Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167718
F. Vázquez-Abad, I. Baltcheva
In CDMA mobile networks, callers that are transmitting through a power station may cause interference at other power stations. When many users are already connected in the network, a new call may cause the signal to noise ratio to drop below a tolerance threshold. This phenomenon is called 'outage' and it provides an important measure of performance, useful in the design and control of the system. Evaluating this probability analytically has proven unsuccessful and only approximations exist today. Direct simulation of such networks is at present very slow because outage occurs infrequently - it may take hours to simulate directly a realistic model if a reasonable precision is desired. Thus this approach is not useful for design problems where one wishes to evaluate and compare performance of many different network models. In this work we implement a change of measure to estimate the outage probability using importance sampling. We present a functional estimator and a stochastic approximation method that are capable of learning the best parameters for the change of measure.
{"title":"Intelligent simulation for the estimation of the uplink outage probabilities in CDMA networks","authors":"F. Vázquez-Abad, I. Baltcheva","doi":"10.1109/WODES.2002.1167718","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167718","url":null,"abstract":"In CDMA mobile networks, callers that are transmitting through a power station may cause interference at other power stations. When many users are already connected in the network, a new call may cause the signal to noise ratio to drop below a tolerance threshold. This phenomenon is called 'outage' and it provides an important measure of performance, useful in the design and control of the system. Evaluating this probability analytically has proven unsuccessful and only approximations exist today. Direct simulation of such networks is at present very slow because outage occurs infrequently - it may take hours to simulate directly a realistic model if a reasonable precision is desired. Thus this approach is not useful for design problems where one wishes to evaluate and compare performance of many different network models. In this work we implement a change of measure to estimate the outage probability using importance sampling. We present a functional estimator and a stochastic approximation method that are capable of learning the best parameters for the change of measure.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126407356","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167692
L. Holloway, A. Khare
Characterizing uncontrollable reachability is a central issue in forbidden state control of discrete event systems. In this paper, we present methods for building expressions which estimate uncontrollable reachability in a general class of Petri nets and which characterize the control sets to ensure future markings will not be forbidden. These expressions are determined by constructing an abstract syntax tree from an analysis of the Petri net model of the system. We show that these expressions represent bounds that are useful for evaluating uncontrollable reachability and for evaluating control actions.
{"title":"Computing bounds for forbidden state reachability functions for controlled Petri nets","authors":"L. Holloway, A. Khare","doi":"10.1109/WODES.2002.1167692","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167692","url":null,"abstract":"Characterizing uncontrollable reachability is a central issue in forbidden state control of discrete event systems. In this paper, we present methods for building expressions which estimate uncontrollable reachability in a general class of Petri nets and which characterize the control sets to ensure future markings will not be forbidden. These expressions are determined by constructing an abstract syntax tree from an analysis of the Petri net model of the system. We show that these expressions represent bounds that are useful for evaluating uncontrollable reachability and for evaluating control actions.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124671695","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167683
E. Garcia, F. Morant, R. Blasco-Gimenez, A. Correcher, E. Quiles
This paper studies modular decomposition as an approach for failure diagnosis based on discrete event systems. This paper also analyses the problem of coupling produced in the implementation of centralized modular diagnosers, as coupled diagnosers cannot carry out their own diagnosis task when there is a failure in another subsystem sharing a common energy or material flow. In addition, we propose a method to avoid diagnoser coupling, by means of decoupling functions using nonlocal information with respect to the coupled diagnoser and generated in the diagnoser where the failure has been isolated.
