• 대한전기학회논문지:시스템및제어부문D
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• 제53권7호
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• pp.501-508
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• 2004

In this paper, a coordinated scheduling algorithm is proposed to reduce end-to-end delay in distributed control of systems. For the algorithm, the analysis of practical end-to-end delay in the worst case is performed priory with considering implementation of the systems. The end-to-end delay is composed of the delay caused by multi-task scheduling of operating systems, the delay caused by network communications, and the delay caused by asynchronous timing between operating systems and network communications. Through some simulation tests based on CAN(Controller Area Network), the proposed worst case end-to-end delay analysis is validated. Through the simulation tests, it is also shown that a real-time distributed control system designed to existing worst case delay cannot guarantee end-to-end time constraints. With the analysis, a coordinated scheduling algorithm is proposed here. The coordinated scheduling algorithm is focused on the reduction of the delay caused by asynchronous timing between operating systems and network communications. Online deadline assignment strategy is proposed for the scheduling. The performance enhancement of the distributed control systems by the scheduling algorithm is shown through simulation tests.

• ETRI Journal
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• 제35권3호
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• pp.406-413
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• 2013

In this paper, an orthogonal frequency division multiple access (OFDMA)-based minimum end-to-end delay (MED) distributed routing scheme for mobile backhaul wireless mesh networks is proposed. The proposed scheme selects routing paths based on OFDMA subcarrier synchronization control, subcarrier availability, and delay. In the proposed scheme, OFDMA is used to transmit frames between mesh routers using type-I hybrid automatic repeat request over multipath Rayleigh fading channels. Compared with other distributed routing algorithms, such as most forward within radius R, farthest neighbor routing, nearest neighbor routing, and nearest with forwarding progress, simulation results show that the proposed MED routing can reduce end-to-end delay and support highly reliable routing using only local information of neighbor nodes.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 학술대회 논문집 정보 및 제어부문
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• pp.657-659
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• 2004

CAN is a serial communication bus for real-time controls and automations in distributed control systems. In distributed control systems, occasionally a sensor module and a controller are not in the same node and physically separated. In order for the signal from a sensor node to reach the controller node, the signal must travel through network. CAN has a certain capabilities to deal with real-time data. However, when many nodes on the networks try to send data on the same network, the arbitration mechanism to solve the data collision problem is necessary. This situation causes the time delay which has detrimental effects on the performance of the control systems. This paper proposes a method to solve the problem due to the time delay in distributed control system using CAN. Time delay is approximated to an element with a rational transfer function using Pade approximation and Mu~synthesis method is applied. Since time delay in the network is not constant, the time delay element is considered to be an uncertainty block with a bound. The proposed method is applied to the experimental system with CAN and proved to be effective.

• ETRI Journal
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• 제28권1호
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• pp.31-44
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• 2006

In a packet switching network, congestion is unavoidable and affects the quality of real-time traffic with such problems as delay and packet loss. Packet fair queuing (PFQ) algorithms are well-known solutions for quality-of-service (QoS) guarantee by packet scheduling. Our approach is different from previous algorithms in that it uses hardware time achieved by sampling a counter triggered by a periodic clock signal. This clock signal can be provided to all the modules of a routing system to get synchronization. In this architecture, a variant of the PFQ algorithm, called digitized delay queuing (DDQ), can be distributed on many line interface modules. We derive the delay bounds in a single processor system and in a distributed architecture. The definition of traffic contribution improves the simplicity of the mathematical models. The effect of different time between modules in a distributed architecture is the key idea for understanding the delay behavior of a routing system. The number of bins required for the DDQ algorithm is also derived to make the system configuration clear. The analytical models developed in this paper form the basis of improvement and application to a combined input and output queuing (CIOQ) router architecture for a higher speed QoS network.

