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  • 151.
    Gustafsson, Jan
    Mälardalen University, Department of Computer Science and Electronics.
    Analyzing Execution-Time of Object-Oriented Programs Using Abstract Interpretation2000Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    As a result of the industrial deployment of real-time systems, there is an increasing demand for methods to perform safe and tight calculation of the worst case execution time (WCET) of programs. The WCET is a necessary prerequisite for guaranteeing correct timing behaviour of real-time systems. WCET calculation means to find the path, often among a huge number of paths, that takes the longest time to execute. The calculation is based on path information for the program, such as the maximum number of iterations in loops and identification of paths that are never executed. In most existing WCET analysis methods, this information is given as manual annotations by the programmer. In this thesis we present a method which automatically calculates path information for object-oriented real-time programs by static analysis. Thus, the method can be used in automating the WCET analysis, thereby relieving the programmer from the tedious and error-prone manual annotation work. The method, which is based on abstract interpretation, generates safe but not necessarily exact path information. A trade-off between quality and calculation cost has to be made, since finding the exact information is a complex, often intractable problem for non-trivial programs. We show how the general abstract interpretation theory can be used, in a structured way, to approximate the semantics of an imperative or object-oriented programming language. We have chosen to analyze RealTimeTalk (RTT), an object-oriented language based on Smalltalk, and have developed a prototype tool which implements our analysis for a subset of the language. We show that the tool is capable of analyzing programs with a complexity which would make manual annotation of the program all but trivial.

  • 152.
    Gustafsson, Jan
    Mälardalen University, Department of Computer Science and Electronics.
    The worst case execution time Tool Challenge 20062007In: Proceedings - ISoLA 2006: 2nd International Symposium on Leveraging Applications of Formal Methods, Verification and Validation, 2007, p. 233-240Conference paper (Refereed)
    Abstract [en]

    Worst Case Execution Time (WCET) analysis has a growing importance for real-time systems, to guarantee correct timing, and to be an aid in developing such systems. The WCET tools are currently making their way out to the market, and there are many research groups developing prototype tools using new and better ways of calculating estimates or bounds on the WCET.

    The purpose of the WCET Tool Challenge is to be able to study, compare and discuss the properties of different WCET tools and approaches, to define common metrics, and to enhance existing WCET benchmarks. The WCET Tool Challenge is designed to find a balance between openness for a wide range of analysis approaches, and specific participation guide¬lines to pro¬vide a level playing field. This should make results transparent and facilitate friendly competition among the par¬ticipants.

    This report describes the participating tools as well as the results of the Challenge 2006. There is also an accompanying report by Lili Tan on the external tests of the tools.

    The WCET Tool Challenge is intended to be an annual event.

  • 153.
    Gustafsson, Jan
    Mälardalen University, Department of Computer Science and Electronics.
    WCET Challenge 2006 - Technical Report2007Report (Other academic)
    Abstract [en]

    Worst Case Execution Time (WCET) analysis has a growing importance for real-time systems, to guarantee correct timing, and to be an aid in developing such systems. The WCET tools are currently making their way out to the market, and there are many research groups active in developing prototype tools using new and better ways of calculating estimates or bounds on the WCET.

    The purpose of the WCET Tool Challenge is to be able to study, compare and discuss the properties of different WCET tools and approaches, to define common metrics, and to enhance the existing WCET benchmarks. The WCET Tool Challenge has been designed to find a good balance between openness for a wide range of analysis approaches, and specific participation guidelines to provide a level playing field. This should make results transparent and facilitate friendly competition among the participants.

    This report describes the participating tools as well as the results of the Challenge 2006. There is also an accompanying report by Lili Tan on the external tests of the tools.

    The WCET Tool Challenge is intended to be an annual event.

  • 154.
    Gustafsson, Jan
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Ermedahl, Andreas
    Mälardalen University, Department of Computer Science and Electronics.
    Experiences from Applying WCET Analysis in Industrial Settings2007In: Proceedings - 10th IEEE International Symposium on Object and Component-Oriented Real-Time Distributed Computing, ISORC 2007, 2007, p. 382-391Conference paper (Refereed)
    Abstract [en]

    Knowing the program timing characteristics is fundamental to the successful design and execution of real-time systems. Today, measurement-based timing analysis tools such as in-circuit emulators, logic analyzers and oscillo-scopes, are used in industry. A critical timing measure is the worst-case execution time (WCET) of a program. Recently, tools for deriving WCET estimates, mostly based on static program analysis, have reached the market. In this article we summarize experiences from five different industrial case-studies. The studies were made on typical industrial systems, in close cooperation with the system developers, using both static and measurement-based tools. The primary purpose was to investigate the difficulties involved in applying current timing analysis methods to industrial code. We were also interested how WCET estimates can be derived by different methods, how labor-intensive the methods are, and the accuracy of obtained results. As a result, we provide observations on the benefits and drawbacks of the different timing analysis methods used and specify general conditions when a particular method should be most beneficial. We also show the benefits of having several types of timing analysis tools available.

