Cyclic Scheduling Research Articles

Job system generation in grid taking into account user preferences

Distributed computing environments like Grid are characterized by heterogeneity, low cohesion and dynamic structure of computing nodes. This is why the task of resource scheduling in such environments is complex. Different approaches to job scheduling in grid exist. Some of them use economic principles. Economic approaches to scheduling have shown their efficiency. One of such approaches is cyclic scheduling scheme which is considered in this paper. Cyclic scheduling scheme takes into account the preferences of computing environment users by means of an optimization criterion, which is included in the resource request. Besides, the scheme works cyclically by scheduling a certain job batch at each scheduling step. This is why there is a preliminary scheduling step which is job batch generation. The purpose of this study was to estimate the infl uence of job batch structure by the user criterion on the degree of its satisfaction. In other words we had to find the best way to form the batch with relation to the user optimization criterion. For example if it is more efficient to form the batch with jobs with the same criterion value or with different criterion values. Also we wanted to find the combination of criterion values which would give the most efficient scheduling results. To achieve this purpose an experiment in a simulation environment was conducted. The experiment consisted of scheduling of job batches with different values of the user criterion, other parameters of the resource request and the characteristics of the computing environment being the same. Three job batch generation strategies were considered. In the first strategy the batch consisted of jobs with the same criterion value. In the second strategy the batch consisted of jobs with all the considered criteria equally likely. The third strategy was similar to the second one, but only two certain criteria were considered. The third strategy was considered in order to find the most favorable combinations of criteria couples. The experiment showed that the second approach showed the best scheduling results. This may be explained by a smaller degree of competition for similar resources in the case of different criteria combination. Experiment results for criteria couples depend on the considered couple. The best scheduling results for this strategy were shown by criteria couples with job runtime and cost minimization criteria and job completion and cost minimization criteria. The results of the study are a part of course “Computing Systems” at the department of Computing engineering at National Research University “Moscow Power Engineering Institute”. Further studies will be dedicated to the search of optimal correlation between user criteria in one batch.

Wavelength channel minimization-based energy-aware mechanism in a multichannel EPON

We propose an energy-aware mechanism (EAM) applicable to the multichannel Ethernet Passive Optical Network that can minimize the number of wavelength channels used and save energy. Wavelength channel minimization is processed by collecting the information such as request message, allocated grant, and start time of each optical network unit (ONU) transmission in the previously elapsed scheduling cycles and comparing it with the buffer occupancy and packet delay conditions of the ONUs required by the user's quality-of-service requirement. They are exchanged between the optical line terminal (OLT) and the ONUs via the multipoint control protocol. In this way, at the beginning of each scheduling cycle, the ONU's buffer occupancy and packet delay conditions can be evaluated, and then, the OLT decides the smallest number of wavelength channels to be used in the current scheduling cycle. By turning off the OLT receivers corresponding to the unused wavelength channels, the OLT can save energy. The performance of the proposed EAM was evaluated through simulations using nonjoint off-line dynamic bandwidth allocation and dynamic wavelength assignment algorithms. The results showed that the OLT receivers' power consumption could be reduced by 48 % on average.

A resource type analysis of the integrated project scheduling and personnel staffing problem

In the integrated project scheduling and personnel staffing problem the project activities are scheduled and simultaneously a staffing plan is composed to carry out a single project. In this way, the project schedule that leads to the staffing plan with minimum cost is determined. In this paper, we evaluate different scheduling policies and practices for different personnel resource types. We examine the impact on the staffing cost when the personnel resources are scheduled in a cyclic versus a non-cyclic manner for different (days on, days off)-patterns. Furthermore, the impact of introducing more flexible resource types, such as overtime and temporary help, is explored in relationship with the activity resource demand variability. Computational results show that non-cyclic scheduling leads to a considerable lower staffing cost under all circumstances compared to cyclic scheduling. However, despite the tractability of the resource requirements, flexible temporary resources are essential on top of the regular personnel resources to respond to the variability in demand. The addition of overtime on a strategic staffing level only marginally decreases the personnel cost.

