Discrete Event System Approach Research Articles

Statistical comparison of Path-Complete Lyapunov Functions: a Discrete-Event Systems perspective

The goal of this paper is to advertise the tight links between the theory of Discrete-Event Systems and Path-Complete Lyapunov Functions. These are algebro-combinatorial stability criteria for hybrid systems, whose meta-parameters are an automaton and a template of candidate Lyapunov functions.To do this, we analyse a phenomenon recently observed in the literature, namely the statistical ordering of Path-Complete Lyapunov Functions, which is by far not well understood yet: Path-Complete Lyapunov functions can be endowed with a preorder structure with respect to their performance. It has been recently shown that the preorder corresponding to relative worst case performance can be characterized with tools from automata theory, but the ordering corresponding to statistical relative performance has remained elusive. We advocate for a Discrete-Event Systems approach to this problem and provide preliminary results in this direction.

Haberleşme Tabanlı Tren Kontrolünün (CBTC) Otomatik Tren Korumasına (ATP) İlişkin Dağıtılmış-Hiyerarşik Kontrol Yaklaşımı

Kentleşme ile birlikte metropollerde yaşayan insan sayısı artmaktadır, nüfus artışına paralel olarak şehir içi ulaşımda çok önemli bir yer tutan raylı ulaşım sistemlerine olan talep, kalabalık şehirlerde her geçen gün daha da artmaktadır.Artan talebe paralel olarak raylarda artacak trafik yoğunluğu, sinyalizasyon sistemlerini güvenlik, kapasite ve rayların verimine etkisi açısından oldukça önemli kılmaktadır. Günümüzde birçok raylı ulaşım sistemlerinde sinyalizasyon sistemi olarak Haberleşme Tabanlı Tren Kontrol (CBTC) tercih edilmektedir. CBTC, Otomatik Tren Koruması (ATP), Otomatik Tren Denetimi (ATS) ve Otomatik Tren İşletmesi (ATO) gibi bazı alt sistemlerden meydana gelmektedir. Alt sistemlerin kendine özgü tanımlanan bazı görevleri bulunmaktadır. Bu görevleri yerine getirirken, alt sistemlerden artan gereksinimlerden etkilenmeden, istenen emniyet fonksiyonlarını en üst düzeyde güvenle uygulaması beklenmektedir. Ancak, bu sistemlerin genel tasarımının, ihtiyaç duyulan yeni gereksinimlere göre değiştirilmesi gerekebilir. Bu bağlamda çeşitli standartların sağlarken, alt sistemlerin kontrol edilmesi ve modellenmeleri büyük önem taşımaktadır. Bu çalışmada, CBTC’nin alt sistemi ATP, ayrık olay sistemi yaklaşımıyla sonlu durum otomatları ile modellenmiştir ve alt sistemlere ait denetimsel gözetleyicilerin tasarımı yapılarak, kontrol edilebilirlik ve kilitlenmesiz kontrol koşullarını karşıladığı gösterilerek, elde edilen sonuçlar yekpare yaklaşım modeli ile karşılaştırılmıştır.

A Discrete-Event System Approach for Modeling and Mitigating Power System Cascading Failures

A power system cascading failure can propagate through sequential tripping of components in the network. As a result, a complete or partial shutdown may occur. In this article, we develop a new systematic approach to identify and prevent cascading failures in power systems using supervisory control of discrete-event systems (DESs). We build the DES model for a power system in a modular fashion by first modeling its components as (small) automata and then combining these automata using parallel composition. To overcome state explosion, we use online lookahead control that can significantly reduce the number of states to be considered. Since some events such as line trips cannot be disabled but can be preempted by forcing some forcible events such as load shedding, we extend supervisory control of DES to include forcible events. This extension allows us to control power systems effectively. The proposed control is implemented in an implementation platform that we build in MATLAB. The platform uses MATPOWER to simulate a power system and then control it using the proposed DES controller. Simulation studies are carried out for IEEE 6-, 30-, and 118-bus systems. The results verify the effectiveness of the proposed approach.

