도 추정치와 실측치 값을 비교하였으며, 오차의 범위는 ${pm}2%$ 이내였다. 연구결과는 승강장 혼잡도를 시간대별로 상시 모니터링할 수 있으며, 장기적인 승강장 혼잡도분석을 통한 승강장 대기공간의 적정성 여부도 판단할 수 있을 것이다. 추후 연구에서는 본 연구에서 반영하지 못한 역별 게이트에서 승강장까지의 혼잡상황을 고려한 동적보행시간이 고려되어야 할 것이다.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제13권4호
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• pp.269-276
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• 2013

Information and communication technology (ICT) is a promising solution for mitigating road traffic congestion. ICT allows road users and vehicles to be managed based on real-time road status information. In Tanzania, traffic congestion causes losses of TZS 655 billion per year. The main objective of this study was to develop an optimal approach for integrating real-time road information (RRI) to mitigate traffic congestion. Our research survey focused on three cities that are highly affected by traffic congestion, i.e., Arusha, Mwanza, and Dar es Salaam. The results showed that ICT is not yet utilized fully to solve road traffic congestion. Thus, we established a possible approach for Tanzania based on an analysis of road traffic data provided by organizations responsible for road traffic management and road users. Furthermore, we evaluated the available road information management techniques to test their suitability for use in Tanzania. Using the floating car data technique, fuzzy logic was implemented for real-time traffic level detection and decision making. Based on this solution, we propose a RRI system architecture, which considers the effective utilization of readily available communication technology in Tanzania.

• 해양환경안전학회지
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• 제23권1호
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• pp.1-8
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• 2017

본 연구에서는 계절별 혼잡도 변화를 검토하기 위해 1년 동안의 주요 연안 통항로 및 항만 입출항로를 대상으로 계절별 기상특보가 발효되지 않은 1주일간의 GICOMS Data를 바탕으로 혼잡도 평가를 실시하였다. 그 결과 시간당 평균 혼잡도의 계절별 차이는 최대 약 11 %, 평균 약 3.5 %, 피크시간 혼잡도의 계절별 차이는 최대 약 82 %, 평균 약 30 %를 보이는 것으로 분석되었다. 향후 혼잡도 평가시에 이러한 계절별 혼잡도 변화를 감안하여야 하며, 특히 해상교통안전진단에서의 평가 시에는 이러한 계절별 차이가 존재하므로 혼잡여부에 대한 해상교통 안전대책 마련에 더욱 주의를 기울여야 할 것이다.

• The Journal of Asian Finance, Economics and Business
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• 제9권4호
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• pp.315-324
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• 2022

The goal of this study is to understand better the relationship between hospital bed occupancy rate and cost rigidity as a proxy for the degree of hospital bed congestion, as well as the relationship between the risk of changes in hospital bed occupancy rate and congestion cost, targeting public hospitals. As public hospitals for analysis, we selected hospital projects from the Public Enterprises Survey Reports published by the Department of Public Enterprises, Ministry of Finance, and obtained unbalanced panel data consisting of 1,505 hospitals and 15 years, totaling 12,595 hospitals and years. The analysis revealed that the risk of changes in the bed occupancy rate increases the degree of cost rigidity and leads to a decrease in the variable cost ratio; furthermore, an increase in the bed occupancy rate decreases the degree of cost rigidity and leads to an increase in the variable cost ratio. These findings suggest that although public hospitals are taking managerial actions to avoid congestion costs, congestion costs resulting from higher bed occupancy rates have not been eliminated. The regression analysis results show that even if congestion costs arise as the occupancy rate increases, they are covered by the increase in revenue associated with the increase in the occupancy rate.