• 대한전자공학회논문지TC
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• 제45권12호
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• pp.49-57
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• 2008

분산할당 OFDMA 시스템에서 순환지연 다이버시티를 적용하면 주파수 다이버시티의 증가로 인해 성능의 증대를 가져온다. 그러나 분산할당 SC-FDMA 시스템에 순환지연 다이버시티를 적용하는 것은 주파수 다이버시티의 증가로 인한 성능증대 효과와 주파수 선택적 채널로 인한 성능감소 효과를 동시에 가져온다. 본 논문에서는 이 상반되는 두 가지 효과에 대해서 논하며 분산할당 SC-FDMA 시스템에서 순환지연 다이버시티를 적용하는 것이 언제 유리하고 언제 불리한지 논의한다.

• 한국전자통신학회논문지
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• 제7권1호
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• pp.53-60
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• 2012

본 논문에서는 실시간 네트워크에서 사용될 개선된 분산 QoS 알고리듬을 제안한다. 이 알고리듬은 DCUR(delay-constrained unicast routing) 알고리듬과 같이 LC(least-cost) 패스나 LD(least-delay) 패스를 사용하고 있지만, 루프를 처리할 때에 DCUR 알고리듬보다도 더 효율적으로 처리한다. 본 알고리듬은 모든 패스를 더욱 더 효율적으로 찾을 수 있다.

• 한국안전학회지
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• 제18권3호
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• pp.154-160
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• 2003

원격지에 위치한 분산제어 시스템과 센서 데이터 또는 제어 명령을 주고받을 때에는 불확실한 시간지연이 발생한다. TCP/IP 프로토콜을 이용한 데이터 네트워크와 마찬가지로 데이터 네트워크와 디바이스 네트워크를 결합한 가상 디자이스 네트워크도 불확실한 시간지연이 내재되어 있다. 이러한 시간지연은 분산제어시스템의 성능을 저하시키고 불안전성을 야기하는 원인이 된다. 본 논문에서는 이러한 네트워크상에 내재하는 시간지연을 평가하고 부정적인 효과를 최소화하기 위하여 Smith Predictor를 적용하였다. 제안된 제어 알고리즘은 실시간 서보제어를 통하여 효과를 입증하였으며 가상 디바이스 네트워크 개념에 근거한 분산제어 시스템을 이용하여 실시간 예지보전을 수행할 때 효과가 있음을 제시하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제28권4호
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• pp.603-610
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• 2004

Time delays are included in most of actual systems, and some of which are shown as time varying. To analyze the time varying time delay system in the time domain. a useful delay module to express the function as a tool is much helpful to get corresponding outputs under given conditions. A method is proposed here to design the algorithm of time delay module for simulation or control purposes, including the problems of initializing and reallocating data in buffer. After classifying the time varying time delay into the distributed mode and lumped mode, an object to describe delay module is configured and tested under the defined input signal and given time delay variation. The simulation results show that the output of module matches reasonably with the case of real system.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 학술회의 논문집 정보 및 제어부문 B
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• pp.677-680
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• 2003

In this paper, the analysis of practical end-to-end delay in worst case is performed for distributed control system considering the implementation of the system. The control system delay is composed of the delay caused by multi-task scheduling of operating system, the delay caused by network communication, and the delay caused by the asynchronous between them. Through simulation tests based on CAN(Controller Area Network), the proposed end-to-end delay in worst case is validated. Additionally, online clock synchronization algorithm is proposed here for the control system. Through another simulation test, the online algorithm is proved to have better performance than offline one in the view of network bandwidth utilization.

• International Journal of Safety
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• 제5권2호
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• pp.6-11
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• 2006

The time delay in servo control on LonWorks/IP Virtual Device Network (VDN) is highly stochastic in nature. LonWorks/IP VDN induced time delay deteriorates the performance and stability of the real-time distributed control system and hinders an effective preventive and predictive maintenance. Especially in real-time distributed servo applications on the factory floor, timely response is essential for predictive and preventive maintenance. In order to guarantee the stability and performance of the system for effective preventive and predictive maintenance, LonWorks/IP VDN induced time delay needs to be predicted and compensated for. In this paper position control simulation of DC servo motor using Zero Phase Error Tracking Controller (ZPETC) as a feedforward controller, and Internal Model Controllers (IMC) based on Smith predictor with disturbance observer as a feedback controller is performed. The validity of the proposed control scheme is demonstrated by comparing the IMC based on Smith predictor with disturbance observer.