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Sökning: WFRF:(Ayani Rassul)

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1.
  • Ayani, Rassul, et al. (författare)
  • Modeling and Simulation of a High Speed LAN
  • 1995
  • Ingår i: Simulation (San Diego, Calif.). - San Diego : Simulation Councils Inc.. - 0037-5497 .- 1741-3133. ; 64:1, s. 7-14
  • Tidskriftsartikel (refereegranskat)abstract
    • Simulation is a tool that can be used to assess functionality and performance of communication networks and protocols. However, efficient simulation of complex communication systems is not a trivial task. In this paper, we discuss modeling and simulation of bus-based communication networks and present the results of modeling and simulation of a multigigabit/s LAN. We used parallel simulation techniques to reduce the simulation time of the LAN and implemented both an optimistic and a conservative parallel simulation scheme. Our experimental results on a shared memory multiprocessor indicate that the conservative parallel simulation scheme is superior to the optimistic one for this specific application. The parallel simulator based on the conservative scheme demonstates a linear speedup for large networks.
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2.
  • Aydt, H., et al. (författare)
  • Symbiotic simulation model validation for radiation detection applications
  • 2009
  • Ingår i: PADS '09. ACM/IEEE/SCS 23rd Workshop on Principles of Advanced and Distributed Simulation, 2009. - : IEEE Computer Society. - 9780769537139 ; , s. 11-18
  • Konferensbidrag (refereegranskat)abstract
    • Detection of radiological dispersal devices (RDDs) is important because of their potential for destruction and psychological impact on the affected population. These devices leave a clear trace which can be followed when using appropriate detection devices. Geiger counter devices provide data regarding the radiation intensity. However, this is not enough information to pinpoint a radiation source. Neither can this information be directly used to classify the radiation source. We describe a method using symbiotic simulation which can be used to classify and localise a radiation source given accurate measurements of radiation intensities at reference points and a detailed model of the environment. Initial classification and localisation, as well as continuous tracking of a moving radiation source, is considered. The effects of a measurement error and a model error are investigated.
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3.
  • Aydt, Heiko, et al. (författare)
  • Toward an Evolutionary Computing Modeling Language
  • 2011
  • Ingår i: IEEE Transactions on Evolutionary Computation. - 1089-778X .- 1941-0026. ; 15:2, s. 230-247
  • Tidskriftsartikel (refereegranskat)abstract
    • The importance of domain knowledge in the design of effective evolutionary algorithms (EAs) is widely acknowledged in the meta-heuristics community. In the last few decades, a plethora of EAs has been manually designed by domain experts for solving domain-specific problems. Specialization has been achieved mainly by embedding available domain knowledge into the algorithms. Although programming libraries have been made available to construct EAs, a unifying framework for designing specialized EAs across different problem domains and branches of evolutionary computing does not exist yet. In this paper, we address this issue by introducing an evolutionary computing modeling language (ECML) which is based on the unified modeling language (UML). ECML incorporates basic UML elements and introduces new extensions that are specially needed for the evolutionary computation domain. Subsequently, the concept of meta evolutionary algorithms (MEAs) is introduced as a family of EAs that is capable of interpreting ECML. MEAs are solvers that are not restricted to a particular problem domain or branch of evolutionary computing through the use of ECML. By separating problem-specific domain knowledge from the EA implementation, we show that a unified framework for evolutionary computation can be attained. We demonstrate our approach by applying it to a number of examples.
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4.
  • Baldoni, R., et al. (författare)
  • An embedded middleware platform for pervasive and immersive environments for-all
  • 2009
  • Ingår i: 2009 6th IEEE Annual Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks Workshops, SECON Workshops 2009. - : IEEE. - 9781424439386 ; , s. 161-163
  • Konferensbidrag (refereegranskat)abstract
    • Embedded systems are specialized computers used in larger systems or machines to control equipments such as automobiles, home appliances, communication, control and office machines. Such pervasivity is particularly evident in immersive realities, i.e., scenarios in which invisible embedded systems need to continuously interact with human users, in order to provide continuous sensed information and to react to service requests from the users themselves. The SM4All project investigates an innovative middleware platform for inter-working of smart embedded services in immersive and person-centric environments, through the use of composability and semantic techniques for dynamic service reconfiguration. This is applied to the challenging scenario of private houses and home-care assistance in presence of users with different abilities and needs (e.g., young, able-bodied, aged and disabled). This paper presentes a brief overview of the SM4All system architecture.
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5.
  • Barriga, Luis, et al. (författare)
  • A model for parallel simulation of distributed shared memory
  • 1996
  • Konferensbidrag (refereegranskat)abstract
    • We present an execution model for parallel simulation of a distributed shared memory architecture. The model captures the processor-memory interaction and abstracts the memory subsystem. Using this model we show how parallel, on-line, partially-ordered memory traces can be correctly predicted without interacting with the memory subsystem. We also outline a parallel optimistic memory simulator that uses these traces, finds a global order among all events, and returns correct data and timing to each processor. A first evaluation of the amount of concurrency that our model can extract for an ideal multiprocessor shows that processors may execute relatively long instruction sequences without violating the causality constraints. However parallel simulation efficiency is highly dependent on the memory consistency model and the application characteristics.
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6.
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7.
  • Eklöf, Martin, et al. (författare)
  • A framework for fault-tolerance in HLA-based distributed simulations
  • 2005
  • Ingår i: Proceedings of the 2005 Winter Simulation Conference. - 0780395190 ; , s. 1182-1189
  • Konferensbidrag (refereegranskat)abstract
    • The widespread use of simulation in future military systems depends, among others, on the degree of reuse and availability of simulation models. Simulation support in such systems must also cope with failure in software or hardware. Research in fault-tolerant distributed simulation, especially in the context of the High Level Architecture (HLA), has been quite sparse. Nor does the HLA standard itself cover fault-tolerance extensively. This paper describes a framework, named Distributed Resource Management System (DRMS), for robust execution of federations. The implementation of the framework is based on Web Services and Semantic Web technology, and provides fundamental services and a consistent mechanism for description of resources managed by the environment. To evaluate the proposed framework, a federation has been developed that utilizes time-warp mechanism for synchronization. In this paper, we describe our approach to fault tolerance and give an example to illustrate how DRMS behaves when it faces faulty federates.
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8.
  • Eklöf, Martin, et al. (författare)
  • Evaluation of a Fault-Tolerance Mechanism for HLA-Based Distributed Simulations
  • 2006
  • Ingår i: 20th Workshop on Principles of Advanced and Distributed Simulation, PADS 2006. - 0769525873 ; , s. 175-182
  • Konferensbidrag (refereegranskat)abstract
    • Successful integration of Modeling and Simulation (M&S) in the future Network-Based Defence (NBD) depends, among other things, on providing fault-tolerant (FT) distributed simulations. This paper describes a framework, named Distributed Resource Management System (DRMS), for robust execution of simulations based on the High Level Architecture. More specifically, a mechanism for FT in simulations synchronized according to the time-warp protocol is presented and evaluated. The results show that utilization of the FT mechanism, in a worst-case scenario, increases the total number of generated messages by 68% if one fault occurs. When the FT mechanism is not utilized, the same scenario shows an increase in total number of generated messages by 90%. Considering the worst-case scenario a plausible requirement on an M&S infrastructure of the NBD, the overhead caused by the FT mechanism is considered acceptable.
