• Journal of the Korea Society of Computer and Information
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• v.26 no.12
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• pp.255-264
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• 2021

In this paper, we propose operations and maintenance (O&M) planning approach for floating offshore wind farm using the mathematical optimization. To be specific, we present a MILP (Mixed Integer Linear Programming that suggests the composition of vessels, technicians, and maintenance works on a weekly basis. We reflect accessibility to wind turbines based on weather data and loss of power generation using the Jensen wake model to identify downtime cost that vary from time to time. This paper also includes a description of two-stage approach for maintenance planning & detailed scheduling and numeric analysis of the number of vessels and technicians on the O&M cost. Finally, the MILP model could be utilized in order to establish the suitable and effective maintenance planning reflecting domestic situation.

• Proceedings of the Korea Information Processing Society Conference
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• 2008.11a
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• pp.1348-1351
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• 2008

최근 인터넷 사용자들의 요구는 멀티미디어로 집중되고 있으며 그중 라이브 미디어 스트리밍 서비스에 대한 요구가 증가하고 있다. 라이브 서비스에서는 적절한 시간에 사용자에게 데이터가 도착하는 것이 중요하다. 따라서 라이브의 시간적절성을 충족시켜 줄 효율적이고 신속한 데이터 전달구조와 전송기법이 요구된다. 이에 본 논문에서는 트리와 메시 구조를 혼합한 하이브리드 방식으로 네트워크 자원을 효율적으로 사용하면서 빠른 데이터 전송으로 라이브의 시간적절성을 충족시킬 수 있는 데이터 분할 전송 방식의 P2P(Peer-to-Peer) 오버레이 구조를 제안한다. 제안하는 ToG(Tree of Groups)는 n개의 피어들이 메시로 그룹을 형성하고, 그렇게 형성된 그룹들이 트리를 이루는 구조이다. ToG에서 그룹 내의 각 피어들은 상위그룹의 피어 한 개와 부모-자식으로 연결되어 있어서 그룹 사이에 여러 개의 연결이 존재하게 된다. 따라서 그룹 내에서 어느 한 피어가 그룹을 빠져 나가더라도 상위그룹과의 여러 연결에 의해서 서비스 지속성을 보장 할 수 있다. ToG는 그룹단위로 트리가 형성되기 때문에 피어의 개수가 같을 때 피어단위로 트리를 형성하는 구조보다 트리의 깊이가 줄어든다. 그에 따라 말단에 있는 피어들에게까지 빠른 시간에 데이터가 전달 될 수 있다. ToG의 데이터 전달은 소스로부터 세그먼트가 일정한 값 n으로 나뉘어져 각 피어들에게 전달된다. 세그먼트 조각은 소스로부터 나뉘어져 전송 될 때 책임적으로 전달해야할 피어와 전달 순서가 정해져있고, 데이터 전송 스케줄링을 위한 버퍼 맵 교환은 필요하지 않다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.8B
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• pp.509-520
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• 2007

In this paper, we propose a real-time sensor node platform that guarantees the real-time scheduling of periodic and aperiodic tasks through a multitask-based software decomposition technique. Since existing sensor networking operation systems available in literature are not capable of supporting the real-time scheduling of periodic and aperiodic tasks, the preemption of aperiodic task with high priority can block periodic tasks, and so periodic tasks are likely to miss their deadlines. This paper presents a comprehensive evaluation of how to structure periodic or aperiodic task decomposition in real-time sensor-networking platforms as regard to guaranteeing the deadlines of all the periodic tasks and aiming to providing aperiodic tasks with average good response time. A case study based on real system experiments is conducted to illustrate the application and efficiency of the multitask-based dynamic component execution environment in the sensor node equipped with a low-power 8-bit microcontroller, an IEEE802.15.4 compliant 2.4GHz RF transceiver, and several sensors. It shows that our periodic and aperiodic task decomposition technique yields efficient performance in terms of three significant, objective goals: deadline miss ratio of periodic tasks, average response time of aperiodic tasks, and processor utilization of periodic and aperiodic tasks.

• The KIPS Transactions:PartC
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• v.14C no.6
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• pp.493-502
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• 2007

In this paper, we propose a handoff-aware DiffServ scheduler which intends to guarantee various QoS requirements of multimedia services for mobile nodes in TDD/CDMA based wireless networks. TDD is widely used duplexing mechanism in wireless communications. Unlike FDD, TDD allows a node to symmetrically communicate with a base station by using a single frequency band, resulting in high utilization of wireless resources. DiffServ is regarded as a relatively simple QoS support mechanism and thus it is easy to be extended. This is because DiffServ is not a per-flow based mechanisms and it does not require any signaling protocol. However, previously proposed DiffServ schedulers for wired networks can not be deployed directly into wireless networks since they do not consider properties of wireless networks. As a solution to the problem, DSS(DiffServ Supporting Scheduler) was proposed. DSS uses uplink channel, which is originally used for a node to require a base station to transmit packets, to support QoS efficiently. However, QoS does not consider handoff so that it can not support QoS for moving nodes from one cell to the other cell. Therefor. the proposed handoff support QoS mechanism is necessary for TCC/CDMA networks. The proposed scheme allows a mobile node to achieve seamless service without QoS degradation even for the handoff duration.

