351 research outputs found
An efficient ant colony system based on receding horizon control for the aircraft arrival sequencing and scheduling problem
The aircraft arrival sequencing and scheduling (ASS) problem is a salient problem in air traffic control (ATC), which proves to be nondeterministic polynomial (NP) hard. This paper formulates the ASS problem in the form of a permutation problem and proposes a new solution framework that makes the first attempt at using an ant colony system (ACS) algorithm based on the receding horizon control (RHC) to solve it. The resultant RHC-improved ACS algorithm for the ASS problem (termed the RHC-ACS-ASS algorithm) is robust, effective, and efficient, not only due to that the ACS algorithm has a strong global search ability and has been proven to be suitable for these kinds of NP-hard problems but also due to that the RHC technique can divide the problem with receding time windows to reduce the computational burden and enhance the solution's quality. The RHC-ACS-ASS algorithm is extensively tested on the cases from the literatures and the cases randomly generated. Comprehensive investigations are also made for the evaluation of the influences of ACS and RHC parameters on the performance of the algorithm. Moreover, the proposed algorithm is further enhanced by using a two-opt exchange heuristic local search. Experimental results verify that the proposed RHC-ACS-ASS algorithm generally outperforms ordinary ACS without using the RHC technique and genetic algorithms (GAs) in solving the ASS problems and offers high robustness, effectiveness, and efficienc
A distributed scheduling algorithm for heterogeneous real-time systems
Much of the previous work on load balancing and scheduling in distributed environments was concerned with homogeneous systems and homogeneous loads. Several of the results indicated that random policies are as effective as other more complex load allocation policies. The effects of heterogeneity on scheduling algorithms for hard real time systems is examined. A distributed scheduler specifically to handle heterogeneities in both nodes and node traffic is proposed. The performance of the algorithm is measured in terms of the percentage of jobs discarded. While a random task allocation is very sensitive to heterogeneities, the algorithm is shown to be robust to such non-uniformities in system components and load
Random trees in queueing systems with deadlines
AbstractWe survey our research on scheduling aperiodic tasks in real-time systems in order to illustrate the benefits of modelling queueing systems by means of random trees. Relying on a discrete-time single-server queueing system, we investigated deadline meeting properties of several scheduling algorithms employed for servicing probabilistically arriving tasks, characterized by arbitrary arrival and execution time distributions and a constant service time deadline T. Taking a non-queueing theory approach (i.e., without stable-stable assumptions) we found that the probability distribution of the random time sT where such a system operates without violating any task's deadline is approximately exponential with parameter λT = 1ΌT, with the expectation E[sT] = ΌT growing exponentially in T. The value ΌT depends on the particular scheduling algorithm, and its derivation is based on the combinatorial and asymptotic analysis of certain random trees. This paper demonstrates that random trees provide an efficient common framework to deal with different scheduling disciplines and gives an overview of the various combinatorial and asymptotic methods used in the appropriate analysis
Application of lean scheduling and production control in non-repetitive manufacturing systems using intelligent agent decision support
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Lean Manufacturing (LM) is widely accepted as a world-class manufacturing paradigm, its currency and superiority are manifested in numerous recent success stories. Most lean tools including Just-in-Time (JIT) were designed for repetitive serial production systems. This resulted in a substantial stream of research which dismissed a priori the suitability of LM for non-repetitive non-serial job-shops. The extension of LM into non-repetitive production systems is opposed on the basis of the sheer complexity of applying JIT pull production control in non-repetitive systems fabricating a high variety of products. However, the application of LM in job-shops is not unexplored. Studies proposing the extension of leanness into non-repetitive production systems have promoted the modification of pull control mechanisms or reconfiguration of job-shops into cellular manufacturing systems. This thesis sought to address the shortcomings of the aforementioned approaches. The contribution of this thesis to knowledge in the field of production and operations management is threefold:
