• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4B
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• pp.270-277
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• 2006

In the wireless adaptive modulation and coding(AMC) systems, the modulation type of user's connection can be changed dynamically. and the ongoing connection might fail due to the change of modulation. In this paper, we approach the AMC-induced CAC problem by focusing on the guaranteed connection. Three kinds of calls, new, handoff, and modulation-changed calls, are considered. We propose a modified guard channel CAC scheme that allows the modulation-changed and handoff calls to use the guard channel. Then we analyze a Markov model for the CAC scheme with long-term AMC in mind. According to the simulation results, the proposed approach reduces the call dropping probability for modulation-changed calls, which suggests the threshold of guard channels can be determined based on the proposed approach.

• Journal of Korean Society of Transportation
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• v.21 no.5
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• pp.19-29
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• 2003

The purpose of this study is to analyse the effect of the parking information on the waiting time using the simulation method. Stated Preference survey has been implemented to construct the parking lot choice model. A queue simulation is carried out to investigate the effect of various parking information on the waiting time. The results show that providing parking information is likely to increase the utilization of parking place and to decease the waiting time of individual vehicle. Furthermore, as the parking demand increases, the detailed and quantitative parking information such as "5 minutes delay" is more effective than qualitative parking information such as "available".

• Journal of the Korean Association of Geographic Information Studies
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• v.9 no.3
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• pp.14-24
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• 2006

There are many problems and limits in equipments being used for traffic-volume analysis in the country. And traffic-volume information acquired through existing equipments is not provided in real-time. In the case of urban, there are limits on guarantee of trust on comprehending a appropriate road-volume because of difficulty on analyzing traffic-volume density and time series. And it is difficult to applicate in deciding a road policy as existing equipments don't provide the control information of traffic-flow. Therefore, it is necessary to build a road-flow policy rapidly and accurately through the road-flow information that analyze post-processed statistics data using traffic-flow investigation based on real time. In this study, we developed TICS(Traffic Information Collection System) based on GPS which could transmit traffic information transformed from car location information to traffic control center. And we developed TCS(Traffic Control System) based on Web GIS, which could manage and analyze transmitted traffic information, and it could offer handled road-flow information to Web-site in realtime.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6B
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• pp.517-526
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• 2006

In order to achieve high capacity and reliable link quality in wireless communication, the significant efforts should be concentrated on mitigating interference between cells. To solve the interference problem, the newly introduced concept of a Distributed Wireless Communication System (DWCS) can provide the capability of joint control of the signals at multiple cells. This paper proposes a new concept of virtual cell: the Dual Virtual Cell (DVC), and also proposes DVC employment strategy based on DWCS network. The proposed system manages two kinds of virtual cell. One is the Active Virtual Cell which exists for user's actual data traffic and the other is the Candidate Virtual Cell which contains a set of candidate antennas to protect user's link quality from performance degradation or interruption. The proposed system constructs DVC by using antenna selection method. Also, for multi-user high-rate data transmission, the proposed system introduces multiple antenna technology to get a spatial and temporal diversity gam and exploits space-Time Trellis Codes known as STTC to increase a spectral efficiency.

• Journal of IKEEE
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• v.22 no.3
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• pp.733-737
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• 2018

In this paper, we describe the effects on the power system by adding renewable generator. In order to examine the stability of the system, the system analysis was performed using the PSS/E software. We confirmed whether occur the line overload of system through the load flow analysis and contingency analysis. and confirmed whether exceed of fault current using the fault current analysis. Dynamic stability of the system is analyzed through dynamic simulation. The analysis of the system according to the addition of the renewable generator was carried out according to the power system reliability and electricity quality maintenance standard.

• Journal of KIISE:Computer Systems and Theory
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• v.36 no.5
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• pp.360-370
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• 2009

Using solar power in wireless sensor networks requires a different approach to energy optimization from networks with battery-based nodes. Solar energy is an inexhaustible supply which can potentially allow a system to run forever, but there are several issues to be considered such as the uncertainty of energy supply and the constraint of rechargeable battery capacity. In this paper, we present SolarSS: a reliable storage system for solar-powered sensor networks, which provides a set of functions, in separate layers, such as sensory data collection, replication to prevent failure-induced data loss, and storage balancing to prevent depletion-induced data loss. SolarSS adapts the level of layers activated dynamically depending on solar energy availability, and provides an efficient resource allocation and data distribution scheme to minimize data loss.

