• 산업경영시스템학회지
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• 제17권32호
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• pp.63-71
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• 1994

The purpose of this paper is to describe an effective cell scheduling system for flexible manufacturing cells. Based on the FMC characteristics, cell scheduling can be defined as a dynamic modified flow shop working in a real-time system. This paper attempt to find the optimal cell scheduling when minimizing the mean flow time for n-job/m-machine problems in static and dynamic environments. Real-time scheduling in an FMC environment requires rapid computation of the schedule.

• 전기전자학회논문지
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• 제5권2호
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• pp.164-173
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• 2001

본 논문은 독립적으로 움직이면서 시간 제약을 만족시키는 새로운 내장형 실시간 시스템을 설계하며 구현하였다. 본 논문에서의 실시간 시스템 커널은 시간적인 요소를 가장 핵심으로 고려하여 설계되었다. 따라서 실시간 커널은 작은 용량을 가지며 빠르게 예측하며, 실시간 스케줄링에 요구되는 많은 변화들을 통해서 실시간 커널에 융통성을 부여한다. 제안한 실시간 커널은 경성 실시간 제약 조건인 인터럽트 지연 시간, 스케줄링의 정확성, 메시지 전달시간을 만족하기 위하여 실시간 커널에는 실시간 태스크 처리와 인터럽트 처리, 타이밍을 처리하도록 하였고 비 실시간 커널은 일반적인 태스크를 처리하도록 하였다. 제안된 실시간 시스템은 RT-Linux, QNX와 인터럽트 지연, 스케줄링 정확성, 메시지 전달시간 등을 비교 분석하여 효율성을 입증하였다.

• 대한전자공학회논문지TC
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• 제39권12호
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• pp.539-546
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• 2002

본 논문에서의 패킷 스케줄러는 무선 채널 환경에서 실시간 비디오 트래픽과 비실시간 인터넷 트래픽을 동시에 서비스한다. 그리고 실시간 트래픽에 대한 지연을 감소 시기키 위하여 누적카운터와 SIR값을 동시에 고려하는 새로운 패킷 스케줄링 알고리즘을 제안한다. 본 알고리즘에서는 실시간 트래픽을 비실시간 트래픽에 비하여 우선적으로 처리한다. 시뮬레이션 결과를 고찰할 때, 실시간 비디오 트래픽과 같이 지연성능에 민감한 서비스의 경우에는 AC(Accumulation Counter) 방식이 기존의 M-LWDF방식보다 더 적합한 알고리즘으로 관찰되었다. 본 논문에서는 HSDPA 시스템과 유사한 구조를 채택하여 시간 축으로는 프레임 주기를 가지며 동시에 코드 축으로는 OVSF 코드를 사용할 수 있는 구조를 채택하여 모의 실험을 수행하였다.

• 제어로봇시스템학회논문지
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• 제12권7호
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• pp.719-727
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• 2006

This paper proposes a new method to obtain a maximum allowable delay bound for a scheduling of networked discrete control systems and event-based scheduling method. The proposed method is formulated in terms of linear matrix inequalities and can give a much less conservative delay bound than the existing methods. A network scheduling method is presented based on the delay obtained through the proposed method, and it can adjust the sampling period to allocate same utilization to each control loop. The presented method can handle three types of data (sporadic, emergency data, periodic data and non real-time message) and guarantees real-time transmission of periodic and sporadic emergency data using modified EDF scheduling method.

• ETRI Journal
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• 제26권5호
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• pp.391-396
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• 2004

In this paper, we propose a packet scheduling discipline called packet loss fair scheduling, in which the packet loss of each user from different real-time traffic is fairly distributed according to the quality of service requirements. We consider an orthogonal frequency division multiple access (OFDMA) system. The basic frame structure of the system is for the downlink in a cellular packet network, where the time axis is divided into a finite number of slots within a frame, and the frequency axis is segmented into subchannels that consist of multiple subcarriers. In addition, to compensate for fast and slow channel variation, we employ a link adaptation technique such as adaptive modulation and coding. From the simulation results, our proposed packet scheduling scheme can support QoS differentiations while guaranteeing short-term fairness as well as long-term fairness for various real-time traffic.