COLREGs-based Situation Awareness for Marine Vessels - a Discrete Event Systems Approach

Autonomy at different levels is envisaged to provide decision support, to enable navigation with temporally unattended bridge or have the navigator placed remotely, being able to take command if required. For this purpose, methods for computer-based situation awareness are needed to avoid risks of collision. Correct interpretation of a situation is crucial, and all navigation decisions must be based on the COLREGs. This paper presents a discrete-event-systems-based framework that facilitates autonomous interpretation of the situation in which the own ship is. This can be used for COLREGs-compliant decision planning when all vessels navigate according to the rules. The proposed framework comprises a set of coupled finite-state deterministic automata and segregates situation understanding from anticipation. The suggested formalism is analysed with respect to avoidance of deadlocks and shows how synchronisation of vessel-specific automata modules is achieved. Simulations illustrate the concept using realistic scenarios.

Resilience Against Sensor Deception Attacks at the Supervisory Control Layer of Cyber-Physical Systems: A Discrete Event Systems Approach

Resilience Against Sensor Deception Attacks at the Supervisory Control Layer of Cyber-Physical Systems: A Discrete Event Systems Approach

A Discrete Event Systems Approach to Model Problem Structure of Drug Ingestion Accidents in Infants

A Discrete Event Systems Approach to Model Problem Structure of Drug Ingestion Accidents in Infants

Robust production scheduling under machine failures - A DES based evaluation approach

Discrete Event Systems (DES) have already proved their efficiency to model and solve scheduling production problems in the field of manufacturing systems. Their main asset is the capacity to represent the dynamic behavior of workshops.The stochastic extensions of DES models offers, actually, interesting characteristics to take into consideration the perturbations in scheduling. In this paper, we propose to use a stochastic DES approach (using stochastic timed automata) to evaluate the robustness of schedules under perturbations. The perturbations that are considered are the machine failures with uncertain reparation duration.

Modeling Flexible Workshops Scheduling problems: evaluating a Timed Automata based approach vs MILP

This paper investigates the relevance of modeling workshop scheduling problems using a Discrete Event System (DES) approach based on timed automata (TA). To realize this study the DES approach is compared with a classical approach based on Mixed Integer Linear Programming (MILP). In order to compare these two modeling approaches, an evaluation system is proposed based on: (i) a problem instances generation system using the classical three-fields notation of Graham (α|β|γ), (ii) a measurement system based on three criteria and associated metrics: complexity, genericity and scalability. This system covers the most common problems when dealing with flexible workshop scheduling. The results obtained by the application of the method is finally discussed.

Supervisory Control for High-Voltage Direct Current Transmission Systems

The growth of renewable energy production is changing the future of power transmission systems. In recent years, High-Voltage Direct Current (HVDC) technologies based on Modular Multilevel Converters (MMC) are embraced by industry and academia as a solution for the efficient integration of renewable energies into electrical grids. Faster and more complex control strategies will be needed in this domain which nowadays relies heavily on human decision. This paper proposes a Discrete Event System (DES) approach to manage the control responses to deploy in an HVDC grid. Based on Discrete Event Systems (DES) modelling and Supervisory Control Theory (SCT), this paper proposes a method for synthesizing a supervisory control for HVDC systems, which focuses on local observations and limits the number of events to be communicated. The method is validated by simulation for the start-up of a point-to-point link.

A Discrete Event System approach to On-line Testing of digital circuits with measurement limitation

In the present era of complex systems like avionics, industrial processes, electronic circuits, etc., on-the-fly or on-line fault detection is becoming necessary to provide uninterrupted services. Measurement limitation based fault detection schemes are applied to a wide range of systems because sensors cannot be deployed in all the locations from which measurements are required. This paper focuses towards On-Line Testing (OLT) of faults in digital electronic circuits under measurement limitation using the theory of discrete event systems. Most of the techniques presented in the literature on OLT of digital circuits have emphasized on keeping the scheme non-intrusive, low area overhead, high fault coverage, low detection latency etc. However, minimizing tap points (i.e., measurement limitation) of the circuit under test (CUT) by the on-line tester was not considered. Minimizing tap points reduces load on the CUT and this reduces the area overhead of the tester. However, reduction in tap points compromises fault coverage and detection latency. This work studies the effect of minimizing tap points on fault coverage, detection latency and area overhead. Results on ISCAS89 benchmark circuits illustrate that measurement limitation have minimal impact on fault coverage and detection latency but reduces the area overhead of the tester. Further, it was also found that for a given detection latency and fault coverage, area overhead of the proposed scheme is lower compared to other similar schemes reported in the literature.

