• Proceedings of the Korea Information Processing Society Conference
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• 2008.05a
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• pp.841-844
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• 2008

본 논문은 공개 네트워크 시뮬레이터 ns-2.31(Network Simulator 2.31)의 802.11 DCF 모듈에서 버그(bug)를 소개하고 이의 영향 결과를 분석한다. ns의 802.11 DCF 모듈은 다음과 같은 문제점을 가지고 있다. 첫째, 백오프(backoff) 알고리즘은 표준안에서 명시한 알고리즘대로 작성되지 않았다. 둘째, 특정조건에 해당되는 충돌에 대하여 트레이스 파일에 출력하지 않는다. 셋째, 전파 오류 모듈을 삽입하여도 전파 오류 결과를 트레이스 파일에 출력하지 않는다. 넷째, MAC(Medium Access Control) 알고리즘만을 평가할 수 있는 기법을 제공하지 않는다. 이러한 문제점을 수정한 ns-2와 수정전의 ns-2와 평균4.6%의 충돌률 차이를 보인다.

• Proceedings of the Korea Information Processing Society Conference
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• 2008.05a
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• pp.885-888
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• 2008

무선 센서 네트워크 라우팅 프로토콜에서의 경로탐색에서 중복 브로드캐스트 메시지에 의한 비용이 증가되고, 많은 노드들이 동시에 통신을 시도하기 때문에 많은 충돌이 발생한다. 이러한 문제를 해결하기 위해 본 논문에서는 Directed Diffusion 라우팅 방법에 지향성 안테나를 도입하여 채널 이용율을 높여 통신에서의 충돌을 줄이고 네트워크 구성 및 유지 시 사용될 flooding의 범위와 노드간의 통신시 불필요한 방향으로의 통신을 최소화하여 중복되는 브로드캐스트 메시지 수를 줄일 수 있는 라우팅 방법을 제안한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.5B
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• pp.310-317
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• 2008

Data collision in LR-WPAN(Low Rate Wireless Personal Area Network) causes retransmission of which energy consumption may reduce life of the entire network. Furthermore LR-WPAN is very sensitive to collision as it has relatively fewer frequencies of backoff retries. LCS(Limited Contention Scheme) suggested in this study is a way to transmit data by certain groups of the total nodes so that it can reduce possibilities of data collision and retransmission by decreasing the number of competing nodes. As a result LCS can increase a throughput and the life of the entire network. As using LCS in designing LR-WPAN in the future can extend battery life, LCS can be useful in any application that requires low energy consumption.

• Journal of the Korea Computer Graphics Society
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• v.6 no.1
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• pp.11-17
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• 2000

We present collision-handling method that includes self-penetration in the case of the colliding between rigid and deformable objects. The collision between objects is detected through the overlap test to the hierarchical structures of the objects. For detecting the collision between the objects at in-between frame, we try overlap test using the structures of a dummy and the rigid objects in addition to the test between the rigid and deformable objects. The dummy object is made from the rigid objects moving direction. When collision occurs, a deformable object must be deformed, as the object doesn't permit penetration. Self-penetration may occur during the object is deformed. It is rapidly detected between the object and a dummy object of another type. The dummy object is made from the object's deformation area between two continuous frames. We constrain the object is deformed until it is self-contacted. Our method can be applied without concerning of the shape of a object.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.11
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• pp.2677-2685
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• 2013

Car running data collected from the vehicle is a native image data and sensing data of it. Hence, it can be used as a set of objective data based on which events that took place outside the car can be analyzed and determined. In this paper, we designed and implemented a emergency situation detection system to sense, store, and analyze signals related to car movements, driver's various operation states, collision pulse, etc when a car collision accident occurs on the actual road by sensing and analyzing the car movements and driver's operation status. The suggested system provides information on the driver's reaction right before the collision, operation state of the vehicle, and physical movement. The collected and analyzed data on vehicle running can be utilized to clarify the cause of a collision accident and to handle it in a just manner. Besides, it can contribute to grasping and correcting wrong driving habits of the driver and to saving.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.6B
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• pp.538-547
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• 2004

Optical Burst Switched (OBS) networks usually employ one-way reservation by sending a burst control packet (BCP) with a specific offset time, before transmitting each data burst frame (BDF). Therefore, The quality of service may be degraded because contentions may lead to loss of BDFs. Especially, this phenomenon becomes more serious when burst size is longer. This necessitates an effective method of prevention to avoid burst collision in nodes. OBS networks can employ several methods to avoid such burst losses. One is that burst size is cut short to reduce burst loss probability during scheduling time. In this paper, we evaluate the burst generation and transmission using Sub-Carrier Multiplexting (SCM) in OBS networks. We propose an appropriate burst assembly architecture and transmission scheme based on SCM in OBS networks. The performance of SCM in OBS networks is examined in terms of number of Sub-Carriers per wavelength, burst loss probability, throughput, and total bandwidth of an optical fiber.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.250-250
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• 2019