Firstly, a Multi-Agent System (MAS) is designed to directly apply pull production control to a good approximation of a real-life job-shop. The scale and complexity of the developed MAS prove that the application of pull production control in non-repetitive manufacturing systems is challenging, perplex and laborious. Secondly, the thesis examines three pull production control mechanisms namely, Kanban, Base Stock and Constant Work-in-Process (CONWIP) which it enhances so as to prevent system deadlocks, an issue largely unaddressed in the relevant literature. Having successfully tested the transferability of pull production control to non-repetitive manufacturing, the third contribution of this thesis is that it uses experimental and empirical data to examine the impact of pull production control on job-shop performance. The thesis identifies issues resulting from the application of pull control in job-shops which have implications for industry practice and concludes by outlining further research that can be undertaken in this direction
Performance Analysis in IP-Based Industrial Communication Networks
S rostoucĂm poÄtem ĆĂdicĂch systĂ©mĆŻ a jejich distribuovanosti zĂskĂĄvĂĄjĂ komunikaÄnĂ sĂtÄ na dĆŻleĆŸitosti a objevujĂ se novĂ© vĂœzkumnĂ© trendy. HlavnĂ problematikou v tĂ©to oblasti, narozdĂl od dĆĂvÄjĆĄĂch ĆĂdicĂch systĂ©mĆŻ vyuĆŸĂvajĂcĂch dedikovanĂœch komunikaÄnĂch obvodĆŻ, je ÄasovÄ promÄnnĂ© zpoĆŸdÄnĂ mÄĆicĂch a ĆĂdicĂch signĂĄlĆŻ zpĆŻsobenĂ© paketovÄ orientovanĂœmi komunikaÄnĂmi prostĆedky, jako napĆ. Ethernet. Aspekty komunikace v reĂĄlnĂ©m Äase byly v tÄchto sĂtĂch jiĆŸ ĂșspÄĆĄnÄ vyĆeĆĄeny. NicmĂ©nÄ, analĂœzy trendĆŻ trhu pĆedpovĂdajĂ budoucĂ vyuĆŸitĂ takĂ© IP sĂtĂ v prĆŻmyslovĂ© komunikaci pro ÄasovÄ kritickou procesnĂ vymÄnu dat. IP komunikace mĂĄ ovĆĄem pouze omezenou podporu v instrumentaci pro prĆŻmyslovou automatizace. Tato vĂœzva byla nedĂĄvno technicky vyĆeĆĄena v rĂĄmci projektu Virtual Automation Networks (virtuĂĄlnĂ automatizaÄnĂ sĂtÄ - VAN) zapojenĂm mechanismĆŻ kvality sluĆŸeb (QoS), kterĂ© jsou schopny zajistit mÄkkou ĂșroveĆ komunikace v reĂĄlnĂ©m Äase. PĆedloĆŸenĂĄ dizertaÄnĂ prĂĄce se zamÄĆuje na aspekty vĂœkonnosti reĂĄlnĂ©ho Äasu z analytickĂ©ho hlediska a nabĂzĂ prostĆedek pro hodnocenĂ vyuĆŸitelnosti IP komunikace pro budoucĂ prĆŻmyslovĂ© aplikace. HlavnĂm cĂlem tĂ©to dizertaÄnĂ prĂĄce je vytvoĆenĂ vhodnĂ©ho modelovacĂho rĂĄmce zaloĆŸenĂ©ho na network calculus, kterĂœ pomĆŻĆŸe provĂ©st worst-case vĂœkonnostnĂ analĂœzu ÄasovĂ©ho chovĂĄnĂ IP komunikaÄnĂch sĂtĂ a jejich prvkĆŻ urÄenĂœch pro budoucĂ pouĆŸitĂ v prĆŻmyslovĂ© automatizaci. V prĂĄci byla pouĆŸita empirickĂĄ analĂœza pro urÄenĂ dominantnĂch faktorĆŻ ovlivĆujĂcĂch ÄasovĂ©ho chovĂĄnĂ sĂĆ„ovĂœch zaĆĂzenĂ a identifikaci parametrĆŻ modelĆŻ tÄchto zaĆĂzenĂ. EmpirickĂĄ analĂœza vyuĆŸĂvĂĄ nĂĄstroj TestQoS vyvinutĂœ pro tyto ĂșÄely. Byla navrĆŸena drobnĂĄ rozĆĄĂĆenĂ rĂĄmce network calculus, kterĂĄ byla nutnĂĄ pro modelovĂĄnĂ ÄasovĂ©ho chovĂĄnĂ pouĆŸĂvanĂœch zaĆĂzenĂ. Bylo vytvoĆeno nÄkolik typovĂœch modelĆŻ zaĆĂzenĂ jako vĂœsledek klasifikace rĆŻznĂœch architektur sĂĆ„ovĂœch zaĆĂzenĂ a empiricky zjiĆĄtÄnĂœch dominantnĂch faktorĆŻ. U modelovanĂœch zaĆĂzenĂ byla vyuĆŸita novĂĄ metoda identifikace parametrĆŻ. PrĂĄce je zakonÄena validacĂ ÄasovĂœch modelĆŻ dvou sĂĆ„ovĂœch zaĆĂzenĂ (pĆepĂnaÄe a smÄrovaÄe) oproti empirickĂœm pozorovĂĄnĂm.With the growing scale of control systems and their distributed nature, communication networks have been gaining importance and new research challenges have been appearing. The major problem, contrary to previously used control systems with dedicated communication circuits, is time-varying delay of control and measurement signals introduced by packet-switched networks, such as Ethernet. The real-time issues in these networks have been tackled by proper adaptations. Nevertheless, market trend analyses foresee also future adoptions of IP-based communication networks in industrial automation for time-critical run-time data exchange. IP-based communication has only a limited support from the existing instrumentation in industrial automation. This challenge has recently been