• Journal of Information Processing Systems
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• 제2권2호
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• pp.88-94
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• 2006

In wireless cellular networks, previous researches on admission control policies and resource allocation algorithm considered the QoS (Quality of Service) in terms of CDP (Call Dropping Probability) and CBP (Call Blocking Probability). However, since the QoS was considered only within a predetermined cell capacity, the results indicated a serious overload problem of systems not guaranteeing both CDP and CBP constraints, especially in the hotspot cell. That is why a close interrelationship between CDP, CBP and cell capacity exists. Thus, it is indispensable to consider optimal cell capacity guaranteeing multiple QoS (CDP and CBP) at the time of initial cell planning for networks deployment. In this paper, we will suggest a distributed determination scheme of optimal cell capacity guaranteeing both CDP and CBP from a long-term perspective for initial cell planning. The cell-provisioning scheme is performed by using both the two-dimensional continuous-time Markov chain and an iterative method called the Gauss-Seidel method. Finally, numerical and simulation results will demonstrate that our scheme successfully determines an optimal cell capacity guaranteeing both CDP and CBP constraints for initial cell planning.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권7호
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• pp.1721-1736
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• 2013

Black and gray hole attack is one kind of routing disturbing attacks and can bring great damage to the network. As a result, an efficient algorithm to detect black and gray attack is important. This paper demonstrate an adaptive approach to detecting black and gray hole attacks in ad hoc network based on a cross layer design. In network layer, we proposed a path-based method to overhear the next hop's action. This scheme does not send out extra control packets and saves the system resources of the detecting node. In MAC layer, a collision rate reporting system is established to estimate dynamic detecting threshold so as to lower the false positive rate under high network overload. We choose DSR protocol to test our algorithm and ns-2 as our simulation tool. Our experiment result verifies our theory: the average detection rate is above 90% and the false positive rate is below 10%. Moreover, the adaptive threshold strategy contributes to decrease the false positive rate.

• 한국정보과학회논문지:정보통신
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• 제27권1호
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• pp.39-47
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• 2000

이 논문은 이동통신 시스템의 제어국에 순간적으로 가해지는 다량의 입력 메시지의 신뢰성있는 제어를 위하여 이동통신 시스템의 제어국에서 처리하는 입력 메시지를 두 가지 형태로 구분하여 메시지가 갖는 특성을 분석하였다. 메시지는 호 접속 관련 메시지와 운용 및 유지보수 관련 메시지로 구분하였으며, M/M/1/K 큐잉모델을 이용하여 메시지별로 입력 메시지의 손실 확률, 큐의 평균 길이, 프로세스 관리기(서버)의 점유율, 큐의 평균 대기 시간을 분석하였다. 그리고 과밀한 메시지 입력에 따른 부하 제어 시 두 메시지에 대한 성능 비교를 컴퓨터 시뮬레이션을 통하여 실시하였다.

• 한국기계가공학회지
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• 제16권3호
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• pp.113-118
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• 2017

In this paper, a study on the performance evaluation of a cycloid reducer for remote weapons systems is presented. Reduction gears applied to remote weapons vehicles need to be compact and capable of large torque transmissions as well as require structural optimization, high load capacity, and high precision position control. To meet these requirements, a cycloid reducer with low backlash, high precision, high overload capability, high rigidity, and high efficiency is required. Thus, a cycloid reducer with a reduction ratio of 127:1, backlash of 1 arcmin (1/60 deg) or less, and reduction gear efficiency of 70% or more, which are the design requirements for a remote weapons system, was designed utilizing a design and analysis program (HEXAGON) for gear engineering. To confirm the performance of the cycloid reducer, the hardness of the main components of the manufactured cycloid reducer, reduction ratio, and efficiency were measured.

• 디지털융복합연구
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• 제12권2호
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• pp.249-255
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• 2014

RFID 시스템은 교통, 출입통제 비롯한 여러 분야에서 활용되고 있다. RFID 시스템에 대한 보안위협 또한 증가하여 정보보안에 대한 연구가 진행되고 있다. 본 논문에서는 행렬기반 RFID 인증 프로토콜을 제안하고 기존에 제안된 프로토콜과 효율성을 비교하고 안전성을 분석한다. 제안된 인증 프로토콜은 도청, 재전송 등의 공격에 안전하며, 서버의 계산량을 줄여 성능면에서 효율이 우수한 장점을 갖는다.

