• Proceedings of the Korea Society for Simulation Conference
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• 1997.04a
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• pp.93-99
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• 1997

Most of the past studies on FMS scheduling problems may be classified into two classes, namely off-line scheduling and on-line scheduling approach. The off-line scheduling methods are used mostly for FMS planning purposes and may not be useful real time control of FMSs, because it generates solutions only after a relatively long period of time. The on-line scheduling methods are used extensively for dynamic real-time control of FMSs although the performance of on-line scheduling algorithms tends vary dramatically depending on various configurations of FMS. Current study is about finding a better on-line scheduling rules for FMS operations. In this study, we propose a method to create priority functions that can be used in setting relative priorities among jobs or machines in on-line scheduling. The priority functions reflect the configuration of FMS and the user-defined objective functions. The priority functions are generated from diverse dispatching rules which may be considered a special priority functions by themselves, and used to determine the order of processing and transporting parts. Overall system of our work consists of two modules, the Priority Function Evolution Module (PFEM) and the FMS Simulation Module (FMSSM). The PFEM generates new priority functions using input variables from a terminal set and primitive functions from a function set by genetic programming. And the FMSSM evaluates each priority function by a simulation methodology. Based on these evaluated values, the PFEM creates new priority functions by using crossover, mutation operation and probabilistic selection. These processes are iteratively applied until the termination criteria are satisfied. We considered various configurations and objective functions of FMSs in our study, and we seek a workable solution rather than an optimum or near optimum solution in scheduling FMS operations in real time. To verify the viability of our approach, experimental results of our model on real FMS are included.

• Journal of KIISE:Computer Systems and Theory
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• v.28 no.11
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• pp.573-580
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• 2001

When tasks access shared resources in real-time systems, the unbounded priority inversion may occur. In such cases it is impossible to guarantee the schedulability of real-time tasks. Several resource access protocols have been proposed to bound the duration of priority inversion and sufficient conditions are given to guarantee the schedulability of periodic task set. In this paper, we show an improved sufficient condition for schedulability when the dynamic priority ceiling protocol is used. Our approach exploits the fact that a lower priority task can continue to execute as far as the higher priority tasks do not miss their deadlines. This permitting execution time of the higher priority tasks for a lower priority task can be excluded from the worst-case blocking time of the higher priority tasks. Since the worst-case blocking time of tasks can be reduced, the sufficient condition for schedulability of dynamic priority ceiling protocol becomes further tight.

• The KIPS Transactions:PartA
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• v.16A no.3
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• pp.189-198
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• 2009

The traditional interrupt-based protocol processing at end hosts has two priority-inversion problems. First, low-priority packets may interrupt and delay high-priority process executionssince interrupts have the highest priority in most operating systems. Second, low-priority packet may delay high priority packets when they arrive almost simultaneously since interrupt processing is performed in a FCFS (first come, first served) order. These problems can be solved by a priority-based protocol processing policy and implementation. However, general priority-based schemes commonly have the problem of starvation and cannot support the each network flow requiring the mutually exclusive QoS since the packets are processed in the FCFS order. Therefore, the priority-based schemes are not appropriate for different QoS-demanding applications. In this paper, we present a bottom-half-based approach that relies on priority- and budget-based processing. The proposed approach allows us to solve both the starvation and priority-inversion problems, and further enables effective QoS isolation between different network connections. This feature also enables bounding the protocol processing time at an end host. We finally show through experiments that the proposed approach achieves QoS isolation and control.

• The KIPS Transactions:PartC
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• v.8C no.6
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• pp.793-805
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• 2001

In the recent priority system, high-priority packet will be served first and low-priority packet will be served when there isn\`t any high-priority packet in the system. By the way, even high-priority packet can be blocked by HOL (Head of Line) contention in the input queueing System. Therefore, the whole switching performance can be improved by serving low-priority packet even though high-priority packet is blocked. In this paper, we study the performance of preemptive priority in an input queueing switch for high speed switch system. The analysis of this switching system is taken into account of the influence of priority scheduling and the window scheme for head-of-line contention. We derive queue length distribution, delay and maximum throughput for the switching system based on these control schemes. Because of the service dependencies between inputs, an exact analysis of this switching system is intractable. Consequently, we provide an approximate analysis based on some independence assumption and the flow conservation rule. We use an equivalent queueing system to estimate the service capability seen by each input. In case of the preemptive priority policy without considering a window scheme, we extend the approximation technique used by Chen and Guerin [1] to obtain more accurate results. Moreover, we also propose newly a window scheme that is appropriate for the preemptive priority switching system in view of implementation and operation. It can improve the total system throughput and delay performance of low priority packets. We also analyze this window scheme using an equivalent queueing system and compare the performance results with that without the window scheme. Numerical results are compared with simulations.