technically tackled within the Virtual Automation Networks (VAN) project by adopting the quality of service (QoS) architecture delivering soft-real-time communication behaviour. This dissertation focuses on the real-time performance aspects from the analytical point of view and provides means for applicability assessment of IP-based communication for future industrial applications. The main objective of this dissertation is establishment of a relevant modelling framework based on network calculus which will assist worst-case performance analysis of temporal behaviour of IP-based communication networks and networking devices intended for future use in industrial automation. Empirical analysis was used to identify dominant factors influencing the temporal performance of networking devices and for model parameter identification. The empirical analysis makes use of the TestQoS tool developed for this purpose. Minor extensions to the network calculus framework were proposed enabling to model the required temporal behaviour of networking devices. Several exemplary models were inferred as a result of classification of different networking device architectures and empirically identified dominant factors. A novel method for parameter identification was used with the modelled devices. Finally, two temporal models of networking devices (a switch and a router) were validated against empirical observations.
Maximising microprocessor reliability through game theory and heuristics
PhD ThesisEmbedded Systems are becoming ever more pervasive in our society, with most
routine daily tasks now involving their use in some form and the market predicted
to be worth USD 220 billion, a rise of 300%, by 2018. Consumers expect
more functionality with each design iteration, but for no detriment in perceived
performance. These devices can range from simple low-cost chips to expensive
and complex systems and are a major cost driver in the equipment design
phase. For more than 35 years, designers have kept pace with Moore's Law, but
as device size approaches the atomic limit, layouts are becoming so complicated
that current scheduling techniques are also reaching their limit, meaning that
more resource must be reserved to manage and deliver reliable operation. With
the advent of many-core systems and further sources of unpredictability such as
changeable power supplies and energy harvesting, this reservation of capability
may become so large that systems will not be operating at their peak efficiency.
These complex systems can be controlled through many techniques, with
jobs scheduled either online prior to execution beginning or online at each time
or event change. Increased processing power and job types means that current
online scheduling methods that employ exhaustive search techniques will not
be suitable to define schedules for such enigmatic task lists and that new techniques
using statistic-based methods must be investigated to preserve Quality
of Service.
A new paradigm of scheduling through complex heuristics is one way to
administer these next levels of processor effectively and allow the use of more
simple devices in complex systems; thus reducing unit cost while retaining reliability a key goal identified by the International Technology Roadmap for Semi-conductors for Embedded Systems in Critical Environments. These changes
would be beneficial in terms of cost reduction and system
exibility within the
next generation of device. This thesis investigates the use of heuristics and
statistical methods in the operation of real-time systems, with the feasibility of
Game Theory and Statistical Process Control for the successful supervision of
high-load and critical jobs investigated. Heuristics are identified as an effective
method of controlling complex real-time issues, with two-person non-cooperative
games delivering Nash-optimal solutions where these exist. The simplified algorithms for creating and solving Game Theory events allow for its use within
small embedded RISC devices and an increase in reliability for systems operating
at the apex of their limits. Within this Thesis, Heuristic and Game Theoretic
algorithms for a variety of real-time scenarios are postulated, investigated, refined and tested against existing schedule types; initially through MATLAB
simulation before testing on an ARM Cortex M3 architecture functioning as a
simplified automotive Electronic Control Unit.Doctoral Teaching Account from the EPSRC
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