• Journal of Communications and Networks
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• 제13권5호
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• pp.463-471
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• 2011

Cooperative communications using relays in wireless networks have similar effects of multiple-input and multiple-output without the need of multiple antennas at each node. To implement cooperation into a system, efficient protocols are desired. In IEEE 802.11 families such as a/b/g, mobile stations can automatically adjust transmission rates according to channel conditions. However throughput performance degradation is observed by low-rate stations in multi-rate circumstances resulting in so-called performance anomaly. In this paper, we propose active relay-based cooperative medium access control (AR-CMAC) protocol, in which active relays desiring to transmit their own data for cooperation participate in relaying, and it is designed to increase throughput as a solution to performance anomaly. We have analyzed the performance of the simplified AR-CMAC using an embedded Markov chain model to demonstrate the gain of AR-CMAC and to verify it with our simulations. Simulations in an infrastructure network with an IEEE 802.11b/g access point show noticeable improvement than the legacy schemes.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2004년도 춘계학술발표대회
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• pp.1521-1524
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• 2004

기존 액티브 네트워크의 대표적인 실행환경에는 Active Network Transfer System(ANTS)와 Active Signaling Protocol(ASP)가 있다. ANTS 실행환경은 중간 노드에서 수행될 코드를 패킷에 포함시켜 전달하는 코드 분배 방식을 통하여 프로토콜을 제공한다. 따라서 패킷으로 전달할 수 있는 코드의 크기에 한계가 있으므로 복잡한 형태의 서비스를 제공 할 수 없으며, 프로토콜 및 응용들은 완전히 분리되어 동작함으로써 상호간의 연동 및 조합이 불가능한 단점이 있다. 반면 ASP 실행환경은 프로토콜 및 응용의 상호 연동이 가능하나 시스템 컨피규레이션과 응용들 사이의 정보교환 방식이 복잡하여 새로운 서비스의 개발 및 제공이 어렵다. 본 논문에서는 이러한 기존 실행환경의 단점을 개선하고 프로토콜을 기능 및 알고리즘별로 구현한 마이크로 프로토콜을 동적으로 조합함으로써 사용자가 원하는 형태의 프로토콜 및 서비스를 제공하는 새로운 실행환경인 Customizable Architecture for Flexible Execution environment(CAFE) 실행환경을 설계 및 구현하였다. 또한 CAFE 실행환경을 기반으로 무선 웹 컨텐츠 서비스를 수행으로써 CAFE 실행환경의 실용성을 확인하였다.

• Nuclear Engineering and Technology
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• 제54권9호
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• pp.3283-3292
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• 2022

Based on the Deep Q-Network(DQN) algorithm of reinforcement learning, an active fault-tolerance method with incremental action is proposed for the control system with sensor faults of the once-through steam generator(OTSG). In this paper, we first establish the OTSG model as the interaction environment for the agent of reinforcement learning. The reinforcement learning agent chooses an action according to the system state obtained by the pressure sensor, the incremental action can gradually approach the optimal strategy for the current fault, and then the agent updates the network by different rewards obtained in the interaction process. In this way, we can transform the active fault tolerant control process of the OTSG to the reinforcement learning agent's decision-making process. The comparison experiments compared with the traditional reinforcement learning algorithm(RL) with fixed strategies show that the active fault-tolerant controller designed in this paper can accurately and rapidly control under sensor faults so that the pressure of the OTSG can be stabilized near the set-point value, and the OTSG can run normally and stably.

• Structural Engineering and Mechanics
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• 제30권6호
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• pp.679-698
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• 2008

On marine vessels, delicate instruments such as navigation radars are normally mounted on ship masts. However the vibrations at the top of mast where the radar is mounted often cause serious deterioration in radar-tracking resolution. The most serious problem is caused by the rotational vibrations at the top of mast that may be due to wind loading, inertial loading from ship rolling and base excitations induced by the running propeller. This paper presents a method of semi-active vibration control using magneto-rheological (MR) dampers to reduce the rotational vibration of the mast. In the study, the classical optimal control algorithm, the independent modal space control algorithm and the double input - single output fuzzy control algorithm are employed for the vibration control. As the phenomenological model of an MR damper is highly nonlinear, which is difficult to analyse, a back- propagation neural network is trained to emulate the inverse dynamic characteristics of the MR damper in the analysis. The trained neural network gives the required voltage for each MR damper based on the displacement, velocity and control force of the MR damper quickly. Numerical simulations show that the proposed control methods can effectively suppress the rotational vibrations at the top of mast.

• Journal of Mechanical Science and Technology
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• 제16권12호
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• pp.1633-1642
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• 2002

Uninterrupted power supply has become indispensable during the maintenance task of active electric power lines as a result of today's highly information-oriented society and increasing demand of electric utilities. The maintenance task has the risk of electric shock and the danger of falling from high place. Therefore it is necessary to realize an autonomous robot system using electro-hydraulic manipulator because hydraulic manipulators have the advantage of electric insulation. Meanwhile it is relatively difficult to realize autonomous assembly tasks particularly in the case of manipulating flexible objects such as electric lines. In this report, a discrete event control system is introduced for automatic assembly task of electric lines into sleeves as one of the typical task of active electric power lines. In the implementation of a discrete event control system, LVQNN (linear vector quantization neural network) is applied to the insertion task of electric lines to sleeves. In order to apply these proposed control system to the unknown environment, virtual learning data for LVQNN is generated by fuzzy inference. By the experimental results of two types of electric lines and sleeves, these proposed discrete event control and neural network learning algorithm are confirmed very effective to the insertion tasks of electric lines to sleeves as a typical task of active electric power maintenance tasks.