{"title":"Centralized modular diagnosis and the phenomenon of coupling","authors":"E. Garcia, F. Morant, R. Blasco-Gimenez, A. Correcher, E. Quiles","doi":"10.1109/WODES.2002.1167683","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167683","url":null,"abstract":"This paper studies modular decomposition as an approach for failure diagnosis based on discrete event systems. This paper also analyses the problem of coupling produced in the implementation of centralized modular diagnosers, as coupled diagnosers cannot carry out their own diagnosis task when there is a failure in another subsystem sharing a common energy or material flow. In addition, we propose a method to avoid diagnoser coupling, by means of decoupling functions using nonlocal information with respect to the coupled diagnoser and generated in the diagnoser where the failure has been isolated.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"41 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124965882","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167664
S. Tripakis
We introduce problems of decentralized control with delayed communication, where delays are either unbounded or bounded by a given constant k. In the k-bounded-delay model, between the transmission of a message and its reception, the plant can execute at most k events. In the unbounded-delay model, the plant can execute any number of events between transmission and reception. We show that our framework yields an infinite hierarchy of control problems, /spl Cscr//spl Cscr/ =/spl Dscr//spl Cscr//spl Cscr//sub 0//spl sup//spl Dscr//spl Cscr//spl Cscr//sub 1//spl sup//spl Dscr//spl Cscr//spl Cscr//sub 2//spl sup//spl middot//spl middot//spl middot//spl sup//spl Dscr//spl Cscr//spl Uscr//spl Cscr//spl sup//spl Dscr//spl Cscr/ , where CC is the set of control problems solvable with a single controller (centralized case) and /spl Dscr//spl Cscr//spl Cscr//sub k/ (resp. /spl Dscr//spl Cscr//spl Uscr//spl Cscr/, /spl Dscr//spl Cscr/) is the set of problems solvable with two controllers in a k-bounded-delay network (resp. two controllers in an unbounded-delay network, two controllers without communication). The above containments are strict. We prove the undecidability of checking the existence of controllers in the unbounded-delay case, or in the case without any communication. Finally, we prove that a decentralized observation problem with bounded-delay communication is decidable.
{"title":"Decentralized control of discrete event systems with bounded or unbounded delay communication","authors":"S. Tripakis","doi":"10.1109/WODES.2002.1167664","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167664","url":null,"abstract":"We introduce problems of decentralized control with delayed communication, where delays are either unbounded or bounded by a given constant k. In the k-bounded-delay model, between the transmission of a message and its reception, the plant can execute at most k events. In the unbounded-delay model, the plant can execute any number of events between transmission and reception. We show that our framework yields an infinite hierarchy of control problems, /spl Cscr//spl Cscr/ =/spl Dscr//spl Cscr//spl Cscr//sub 0//spl sup//spl Dscr//spl Cscr//spl Cscr//sub 1//spl sup//spl Dscr//spl Cscr//spl Cscr//sub 2//spl sup//spl middot//spl middot//spl middot//spl sup//spl Dscr//spl Cscr//spl Uscr//spl Cscr//spl sup//spl Dscr//spl Cscr/ , where CC is the set of control problems solvable with a single controller (centralized case) and /spl Dscr//spl Cscr//spl Cscr//sub k/ (resp. /spl Dscr//spl Cscr//spl Uscr//spl Cscr/, /spl Dscr//spl Cscr/) is the set of problems solvable with two controllers in a k-bounded-delay network (resp. two controllers in an unbounded-delay network, two controllers without communication). The above containments are strict. We prove the undecidability of checking the existence of controllers in the unbounded-delay case, or in the case without any communication. Finally, we prove that a decentralized observation problem with bounded-delay communication is decidable.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126852615","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-10-02DOI: 10.1109/WODES.2002.1167674
Tae-Eog Lee, Jeong-Won Seo, Seong-Ho Park
We introduce negative places and negative tokens into timed event graphs in order to model and analyze time window constraints. A negative token moves backward at an associated transition firing. We develop a necessary and sufficient condition, based on the circuits, for the event graph to be live. A sequence of feasible infinite firing epochs exists for each transition. We present a linear programming model for finding a stable firing schedule. We also characterize the minimal cycle time as a revised critical circuit ratio and the range of the feasible cycle times.
{"title":"An extended event graph with negative places and negative tokens for time window constraints","authors":"Tae-Eog Lee, Jeong-Won Seo, Seong-Ho Park","doi":"10.1109/WODES.2002.1167674","DOIUrl":"https://doi.org/10.1109/WODES.2002.1167674","url":null,"abstract":"We introduce negative places and negative tokens into timed event graphs in order to model and analyze time window constraints. A negative token moves backward at an associated transition firing. We develop a necessary and sufficient condition, based on the circuits, for the event graph to be live. A sequence of feasible infinite firing epochs exists for each transition. We present a linear programming model for finding a stable firing schedule. We also characterize the minimal cycle time as a revised critical circuit ratio and the range of the feasible cycle times.","PeriodicalId":435263,"journal":{"name":"Sixth International Workshop on Discrete Event Systems, 2002. Proceedings.","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133261585","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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