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9.
  • Eklöf, Martin (författare)
  • Fault-tolerance in HLA-based distributed simulations
  • 2006
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Successful integration of simulations within the Network-Based Defence (NBD), specifically use of simulations within Command and Control (C2) environments, enforces a number of requirements. Simulations must be reliable and be able to respond in a timely manner. Otherwise the commander will have no confidence in using simulation as a tool. An important aspect of these requirements is the provision of fault-tolerant simulations in which failures are detected and resolved in a consistent manner. Given the distributed nature of many military simulations systems, services for fault-tolerance in distributed simulations are desirable. The main architecture for distributed simulations within the military domain, the High Level Architecture (HLA), does not provide support for development of fault-tolerant simulations. A common approach for fault-tolerance in distributed systems is check-pointing. In this approach, states of the system are persistently stored through-out its operation. In case a failure occurs, the system is restored using a previously saved state. Given the abovementioned shortcomings of the HLA standard this thesis explores development of fault-tolerant mechanisms in the context of the HLA. More specifically, the design, implementation and evaluation of fault-tolerance mechanisms, based on check-pointing, are described and discussed.
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10.
  • Eklöf, Martin, et al. (författare)
  • Peer-to-peer-based resource management in support of HLA-based distributed simulations
  • 2004
  • Ingår i: Simulation (San Diego, Calif.). - : SAGE Publications. - 0037-5497 .- 1741-3133. ; 80:4-5, s. 181-190
  • Tidskriftsartikel (refereegranskat)abstract
    • In recent years, the concept of peer-to-peer computing has gained renewed interest for sharing resources within and between organizations or individuals. This article describes a decentralized resource management system (DRMS) that uses a network of workstations for the execution and storage of high-level architecture (HLA) federations/federates in a peer-to-peer environment. The implementation of DRMS is based on the open-source project JXTA, which represents an attempt to standardize the peer-to-peer domain. DRMS is part of a Web-based simulation environment supporting collaborative design, development, and execution of HLA federations. This study evaluates the possibilities of using peer-to-peer technology for increasing the reuse and availability of simulation components within the defense modelling and simulation community. More specifically, it addresses the necessary adjustments of simulation components to conform to the requirements of the DRMS and shows that JXTA could provide the foundation for a distributed system that increases the possibilities for reusing simulation components.
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11.
  • García Lozano, Marianela, et al. (författare)
  • SDR : a semantic based Distributed Repository for Simulation Models and Resources
  • 2007
  • Ingår i: AMS 2007. - 0769528457 ; , s. 171-176
  • Konferensbidrag (refereegranskat)abstract
    • Recent advances in Internet, Peer-to-Peer and Grid technologies have made collaboration and resource sharing across organizational boundaries more feasible. Today, it is essential for many organizations to be able to discover share and manage distributed resources in a transparent, meaningful and secure way. A fundamental problem is locating, matching and composing resources or services of interest. In this paper we describe our initial work designing and developing a semantic based distributed repository for secure sharing of simulation models, components and related resources such as computer resources. We propose an overlay architecture which combines advances in Semantic Web, Peer-to-Peer and Grid techniques. In our project at the Swedish Defence Research Agency (FOI) we had a need for a repository of simulation related resources and having identified our requirements we found that there was no suitable of-the-shelf system available. We describe the design, tools and a prototype implementation of this system - the Semantic based Distributed Repository (SDR) and conclude with our experiences and some raised issues. We argue that although some of the used techniques still are a bit immature and need further improvements a system like the SDR has a lot of potential and can also be used in other domains than modeling and simulation.
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12.
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13.
  • Kamrani, Farzad, 1961-, et al. (författare)
  • A framework for simulation-based optimization of business process models
  • 2012
  • Ingår i: Simulation (San Diego, Calif.). - : Sage Publications. - 0037-5497 .- 1741-3133. ; 88:7, s. 852-869
  • Tidskriftsartikel (refereegranskat)abstract
    • The Assignment Problem is a classical problem in the field of combinatorial optimization, having a wide range of applications in a variety of contexts. In general terms, the Assignment Problem consists of determining the best assignment of tasks to agents according to a predefined objective function. Different variants of the Assignment Problem have been extensively investigated in the literature in the last 50 years. In this work, we introduce and analyze the problem of optimizing a business process model with the objective of finding the most beneficial assignment of tasks to agents. Despite similarities, this problem is distinguished from the traditional Assignment Problem in that we consider tasks to be part of a business process model, being interconnected according to defined rules and constraints. In other words, assigning a business process to agents is a more complex form of the Assignment Problem. Two main categories of business processes, assignment-independent and assignment-dependent, are distinguished. In the first category, different assignments of tasks to agents do not affect the flow of the business process, while processes in the second category contain critical tasks that may change the workflow, depending on who performs them. In each category several types of processes are studied. Algorithms for finding optimal and near-optimal solutions to these categories are presented. For the first category, depending on the type of process, the Hungarian algorithm is combined with either the analytical method or simulation to provide an optimal solution. For the second category, we introduce two algorithms. The first one finds an optimal solution, but is feasible only when the number of critical tasks is small. The second algorithm is applicable to large number of critical tasks, but provides a near-optimal solution. In the second algorithm a hill-climbing heuristic method is combined with the Hungarian algorithm and simulation to find an overall near-optimal solution. A series of tests is conducted which demonstrates that the proposed algorithms efficiently find optimal solutions for assignment-independent and near-optimal solutions for assignment-dependent processes.
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14.
  • Kamrani, Farzad, 1961-, et al. (författare)
  • A Model for Estimating the Performance of a Team of Agents
  • 2011
  • Ingår i: Proceedings of the 2011 IEEE International Conference on Systems, Man and Cybernetics (SMC 2011). - : IEEE Press. - 9781457706523 ; , s. 2393-2400
  • Konferensbidrag (refereegranskat)abstract
    • In this paper, we present a model for estimatingthe performance of a team of agents, based on the capabilities of the agents and importance of these capabilities for the task. Performance of a team is assumed to be the sum of contributions of individual agents and contributions of subgroups built in the team. We introduce a set of notations, which is required for discussing the suggested models. We also propose a model to estimate the benefit of an agent from interaction with other agents in a subgroup. Based on this benefit model and different (common) strategies, the agents devise plans in which they formulate to what extent they are willing to cooperate with other agents. A negotiation algorithm that resolves the conflicts between the desires of the agents is presented. The effect of this algorithm and different strategies are tested on a set of generated data. The test results show that the performance of a team when the agents choose a cooperation strategy that follows the principle of least effort (Zipf’s law) is higher than teams with other cooperation strategies.
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15.
  • Kamrani, Farzad, et al. (författare)
  • Estimating performance of a business process model
  • 2009
  • Ingår i: Winter Simulation Conference. - 9781424457700 ; , s. 2828-2839
  • Konferensbidrag (refereegranskat)abstract
    • In this paper we suggest a model for estimating performance of human organizations and business processes. This model is based on subjective assessment of the capabilities of the available human resources, the importance of these capabilities, and the influence of the peripheral factors on the resources. The model can be used to compare different resource allocation schemes in order to choose the most beneficial one. We suggest an extension to Business Process Modeling Notation (BPMN) by including performance measure of performers and the probability by which an outgoing Sequence Flow from a Gateway is chosen. We also propose an analytical method for estimating the overall performance of BPMN in simple cases and a simulation method, which can be used for more complicated scenarios. To illustrate how these methods work, we apply them to part of a military Operational Planning Process and discuss the results.