• 한국해양공학회지
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• 제20권5호
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• pp.1-8
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• 2006

Offshore structures are subjected to wave, wind, and earthquake loads. The failure of offshore structures can cause sea pollution, as well as losses of property and lives. Therefore, safety of the structure is an important issue. The reduction of the dynamic response of offshore towers, subjected wind generated random ocean waves, is a critical problem with respect to serviceability, fatigue life and safety of the structure. In this paper, a structural control method is proposed to control the vibration of offshore structures by the probabilistic neural network (PNN). The state vectors of the structure and control forces are used for training patterns of the PNN, in which control forces are prepared by linear quadratic regulator (LQR) control algorithm. The proposed algorithm is applied to a fixed offshore structure under random ocean waves. Active control of the fixed offshore structure using the PNN control algorithm shows good results.

• 한국군사과학기술학회지
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• 제14권1호
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• pp.123-131
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• 2011

In this paper, modeling and design of a distributed detection system are considered for an active sonar sensor network. The sensor network has a parallel configuration and it consists of a fusion center and a set of receiver nodes. A system with two receiver nodes is considered to investigate a theoretical aspect of design. To be specific, AND rule and OR rule are considered as the fusion rules of the sensor network. For the fusion rules, it is shown that a threshold rule of each sensor node has uniformly most powerful properties. Optimum threshold for each sensor is obtained that maximizes the probability of detection given probability of false alarm. Numerical experiments were also performed to investigate the detection characteristics of a distributed detection system with multiple sensor nodes. The experimental results show how signal strength, false alarm probability, and the distance between nodes in a sensor field affect the system detection performances.

• 한국정보통신학회논문지
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• 제14권9호
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• pp.2040-2048
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• 2010

현대 사회에서는 정보 시스템을 이용한 업무의 편의성과 효율성은 높아지고 있지만, 네트워크의 발달로 인한 악성코드, 시스템 해킹, 내부자 정보유출 등의 역기능이 날로 대두되고 있다. 이로 인하여 시스템의 복구와 관리에 막대한 인력과 비용이 소요되고 있다. 기존의 시스템은 두 가지 측면에서 바이러스, 악성코드를 감시하고 치료하는 보안 솔루션과 컴퓨터의 시스템감시, 관리, 복구, 백업 등 유지보수를 하는 네트워크 관리 솔루션으로 나눌 수 있다. 본 논문에서는 Active Write Filter 메커니즘, NFS기반의 기술을 응용하여 기존 시스템의 사용자 데이터 등의 보전문제점을 보완하여 정보보호 및 불법 저작물 등 지적재산권의 문제 해결이 가능한 시스템을 설계하였다.

• 한국컴퓨터정보학회논문지
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• 제12권3호
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• pp.177-183
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• 2007

인터넷에서 종단간 혼잡제어 방식을 지원하기 위해 제안된 라우터에서 큐에 적용되어 패킷을 폐기하는 방법으로 능동적 큐 관리(AQM;Active queue management) 방법이 적용되고 있다. IETF에서 제안된 AQM 알고리즘은 RED(Random Early Detection) 방식이다. RED 알고리즘은 망의 높은 처리율과 낮은 평균 지연을 얻기 위해 네트워크에서 운영된다. 하지만 평균 큐 길이는 네트워크의 혼잡 레벨에 민감한 결과를 갖게 된다. 본 논문에서는 RED 성능에 영향을 미치는 파라메터의 민감성을 감소시키고 성능을 개선시키기 위해 정련된 적응 RED(RARED; Refined Adaptive RED)를 제안한다. 시뮬레이션을 통해 네트워크 전체의 개선된 RARED 알고리즘을 관찰하고 RARED가 패킷 폐기율의 감소와 성공적인 전송률의 개선이 이루어짐을 보여준다.

• 한국정보통신학회논문지
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• 제8권3호
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• pp.733-739
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• 2004

최근 차량의 안전에 관한 기술은 전자 및 제어분야의 기술이 접목되어 능동 안전 시스템이 개발되고 있다. ABC(Active Body Control), ABS(Antilock Brake System), ACC(Adaptive Cruise Control) 기술이 대표적이라 할 수 있다. 이러한 기술은 전자 제어 장치를 기반으로 하고 있으며, 차량 네트워크로 데이터를 실시간으로 공유한다. 따라서 본 논문에서는 기계식으로 구성되어 수동으로 작동되는 주차 브레이크 장치를 차량용 네트워크인 CAN를 이용하여 자동으로 작동될 수 있도록 제어 알고리즘 구현과 응용 어플리케이션을 구현한다. 또한 구현되는 제어시스템을 통해 기존의 차량내 전자제어시스템과 통합 운영할 수 있는 가능성을 확인한다.