• 대한전자공학회논문지
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• 제26권12호
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• pp.1947-1955
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• 1989

With the increasing complexity of cabling at sensory level in process control and manufacturing automation, field buses were introduced to replace the traditional point to point links from each sensor or acruator to its controlling equipments by a single link on which all information is transmitted seriall and multiplexed in time. In this papr, we introduce the BITBUS network as a field bus. For the service discipline of the BITBUS network, two service strategies are proposed to obtain the performance of the network. They are the equal priority cyclic service strategy and the non-equal priority cyclic service strategy. The former assigns equal priority to each node for polling and the latter assumes non-equal priority. The BITBUS network was modeled as a cyclic queueing model and it is analyzed by two methods: the Kuehn's and the Boxma's. Computer simulation was also done for the cyclic queueing model and simulation results were compared with those. Under mathematically non-analyzable environment, only the computer simulation was done. From the simulation result, in order to meet the response time requirement of 5 msec imposed by International Electrotechnical Commission when each node has the average traffic of 5000 messages/sec in manufacturing automation the number of slave nodes should be smaller than 10 at the transmission rate of 2.5 Mbps.

• 대한교통학회지
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• 제22권4호
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• pp.85-96
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• 2004

합리적 통행경로는 "경로를 노드 또는 링크의 순서로 표현할 때, 경로를 구성하는 노드의 반복은 존재해도 링크의 반복은 존재하지 않는다"는 원리에 근거한다. 최적경로 탐색과정에서 합리적 통행현상을 포함하는 방법은 링크로 구성된 표지(Link-Based Label)를 적용하는 방안이 적용하기 용이하다. 링크표지를 활용하는 경우 링크의 중복 표현을 허용되지 않는 상황에서 노드의 중복표현이 가능하여 합리적인 통행을 원칙적으로 보장될 뿐만 아니라 목적지에서 출발지로 경로를 역 추적(Backward Trace)하는 과정에서 전 링크(Pvevious Link)의 단일정보만 이용하므로 Bellman의 최적원리(Optimality Condition)에 의한 최적해(Optimal Solution)가 보장된다. 본 연구는 다수의 경로를 선정함에 있어 합리적 통행행태를 고려하기 위한 링크표지고정방식(Link-Based Label Setting)을 제안한다. 기존에 표지고정(Label Setting)을 기반으로 제안되었던 노드기반 다수경로알고리즘을 기반으로 링크표지로 전환하는 방안을 개발한다. 또한 알고리즘의 대규모 교통망에 적용한 수행결과를 통해 대안경로정보제공을 위한 현실적용의 문제점을 도출하고, 도로의 연속주행을 보장하려는 운전자의 경로선택행태를 반영하는 방안에 대해 검토한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권10호
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• pp.3851-3866
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• 2015

The dynamic nature of opportunistic networks results in long delays, low rates of success for deliveries, etc. As such user experience is limited, and the further development of opportunistic networks is constrained. This paper proposes a prediction-based routing method for opportunistic networks (PB-OppNet). Firstly, using an ARIMA model, PB-OppNet describes the historical contact information between a node pair as a time series to predict the average encounter time interval of the node pair. Secondly, using an optimal stopping rule, PB-OppNet obtains a threshold for encounter time intervals as forwarding utility. Based on this threshold, a node can easily make decisions of stopping observing, or delivering messages when potential forwarding nodes enter its communication range. It can also report different encounter time intervals to the destination node. With the threshold, PB-OppNet can achieve a better compromise of forwarding utility and waiting delay, so that delivery delay is minimized. The simulation experiment result presented here shows that PB-OppNet is better than existing methods in prediction accuracy for links, delivery delays, delivery success rates, etc.