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16.
  • Kamrani, Farzad, 1961-, et al. (författare)
  • Optimizing a Business Process Model by Using Simulation
  • 2010
  • Ingår i: 2010 IEEE Workshop on Principles of Advanced and Distributed Simulation. - : IEEE Press. - 9781424472925 ; , s. 1-8
  • Konferensbidrag (refereegranskat)abstract
    • In this paper we present the problem of optimizing a business process model with the objective of finding the most beneficial assignment of tasks to agents, without modifying the structure of the process itself. The task assignment problem for four types of processes are distinguished and algorithms for finding optimal solutions to them are presented: 1) a business process with a predetermined workflow, for which the optimal solution is conveniently found using the well-known Hungarian algorithm. 2) a Markovian process, for which we present an analytical method that reduces it to the first type. 3) a nonMarkovian process, for which we employ a simulation method to obtain the optimal solution. 4) the most general case, i.e. a nonMarkovian process containing critical tasks. In such processes, depending on the agents that perform critical tasks the workflow of the process may change. We introduce two algorithms for this type of processes. One that finds the optimal solution, but is feasible only when the number of critical tasks is few. The second algorithm is even applicable to large number of critical tasks but provides a near-optimal solution. In the second algorithm a hill-climbing heuristic method is combined with Hungarian algorithm and simulation to find an overall near-optimal solution for assignments of tasks to agents. The results of a series of tests that demonstrate the feasibility of the algorithms are included.
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17.
  • Kamrani, Farzad, et al. (författare)
  • Path planning for UAVs using symbiotic simulation
  • 2006
  • Ingår i: Modelling and Simulation 2006. - 9789077381304 ; , s. 207-213
  • Konferensbidrag (refereegranskat)abstract
    • The problem of efficient path planning for Unmanned Aerial Vehicles (UAV) with a surveillance mission in a dynamic environment can in some cases be solved using Symbiotic Simulation (S2), i.e. an on-line simulation that interacts in real-time with the UAV and chooses its path. Sequential Monte Carlo Simulation, known also as Particle Filtering (PF) is an instance of such a simulation. In this paper we describe a methodology and an algorithm to use PF for efficient path planning of a UAV which searches a road network for a target. To verify whether this method is feasible and to supply a tool to compare different methods a simulator is developed. This simulator and its features are presented in this paper as well.
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18.
  • Kamrani, Farzad, et al. (författare)
  • Simulation-aided path planning of UAV
  • 2007
  • Ingår i: Proceedings Of The 2007 Winter Simulation Conference. - 9781424413058 ; , s. 1285-1293
  • Konferensbidrag (refereegranskat)abstract
    • The problem of path planning for Unmanned Aerial Vehicles (UAV) with a tracking mission, when some a priori information about the targets and the environment is available can in some cases be addressed using simulation. Sequential Monte Carlo Simulation can be used to assess the state of the system and target when the UAV reaches the area of responsibility and during the tracking task. This assessment of the future is then used to compare the impact of choosing different alternative paths on the expected value of the detection time. A path with a lower expected value of detection time is preferred. In this paper the details of this method is described. Simulations are performed by a special purpose simulation tool to show the feasibility of this method and compare it with an exhaustive search.
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19.
  • Kamrani, Farzad, 1961- (författare)
  • Simulation-based Optimization and Decision Making with Imperfect Information
  • 2011
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The purpose of this work is to provide simulation-based support for making optimal (or near-optimal) decisions in situations where decision makers are faced with imperfect information. We develop several novel techniques and algorithms for simulation-based optimization and decision support and apply them to two categories of problems: (i) Unmanned Aerial Vehicle (UAV) path planning in search operations, and; (ii) optimization of business process models. Common features of these two problems for which analytical approaches are not available, are the presence of imperfect information and their inherent complexity. In the UAV path planning problem, the objective is to define the path of a UAV searching for a target on a known road network. It is assumed that the target is moving toward a goal and we have some uncertain information about the start point of the target, its velocity, and the final goal of the target. The target does not take evasive action to avoid being detected. The UAV is equipped with a sensor, which may detect the target once it is in the sensor’s scope. Nevertheless, the detection process is uncertain and the sensor is subject to both false-positive and false-negative errors. We propose three different solutions, two of which are simulation-based. The most promising solution is an on-line simulation-based method that estimates the location of the target by using a Sequential Monte Carlo (SMC) method. During the entire mission, different UAV paths are simulated and the one is chosen that most reduces the uncertainty about the location of the target. In the optimization of the business process models, several different but related problems are addressed: (i) we define a measure of performance for a business process model based on the value added by agents (employees) to the process; (ii) we use this model for optimization of the business process models. Different types of processes are distinguished and methods for finding the optimal or near-optimal solutions are provided; (iii) we propose a model for estimating the performance of collaborative agents. This model is used to solve a class of Assignment Problems (AP), where tasks are assigned to collaborative agents; (iv) we propose a model for team activity and the performance of a team of agents. We introduce different collaboration strategies between agents and a negotiation algorithm for resolving conflicts between agents. We compare the effect of different strategies on the output of the team. Most of the studied cases are complex problems for which no analytical solution is available. Simulation methods are successfully applied to these problems. They are shown to be more general than analytical models for handling uncertainty since they usually have fewer assumptions and impose no restrictions on the probability distributions involved. Our investigation confirms that simulation is a powerful tool for providing decision-making support. Moreover, our proposed algorithms and methods in the accompanying articles contribute to providing support for making optimal and in some cases near-optimal decisions: (i) our tests of the UAV simulation-based search methods on a simulator show that the on-line simulation method has generally a high performance and detects the target in a reasonable time. The performance of this method was compared with the detection time when the UAV had the exact information about the initial location of the target, its velocity, and its path (minimum detection time). This comparison indicated that the online simulation method in many cases achieved a near-optimal performance in the studied scenario; (ii) our business process optimization framework combines simulation with the Hungarian method and finds the optimal solution for all cases where the assignment of tasks does not change the workflow of the process. For the most general cases, where the assignment of tasks may change the workflow, we propose an algorithm that finds near-optimal solutions. In this algorithm, simulation, which deals with the uncertainty in the process, is combined with the Hungarian method and hill-climbing heuristics. In the study of assigning tasks to collaborative agents we suggest a Genetic Algorithm (GA) that finds near-optimal solutions with a high degree of accuracy, stability, scalability and robustness. While investigating the effect of different agent strategies on the output of a team, we find that the output of a team is near-optimal, when agents choose a collaboration strategy that follows the principle of least effort (Zipf’s law) and use our suggested algorithm for negotiation and resolving conflicts. 
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20.
  • Kamrani, Farzad, 1961-, et al. (författare)
  • UAV Path Planning in Search Operations
  • 2009
  • Ingår i: Aerial Vehicles. - : InTech. - 9789537619411 ; , s. 331-344
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)
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21.
