• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.12
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• pp.2328-2339
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• 1994

The PBS(Partial Buffer Sharing) space priority mechanism is one of priority control methods which may improve the performance of a single server queueing system when mixed traffic with different performance requirements is applied to the system. This paper analyzes the cell loss behavior of PBS assuming loss sensitive traffic and delay sensitive traffic are applied to the system. To derive the successive cell loss probabilities. which are an important performance measure of realtime traffic, we develop a recursive algorithm. Performance results show the successive cell loss probabilities obtained by our method are lager than the probabilities derived from an independent cell loss assumption. These results may indicate the limitation of PBS for realtime traffic and the increase of the admissible load with the criterion of quality of service.

• KSCI Review
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• v.1 no.2
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• pp.95-107
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• 1995

The concurrency control can be critical to the performance of transaction processing systems. Conventional locking takes the blocking phenomenon, where waiting transactions continue to hold locks and block other transactions from progressing. The proposed scheme reduces the blocking probability by deferring the blocking behavior of transactions to the later stages of their execution. The transaction execution can be divided into a nonblocking phase where transactions wait for locks but do not block other transactions and a blocking phase as in conventional locking. However data accessed during the nonblocking phase can lead to transaction abort. By properly balancing the blocking and abort effects, the proposed scheme can lead to better performance than either the conventional locking or the optimistic concurrency control(OCC) scheme at all data and resource contention levels.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.11
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• pp.675-681
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• 2014

As the recently soaring wireless traffic, small-cell techniques have been actively studied in order to support such a wireless demand for cellular wireless networks. This paper studies interference mitigation methods for random-access small-cell networks. Although inter-cell interference between small random-access cells is one of the main factors to degrade overall performance, most of the previous works focused on interference mitigation between users in each cell. To address such limitation, dynamic opportunistic interference alignment is proposed exploiting statistical characteristics of random-access. It is demonstrated by simulation that the proposed scheme outperforms the previous approach as the number of cells or the number of users in each cell increases.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.2A
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• pp.61-65
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• 2005

We propose a soft QoS-based borrowing scheme for call admission control(CAC) in DVB-RCS(Digital Video Broadcast-Return Channel via Satellite). Some of the ongoing calls temporarily and fairly release bandwidths that can be used to accommodate a new call in an overloaded satellite network. The amount of bandwidth borrowed from each call is proportional to each user's critical bandwidth ratio, one of parameters for soft QoS mechanism. Simulation results show that the proposed scheme improves the system performance in terms of call blocking probability and bandwidth utilization.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.189-189
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• 2015

본 연구는 기후변화의 영향을 고려한 포아송 강우생성모형의 일종인 MBLRP(Modified Bartlett-Lewis Rectangular Pulse)를 개발하고, 대한민국 주요 도시에 대해 향후 100년간 강우의 변화를 살펴보았다. 기존 MBLRP 모형에서 기후변화에 따른 강우량 변화를 고려할 수 있도록 GCM 모형의 강우 자료를 활용하였고, GCM 모형으로부터 발생하는 불확실성을 고려하기 위해 IPCC의 RCP(Representative Concentration Pathways) 시나리오를 모의한 16개의 GCM 모형을 사용하였다. 2007년부터 2099년까지의 미래기간을 3개의 시 구간으로 구분하고, 16개 GCM 앙상블을 사용하여 미래기간 동안 대한민국 16개 도시에 대해 1000개의 샘플을 BWA 방법을 이용하여 생성하였다. 제어기간(1973-2005) 대비 미래기간(2007-2099)의 변화율을 나타내는 FOC(factor of change)와 온도의 연별 변화율을 나타내는 SF(scaling factor)의 개념을 결합하여 미래기간에 대한 CF(correction factor)를 산정하였다. 이때 CF는 16개 도시의 연 단위 강우량 변화 비율을 월별로 나타내며, 제어기간의 월 강우 관측치와 CF를 몬테카를로 모의를 실시하여 미래기간의 강우 시나리오를 산정한다. 이를 통해 월 평균 강우량 통계치를 연 단위로 얻을 수 있으며, 월 평균 강우량이 월 평균 분산, 무강우확률, 자기상관계수와 가지는 선형 관계를 통해 강우 통계치를 산출한다. 이와 같은 강우 통계치는 가상강우생성모형인 MBLRP 모형에 입력 자료로 활용되어 월 강우량을 시 단위의 강우 시계열 자료로 생성해낸다. 최종적으로 MBLRP 모형으로 산정된 시 단위 강우 시계열은 기후변화 영향을 고려한 GCMs 앙상블로 생성된 강우 시나리오를 기반으로 산출되기 때문에 향후 수자원 분석에 활용 가능할 것이라 기대된다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.05a
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• pp.477-480
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• 2009