  • 155.
    Gustafsson, Jan
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Ermedahl, Andreas
    Mälardalen University, Department of Computer Science and Electronics.
    Lisper, Björn
    Mälardalen University, Department of Computer Science and Electronics.
    Algorithms for Infeasible Path Calculation2006In: OpenAccess Series in InformaticsVolume 4, 2006, 2006Conference paper (Refereed)
    Abstract [en]

    Static Worst-Case Execution Time (WCET) analysis is a technique to derive upper bounds for the execution times of programs. Such bounds are crucial when designing and verifying real-time systems. A key component in static WCET analysis is to derive flow information, such as loop bounds and infeasible paths. Such flow information can be provided as either as annotations by the user, can be automatically calculated by a flow analysis, or by a combination of both. To make the analysis as simple, automatic and safe as possible, this flow information should be calculated automatically with no or very limited user interaction. In this paper we present three novel algorithms to calculate infeasible paths. The algorithms are all designed to be simple and efficient, both in terms of generated flow facts and in analysis running time. The algorithms have been implemented and tested for a set of WCET benchmarks programs.

  • 156.
    Gustafsson, Jan
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Ermedahl, Andreas
    Mälardalen University, Department of Computer Science and Electronics.
    Sandberg, Christer
    Mälardalen University, Department of Computer Science and Electronics.
    Lisper, Björn
    Mälardalen University, Department of Computer Science and Electronics.
    Automatic Derivation of Loop Bounds and Infeasible Paths for WCET Analysis using Abstract Execution2006In: Proceedings - Real-Time Systems Symposium, 2006, p. 57-66Conference paper (Refereed)
    Abstract [en]

    Static Worst-Case Execution Time (WCET) analysis is a technique to derive upper bounds for the execution times of programs. Such bounds are crucial when designing and verifying real-time systems. A key component for statically deriving safe and tight WCET bounds is information on the possible program flow through the program. Such flow information can be provided manually by user annotations, or automatically by a flow analysis. To make WCET analysis as simple and safe as possible, it should preferably be automatically derived, with no or very limited user interaction. In this paper we present a method for deriving such flow information called abstract execution. This method can automatically calculate loop bounds, bounds for including nested loops, as well as many types of infeasible paths. Our evaluations show that it can calculate WCET estimates automatically, without any user annotations, for a range of benchmark programs, and that our techniques for nested loops and infeasible paths sometimes can give substantially better WCET estimates than using loop bounds analysis only.

  • 157.
    Gustafsson, Jan
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Lisper, Björn
    Mälardalen University, Department of Computer Science and Electronics.
    Kirner, Raimund
    Technische Universität Wien, Austria.
    Puschner, Peter
    Technische Universität Wien, Austria.
    Code Analysis for Temporal Predictability2006In: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 32, no 3, p. 253-277Article in journal (Refereed)
    Abstract [en]

    The execution time of software for hard real-time systems must be predictable. Further, safe and not overly pessimistic bounds for the worst-case execution time (WCET) must be computable. We conceived a programming strategy called WCET-oriented programming and a code transformation strategy, the single-path conversion, that aid programmers in producing code that meets these requirements. These strategies avoid and eliminate input-data dependencies in the code. The paper describes the formal analysis, based on abstract interpretation, that identifies input-data dependencies in the code and thus forms the basis for the strategies provided for hard real-time code development.

  • 158.
    Gustavsson, Håkan
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Axelsson, Jakob
    Mälardalen University, Department of Computer Science and Electronics.
    Coping with Variability in Automotive Product line Architectures Using Real Options2007Conference paper (Refereed)
    Abstract [en]

    The automotive customers demand new functionality with every new product release and the time-to-market is

    constantly shortened. The automotive embedded systems are characterized by being mechatronic system which adds

    complexity. The systems are often resource constrained and trade-offs between the system behavior and the resources required is of great importance. The decisions are usually based on many factors that pull in different directions such as maintenance, portability, usability etc. The complex system and the many uncertain factors create a need for support in the design process. In this paper the use of Real Options is evaluated on a hypothetic but realistic case taken from the automotive industry. The case show how real option valuation provides additional guidance when making system design decisions. Real Options provide the opportunity to analyze the cost of designing for future growth of an platform, based on the estimated value of the future functionality. The value of a flexible design can thereby be quantified making the trade-off between short and long term solution more accurate.