Performance Assessment of an Urbain Collective Cars System

A constrained optimization framework of an autonomous urban transport system, associated with reduced rates, is presented. A decentralized management is considered where prior seat reservation is not a prerequisite for the system functioning. Well-adapted vehicle itineraries based on the current demand and vehicle state are constructed. The event-driven system dynamics characterizing the non-deterministic features of the corresponding complex mathematical problem, encourage for a discrete event system approach. The implied stressing needs of a comprehensive study, will be achieved by intense simulations. Various strategies, related to real time controls and system dimensioning as well, are studied. A methodology appraising the system performance is introduced where the resulting system behaviour is evaluated in terms of client waiting time, detours, vehicle occupancy, travel times etc. Moreover, optimal parameter tuning is discussed underlying the importance of reasonable trade-offs for achieving the desired performance. Thus, involving optimisation, operational research methods and simulation techniques a significantly efficacious well-operating system can be achieved, providing the best suited configuration for any demand level and geometry. Utilising previously wasted vehicle capacity may reduce costs for both vehicles and clients while forms an ongoing attempt to control extended traffic congestion, air pollution, energy consumption etc.

A Discrete Event System Approach to Online Testing of Speed Independent Circuits

With the increase in soft failures in deep submicron ICs, online testing is becoming an integral part of design for testability. Some techniques for online testing of asynchronous circuits are proposed in the literature, which involves development of a checker that verifies the correctness of the protocol. This checker involves Mutex blocks making its area overhead quite high. In this paper, we have adapted the Theory of Fault Detection and Diagnosis available in the literature on Discrete Event Systems to online testing of speed independent asynchronous circuits. The scheme involves development of a state based model of the circuit, under normal and various stuck-at fault conditions, and finally designing state estimators termed as detectors. The detectors monitor the circuit online and determine whether it is functioning in normal/failure mode. The main advantages are nonintrusiveness and low area overheads compared to similar schemes reported in the literature.

Decision‐making strategies in fixed‐block railway signaling systems: A discrete event systems approach

Ensuring the system safety at all times is most important in railway systems where small failures may result in a large number of casualties and property loss. Although there are various design methods, safety precautions, and recommendations of the railway‐related safety standards, sometimes the occurrence of accidents cannot be prevented. In this paper, according to the recommendations of the railway‐related safety standards, an interlocking system architecture, which consists of two controllers and a coordinator, for a fixed‐block railway signaling system is studied. Based on the Petri net models of railway field components, decision‐making strategies including fault diagnosis are presented. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Learning Diagnosis Based on Evolving Fuzzy Finite State Automaton


 
 
 Nowadays, determining faults (or critical situations) in non- stationary environment is a challenging task in complex systems such as Nuclear center, or multi-collaboration such as crisis management. A discrete event system or a fuzzy discrete event system approach with a fuzzy role-base may re- solve the ambiguity in a fault diagnosis problem especially in the case of multiple faults (or multiple critical situations). The main advantage of fuzzy finite state automaton is that their fuzziness allows them to handle imprecise and uncertain data, which is inherent to real-world phenomena, in the form of fuzzy states and transitions. Thus, most of approaches proposed for fault diagnosis of discrete event systems require a complete and accurate model of the system to be diagnosed. However, in non-stationary environment it is hard or impossible to obtain the complete model of the system. The focus of this work is to propose an evolving fuzzy discrete event system whose an activate degree is associated to each active state and to develop a fuzzy learning diagnosis for incomplete model. Our approach use the fuzzy set of output events of the model as input events of the diagnoser and the output of a fuzzy system should be defuzzified in an appropriate way to be usable by the environment.
 