In the process of transmitting images, there are several different underlying causes of degradation that have been occuring. The main underlying cause of the degradation has been attributed to the noise. The most representive method of removal noise of image, which is caused by impulse noise, is using the SM filter. At edge the filter has a special feature which has a tendency to decrease. As a result, this paper we proposed the nonlinear filter using the form of mask and the probability of the impulse noise to restore the image considering edge quality in the impulse noise environment. And through the simulation, we compared with the existing methods and capabilties.

• The Journal of the Acoustical Society of Korea
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• v.29 no.2
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• pp.133-140
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• 2010

We improve the performance of cardiac disorder classification by adding new temporal features extracted from continuous heart sound signals. We add three kinds of novel temporal features to a conventional feature based on mel-frequency cepstral coefficients (MFCC): Heart sound envelope, murmur probabilities, and murmur amplitude variation. In cardiac disorder classification and detection experiments, we evaluate the contribution of the proposed features to classification accuracy and select proper temporal features using the sequential feature selection method. The selected features are shown to improve classification accuracy significantly and consistently for neural network-based pattern classifiers such as multi-layer perceptron (MLP), support vector machine (SVM), and extreme learning machine (ELM).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.9
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• pp.751-764
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• 2013

In cognitive radio ad-hoc networks, common control channel overload and packet collisions are occured due to indiscriminate broadcasting of control packets. So that the path reliability is reduced and control channel is easily saturated. In this paper, we propose a new routing algorithm considering the probability of appearance of primary user and channel status of neighbor nodes. When the source node needs to transmit a data packet to the destination, it performs route discovery process by exchanging control messages using a control channel in ADOV CR Ad-hoc networks. If any intermediate node doesn't have common data channel with previous node to transmit data, it doesn't rebroadcast control packet. And if it has common data channels with previous node, each node determines channel contribution factor with the number of common channels. Based on the channel contribution factor, each node performs different back-off broadcasting. In addition, each node controls control packet flooding by applying to proposed advanced mode using such as number of available channels and channel stability. With the proposed method, the number of control packets to find the data transmission path and the probability of collision among control packets can be decreased. While the path reliability can be increased. Through simulation, we show that our proposed algorithm reduces packet collisions in comparison with the traditional algorithm.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.36C no.7
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• pp.36-45
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• 1999

In order to control the flow of traffics in ATM networks and optimize the usage of network resources, an efficient control mechanism is necessary to cope with congestion and prevent the degradation of network performance caused by congestion. In this paper, Buffered Leaky Bucket which applies the same control scheme to a variety of traffics requiring the different QoS(Quality of Service) and Neural Networks lead to the effective buffer utilization and QoS enhancement in aspects of cell loss rate and mean transfer delay. And the cell scheduling algorithms such as DWRR and DWEDF for multiplexing the incoming traffics are enhanced to get the better fair delay. The network congestion information from cell scheduler is used to control the predicted traffic loss rate of Neural Leaky Bucket, and token generation rate and buffer threshold are changed by the predicted values. The prediction of traffic loss rate by neural networks can enhance efficiency in controlling the cell loss rate and cell transfer delay of next incoming cells and also be applied for other traffic controlling schemes. Computer simulation results performed for random cell generation and traffic prediction show that QoSs of the various kinds of traffcis are increased.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.05a
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• pp.882-885
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• 2008

무선 센서 네트워크는 저가의 한정된 자원들을 갖는 수많은 센서 노드들로 구성된다. 보편적으로 대부분의 센서들은 안전하지 않거나 제어할 수 없는 환경에 배치되며, 만일 넓은 목표 지역에 센서노드들을 무작위로 배치할 때에는 센서 노드들의 정확한 위치를 파악하기 매우 어렵다. 따라서 본 논문에서는 이러한 문제를 해결하기 위한 방안으로서 효율적인 키 분배 기법을 제안하고자 한다. 이에 제안된 기법을 통해 센서 노드들이 선-분배된 키들을 사용하여 안전한 링크를 확립한 후 근접한 이웃 노드들과 서로 정보를 교환할 수 있도록 하였다. 또한 제안된 기법에서는 센서노드의 위치 정보를 이용함으로써 노드간에 공통-키를 발견할 수 있는 확률을 높일 수 있게 하였다.