Power Scheduling for Energy Harvesting Wireless Communications With Battery Capacity Constraint

Power scheduling is an important issue for energy harvesting systems. In this work, we study the power control policy for minimizing the weighted sum of the outage probabilities under a set of predetermined transmission rates over a finite horizon. This problem is challenging in that the objective function is non-convex. To make the analysis tractable, we apply the approximation at high signal-to-noise ratios and obtain a near-optimal offline solution. In the case of infinite battery capacity, we demonstrate that the allocated power has a piecewise structure, i.e., each power scheduling cycle should be divided into disjoint segments and the normalized power should remain constant within each segment. An iterative algorithm is developed to obtain the power solution. In the case of finite battery capacity, we show that the piecewise structure still holds true, and we develop a divide-and-conquer algorithm to recursively solve the power allocation problem. Finally, we obtain a simple online power control policy that is fairly robust to prediction errors of the harvested energy. Simulations demonstrate that the proposed power solution has better performance than other strategies such as best-effort, fixed-ratio and random allocation.

Cyclic scheduling of flexible mixed model assembly lines with parallel stations

In this paper, the problem of balancing and cyclic scheduling of flexible mixed model assembly lines with parallel stations is studied. To exploit the connection between balancing and cyclic scheduling problems for an efficient line management, they are considered simultaneously. A novel constraint programming model including problem specific symmetry breaking constraints is proposed to solve this problem. Experiments on extensive number of test instances with various sizes are also presented.

Scheduling in two-machine robotic cells with a self-buffered robot

ABSTRACTThis study considers a production cell consisting of two machines and a material handling robot. The robot has a buffer space that moves with it. Identical parts are to be produced repetitively in this flowshop environment. The problem is to determine the cyclic schedule of the robot moves that maximizes the throughput rate. After developing the necessary framework to analyze such cells, we separately consider the single-, double-, and infinite-capacity buffer cases. For single- and double-capacity cases, consistent with the literature, we consider one-unit cycles that produce a single part in one repetition. We compare these cycles with each other and determine the set of undominated cycles. For the single-capacity case, we determine the parameter regions where each cycle is optimal, whereas for the double-capacity case, we determine efficient cycles and their worst-case performance bounds. For the infinite-capacity buffer case, we define a new class of cycles that better utilizes the benefits of the buffer space. We derive all such cycles and determine the set of undominated ones.We perform a computational study where we investigate the benefits of robots with a buffer space and the effects of the size of the buffer space on the performance. We compare the performances of self-buffered robots, dual-gripper robots, and robots with swap ability.

Формирование и планирование пакетов заданий в распределенных вычислительных средах

The paper considers approaches to ranked jobs system generation in the model of cyclic scheduling in the virtual organizations of distributed computing environments. Two different methodologies of job selection for scheduling are proposed and compared: the first one is based on the solution of knapsack problem, the second one utilizes a heuristic compatibility indicator of jobs and computing domains. Experimental results that allow estimating of the proposed solutions efficiency are presented, the solutions are compared to random job selection.

Addressing the Multichannel Selection, Scheduling and Coordination Cost

We discuss a new multichannel coordination and scheduling challenge called the Multichannel Scheduling Cost (MSC). It is caused by the inability of the control channel to schedule simultaneous transmissions resulting in data channels lying idle and their bandwidth underutilized. As a result, wasted bandwidth increases as the number of data channels increases. To address this challenge, a cyclic scheduling Algorithm (CSA) is proposed. It employs one dedicated signaling channel and 4 data channels. It is premised on a proactive channel reservation scheme which reduces the idleness of channels. The scheme ensures that data channels are reserved while they are still busy. The data channels are reserved while their remaining transmission duration is equal to the virtual carrier sensing duration. This gives the next pair sufficient time to reserve the current data channel before it becomes available, limiting the MSC to the first cycle. The simulation results show a performance benefit of the CSA scheme in addressing the effects of the MSC.