  • Kamrani, Farzad, et al. (författare)
  • Using on-line simulation for adaptive path planning of UAVs
  • 2007
  • Ingår i: DS-RT 2007. - LOS ALAMITOS : IEEE COMPUTER SOC. - 9780769530116 ; , s. 167-174
  • Konferensbidrag (refereegranskat)abstract
    • In a surveillance mission, the task of Unmanned. Aerial Vehicles (UAV) path planning can in some cases be addressed using Sequential Monte Carlo (SMC) simulation. If sufficient a priori information about the target and the environment is available an assessment of the future state of the target is obtained by the SMC simulation. This assessment is used in a set of "what-if" simulations to compare different alternative UAV paths. In a static environment this simulation can be conducted prior to the mission. However if the environment is dynamic, it is required to run the "what-if" simulations on-line i.e. in real-time. In this paper the details of this on-line simulation approach in UAV path planning is studied and its performance is compared with two other methods: an off-line simulation aided path planning and an exhaustive search method. The conducted simulations indicate that the on-line simulation has generally a higher performance compared with the two other methods.
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22.
  • Kamrani, Farzad (författare)
  • Using on-line simulation in UAV path planning
  • 2007
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In this thesis, we investigate the problem of Unmanned Aerial Vehicle (UAV) path planning in search or surveillance mission, when some a priori information about the targets and the environment is available. A search operation that utilizes the available a priori information about the initial location of the targets, terrain data, and information from reasonable assumptions about the targets movement can in average perform better than a uniform search that does not incorporate this information. This thesis provides a simulation-based framework to address this type of problem. Search operations are generally dynamic and should be modified during the mission due to new reports from other sources, new sensor observations, and/or changes in the environment, therefore a Symbiotic Simulation method that employs the latest data is suggested. All available information is continuously fused using Particle Filtering to yield an updated picture of the probability density of the target. This estimation is used periodically to run a set of what-if simulations to determine which UAV path is most promising. From a set of different UAV paths the one that decreases the uncertainty about the location of the target is preferable. Hence, the expectation of information entropy is used as a measure for comparing different courses of action of the UAV. The suggested framework is applied to a test case scenario involving a single UAV searching for a single target moving on a road network. The performance of the Symbiotic Simulation search method is compared with an off-line simulation and an exhaustive search method using a simulation tool developed for this purpose. The off-line simulation differs from the Symbiotic Simulation search method in that in the former case the what-if simulations are conducted before the start of the mission. In the exhaustive search method the UAV searches the entire road network. The Symbiotic Simulation shows a higher performance and detects the target in the considerably shorter time than the other two methods. Furthermore, the detection time of the Symbiotic Simulation is compared with the detection time when the UAV has the exact information about the initial location of the target, its velocity and its path. This value provides a lower bound for the optimal solution and gives another indication about the performance of the Symbiotic Simulation. This comparison also suggests that the Symbiotic Simulation in many cases achieves a “near” optimal performance.
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23.
  • Khatib, Iyad Al, et al. (författare)
  • Wireless LAN Access Points as a Queuing System
  • 2002
  • Ingår i: Proceedings of The Communications and Computer Networks 2002 Conference (CCN 2002). ; , s. 463-468
  • Konferensbidrag (refereegranskat)abstract
    • This paper presents a research study of wireless LAN access points for IEEE 802.11b, where we seek to model the access point as a queuing system. The model can be used to compare performance metrics of different wireless LAN access points and to investigate the QoS of specific applications in the presence of a wireless LAN access point. In this paper, we focus on two parameters: the delay introduced by a wireless LAN access point and the average service time required to serve a packet passing through an access point. A major result is an analytic solution for the average service time of a packet in relationship to payload.
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24.
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25.
  • Khatib, Iyad Al, et al. (författare)
  • Wireless LAN Access Points as Queuing Systems : Performance Analysis and Service Time
  • 2003
  • Ingår i: Mobile Computing and Communications Review. - : Association for Computing Machinery (ACM). - 1559-1662 .- 1931-1222. ; 7:1, s. 28-30
  • Tidskriftsartikel (refereegranskat)abstract
    • Since the approval of the IEEE 802.11b by the IEEE in 1999, the demand for WLAN equipment and networks has been growing quickly. We present a queuing model of wireless LAN (WLAN) access points (APs) for IEEE 802.11b. We use experimentation to obtain the characteristic parameters of our analytic model. The model can be used to compare the performance of different WLAN APs as well as the QoS of different applications in the presence of an AP. We focus on the delay introduced by an AP. The major observations are that the delay to serve a packet going from the WLAN medium to the wired medium (on the uplink) is less than the delay to serve a packet, with identical payload, but travelling from the wired medium to the WLAN medium (on the downlink). A key result is an analytic solution showing that the average service time of a packet is a strictly increasing function of payload.
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26.
  • Khatib, Iyad Al, et al. (författare)
  • Wireless LAN Access Points Uplink and Downlink Delays : Packet Service-Time Comparison
  • 2002
  • Ingår i: Proceedings of 16th Nordic Teletraffic Seminar, 2002. ; , s. 253-264
  • Konferensbidrag (refereegranskat)abstract
    • Wireless LAN access points are very important connecting nodes transferring traffic between two media in opposite directions. Hence the performance of the wireless LAN access point should be looked upon from two different reference points: uplink (from WLAN to Ethernet) and Downlink (from Ethernet to WLAN). This paper builds on our previous modeling of the wireless access point as a single server, FIFO, queuing system to analyze the service times in both directions. The previous analysis showed that the average service time is a function of payload. Measurements have revealed that the uplink service time is much smaller than the downlink service time for the same payload. In this paper, we investigate the absolute value of the difference between the uplink and downlink service-times. We refer to the absolute value of the difference in time between uplink and downlink as the UDC, or the"Uplink-Downlink Contrast". Results show that as the packet size increases, the UDC either decreases or increases monotonically depending on the brand of the access point. For a decreasing UDC, the absolute value of the difference between the uplink and downlinkservice-times decreases, hence the UDC is convergent. Similarly, the UDC is divergent if it increases with increasing packet size. These results can be used to select a WLAN accesspoint given the size of packets transmitted by an application or multiple applications over a Local Area Network.
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27.
  • Li, Fei, et al. (författare)
  • Proactive Service Discovery in Pervasive Environments
  • 2010
  • Ingår i: Proceedings of the 7th ACM International Conference on Pervasive Services (ICPS). ; , s. 126-133
  • Konferensbidrag (refereegranskat)abstract
    • Pervasive environments are characterized by rich and dy-namic context, where users need to be continuously informed about services relevant to their current context. Implicit discovery requests, triggered by changes of user context, avail-able services, or user preferences are prevalent in such environments.This paper proposes a proactive service discovery approach for pervasive environments to address these implicit requests. Services and user preferences are described by a formal context model, which effectively captures the dynamics of context and the relationship between services and users. Based on the model, we propose a proactive discovery algorithm to continuously present the most relevant services to the user in response to changes of context, services or user preferences. Numeric coding methods are applied in different phases of the algorithm to improve its performance. A proactive service discovery system is proposed and the context model is grounded in a smart home environment. Experimental results show that our approach can efficiently provide the user with up-to-date information about useful services.
  •  
28.
  • Li, F., et al. (författare)
  • Unsupervised context-aware user preference mining
  • 2013
  • Ingår i: Proceeding of Workshop on Activity Context-Aware System Architectures at the 27th AAAI Conference on Artificial Intelligence. - 9781577356165 ; , s. 36-43
  • Konferensbidrag (refereegranskat)abstract
    • In pervasive environments, users are situated in rich context and can interact with their surroundings through various services. To improve user experience in such environments, it is essential to find the services that satisfies user preferences in certain context. Thus the suitability of discovered services is highly dependent on how much the context-aware system can understand users' current context and preferred activities. In this paper, we propose an unsupervised learning solution for mining user preferences from the user's past context. To cope with the high dimensionality and heterogeneity of context data, we propose a subspace clustering approach that is able to find user preferences identified by different feature sets. The results of our approach are validated by a series of experiments.