• ETRI Journal
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• v.42 no.1
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• pp.36-45
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• 2020

A priority-based data communication approach, developed by employing cognitive radio capacity for sensor nodes in a wireless terrestrial sensor network (TSN), has been proposed. Data sensed by a sensor node-an unlicensed user-were prioritized, taking sensed data importance into account. For data of equal priority, a first come first serve algorithm was used. Non-preemptive priority scheduling was adopted, in order not to interrupt any ongoing transmissions. Licensed users used a nonpersistent, slotted, carrier sense multiple access (CSMA) technique, while unlicensed sensor nodes used a nonpersistent CSMA technique for lossless data transmission, in an energy-restricted, TSN environment. Depending on the analytical model, the proposed wireless TSN environment was simulated using Riverbed software, and to analyze sensor network performance, delay, energy, and throughput parameters were examined. Evaluating the proposed approach showed that the average delay for sensed, high priority data was significantly reduced, indicating that maximum throughput had been achieved using wireless sensor nodes with cognitive radio capacity.

• Journal of the Korean Operations Research and Management Science Society
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• v.35 no.2
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• pp.1-17
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• 2010

This paper aims to compare four operating priority rules of RMGC (Rail Mounted Gantry Crane) used in semi-automated container terminal. The four priority rules employed in this paper are FCFS (First-come-first-served), LCFS (Last-come-first-served), TOS (Turn-over-served) and NFS (Nearest-first-served). And to compare the four operating priority rules, this paper analyzed productivity of RMGC and CC (Container Crane), waiting time of YT (Yard Truck) and RT (Road Truck) in container yard, and turnaround time of RT in container terminal of each priority rule by using stevedoring simulation. As a result, NFS was evaluated as the best rule to improve the overall productivity of container terminal in terms of all criteria.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2000.10a
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• pp.259-262
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• 2000

The Cross-impact Hierarchy Process (CHP), an extended model of the Analytic Hierarchy Process(AHP) which is linked to Cross Impact Analysis(CIA), is a powerful decision making tool to assist in the ranking of large number of dependent technological alternatives. In this paper, we will describe an application of the CHP to the aerospace industry. We here conducted a questionnaire survey for S company that is one of the representative aerospace companies in Korea. A questionnaire was designed to obtain both the priority with dependence (the CHP priority) and the priority with independence (the AHP priority) in order to compare the priority derived by each of two methods. The hierarchy in this case study is concerned with priority setting for R&D area to ensure dependent aerospace design technology of the company, The result shows that there exists the difference hard to neglect between the final priorities gained by two methods.

• Journal of the Korean Institute of Landscape Architecture
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• v.24 no.1
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• pp.42-54
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• 1996

Many of urban parks which have been designated for urban planning regulation are not well developed because the priority of investment is inferior to that of other public facilities. Park development is an urgent urban policy and it is hard to decide priority among parks. Therefore, it is necessary to evaluate the priority of park development. Thus the Analytic Hierarchy Process has been introduced because it is suitable for achieving objectivity by collecting the professional opinions. The goals of park development are evaluated by AHP method and the priorities among goals are conservation of natural environment, satisfying the residents' residents' needs, population density, regional pollution, land acquisition cost, ratio of greeneries and facilities within park areas. Priority of park development is decided by the standardization of each individual inventory data and considering of the professional opinions. Among the multi-attribute judgement methods, AHP method may be the most widely used. Despite the critical evaluations of the AHP, such as limitation of the nine-point scale and the rank reversal problem, application of AHP to decide the priority of park development is suitable for actual circumstances.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.3C
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• pp.224-232
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• 2012

Priority MAC is an important issue in every communication system when we consider differentiated service applications. In this paper, we propose a mechanism to support priority MAC based on multi-parameters for IEEE 802.15.7 visible light communication (VLC). By using three parameters such as number of backoff times (NB), backoff exponent (BE) and contention window (CW), we provide priority for multi-level differentiated service applications. We consider beacon-enabled VLC personal area network (VPAN) mode with slotted version for random access algorithm in this paper. Based on a discrete-time Markov chain, we analyze the performance of proposed mechanism under non-saturation environments. By building a Markov chain model for multi-parameters, this paper presents the throughput and transmission delay time for VLC system. Numerical results show that we can apply three parameters to control the priority for VLC MAC protocol.

• The KIPS Transactions:PartA
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• v.16A no.3
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• pp.217-222
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• 2009

Priority queues can be used in applications such as scheduling, sorting, retrival based on a priority like gene searching, shortest paths computation. This paper proposes a data structure using array representation for double-ended priority queue in which insertion and deletion takes O(1) amortized time and O(logn) time, respectively. To the author's knowledge, all the published array-based data structures for double ended priority queue support O(logn) time insertion and deletion operations.