| 1. |
- Ayani, Rassul, et al.
(author)
-
Modeling and Simulation of a High Speed LAN
- 1995
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In: Simulation (San Diego, Calif.). - San Diego : Simulation Councils Inc.. - 0037-5497 .- 1741-3133. ; 64:1, s. 7-14
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Journal article (peer-reviewed)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.
(author)
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Symbiotic simulation model validation for radiation detection applications
- 2009
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In: PADS '09. ACM/IEEE/SCS 23rd Workshop on Principles of Advanced and Distributed Simulation, 2009. - : IEEE Computer Society. - 9780769537139 ; , s. 11-18
-
Conference paper (peer-reviewed)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.
(author)
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Toward an Evolutionary Computing Modeling Language
- 2011
-
In: IEEE Transactions on Evolutionary Computation. - 1089-778X .- 1941-0026. ; 15:2, s. 230-247
-
Journal article (peer-reviewed)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.
(author)
-
An embedded middleware platform for pervasive and immersive environments for-all
- 2009
-
In: 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
-
Conference paper (peer-reviewed)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.
(author)
-
A model for parallel simulation of distributed shared memory
- 1996
-
Conference paper (peer-reviewed)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.
(author)
-
A framework for fault-tolerance in HLA-based distributed simulations
- 2005
-
In: Proceedings of the 2005 Winter Simulation Conference. - 0780395190 ; , s. 1182-1189
-
Conference paper (peer-reviewed)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.
(author)
-
Evaluation of a Fault-Tolerance Mechanism for HLA-Based Distributed Simulations
- 2006
-
In: 20th Workshop on Principles of Advanced and Distributed Simulation, PADS 2006. - 0769525873 ; , s. 175-182
-
Conference paper (peer-reviewed)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
(author)
-
Fault-tolerance in HLA-based distributed simulations
- 2006
-
Licentiate thesis (other academic/artistic)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.
(author)
-
Peer-to-peer-based resource management in support of HLA-based distributed simulations
- 2004
-
In: Simulation (San Diego, Calif.). - : SAGE Publications. - 0037-5497 .- 1741-3133. ; 80:4-5, s. 181-190
-
Journal article (peer-reviewed)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.
(author)
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SDR : a semantic based Distributed Repository for Simulation Models and Resources
- 2007
-
In: AMS 2007. - 0769528457 ; , s. 171-176
-
Conference paper (peer-reviewed)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.
(author)
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A framework for simulation-based optimization of business process models
- 2012
-
In: Simulation (San Diego, Calif.). - : Sage Publications. - 0037-5497 .- 1741-3133. ; 88:7, s. 852-869
-
Journal article (peer-reviewed)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.
(author)
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A Model for Estimating the Performance of a Team of Agents
- 2011
-
In: Proceedings of the 2011 IEEE International Conference on Systems, Man and Cybernetics (SMC 2011). - : IEEE Press. - 9781457706523 ; , s. 2393-2400
-
Conference paper (peer-reviewed)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.
(author)
-
Estimating performance of a business process model
- 2009
-
In: Winter Simulation Conference. - 9781424457700 ; , s. 2828-2839
-
Conference paper (peer-reviewed)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.
(author)
-
Optimizing a Business Process Model by Using Simulation
- 2010
-
In: 2010 IEEE Workshop on Principles of Advanced and Distributed Simulation. - : IEEE Press. - 9781424472925 ; , s. 1-8
-
Conference paper (peer-reviewed)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.
(author)
-
Path planning for UAVs using symbiotic simulation
- 2006
-
In: Modelling and Simulation 2006. - 9789077381304 ; , s. 207-213
-
Conference paper (peer-reviewed)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.
(author)
-
Simulation-aided path planning of UAV
- 2007
-
In: Proceedings Of The 2007 Winter Simulation Conference. - 9781424413058 ; , s. 1285-1293
-
Conference paper (peer-reviewed)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-
(author)
-
Simulation-based Optimization and Decision Making with Imperfect Information
- 2011
-
Doctoral thesis (other academic/artistic)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. |
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| 21. |
- Kamrani, Farzad, et al.
(author)
-
Using on-line simulation for adaptive path planning of UAVs
- 2007
-
In: DS-RT 2007. - LOS ALAMITOS : IEEE COMPUTER SOC. - 9780769530116 ; , s. 167-174
-
Conference paper (peer-reviewed)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
(author)
-
Using on-line simulation in UAV path planning
- 2007
-
Licentiate thesis (other academic/artistic)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.
(author)
-
Wireless LAN Access Points as a Queuing System
- 2002
-
In: Proceedings of The Communications and Computer Networks 2002 Conference (CCN 2002). ; , s. 463-468
-
Conference paper (peer-reviewed)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.
(author)
-
Wireless LAN Access Points as Queuing Systems : Performance Analysis and Service Time
- 2003
-
In: Mobile Computing and Communications Review. - : Association for Computing Machinery (ACM). - 1559-1662 .- 1931-1222. ; 7:1, s. 28-30
-
Journal article (peer-reviewed)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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