현재 우리나라에서 이용하고 있는 소류사량 직접계측방법에는 Arnhem 소류사 채취기와 Helley-Smith 소류사 채취기 등이 있다. 하지만 이러한 방법은 현장에서 계측하기가 매우 어렵고 많은 비용과 인력, 시간이 소모되며 특히 연속적인 계측이 어려워 소류사량의 직접계측자료를 기초로 하는 연구는 거의 전무한 상태이다. 이에 대한 대안으로 최근 국내외에서는 마이크로폰을 내장한 금속관에 토사가 충돌 시 발생하는 음향데이터를 수집 및 분석하여 소류사량을 계측하는 간접계측방법 하이드로폰을 사용하고 있다. 하이드로폰 시스템의 대부분이 증폭채널방법을 사용하고 있는데 이러한 방법은 개별입자에 대한 음향특성을 반영하기에는 다양한 크기를 가지는 소류사 입자에 대한 음향신호를 하나의 임계치 기준으로 필터링 하기 때문에 한계가 있다. 즉 기존의 방법은 소류사량의 상대적인 크기만 추정할 수 있을 뿐 소류사량을 정량화할 수 없다. 따라서 본 연구는 소류사가 이동할 때 발생하는 충돌음향을 신호 처리하여 소류사량을 추정하는 계측기기인 하이드로폰을 이용하여 기존 소류사량의 계측 방법을 개선하기 위한 실험적 연구를 수행하였다. 실험은 하이드로폰을 적용한 수리모형 실험 장치를 구축하고 현장에서 취득한 시료 중 대표시료로 분류된 두 가지 입자에 대해서 수리 조건 변화에 따른 충돌음향을 계측 및 분석하였다. 연구결과 입자크기 및 수리조건 변화에 따른 하이드로폰의 인지특성을 파악할 수 있었고 소류사 충돌음과 연관성 높은 주파수 대역을 분리하여 소류사 충돌음을 판독할 수 있는 계측알고리즘을 제시하였다. 특히 본 연구에서 제안하는 하이드로폰 충돌음향 분석법 B-P Method는 낮은 유속과 작은 입경의 소류사의 조건일 때 타 방법에 비해 제안된 B-P Method가 높은 판독률을 보여주었다.

• The Transactions of the Korea Information Processing Society
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• v.1 no.2
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• pp.172-183
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• 1994

In the multidatabase systems(MDBS), local autonomy and global consistency are important issues. Global consistency could be maintained by a global concurrency control algorithm and a global recovery algorithm. In this thesis, we propose a global concurrency control algorithm to ensure local autonomy and to guarantee global serializability, and a global recovery algorithm which is possible to recover the multudatabase from any failures. The proposed global concurrency control algorithm uses bottom-up approach, based on three-level transaction processing model. It can produce a local history that the execution order of subtransactions is identical to their serialization order by using dummy-operations in the server when an indirect conflict is caused between subtransactions due to local transactions. At the global module, it can efficiently validate global serializability of global transactions by checking global serializability only for the global transactions which conflict with each other.

• Journal of KIISE:Information Networking
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• v.35 no.4
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• pp.337-344
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• 2008

Underwater acoustic sensor networks exhibit characteristics such as high propagation delay and low data rates, which are different from those of terrestrial wireless networks. Therefore, the conventional protocols used in wireless networks can be restrictive and inefficient when applied to underwater acoustic sensor networks. In this paper, we propose a medium access control protocol (MAC) to enhance the energy efficiency and throughput in underwater acoustic sensor networks. The proposed protocol employs a slot-based competition mechanism that reserves a time slot to send a data packet in advance. In the proposed protocol, collision between nodes can occur due to competition to obtain a slot. However, the proposed protocol minimizes the collisions between nodes because the nodes store the reservation information of the neighboring nodes, this reduces unnecessary energy consumption and increases throughput. We perform a simulation to evaluate the performance of the proposed protocol with regard to the energy consumption, the number of collision, channel utilization, throughput and transmission delay. We compare the proposed protocol with the conventional protocol, and the performance results show that the proposed protocol outperforms the conventional protocol.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11C
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• pp.64-74
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• 2001

In this paper, a dynamic minislot reservation protocol(DMRP) is proposed and analyzed to improve the performance of the multicast traffic processing in wavelength division multiplexing(WDM) networks. For the proposed protocol analysis, the WDM network architecture with a passive star coupler is used. One pair of transceiver is used for a control channel and the ocher pair of transceiver with one fixed transmitter and one tunable receiver are used for data transmission. In this protocol. the packets which fail to have successful transmission in the present time slot due to data channel and destination collisions, have priority to have successful reservation in the contention-less minislots of the next time slot. Therefore, protocols have improved the throughput and the system delay performance caused by the reduced probabilities of control channel contentions and destination collisions probability. Today, the efficient protocol that can handle the various types of data traffic is needed. As results, the DMRP is useful to improve the performance of throughput and system delay characteristics regardless of the kinds of traffic.