Scheduling cluster tools for concurrent processing of two wafer types with PM sharing

We examine cyclic scheduling of single-armed and dual-armed cluster tools that concurrently process two wafer types by sharing a process module (PM). Because a PM is shared by two different wafers, the backward and swap sequences, which are prevalently used for single-armed and dual-armed tools without such complexity, respectively, are not effective. We therefore propose new sequences, called alternating backward and alternating swap sequences, for steady cycles of single-armed and dual-armed tools, respectively. We then develop optimality conditions for which the proposed sequences achieve the minimum cycle times in a fundamental cycle, and show that the optimality conditions hold for most practical cases. We also develop a condition for which a shared PM becomes the bottleneck and hence the PM sharing increases the cycle time. For general cycles, we propose heuristic scheduling methods that combine both the alternating backward (or swap) sequence and the conventional backward (or swap) sequence. Finally, we experimentally verify the efficiency and effectiveness of the proposed algorithm for dual-armed cluster tools.

Optimal multi-degree cyclic scheduling of multiple robots without overlapping in robotic flowshops with parallel machines

This paper considers scheduling robotic flowshops with parallel machines and multiple robots. Robots share the same track and cannot crossover each other. To avoid conflicts among robots, the principle without overlapping is applied. Identical parts with time window constraints are produced. It is challenging to obtain better cyclic schedules to improve the throughput. Moreover, multi-degree cycles are considered to obtain better schedules comparing to simple cycles, i.e. 1-degree cycles. To our knowledge, this is the first work to deal with the multi-degree cyclic scheduling in this complicated scenario. This is the main contribution of this research. The objective is to maximize the throughput of the flowshop by obtaining optimal schedules. As for given degree cycles, it is equivalent to minimizing the cycle time. Operations in robotic flowshops considering multi-degree cycles are analyzed in detail. Based on the analyses, a mixed integer linear programming model is formulated for this challengeable problem. A numerical example modified from the previous work is used to illustrate the model proposed, which is solved by CPLEX. Results show the benefits of the model, especially considering multi-degree cycles.

Integrated Operation and Cyclic Scheduling Optimization for an Ethylene Cracking Furnaces System

Multiple cracking furnaces in an ethylene plant run in parallel to produce ethylene, propylene, and other products from different hydrocarbon feedstocks. Because both coke formation in radiant coils and change of operation conditions with time have significant effects on the performance of cracking furnaces, it is better for the cyclic scheduling to be simultaneously optimized with the operation conditions. To match this real requirement, a mixed-integer dynamic optimization (MIDO) problem is presented for the optimization of both operation conditions and cyclic scheduling simultaneously, through which the optimal assignment, the processing time, the subcycle number, and the optimal operation conditions of different feeds in different cracking furnaces are determined at the same time. To solve the MIDO problem, it is discretized and converted into a large scale mixed-integer nonlinear programming (MINLP) problem. The two scheduling cases of a cracking furnaces system are illustrated showing a remarkable i...

Noncyclic Scheduling of Cluster Tools With a Branch and Bound Algorithm

Cluster tools, each of which consists of multiple processing modules, one material handling robot, and loadlocks, are widely used for wafer fabrication processes, such as lithography, etching, and deposition. There have been many approaches and algorithms for cyclic scheduling of cluster tools in which the robot repeats a specified sequence for processing identical wafers. However, the lot order size has recently been decreasing due to the larger wafer size and circuit width reductions. In modern fabs, each wafer lot can have different flow patterns and process times for the same process step, and heterogeneous lots are processed consecutively in a tool. Even some tools in a fab have idle time waiting for wafer lots depending on the work-in-process fluctuations. Such different wafer lots and frequent tool state changes cannot be handled with cyclic scheduling methods, and accordingly noncyclic scheduling methods for such cases are required. Therefore, we develop an efficient branch and bound (B&B) procedure for noncyclic scheduling problems of cluster tools to minimize the makespan. Since a timed Petri net (TPN) is known for its powerful modeling ability and analysis capability, the algorithm is developed based on a TPN. We verify the efficiency of the B&B procedure with various cluster tool scheduling problems.