• The Transactions of the Korea Information Processing Society
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• v.6 no.4
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• pp.877-890
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• 1999

In this paper, a multimedia mail including video, sound, graphic data has been proposed as the next generation mail of the text based mail. In order to develop the multimedia mail, the most outstanding problem is the fact that the multimedia data are too huge to send them to the receiving end directly. The fact of big data may cause many problems in both transferring and storing the data of the multimedia mail. Our main idea is to separate between a control program for the multimedia presentation and multimedia data. Since the size of a control program is as small as a plain text mail, it has no problem to send it attached to the internet mail to the receiver directly. Instead, the big multimedia data themselves may remain on the sender's computer or be sent to a designated server so that the data may be transferred to the receiver only when the receiver activates the play of the multimedia mail. In this scheme, our research focus is paced on the buffer management and the thread scheduling for the real time play of the multimedia mail on internet. Another problem is to provide an easy way of editing a multimedia presentation for an ordinary people having no programming knowledge. For the purposed, VIP(Visual Interface Player) has been used and the results or multimedia mail implemented on LAN has been described.

• Journal of IKEEE
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• v.5 no.1 s.8
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• pp.100-110
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• 2001

In this paper, we investigated several buffer management schemes for the design of shared-memory type ATM switches, which can enhance the utilization of switch resources and can support quality-of-service (QoS) functionalities. Our results show that dynamic threshold (DT) scheme demonstrate a moderate degree of robustness close to pushout(PO) scheme, which is known to be impractical in the perspective of hardware implementation, under various traffic conditions such as traffic loads, burstyness of incoming traffic, and load non-uniformity across output ports. Next, we considered buffer management strategies to support QoS functions, which utilize parameter values obtained via connection admission control (CAC) procedures to set tile threshold values. Through simulations, we showed that the buffer management schemes adopted behave well in the sense that they can protect regulated traffic from unregulated cell traffic in allocating buffer space. In particular, it was observed that dynamic partitioning is superior in terms of QoS support than virtual partitioning.

• Korean Journal of Construction Engineering and Management
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• v.10 no.6
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• pp.3-12
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• 2009

In order to effectively distribute the resources, it is very critical to understand the status or progress of construction site quickly and accurately. Augmented Reality (AR) can provide this situation with information which is convenient and intuitive. Conventional implementation of AR in outdoor or construction site condition requires additional sensors or markers to track the position and direction of camera. This research is aimed to develop the technologies which can be utilized in gathering the information of constructing or constructed buildings and structures. The AR technique that does not require additional devices except for the camera was implemented to simplify the system and improve utility in inaccessible area. In order to do so, the position of camera's perspective center and direction of camera was estimated using exterior orientation techniques. And 3D drawing model of building was projected and overlapped using this information. The result shows that by using this technique, the virtual drawing image was registered on real image with few pixels of error. The technique and procedure introduced in this paper simplifies the hardware organization of AR system that makes it easier for the AR technology to be utilized with ease in construction site. Moreover, this technique will help the AR to be utilized even in inaccessible areas. In addition to this, it is expected that combining this technique and 4D CAD technology can provide the project manager with more intuitive and comprehensive information that simplifies the monitoring work of construction progress and planning.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.11
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• pp.846-850
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• 2009

Recently, wireless sensor networks have found their way into a wide variety of applications and systems with vastly varying requirements and characteristics such as environmental monitoring, smart spaces, medical applications, and precision agriculture. The sensor nodes are battery powered. Therefore, the energy is the most precious resource of a wireless sensor network since periodically replacing the battery of the nodes in large scale deployments is infeasible. Energy efficient mechanisms for gathering sensor readings are indispensable to prolong the lifetime of a sensor network as long as possible. There are two energy-efficient approaches to prolong the network lifetime in sensor networks. One is the compression scheme to reduce the size of sensor readings. When the communication conflict is occurred between two sensor nodes, the sender must try to retransmit its reading. The other is the MAC protocol to prevent the communication conflict. In this paper, we propose a novel approaches to reduce the size of the sensor readings in the MAC layer. The proposed scheme compresses sensor readings by allocating the time slots of the TDMA schedule to them dynamically. We also present a mathematical model to predict latency from collecting the sensor readings as the compression ratio is changed. In the simulation result, our proposed scheme reduces the communication cost by about 52% over the existing scheme.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.151-157
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• 2017

Recently, the retail industry has created efficient store operations, and has differentiated customer service through the future store. The intelligence of these stores is being applied by using technologies such as the Internet of Things (IoT), and the business process is being improved through this. The process also focuses on efficient store operations and service developments to provide customers with shopping convenience. The change in trends in the industry means that domestic distribution has already reached maturity. Even in countries where retail industries are mature, such as the U.S. and Europe, recent trends are moving toward maximizing operational efficiency and customer service. The reason is that many retailers have already reached saturation and survived the competition. This paper is a study of a drive-through service for automation and efficiency in receiving service after ordering by a customer of the distribution store. When ordering a product being purchased by a customer, the product picking process is done in a timely fashion through a picking scheduling agent. When the customer enters the store parking lot, a service supports the entry of information and finding a parking place so the customer can quickly pick up the goods. The proposed service can be applied to a retail store drive-through system, the distribution store's delivery system, the digital picking system, and indoor/outdoor large parking management systems, and it is possible to provide one-dimensional customer service through the application of IoT technology.

• The KIPS Transactions:PartA
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• v.16A no.6
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• pp.463-472
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• 2009

Real-time operating systems must have satisfying various conditions such as effective scheduling policies, minimized interrupt delay, resolved priority inversion problems, and its applications to be completed within desired deadline. The real-time operating systems, therefore, should be designed and developed to be optimal for these requirements. MicroC/OS-II, a kind of Real-time operating systems, uses the basic priority inheritance with a mutex to solve priority inversion problems. For the implementation of mutex, the kernel in an operating system should provide supports for numerous tasks with same priority. However, MicroC/OS-II does not provide this support for the numerous tasks of same priority. To solve this problem, MicroC/OS-II cannot but using priority reservation, which leads to the waste of unnecessary resources. In this study, we have dealt with new design a protocol, so called TPSP(Temporary Priority Swap Protocol), by an effective solution for above-mentioned problem, eventually enabling embedded systems with constrained resources environments to run applications.