• The Journal of the Korea Contents Association
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• v.7 no.6
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• pp.69-78
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• 2007

In recent years, embedded mobile systems have been expanding their application domains from embedded portable devices which only execute a specialized application such as MP3 player or digital camcoder to digital convergence devices which execute more complicated applications converged various functionalities such as video and audio play, digital dictionary, DMB, games, phone, etc. As it requires the increasing hardware performance such as more faster CPU and more larger RAM, display, disk size, it has brought about a corresponding increase in power consumption. However, coupled with relatively small gains in battery capacity over recent years, the importance of software architecture including intelligent power management has become paramount. In this paper, we have ported UbiFOSTM with energy saving techniques on the ARM9-based MBA2440 platform. For energy savings, we adapted the dynamic power management and the device power management schemes based on monitoring workload. Experimental results with some well-known applications show that proposed low power technique could save energy up to 24 %.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11C
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• pp.33-42
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• 2001

We consider a model describing large scale performance of multiservice networks supporting both constant- and adaptive-rate services. As the number of constant-rate connection changes over time in multiservice networks, the available bandwidth for adaptive-rate connections changes as well. We estimate the available bandwidth for adaptive-rate service in a dynamically changing traffic environment based on Erlang fixed point equation and Little\`s law. The bandwidth allocation for adaptive-rate service is determined by the max-min fairness criterion. We find an upper bound on the average minimum throughput for adaptive-rate service, and 7how that the bound is achieved in large-capacity networks. This is verified using network examples. Since max-min fair allocation may not maximize the total throughput or revenue in a network, we consider adjustments via network level priority schemes to increase efficiency.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2002.05a
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• pp.371-377
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• 2002

근래 정보 시스템의 흐름은 생산 분야의 관리뿐만 아니라, 고객과의 관계를 중시하는 CRM(Costumer Relation Management)과 공급업체와의 협업 관계를 유지하는 eProcurement시스템에 초점을 맞추고 있다. 즉, 기존에는 단위 생산 시스템의 관리에 중점을 두었지만 최근에는 그 외부 요소들에 대한 관리의 중요성을 인식하게 되었고 이를 통징하여 공급망 관리(SCM Supply Chain Management)라고 한다. 본 논문에서는 공급망 관리에서 필요한 생산 계획수립 문제에 대해서 살펴본다. 특히 고객과의 관계에서 중요한 기능인 납기 회답을 지원하는 생산 계획 수립의 실행 주기에 대해서 살펴본다. 첫째, 단위 생산 시스템에서 사용하는 작업지시(Work Order)와 구매 지시(Purchase Order)를 생성하는 정규계획 모델에 대해서 설명한다. 정규계획 모델에서 필요로 하는 정적 정보와 동적 정보의 수집 및 계획의 실행을 담당하는 ERP 시스템과의 관계에 대해서 정의하고 정규계획 모델의 운영 주기를 정의한다. 둘째, 정규계획 모델과 상호 협조하면서 납기 회답을 지원하는 납기회답 모델의 설계에 대해서 살펴본다. 정규계획 모델과 달라지는 입력 부분의 정의와 정규계획 모델과의 상호 관계를 정의한다. 다음으로, 정해진 납기를 지키기 위해서 정규계획 모델에서 고려래야 하는 요소에 대해서 알아본다. 가장 중요한 것으로 작업 부하와 생산 용량을 고려한 계획 일자(PST)와 고객 납기와 제조 공정 LT를 고려한 계획 일자(LPST)중 최소값을 원자재의 납기 일자로 사용하는 것을 제안한다. 동시에 신규 구매 지시 계획을 생성하기보다는 기존에 발생된 구매 지시의 우선적 사용과 기존 구매 지시의 납기 일자를 고객 납기에 가장 잘 맞출 수 있도록 변경하는 방안을 제시한다. 이렇게 함으로써 최대한 고객 납기를 만족하도록 계획을 수립할 수 있게 된다. 본 논문에서 제시하는 계획 모델을 사용함으로써 고객 주문에 대한 대응력을 높일 수 있고, 계획의 투명성으로 인한 전체 공급망의Bullwhip effect를 감소시킬 수 있는 장점이 있다. 동시에 이것은 향후 e-Business 시스템 구축을 위한 기본 인프라 역할을 수행할 수 있게 된다.

• Journal of KIISE:Information Networking
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• v.30 no.2
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• pp.155-166
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• 2003

Mobile computing becomes a new issue of researches in computing due to the advances of mobile equipment and the connection with Internet. In mobile environment, there are many constraints such as limited bandwidth, intermittent disconnection, limited battery life, and so on. By these reasons, broadcasting has been generally used to disseminate data efficiently by the mobile applications. This paper proposes an adaptive broadcasting method which logically divides broadcast channel into the periodic broadcast channel and the on-demand broadcast channel and dynamically assigns the bandwidths of both channel. The former disseminates data that are selected based on both the popularity and the size of each datum, the latter disseminates data that are selected based on the requests of mobile clients. When selecting data to be disseminated, the proposed broadcasting method considers the mobility of a mobile client and also considers the size of each datum by using SF(size factor) proposed in this paper. This paper also evaluates the proposed broadcasting method by measuring the energy expenditure of mobile client in experiments.