  •  
29.
  • Liljenstam, M., et al. (författare)
  • Partitioning WCN models for parallel simulation of radio resource management
  • 2001
  • Ingår i: Wireless networks. - 1022-0038 .- 1572-8196. ; 7:3, s. 307-324
  • Tidskriftsartikel (refereegranskat)abstract
    • Parallel Simulation techniques have been proposed as a possible solution to execution time and memory constraints often found in detailed simulations of Wireless Cellular Networks. However, partitioning represents a major challenge for models that encompass elements of radio propagation phenomena. This paper discusses the partitionings problem with respect to Parallel Discrete Event Simulation and we formulate an approach to study partitioning of a WCN model that includes radio propagation. Various options for a model of moderate size and where interference is calculated over the whole system are evaluated through experimentation and some limited mathematical analysis. Results indicate that radio spectrum based partitioning is preferable to geographically based partitionings for this model in many realistic scenarios. It is also noted that characteristics of the model differ sufficiently from other previously studied spatially explicit problems to reduce or even annihilate the effectiveness of some commonly used partitioning techniques.
  •  
30.
  • Mahmood, Imran, 1978- (författare)
  • A Verification Framework for Component Based Modeling and Simulation : “Putting the pieces together”
  • 2013
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The discipline of component-based modeling and simulation offers promising gains including reduction in development cost, time, and system complexity. This paradigm is very profitable as it promotes the use and reuse of modular components and is auspicious for effective development of complex simulations. It however is confronted by a series of research challenges when it comes to actually practice this methodology. One of such important issue is Composability verification. In modeling and simulation (M&S), composability is the capability to select and assemble components in various combinations to satisfy specific user requirements. Therefore to ensure the correctness of a composed model, it is verified with respect to its requirements specifications.There are different approaches and existing component modeling frameworks that support composability however in our observation most of the component modeling frameworks possess none or weak built-in support for the composability verification. One such framework is Base Object Model (BOM) which fundamentally poses a satisfactory potential for effective model composability and reuse. However it falls short of required semantics, necessary modeling characteristics and built-in evaluation techniques, which are essential for modeling complex system behavior and reasoning about the validity of the composability at different levels.In this thesis a comprehensive verification framework is proposed to contend with some important issues in composability verification and a verification process is suggested to verify composability of different kinds of systems models, such as reactive, real-time and probabilistic systems. With an assumption that all these systems are concurrent in nature in which different composed components interact with each other simultaneously, the requirements for the extensive techniques for the structural and behavioral analysis becomes increasingly challenging. The proposed verification framework provides methods, techniques and tool support for verifying composability at its different levels. These levels are defined as foundations of a consistent model composability. Each level is discussed in detail and an approach is presented to verify composability at that level. In particular we focus on theDynamic-Semantic Composability level due to its significance in the overallcomposability correctness and also due to the level of difficulty it poses in theprocess. In order to verify composability at this level we investigate the application ofthree different approaches namely (i) Petri Nets based Algebraic Analysis (ii) ColoredPetri Nets (CPN) based State-space Analysis and (iii) Communicating SequentialProcesses based Model Checking. All the three approaches attack the problem ofverifying dynamic-semantic composability in different ways however they all sharethe same aim i.e., to confirm the correctness of a composed model with respect to itsrequirement specifications. Beside the operative integration of these approaches inour framework, we also contributed in the improvement of each approach foreffective applicability in the composability verification. Such as applying algorithmsfor automating Petri Net algebraic computations, introducing a state-space reductiontechnique in CPN based state-space analysis, and introducing function libraries toperform verification tasks and help the molder with ease of use during thecomposability verification. We also provide detailed examples of using each approachwith different models to explain the verification process and their functionality.Lastly we provide a comparison of these approaches and suggest guidelines forchoosing the right one based on the nature of the model and the availableinformation. With a right choice of an approach and following the guidelines of ourcomponent-based M&S life-cycle a modeler can easily construct and verify BOMbased composed models with respect to its requirement specifications.
  •  
31.
  • Mahmood, Imran, et al. (författare)
  • Behavioral verification of BOM based composed models
  • 2010
  • Ingår i: 22th European Modeling and Simulation Symposium, EMSS 2010. - Fes, Moroco : ESISA Ecole Supérieure d'Ingénierie en Sciences Appliquées. - 2952474788 - 9782952474788 ; , s. 341-350
  • Konferensbidrag (refereegranskat)abstract
    • A verified composition of predefined reusable simulation components such as BOM (Base Object Model) plays a significant role in saving time and cost in the development of various simulations. BOM represents a reusable component framework and posses the ability to rapidly compose simulations but lacks semantic and behavioral expressiveness required to match components for a suitable composition. Moreover external techniques are required to evaluate behavioral verification of BOM based components. In this paper we discuss behavioral verification and propose an approach to verify the dynamic behavior of a set of composed BOM components against given specifications. We further define a Model Tester that provides means to verify behavior of a composed model during its execution. We motivate our verification approach by suggesting solutions for some of the categories of system properties. We also provide a case study to clarify our approach.
  •  
32.
  • Mahmood, Imran, et al. (författare)
  • Composability Test of BOM based models using Petri Nets
  • 2010
  • Ingår i: Proceedings of the 22nd IFIP International Conferenceon Testing Software and Systems: Short Papers. - Montreal, QC Canada : CRIM (Centre de recherche informatique de Montréal). - 9782895221364 ; , s. 7-12
  • Konferensbidrag (refereegranskat)abstract
    • Reusability is a widely used concept which has recently receivedrenewed attention to meet the challenge of reducing cost and timeof simulation development. An approach to achieve effective reusabilityis through composition of predefined components which is promising buta daunting challenge in the research community. Base Object Model(BOM) is a component-based standard designed to support reusabilityand composability in distributed simulation community. BOM providesgood model representation for component reuse however this frameworklacks capability to express semantic and behavioral matching at the conceptuallevel. Furthermore there is a need for a technique to test thecorrectness of BOM-compositions in terms of structure and behavior. Inthis paper we discuss verification of BOM based model and test its suitabilityfor the intended purpose and objectives. We suggest a techniquethrough which the composed model can automatically be transformedinto a single Petri Net (PN) model and thus can further be verified usingdifferent existing PN analysis tools. We further motivate our approachby suggesting a deadlock detection technique as an example, and providea case study to clarify our approach.
  •  
33.
  • Mahmood, Imran, 1978-, et al. (författare)
  • Composability Verification of Real Time System Models Using Colored Petri Nets
  • 2013
  • Ingår i: Proceedings - UKSim 15th International Conference on Computer Modelling and Simulation, UKSim 2013. - New York : IEEE. - 9780769549941 ; , s. 407-412
  • Konferensbidrag (refereegranskat)abstract
    • The discipline of component based modeling and simulation offers promising gains including reduction in development cost, time, and system complexity. It also promotes (re)use of modular components to build complex simulations. Many important issues in this area have been addressed, but composability verification is still considered a daunting challenge. In our observation most of the component based modeling frameworks possess weak built-in support for the composability verification, which is required to guarantee the correctness of the structural, behavioral and temporal aspects of the composition. In this paper we stage a practical approach to alleviate some of the challenges in composability verification and propose a process to verify composability of real-time system models. We emphasize on dynamic semantic level and present our approach using Colored Petri Nets and State Space analysis. We also present a Field Artillery model as an example of real-time system and explain how our approach verifies model composability.