• 유통과학연구
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• 제14권2호
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• pp.41-45
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• 2016

Purpose - Finding an optimal path is an essential component for the design and operation of smart transportation or logistics network. Many applications in navigation system assume that travel time of each link is fixed and same. However, in practice, the travel time of each link changes over time. In this paper, we introduce a new transportation problem to find a latest departing time and delivery path between the two nodes, while not violating the appointed time at the destination node. Research design, data, and methodology - To solve the problem, we suggest a mathematical model based on network optimization theory and a backward search method to find an optimal solution. Results - First, we introduce a dynamic transportation problem which is different with traditional shortest path or minimum cost path. Second, we propose an algorithm solution based on backward search to solve the problem in a large-sized network. Conclusions - We proposed a new transportation problem which is different with traditional shortest path or minimum cost path. We analyzed the problem under the conditions that travel time is changing, and proposed an algorithm to solve them. Extending our models for visiting two or more destinations is one of the further research topics.

• 대한전자공학회논문지TC
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• 제46권6호
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• pp.94-102
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• 2009

참고문헌 [1]에서 full diversity를 달성할 수 있을 뿐만 아니라 각 relay node에서의 시간 지연을 제거하기 위해서 새로운 기법을 제안했다. 그러나 복호 후 전달 (DF) 모델 연산 모드는 relay에 더욱 많은 처리 부담을 준다. 본 논문에서는 [2],[3]에서 제안한 증폭 후 전달 (AF) model로 확장할 뿐만 아니라 source-relay link와 relay-destination link로 이루어진 모든 채널의 결합 채널 계수의 순서를 정하고 다음 복호 절차에서 이전의 복호된 심벌을 지우는 효율적인 복호 알고리즘을 제안한다. 컴퓨터 모의실험 결과를 통하여 제안한 알고리즘을 이용하면 높은 SNR 영역에서 참고문헌 [1]과 비교하여 상대적으로 2-3dB의 이득을 가져오기에 효율적으로 성능을 향상시킬 수 있다는 것을 알 수 있었다. 또한 제안한 알고리즘이 원래의 알고리즘과 비교하여 상대적으로 3dB 이상의 이득을 얻을 수 있는 복호 후 전달 (DF)에 유용하다는 것을 알 수 있었다.

• Spatial Information Research
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• 제14권2호
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• pp.245-260
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• 2006

이동성을 지원하는 모바일 환경에서 위치정보의 활용과 사용자 요구가 증가되고 GIS 공간 DB와 연계된 다양한 서비스가 진행되고 있다. 일반적으로 도로 DB를 구성하는 교통 네트워크의 논리적 관계의 표현은 노드-링크 구조를 사용한다. 이러한 단일 수준에 적합하게 설계된 구조는 다양한 모형 적용에 유연하지 못하고, 데이터베이스 검색과 유지관리 측면에서 비효율적이다. 본 연구에서는 동적 분할(Dynamic Segmentation)을 이용한 네트워크 모델의 설계와 구축을 통해 기존 도로망 모델의 문제점과 구축상의 한계점을 보완하고, 네트워크의 검색과 표현에 효율적인 계층 모델을 구현하고자 하였다. 설계된 모델은 다양한 수준의 단계별 표현과 계층 간 개체 관계성을 지원하며, GIS가 지닌 네트워크 공간 모델링 기능을 대폭 보완할 수 있을 것으로 기대 된다.

• 대한교통학회:학술대회논문집
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• 대한교통학회 2003년도 제43회 학술발표회논문집
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• pp.127-150
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• 2003

This research presents a novel application of static traffic assignment methods, but with a variable time value, for estimating the market share of a high-speed rail (HSR) in the NW-SE corridor of Korea which is currently served by the airline (AR), conventional rail (CR), and highway (HWY) modes. The proposed model employs the time-space network structure to capture the interrelations among all competing transportation modes, and to reflect their supply- and demand-sides constraints as well as interactions through properly formulated link-node structures. The embedded cost function for each network link offers the flexibility for incorporating all associated factors, such as travel time and fare, in the model computation, and enables the use of a distribution rather than a constant to represent the time-value variation among all transportation mode users. To realistically capture the tripmakers' value-of-time (VOT) along the target area, a novel method for VOT calibration has been developed with aggregate demand information and key system performance data from the target area. Under the assumption that intercity tripmakers often have nearly "perfect" travel information, one can solve the market share of each mode after operations of HSR for each O-D pair under the time-dependent demand with state-of-the-art traffic assignment. Aside from estimating new market share, this paper also investigated the impacts of HSR on other existing transportation modes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권11호
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• pp.5338-5359
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• 2017