Heuristic strategies for preference-based scheduling in virtual organizations of utility grids

Distributed environments with the users decoupling from resource providers are generally defined as utility Grids. This paper focuses on the problems of an efficient scheduling in virtual organizations (VOs) of utility Grids. The proposed scheduling model ensures the VO stakeholders preferences and provides strategies for effective resources utilization. An approach based on the combination of the cyclic scheduling scheme, backfilling and several heuristic procedures is proposed and studied. Comparative simulation results are introduced for different algorithms and heuristics. Resource domain composition and heterogeneity as well as the VO pricing policy are taken into account. Considered scheduling approaches provide different benefits depending on the VO scheduling objectives. The results justify the use of the proposed approaches in a broad range of the resource environment parameters.

Schedulability and Scheduling Analysis of Dual-Arm Cluster Tools with Wafer Revisiting and Residency Time Constraints Based on a Novel Schedule

Some wafer fabrication processes require a wafer to visit some processing modules in a cluster tool multiple times, leading to a wafer revisiting process. They may pose wafer residency time constraints, i.e., a wafer can stay in a module for a limited time after it is processed. Although techniques exist for scheduling cluster tools with either wafer residency time constraints or wafer revisiting, it is much more challenging to schedule tools with both of them. Considering that atomic layer deposition is a typical wafer revisiting process, this paper intends to schedule a dual-arm cluster tool dealing with it. Based on the analysis of such a tool's properties, a novel scheduling strategy called modified 1-wafer cyclic scheduling is derived. With this strategy, necessary and sufficient schedulability conditions are presented. If schedulable, highly efficient scheduling algorithms are developed to obtain a feasible and optimal schedule together with a way to implement the obtained one. Illustrative examples are given to show the application of the proposed approach.

Resource Allocation Algorithm of Joint Channel Quality Evaluation Based on Non-cooperative Game in Cognitive Radio Network

For the centralized cognitive radio network, a resource allocation algorithm of joint channel quality evaluation based on non-cooperative game is proposed. The utility function for the game module considers both the receiving SINR threshold and transmitted power and tries to reduce interference as much as possible on the basis of guaranteeing the QoS demands for various services. The available channels can be evaluated through primary users occupying channel time and channel idle/occupied switching times. CR-BS (Cognitive Radio Base Station) calculates queue priority in a scheduling cycle based on users’ difierent services and dynamically adjusts service opportunities for realtime services and non-realtime services, which can provide difierential services and guarantee the equality for difierent services. The simulation shows that the proposed algorithm converges fast, can still ensures each user’s SINR value higher than its QoS demand threshold in low SNR environment, reduce the interference to primary users, and enhance network performance.

Cyclic supplementation of 5-MTHF is effective for the correction of hyperhomocysteinemia

Folic acid supplementation is the mainstay treatment of hyperhomocysteinemia (HHcy). However, no recommendations are currently available in regard to the optimal replacement therapy. Therefore, this prospective study hypothesized that a cyclic schedule (1 month of therapy followed by 2 months of withdrawal) of 5-methyltetrahydrofolate (5-MTHF) would reduce plasma levels of fasting total homocysteine (tHcy) in patients with mild/moderate HHcy. Patients with a new diagnosis of mild/moderate HHcy were evaluated for the methylenetetrahydrofolate reductase genotype and the presence of major features of metabolic syndrome. All enrolled subjects received a cyclic 5-MTHF oral supplementation and were reevaluated after each treatment cycle for a total of 2 years. In the 246 enrolled subjects, a significant reduction of tHcy levels occurred after the first cycle of treatment (from 31.6 ± 13.6 to 14.4 ± 5.77 μmol/L, P < .001) and during the whole 2-year follow-up (from 31.6 ± 13.6 to 12.18 ± 3.03 μmol/L, P < .001). The values of tHcy returned to reference range in 117 subjects (51.3%) after the first cycle and in 198 (86.8%) during the follow-up. The risk of failure in tHcy level normalization was increased in patients with metabolic syndrome (hazard ratio [HR], 3.49; 95% confidence interval [CI], 1.46-8.36), higher baseline tHcy levels (HR, 1.045; 95% CI, 1.018-1.073), or methylenetetrahydrofolate reductase homozygous mutation (HR, 6.59; 95% CI, 2.64-16.4). This study clearly shows that a cyclic schedule (1 month of therapy followed by 2 months of withdrawal) of 5-MTHF supplementation is able to significantly reduce tHcy levels in patients with mild/moderate HHcy.