  •  
34.
  • Mahmood, Imran, 1978-, et al. (författare)
  • Fairness Verification of BOM-Based Composed Models Using Petri Nets
  • 2011
  • Ingår i: Proceedings of the 2011 IEEE Workshop on Principles of Advanced and Distributed Simulation. - Washington, DC, USA : IEEE Computer Society. - 9781457713637 ; , s. 5936770-
  • Konferensbidrag (refereegranskat)abstract
    • Model reuse is a promising and appealing convention for effective development of simulation systems. However it poses daunting challenges to various issues in research such as Reusability and Composability in model integration. Various methodological advances in this area have given rise to the development of different component reusability frameworks such as BOM (Base Object Model). However, lack of component matching and support for composability verification and validation makes it difficult to achieve effective and meaningful reuse. For this reason there is a need for adequate methods to verify and validate composability of a BOM based composed model. A verified composed model ensures the satisfaction of desired system properties. Fairness, as defined in section II, is an important system property which ensures that no component in a composition is delayed indefinitely. Fairness in a composed model guarantees the participation of all components in order to achieve the desired objectives. In this paper we focus on verification and propose to transform a composed BOM into a Petri Nets model and use different analysis techniques to perform its verification. We propose an algorithm to verify fairness property and provide a case study of a manufacturing system to explain our approach.
  •  
35.
  • Mahmood, Imran, et al. (författare)
  • Statemachine Matching in BOM based model Composition
  • 2009
  • Ingår i: IEEE ACM DIS SIM REAL TIME. - Los Alamitos, CA : IEEE COMPUTER SOC. - 9780769538686 ; , s. 136-143
  • Konferensbidrag (refereegranskat)abstract
    • Base Object Model (BOM) is a component-based standard designed to support reusability and Composability. Reusability helps in reducing time and cost of the development of a simulation process. Composing predefined components such as BOMs is a well known approach to achieve reusability. However, there is a need for a matching mechanism to identify whether a set of components are composable or not. Although BOM provides good model representation, it lacks capability to express semantic and behavioral matching. In this paper we propose an approach for matching behavior of BOM components by matching their statemachines. Our proposed process includcs a static and a dynamic matching phase. In the static matching phase, we apply a set of rules to validate the structure of statemachines. In the dynamic matching phase, we execute the statemachines together at an abstract level on our proposed execution framework. We have developed this, framework using the Slate Chart Extensible Markup Language (SCXML), which is a W3C compliant standard. If the execution terminates successfully (i.e. reaches specified final stales) we conclude that there is a positive match and the behavior of these BOMs is composable. We describe the matching process and the implementation of our runtime environment in detail and present a case study as proof of concept.
  •  
36.
  • Mahmood, Imran, et al. (författare)
  • Verifying dynamic semantic composability of BOM-based composed models using colored petri nets
  • 2012
  • Ingår i: Principles of Advanced and Distributed Simulation (PADS), 2012 ACM/IEEE/SCS 26th Workshop on. - : IEEE. - 9780769547145 ; , s. 250-257
  • Konferensbidrag (refereegranskat)abstract
    • Model reuse is a promising and appealing convention for effective development of simulation systems as it offers reduction in development cost and time. Various methodological advances in this area have given rise to the development of different component reusability frameworks such as BOM (Base Object Model). But lack of component matching and weak support for compos ability verification and validation, in these frameworks, makes it difficult to achieve effective and meaningful reuse. In this paper we focus on Compos ability verification and propose a process to verify BOM based composed model at dynamic semantic level. We suggest an extension to the BOM components, to capture behavior at a greater detail. Then we transform the extended BOM into our proposed Colored Petri Nets (CPN) based component model so that the components can be composed and executed at an abstract level. Subsequently we advocate to use CPN tools and analysis techniques to verify that the model satisfy given requirements. We classify the properties of a system among different groups and express the model's requirements by selecting some of the properties from these groups to form requirement specification. Also we present an example of a Field Artillery model, in which we select a set of properties as requirement specification, and explain how CPN state-space analysis technique is used to verify the required properties. Our experience confirms that CPN tools provide strong support for verification of composed models.
  •  
37.
  • March, V., et al. (författare)
  • Collision detection and resolution in hierarchical peer-to-peer systems
  • 2005
  • Ingår i: Proceedings - Conference on Local Computer Networks, LCN. - 0769524214 - 9780769524214 ; , s. 2-9
  • Konferensbidrag (refereegranskat)abstract
    • Structured peer-to-peer systems can be organized hierarchically as two-level overlay networks. The top-level overlay consists of groups of nodes, where each group is identified by a group identifier. In each group, one or more nodes are designated as supernodes and act as gateways to the nodes at the second level. A collision occurs during join operations, when two or more groups with the same group identifier are created at the top-level overlay. Collisions increase the lookup path length and the stabilization overhead, and reduce the scalability of hierarchical peer-to-peer systems. We propose a new scheme to detect and resolve collisions, and we study the impact of the collision problem on the performance of peer-to-peer systems. Our simulation results show the effectiveness of our scheme in reducing collisions and maintaining the size of the top-level overlay close to the ideal size.
  •  
38.
  • Moradi, Farshad, 1966- (författare)
  • A Framework for Component Based Modelling and Simulation using BOMs and Semantic Web Technology
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Modelling and Simulation (M&S) is a multi-disciplinary field that is widely used in various domains. It provides a means to study complex systems before actual physical prototyping and helps lowering, amongst others, manufacturing and training costs. However, as M&S gains more popularity, the demand on reducing time and resource costs associated with development and validation of simulation models has also increased. Composing simulation models of reusable and validated simulation components is one approach for addressing the above demand. This approach, which is still an open research issue in M&S, requires a composition process that is able to support a modeller with discovery and identification of components as well as giving feedback on feasibility of a composition. Combining components in order to build new simulations raise the non-trivial issue of composability. Composability has been defined as the capability to select and assemble reusable simulation components in various combinations into simulation systems to meet user requirements. There are three main types of composability, syntactic, semantic and pragmatic. Syntactic composability is concerned with the compatibility of implementation details, such as parameter passing mechanisms, external data accesses, and timing mechanisms. It is the question of whether a set of components can be combined. Semantic composability, on the other hand, is concerned with the validity of the composition, and whether the composed simulation is meaningful. Pragmatic composability is yet another type which is concerned with the context of the simulation, and whether the composed simulation meets the intended purpose of the modeller. Of these three types syntactic composability is easiest to accomplish and some significant progresses on this issue have been reported in the literature. Semantic and pragmatic composability are much harder to achieve and has inspired many researchers to conduct both theoretical and experimental research. The Base Object Model (BOM) is a new concept identified within M&S community as a potential facilitator for providing reusable model components for the rapid construction and modification of simulations. Although BOMs exhibit good capabilities for reuse and composability they lack the required semantic information for semantic matching and composition. There is little support for defining concepts and terms in order to avoid ambiguity, and there is no method for matching behaviour of conceptual models (i.e., state machines of the components), which is required for reasoning about the validity of BOM compositions. In this work we have developed a framework for component-based model development that supports both syntactic and semantic composability of simulation models by extending the BOM concept using ontologies, Semantic Web and Web Services technologies, and developing a rule-based method for reasoning about BOM compositions. The issue of pragmatic composability has not been the focus of this work, and it has only been partly addressed. The framework utilises intelligent agents to perform discovery and composition of components, according to the modeller needs. It includes a collaborative environment, a semantic distributed repository and an execution environment to support model development and execution process. The basic assumption of this work is that semantic composability should be achieved at conceptual level. Through precise definition and specification of components’ semantic and syntax one can capture the basic requirements for matching and semantically meaningful composition of those components. This requires a common methodology for specification of simulation components. The specification methodology consists of meta-models describing simulation components at different levels. In order to enable automatic matching of meta-models they are formalized and structured using Semantic Web technology in OWL (Web Ontology Language). Hence, the models are based on ontologies to avoid misunderstanding and to provide unambiguous definitions as a basis for reasoning about syntactic and semantic validity of compositions.