• 전자공학회논문지A
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• 제31A권2호
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• pp.26-38
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• 1994

We demonstrate a repeatless transmission of 2.5 Gbps digital signal over 98 km opticla filbers using optical transmitter and optcial receiver which are designed and implemented using commercially available devices. The optical transmitter is realized by using a distributed feedback(DFB) laser. Temperature of the laser is thermoelectrically stabilized and the output optical power is also stabilized by using negative feedback. The output power of the transmitter is 0 dBm. The optical receiver consists of an InGaAs avalanche photodiode, a preamplifier. an automatic gain control amplifier, and a clock/data regenerator. We find an optimum decision threshold that gives the best receiver sensitivity form the measured V curve. The best sensitivity is -35.5dBm( BER-1*10S010T, PRBS=2S023T -1 ) and the overload power is -9 dBm. Finally, we achieve error free optical transmission with 98 km optical fibers. The exinction ration penalty of 2 dB. the chromatic dispersion penalty of 1 dB, and the total power penalty of 3.0 dB are measured. These results satisfy CCITT recommendation.

• 한국항행학회논문지
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• 제18권4호
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• pp.268-277
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• 2014

비행계획 연관은 안전하고 신속한 관제 업무를 위해 매우 중요한 기능이다. 본 논문에서는 레이더 감시자료 중 MRT 데이터와 비행계획을 연관시키는 과정에서 발생하는 네트워크 부하를 최소화함으로써 전체적인 항공교통 자동화 시스템의 성능을 향상을 도모할 수 있는 CWP MRT 처리 모듈을 구현하였다. 구현 모듈은 분산형 연관 방식을 적용함으로써 항공교통관제 자동화 시스템의 효율성과 안전성을 동시에 확보하며, 인코딩 방식의 비행계획 연관 MRT 데이터 포맷을 사용함으로써 네트워크 사용률을 감소시킨다. 구현 모듈은 독립형 연관 방식에 비해 네트워크 사용량이 8.54~12.11% 낮았으며, 네트워크 공정성이 8.37~11.27% 높은 것을 확인하였다.

• ETRI Journal
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• 제19권3호
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• pp.186-201
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• 1997

In this paper, a home location register (HLR) for CDMA mobile communication system (CMS) is introduced. It stores the mobile station (MS) subscribers locations and supplementary service information. Call processing procedures for HLR are developed to receive and store subscriber's location coming from mobile exchange (MX) during the location registration, and to transfer subscriber's location and supplementary service information to the MX during the mobile-terminated call setup. For fast call processing by increasing database access speed, a memory-resident database management system is devised. For Easy and secure HLR operation, administration and maintenance functions and overload control mechanisms are implemented. Designed HLR hardware platform is expandable and flexible enough to reallocated software blocks to any subsystems within the platform. It is configurable according to the size of subscribers. An authentication center (AC) is developed on the same platform. It screens the qualified MS from the unqualified. The calls to and from the unqualified MS are rejected in CMS. To authenticate the MS, the AC generates a new authentication parameter called "AUTHR" using shared secret data (SSD) and compared it with the other AUTHR received from the MS. The MC also generates and stores seed keys called "A-keys" which are used to generate SSDs. The HLR requirements, the AC requirements, software architecture, hardware platform, and test results are discussed.

• 전력전자학회논문지
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• 제25권5호
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• pp.369-375
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• 2020

Distribution energy resources have been increasing in recent years. However, output power is limited for distribution network stability. This study proposes an active distribution network that can reconfigure distribution lines by using an active phase controller. A conventional distribution network has a fixed structure, whereas an active distribution network has a variable structure. Therefore, the latter can increase the output power of distribution energy resources and decrease the overload of distribution line facilities. An active phase controller has two operation modes for minimizing circulating current during dynamic reconfiguration. In this study, voltage and current control algorithms are proposed for active phase controllers. The simulation of the proposed methods for active phase controllers is performed using PSIM software.

• ETRI Journal
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• 제28권3호
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• pp.282-290
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• 2006

In vertically overlaid cellular systems, a temporary traffic concentration can occur in a hot-spot area, and this adversely affects overall system capacity. In this paper, we develop an adaptive hot-spot operating scheme (AHOS) to mitigate the negative effects from the nonuniform distribution of user location and the variation in the mixture of QoS requirements in orthogonal frequency division multiple access downlink systems. Here, the base station in a macrocell can control the operation of picocells within the cell, and turns them on or off according to the system overload estimation function. In order to determine whether the set of picocells is turned on or off, we define an AHOS gain index that describes the number of subcarriers saved to the macrocell by turning a specific picocell on. For initiating the picocell OFF procedure, we utilize the changes in traffic concentration and co-channel interference to the neighboring cells. According to computer simulation, the AHOS has been proved to have maximize system throughput while maintaining a very low QoS outage probability under various system scenarios in both a single-cell and multi-cell environments.