On the economic lot scheduling problem: stock-out prevention and system feasibility

The Economic Lot Scheduling Problem is a classical scheduling problem with the objective of minimising the long-run inventory and set-up costs of a single machine, multi-product inventory system. Demand rates, production rates and set-up times are assumed to be deterministic. The problem has been extensively studied and methods exist to obtain cyclic schedules which minimise total cost. In order to apply a cyclic schedule without a stock-out occurring, certain initial inventory levels are required. This paper considers the scenario where inventory levels are critically low and the cyclic schedule cannot be applied. Analytical methods are developed to determine: if the initial inventory is sufficient to prevent a stock-out from occurring; the maximum time until a stock-out will occur if a stock-out is unavoidable; and the minimum time required to obtain the necessary inventory to resume the cyclic schedule if a stock-out can be avoided.

Scheduling of Single-Arm Multi-cluster Tools With Wafer Residency Time Constraints in Semiconductor Manufacturing

This paper studies the challenging problem of scheduling single-arm multi-cluster tools with wafer residency time constraints. They have a linear topology and their bottleneck tool is process-bound. This work aims to find an optimal one-wafer cyclic schedule. With the Petri net model developed in our previous work and the minimal cycle time for a multicluster tool without wafer residency time constraints, it derives the necessary and sufficient schedulability conditions for multicluster tools with wafer residency time constraints for the first time. Then, it gives an algorithm to find an optimal one-wafer cyclic schedule if schedulable. This is done by simply setting the robots' waiting time for each tool. Thus, it is very computationally efficient and applicable to practical problems. An example is presented to illustrate the proposed method.

A Branch and Bound Algorithm for Cyclic Scheduling of Timed Petri Nets

A timed Petri net (TPN) has been widely used for modeling, scheduling, and analyzing discrete event dynamic systems. This study examines cyclic scheduling problems of a TPN to minimize the cycle time especially for automated manufacturing systems. Appropriate token routing at each conflict place can make a TPN repeat an identical firing sequence. We propose a systematic procedure to transform a TPN with such cyclic token routing into an equivalent timed event graph (TEG) for which the cycle time and firing schedules can be evaluated by a linear programming (LP). Based on the transformation procedure, we develop an efficient branch and bound algorithm to solve the scheduling problem. A partial solution is defined as a partial token route that has only a subset of token routes for determining the complete schedule. The lower bound of a partial solution is determined by the cycle time of a TEG that has the partial token route. The cycle time of a TEG with an additional token route for a new partial solution is computed by a dual-simplex algorithm which avoids solving the LP completely again. A dynamic branching strategy that prevents unnecessary branching for the scheduling decision is also proposed. We demonstrate the computational efficiency through intensive experiments of cluster tools and robotic flow shops.

Multi-Level Job Flow Cyclic Scheduling in Grid Virtual Organizations

Distributed environments with the decoupling of users from resource providers are generally termed as utility Grids. The paper focuses on the problems of efficient job flow distribution and scheduling in virtual organizations (VOs) of utility Grids while ensuring the VO stakeholders preferences and providing dependable strategies for resources utilization. An approach based on the combination of the cyclic scheduling scheme, backfilling and several heuristic procedures is proposed and studied. Comparative simulation results are introduced for different algorithms and heuristics depending on the resource domain composition and heterogeneity. Considered scheduling approaches provide different benefits depending on the VO scheduling objectives. The results justify the use of the proposed approaches in a broad range of the considered resource environment parameters.