  •  
39.
  • Moradi, Farshad, et al. (författare)
  • A rule-based approach to syntactic and semantic composition of BOMs
  • 2007
  • Ingår i: 11th IEEE International Symposium on Distrubuted Simulation and Real Time Applications. ; , s. 145-155
  • Konferensbidrag (refereegranskat)abstract
    • Creating simulation models via composition of predefined and reusable components is an efficient way of reducing costs and time associated with the simulation model development process. However, in order to successfully compose models one has to solve the issues of syntactic and semantic composability of components. HLA is the most widely used architecture for distributed simulations today. It provides a simulation environment and standards for specifying simulation parts and interactions between simulation parts. But it provides little support for semantic composability. The Base Object Model (BOM) standard is an attempt to ease reusability and composition of simulation models. However, BOMs do not contain sufficient information for defining concepts and terms in order to avoid ambiguity, and provide no methods for matching conceptual models (state machines). In this paper, we present our approach for enhancement of the semantic contents of BOMs and propose a three-layer model for syntactic and semantic matching of BOMs. The semantic enhancement includes ontologies for entities, event and interactions in each component. We also present an OWL-S description for each component including the state machines. The three-layer model, consists of syntactic matching, static semantic matching and dynamic semantic matching utilising a set of rules for reasoning about the compositions. We also describe our discovery and matching rules, which have been implemented in the Jess inference engine. In order to test our approach we have defined some simulation scenarios and implemented BOMs as building blocks for development of those scenarios, one of which has been presented in this paper. Our result shows that the three-layer model is promising and can improve and simplify composition of BOM-based components.
  •  
40.
  • Moradi, F., et al. (författare)
  • A rule-based semantic matching of base object models
  • 2009
  • Ingår i: International Journal of Simulation and Process Modelling. - 1740-2123 .- 1740-2131. ; 5:2, s. 132-145
  • Tidskriftsartikel (refereegranskat)abstract
    • Creating simulation models via composition of predefined and reusable components is an efficient way of reducing costs and time associated with the simulation model development. However, to successfully compose models one has to solve the issues of syntactic and semantic composability of components. The Base Object Model (BOM) standard is an attempt to ease reusability and composition of simulation models. However, the BOM does not contain sufficient information for defining necessary concepts and terms to avoid ambiguity, and neither does it have any method for dynamic aspects matching conceptual models (i.e., their state-machines). In this paper, we present our approach for enhancement of the semantic contents of BOMs and propose a three-layer model for syntactic and semantic matching of BOMs. The enhancement includes ontologies for entities, events and interactions in each component. We also present an OWL-S description for each component, including the state-machines. To test our approach, we specify some simulation scenarios and implement BOMs as building blocks for development of those scenarios, one of which is presented in this paper. We also define composability degree, which quantifies closeness of the composed model to a given model specification. Our results show that the three-layer model is promising and can improve and simplify the composition of BOM-based components.
  •  
41.
  • Moradi, Farshad, et al. (författare)
  • An Agent-based Environment for Simulation Model Composition
  • 2008
  • Ingår i: Proceedings of the 22nd ACM/IEEE/SCS Workshop on Principles of Advanced and Distributed Simulation PADS. - 9780769531595 ; , s. 175-184
  • Konferensbidrag (refereegranskat)abstract
    • As Modelling and Simulation gains more popularity, the demand on reducing time and resource costs associated with development and validation of simulation models has also increased. Composing simulation models of reusable and validated simulation components is one approach for addressing the above demand. This approach requires a composition process that is able to support a modeller with discovery and identification of components as well as giving feedback on feasibility of a composition. Software agents are programs that can with some degree of autonomy perform tasks on behalf of a user or another program. In a Multi Agent System (MAS) autonomous agents interact and collaborate with each other in order to solve complex problems that are beyond the individual capabilities or knowledge of each agent, thus providing modularity and scalability. The objective of this work has been to develop a Multi Agent System for discovery and composition of BOM (Base Object Model) based simulation models, which provides the flexibility and adaptability to test and assess, amongst others different discovery and composition methods and techniques. The MAS that we developed is based on the JACK (TM) Intelligent Agents and executes a rule-based process for discovery and composition of BOMB. Our preliminary results indicate its feasibility, portability, adaptability and flexibility.
  •  
42.
  • Moradi, Farshad, et al. (författare)
  • Parallel and distributed simulation
  • 2003
  • Ingår i: Applied system simulation. - : Kluwer. - 1402076037 ; , s. 457-486
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)
  •  
43.
  • Moradi, Farshad, et al. (författare)
  • Simulation Model Composition using BOMs
  • 2006
  • Ingår i: 10th IEEE International Symposium on Distributed Simulation and Real Time Applications. - 0769526977 ; , s. 242-249
  • Konferensbidrag (refereegranskat)abstract
    • The Base Object Model, BOM, is a new standard for defining reusable and composable simulation components. The introduction of BOMs into the simulation community opens zip the possibility of component based simulation development approach that is faster and more efficient than today's simulation creation process. In this paper we describe a process that has been developed at the Swedish Defence Research Agency (FOI) with the aim to speed up and improve the development of simulation models. This process utilizes the BOM concept coupled with Ontologies in simulation development, and employs SRML (Simulation Reference Markup Language) as a means to define a component based simulation on a high-level. We will present out, experimental results and findings based on our implementation of the proposed process. Our experience indicates that including ontological information in BOMs will further increase their usability.
  •  
44.
  • Moradi, Farshad, et al. (författare)
  • Some Ownership Management Issues in Distributed Simulation Using HLA/RTI
  • 2001
  • Ingår i: Parallel and Distributed Computing Practices. - 1097-2803. ; 4:1
  • Tidskriftsartikel (refereegranskat)abstract
    • To study the High Level Architecture (HLA) and the services that are provided by the Runtime Infrastructure (RTI), in particular Object Management and Ownership Management, we have developed a distributed air traffic controller simulator. In our simulation model, each airport is represented by a federate and controls a number of aircraft. The control of the aircraft is transferred among airports as the aircraft fly to different airports. In this paper we discuss two different approaches that we have used to facilitate the exchange of ownership of aircraft attributes among federates, namely the pull and the negotiated push method. We present a comparison of the two methods and also discuss the problems associated with each method and our approach to resolving them. These problems include the oscillation effect, which causes aircraft attributes to be pulled back and forth between federates, and the pending attribute acquisition requests, which result in loss of aircraft (or unattended aircraft attributes). We have experienced that in such scenarios, the push method is more efficient and accurate. We also present our experiences and observations from our experimentation with the RTI. We have noticed some shortcomings in the current RTI interface specification that we will discuss in the paper.