• 제어로봇시스템학회논문지
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• 제16권4호
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• pp.403-410
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• 2010

The switched Ethernet has many features for real-time communications such as providing traffic isolation, large bandwidth, and full-duplex links, and so on. The switched Ethernet, however, cannot guarantee the timely delivery of a real-time message because message delay increases when collisions occurs at the output ports and message loss can even occur due to the overflow at the output buffer. Recently, many research efforts have been done to use the switched Ethernet as an industrial control network. In the industrial control network, sensors periodically sense the physical environment and transmit the sensed data to an actuator, and the periodic messages from sensors to actuators have typically real-time requirements such that those messages must be transmitted within their deadlines. This paper first suggests a feasible condition for EDF (Earliest Deadline First)-based scheduling of periodic messages on a synchronized switched Ethernet and a message scheduling algorithm which satisfies the proposed feasible condition. Pedreiras, et al. [10] suggested a feasible condition for message scheduling on the Ethernet (shared media Ethernet), but there has been no research result on the scheduling condition on the switched Ethernet until now. We compared the real-time message scheduling capacity between the Ethernet and the switched Ethernet by simulation. The simulation result shows that the message scheduling capacity of the Ethernet has almost remained constant as the number of nodes on the network increases, but, in the case of the switched Ethernet, the message scheduling capacity has increased linearly according to the number of nodes on the network.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.747-752
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• 2004

Researches about scheduling of the distributed real-time systems have been proposed. However, they have some weak points, not scheduling both sporadic and periodic tasks and messages or being unable to guaranteeing the end-to-end constraints due to omitting precedence relations between sporadic tasks. So this paper proposes a new scheduling method for distributed real-time systems consisting of sporadic and periodic tasks with precedence relations and sporadic and periodic messages, guaranteeing end-to-end constraints. The proposed method is based on a binary search-based period assignment algorithm, an end-to-end laxity-based priority assignment algorithm, and three kinds of schedulability analysis, node, network, and end-to-end schedulability analysis. In addition, this paper describes the application model of sporadic tasks with precedence constraints in a distributed real-time system, shows that existing scheduling methods such as Rate Monotonic (RM) scheduling are not proper to be applied to the system having sporadic tasks with precedence constraints, and proposes an end-to-end laxity-based priority assignment algorithm.

• 한국멀티미디어학회논문지
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• 제8권12호
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• pp.1589-1596
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• 2005

The imprecise real-time system provides flexibility in scheduling time-critical tasks. Most scheduling problems of satisfying both 0/1 constraint and timing constraints, while the total error is minimized, are NP complete when the optional tasks have arbitrary processing times. Liu suggested a reasonable strategy of scheduling tasks with the 0/1 constraint on uniprocessors for minimizing the total error. Song et al suggested a reasonable strategy of scheduling tasks with the 0/1 constraint on multiprocessors for minimizing the total error. But, these algorithms are all off-line algorithms. On the other hand, in the case of on line scheduling, Shih and Liu proposed the NORA algorithm which can find a schedule with the minimum total error for a task system consisting solely of on-line tasks that are ready upon arrival. But, for the task system with 0/1 constraint, it has not been known whether the NORA algorithm can be optimal or not in the sense that it guarantees all mandatory tasks are completed by their deadlines and the total error is minimized. So, this paper suggests an optimal algorithm to search minimum total error for the imprecise on-line real-time task system with 0/1 constraint. Furthermore, the proposed algorithm has the same complexity, O(N log N), as the NORA algorithm, where N is the number of tasks.

• Journal of Computing Science and Engineering
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• 제9권2호
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• pp.108-117
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• 2015

Interrupt handling is generally separated from process scheduling. This can lead to a scheduling anomaly and priority inversion. The processor can interrupt a higher priority process that is currently executing, in order to handle a network packet reception interruption on behalf of its intended lower priority receiver process. We propose a new network interrupt handling scheme that combines interrupt handling with process scheduling and the priority of the process. The proposed scheme employs techniques to identify the intended receiver process of an incoming packet at an earlier phase. We implement a prototype system of the proposed scheme on Linux 2.6, and our experiment results show that the prototype system supports the predictable real-time behavior of higher priority processes even when excessive traffic is sent to lower priority processes.

• 산업경영시스템학회지
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• 제21권47호
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• pp.35-45
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• 1998

Scheduling problem in Flexible Manufacturing Systems(FMS) is complex because of various situation of Manufacturing Systems. Especially, in case of short-term scheduling demanding high efficiency, low cost at short-period, efficient scheduling is a serious problem. To solve this problem, many dispatching rules are developed. But, it leave much to be desired, because real situation in shop floor is complex and real-time scheduling is needed in real manufacturing shop floor. In this paper, search algorithm that allocate different dispatching rules to each machine is presented to complement lack of dispatching rule and develop practical real-time scheduling system. The search algorithm is described in detail. First, algorithm detect machine breakdown, evaluate each dispatching rule. dispatching rules for each machine meeting performance criteria are ranked. The algorithm selects new dispatching nile for bottleneck machine. The effectivenes and efficiency of the mixed dispatching rule and search algorithm is demonstrated.