In-band full-duplex (IBFD) wireless communication supports symmetric dual transmission between two nodes and asymmetric dual transmission among three nodes, which allows improved throughput for distributed IBFD wireless networks. However, inter-node interference (INI) can affect desired packet reception in the downlink of three-node topology. The current Half-duplex (HD) medium access control (MAC) mechanism RTS/CTS is unable to establish an asymmetric dual link and consequently to suppress INI. In this paper, we propose a medium access control mechanism for use in distributed IBFD wireless networks, FD-DMAC (Full-Duplex Distributed MAC). In this approach, communication nodes only require single channel access to establish symmetric or asymmetric dual link, and we fully consider the two transmission modes of asymmetric dual link. Through FD-DMAC medium access, the neighbors of communication nodes can clearly know network transmission status, which will provide other opportunities of asymmetric IBFD dual communication and solve hidden node problem. Additionally, we leverage FD-DMAC to transmit received power information. This approach can assist communication nodes to adjust transmit powers and suppress INI. Finally, we give a theoretical analysis of network performance using a discrete-time Markov model. The numerical results show that FD-DMAC achieves a significant improvement over RTS/CTS in terms of throughput and delay.

• 한국통신학회논문지
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• 제11권2호
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• pp.108-121
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• 1986

音聲과 데이터가 集積된 패킷 通信網의 性能을 豫測하고 시스템 파라메터를 最適化하기 위한 시뮬레이터의 개발에 관하여 記述하였다. 具現된 시뮬레이터는 CCITT의 勸告事項에 따라 運用되는 데이터 터미널이나 host는 물론 패킷 音聲터미널도 연결가능한 音聲 및 데이터集積通信網의 性能을 여러 상황에서 豫測할 수 있다. 시뮬레이션 技法으로는 지금까지 알려진 세가지 discrete event 시뮬레이션 技法 중 process interaction 方法이 사용되었는데 이 方法을 사용하면 실제 시스템과 가장 비슷한 시뮬레이터를 具現할 수 있다. 시뮬레이터는 약 4,000line의 GPSS 시뮬레이션 언어와 PL/I으로 具現되었다. 시뮬레이터의 컴퓨터 run time을 줄이기 위하여 GPSS의 LINK block을 사용함으로써 條件的 event의 數를 줄이는 方法을 사용하였다. 구현된 시뮬레이터를 사용하여 7-node 通信網의 性能을 豫測하였다. 또 개발된 시뮬레이터의 妥當性을 檢證하기 위하여 간단한 音聲과 데이터 multiplexer를 시뮬레이션 모델로 구성한 뒤 그 시뮬레이션 결과를 解釋的 방법에 依한 결과와 比較하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권4호
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• pp.1773-1795
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• 2020

Unmanned aerial vehicles (UAVs) network are a very vibrant research area nowadays. They have many military and civil applications. Limited bandwidth, the high mobility and secure communication of micro UAVs represent their three main problems. In this paper, we try to address these problems by means of secure clustering, and a security clustering algorithm based on integrated trust value for UAVs network is proposed. First, an improved the k-means++ algorithm is presented to determine the optimal number of clusters by the network bandwidth parameter, which ensures the optimal use of network bandwidth. Second, we considered variables representing the link expiration time to improve node clustering, and used the integrated trust value to rapidly detect malicious nodes and establish a head list. Node clustering reduce impact of high mobility and head list enhance the security of clustering algorithm. Finally, combined the remaining energy ratio, relative mobility, and the relative degrees of the nodes to select the best cluster head. The results of a simulation showed that the proposed clustering algorithm incurred a smaller computational load and higher network security.