  •  
45.
  • Popescu, Adrian, et al. (författare)
  • Modeling and Analysis of Multi-Access Mechanisms in SUPERLAN
  • 1999
  • Ingår i: Network Systems Design. - : Gordon and Breach Science Publishers. - 9056996355 ; , s. 47-68
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • Today, new multi-Gbps LANs are designed to support a wide range of applications generating isochronous and nonisochronous traffic at arbitrary bit rates. The growing demand for high bandwidth networking, under increasing performance constraints, has posed fundamental challenges to LAN design and implementation. Three fundamental bottlenecks exist in a multi-Gbps LAN environment that must be handled in order to achieve optimal performance. These are: opto-electronic bottleneck, service bottleneck, and processing bottleneck. A novel architectural solution is proposed to open up these bottlenecks. Total network throughput of about 20 Gbps is achievable. Performance modeling, analysis and evaluation is reported for a class of Medium Access Protocols (MAC) for isochronous traffic. The performance results show good and very good performance for this solution.
  •  
46.
  • Rasch, Katharina, et al. (författare)
  • Automatic description of context-altering services through observational learning
  • 2012
  • Ingår i: Pervasive Computing. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642312045 ; , s. 461-477
  • Konferensbidrag (refereegranskat)abstract
    • Understanding the effect of pervasive services on user context is critical to many context-aware applications. Detailed descriptions of context-altering services are necessary, and manually adapting them to the local environment is a tedious and error-prone process. We present a method for automatically providing service descriptions by observing and learning from the behavior of a service with respect to its environment. By applying machine learning techniques on the observed behavior, our algorithms produce high quality localized service descriptions. In a series of experiments we show that our approach, which can be easily plugged into existing architectures, facilitates context-awareness without the need for manually added service descriptions.
  •  
47.
  • Rasch, Katharina, 1982-, et al. (författare)
  • Context-driven personalized service discovery in pervasive environments
  • 2011
  • Ingår i: World wide web (Bussum). - MA, USA : Kluwer Academic Publishers Hingham. - 1386-145X .- 1573-1413. ; 14:4, s. 295-319
  • Tidskriftsartikel (refereegranskat)abstract
    • Pervasive environments are characterized by a large number of embedded devices offering their services to the user .Which of the available services are of most interest to the user considerably depends on the user’s current context. User context is often rich and very dynamic; making an explicit, user-driven discovery of services impractical. Users in such environments would instead like to be continuously informed about services relevant to them. Implicit discovery requests triggered by changes in the context are therefore prevalent. This paper proposes a proactiveservice discovery approach for pervasive environments addressing these implicit requests. Services and user preferences are described by a formal context modelcalled Hyperspace Analogue to Context, which effectively captures the dynamics of context and the relationship between services and context. Based on the model, we propose a set of algorithms that can continuously present the most relevant services to the user in response to changes of context, services or user preferences. Numeric coding methods are applied to improve the algorithms’ performance. The algorithms are grounded in a context-driven service discovery system that automatically reacts to changes in the environment. New context sources and services can be dynamically integrated into the system. A client for smart phones continuously informs users about the discovery results. Experiments show, that the system can efficiently provide the user with continuous, up-to-date information about the most useful services in real time.
  •  
48.
  • Rasch, Katharina, 1982- (författare)
  • Plug and play context-awareness for pervasive environments
  • 2011
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Pervasive environments are physical environments interwoven with a rich set of embedded sensors, actuators and displays offering their services to the user. The considerable amount of computing technology in such environments should be as unobtrusive as possible, aiding the user in everyday activities instead of being distracting. Context-awareness, i.e. the adaptiveness of the environment to the current situation of the user, is of tremendous importance for achieving the desired unobtrusiveness. This licentiate dissertation begins by looking at one aspect of pervasive systems where user experience can be considerably improved through context-awareness: of the thousands of services that may be available in a pervasive environment, only a small percentage will be of interest to the user in any given situation. Instead of having to issue explicit service discovery requests, users would like to be continuously informed about services relevant to them, depending on their current context and their preferences. In this dissertation a proactive service discovery approach for pervasive environments is proposed that addresses these implicit discovery requests. Services and user preferences are described by a formal context model which can effectively capture the dynamics of context and the relationship between services and context. Based on this model a set of algorithms is described that can continuously identify the services most relevant to the user in near real time. Proactive service discovery presumes detailed descriptions of user preferences and service capabilities. Manually providing this information is tedious and error-prone, hindering the adoption of the technology by non-expert users. In the second part of this dissertation it is shown how user preferences can instead be automatically identified by studying the user's interaction with the system. Furthermore an approach is presented for automatically providing service descriptions by observing the conditions under which services are executed and the typical effects they induce in the environment. By applying machine-learning techniques such as subspace clustering and classification on the observed data, these approaches are able to produce high-quality descriptions for both user preferences and service capabilities, without any need for manual annotation. Based on these results it is shown how discovery and learning algorithms can be seamlessly integrated into existing pervasive environments to provide plug and play context-awareness.
  •  
49.
  • Rasch, Katharina, 1982- (författare)
  • Smart assistants for smart homes
  • 2013
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The smarter homes of tomorrow promise to increase comfort, aid elderly and disabled people, and help inhabitants save energy. Unfortunately, smart homes today are far from this vision – people who already live in such a home struggle with complicated user interfaces, inflexible home configurations, and difficult installation procedures. Under these circumstances, smart homes are not ready for mass adoption.This dissertation addresses these issues by proposing two smart assistants for smart homes. The first assistant is a recommender system that suggests useful services (i.e actions that the home can perform for the user). The recommended services are fitted to the user’s current situation, habits, and preferences. With these recommendations it is possible to build much simpler user interfaces that highlight the most interesting choices currently available. Configuration becomes much more flexible: since the recommender system automatically learns user habits, user routines no longer have to be manually described. Evaluations with two smart home datasets show that the correct service is included in the top five recommendations in 90% of all cases.The second assistant addresses the difficult installation procedures. The unique feature of this assistant is that it removes the need for manually describing device functionalities (such descriptions are needed by the recommender system). Instead, users can simply plug in a new device, begin using it, and let the installation assistant identify what the device is doing. The installation assistant has minimal requirements for manufacturers of smart home devices and was successfully integrated with an existing smart home. Evaluations performed with this smart home show that the assistant can quickly and reliably learn device functionalities.
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50.
  • Rönngren, Robert, et al. (författare)
  • Parallel Simulation of a High Speed LAN
  • 1994
  • Konferensbidrag (refereegranskat)abstract
    • In this paper we discuss modeling and simulation of a multigigabit/s LAN. We use parallel simulation techniques to reduce the simulation time. Optimistic and conservative parallel simulators have been used. Our results on a shared memory multiprocessor indicate that the conservative method is superior to the optimistic one for the specific application. Further, the parallel simulator based on the conservative scheme shows a linear speedup for large networks.
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