 

Fault diagnosis in fixed‐block railway signaling systems: a discrete event systems approach

AbstractIn conventional railway systems (or fixed‐block railway signaling systems), railway lines are divided into subsections, called railway blocks, which start and end with a signal. In order to prevent collisions, only one train is allowed in each railway block at a time. Since the occupancy of the next block is indicated by the signals, train drivers have to pay attention to the signals during their journey. In spite of the conventional railway systems having several drawbacks such as the reduction in railway line capacity and the same safe braking distances for all kinds of trains, they have been in use since the mid‐1800s. In this paper, we study fault diagnosis in fixed‐block railway signaling systems from the discrete event systems point of view: first the signaling system equipment are modeled by using Petri nets, and next a diagnoser is designed to show the diagnosability of the system. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

An Integrated Approach to Mode Tracking and Diagnosis of Hybrid Systems

In this paper, information from a hybrid bond graph (HBG) model and from discrete-event systems (DESs) is integrated into a fault diagnosis method for hybrid systems. In a pure-HBG framework, mode-change detection and isolation is handled by the mode-change signature and the mode-change signature matrix. In a DES approach, discrete states and faults are traced based on observable events (e.g., control signals) and diagnosers. Based on the two approaches, a new diagnoser that is driven by both observable events and consistency indicators generated by continuous residuals is presented. The proposed method allows not only to effectively trace the system mode but also to decide whether this mode is faulty or normal. The new method is presented and implemented on a testbed. The experimental results presented in this paper demonstrate the effectiveness of the method.

A discrete event systems approach to discriminating intermittent from permanent faults

Almost all work on model-based diagnosis (MBD) potentially presumes faults are persistent and does not take intermittent faults (IFs) into account. Therefore, it is common for diagnosis systems to misjudge IFs as permanent faults (PFs), which are the major cause of the problems of false alarms, cannot duplication and no fault found in aircraft avionics. To address this problem, a new fault model which includes PFs and IFs is presented based on discrete event systems (DESs). Thereafter, an approach is given to discriminate between PFs and IFs by diagnosing the current fault. In this paper, the regulations of (PFs and IFs) fault evolution through fault and reset events along the traces of system are studied, and then label propagation function is modified to account for PFs and the dynamic behavior of IFs and diagnosability of PFs and IFs are defined. Finally, illustrative examples are presented to demonstrate the proposed approach, and the analysis results show the fault types can be discriminated within bounded delay if the system is diagnosable.

Discrete Event Systems Approach for Deadlock Avoidance and Scheduling

Discrete Event Systems Approach for Deadlock Avoidance and Scheduling

A discrete event systems approach to network fault management: detection and diagnosis of faults

An important aspect of network management is fault management, which involves, detecting, locating, isolating, correcting and adapting to faults in the network. We study modeling of communication network protocol and fault detection, identification and localization in the discrete event system diagnosis framework. As an illustration of the approach, normal and faulty behavior of the X.25 network protocol is modeled as a finite state machine. This modeling formalism allows the utilization of discrete event system analysis for the detection and diagnosis of faults. Our approach provides a systematic way of performing fault diagnosis for network fault management. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society

LAN attack detection using Discrete Event Systems

Address Resolution Protocol (ARP) is used for determining the link layer or Medium Access Control (MAC) address of a network host, given its Internet Layer (IP) or Network Layer address. ARP is a stateless protocol and any IP–MAC pairing sent by a host is accepted without verification. This weakness in the ARP may be exploited by malicious hosts in a Local Area Network (LAN) by spoofing IP–MAC pairs. Several schemes have been proposed in the literature to circumvent these attacks; however, these techniques either make IP–MAC pairing static, modify the existing ARP, patch operating systems of all the hosts etc. In this paper we propose a Discrete Event System (DES) approach for Intrusion Detection System (IDS) for LAN specific attacks which do not require any extra constraint like static IP–MAC, changing the ARP etc. A DES model is built for the LAN under both a normal and compromised (i.e., spoofed request/response) situation based on the sequences of ARP related packets. Sequences of ARP events in normal and spoofed scenarios are similar thereby rendering the same DES models for both the cases. To create different ARP events under normal and spoofed conditions the proposed technique uses active ARP probing. However, this probing adds extra ARP traffic in the LAN. Following that a DES detector is built to determine from observed ARP related events, whether the LAN is operating under a normal or compromised situation. The scheme also minimizes extra ARP traffic by probing the source IP–MAC pair of only those ARP packets which are yet to be determined as genuine/spoofed by the detector. Also, spoofed IP–MAC pairs determined by the detector are stored in tables to detect other LAN attacks triggered by spoofing namely, man-in-the-middle (MiTM), denial of service etc. The scheme is successfully validated in a test bed.