  • 159.
    Hansen, Ewa
    Mälardalen University, Department of Computer Science and Electronics.
    Centralized Routing for Prolonged Network Lifetime in Wireless Sensor Networks2008Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In this thesis centralized routing methods for wireless sensor networks have been studied. The aim has been to prolong network lifetime by reducing the energy consumed by sensor-node communication.

    Wireless sensor networks are rapidly becoming common in application areas where information from many sensors is to be collected and acted upon. The use of wireless sensor networks adds flexibility to the network, and the cost of cabling can be avoided.

    Wireless sensor networks may consist of several hundreds of small devices, equipped with sensors (e.g. acoustic, seismic or image) that form a wireless network. Each sensor node collects information from its surroundings and sends it to a base station, either from sensor node to sensor node, or directly to the base station.

    We have made simulations that show that asymmetric communication with multihop extends the lifetime of large wireless sensor networks. We have also investigated the usefulness of enforcing a minimum separation distance between cluster heads in a cluster based wireless sensor network. The results show that our sensor network performs up to 150% better when introducing a minimum separation distance between cluster heads. The simulations also show that the minimum separation distance resulting in the lowest energy consumption in our network varies with the number of clusters. We have also made an initial study of maximum lifetime routing in sparse wireless sensor networks to be able to see how different heuristic routing algorithms influence the energy consumption of individual sensor nodes, and thus the lifetime of a sparse sensor network. We have also compared the maximum lifetime of the heuristic algorithms to the maximum lifetime of an optimal routing solution. These simulations showed that for some types of applications the choice of heuristic algorithm is more important to prolong network lifetime, than for other types of applications.

  • 160.
    Hansen, Ewa
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Neander, Jonas
    Mälardalen University, Department of Computer Science and Electronics.
    Nolin, Mikel
    Mälardalen University, Department of Computer Science and Electronics.
    Björkman, Mats
    Mälardalen University, Department of Computer Science and Electronics.
    Energy-Efficient Cluster Formation for Large Sensor Networks using a Minimum Separation Distance2006In: In proceedings of the Fifth Annual Mediterranean Ad Hoc Networking Workshop, 2006Conference paper (Refereed)
  • 161.
    Hansen, Ewa
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Neander, Jonas
    Mälardalen University, Department of Computer Science and Electronics.
    Sjödin, Mikael
    Mälardalen University, Department of Computer Science and Electronics.
    Björkman, Mats
    Mälardalen University, Department of Computer Science and Electronics.
    Efficient Cluster Formation for Sensor Networks2006Report (Other academic)
    Abstract [en]

    The interest in wireless sensor networks is growing and the development of energy efficient infrastructures for such networks is becoming increasingly important.

    In this paper we investigate the usefulness of enforcing a minimum separation distance between cluster heads in a cluster based sensor network, i.e. prolonging network lifetime by lowering the energy consumption.

    The simulations where performed in order to determine how much we can lower the energy consumption in the sensor network by separating the cluster heads. We have also investigated how the number of clusters affect the energy consumption for a given minimum separation distance.

    We show that our sensor network performs up to 150\% better when introducing a minimum separation distance between cluster heads, comparing the number of messages received at the base station.

    The simulations also show that the minimum separation distance that result in the lowest energy consumption in our network varies with the number of clusters.

  • 162.
    Hansen, Ewa
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Neander, Jonas
    Mälardalen University, Department of Computer Science and Electronics.
    Sjödin, Mikael
    Mälardalen University, Department of Computer Science and Electronics.
    Björkman, Mats
    Mälardalen University, Department of Computer Science and Electronics.
    Energy-Efficient Cluster Formation for Large Sensor Networks using a Minimum Separation Distance2006In: Proceedings of The Fifth Annual Mediterranean Ad Hoc Networking Workshop (Med-Hoc-Net 2006), 2006Conference paper (Refereed)
    Abstract [en]

    In this paper we investigate the usefulness of enforcing a minimum separation distance between cluster heads in a cluster based sensor network, thereby prolonging network lifetime by spreading the cluster heads, thus lowering the average communication energy consumption.

    We have performed initial simulations in order to determine how much we can lower the energy consumption in the sensor network by separating the cluster heads. We have also investigated how the number of clusters affect the energy consumption for a given minimum separation distance.

    The results show that our sensor network performs up to 150% better when introducing a minimum separation distance between cluster heads, comparing the number of messages received at the base station.

    The simulations also show that the minimum separation distance resulting in the lowest energy consumption in our network varies with the number of clusters.

  • 163.
    Hansen, Ewa
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Nolin, Mikael
    Björkman, Mats
    A Study of Maximum Lifetime Routing in Sparse Sensor Networks2008In: CISIS 2008: THE SECOND INTERNATIONAL CONFERENCE ON COMPLEX, INTELLIGENT AND SOFTWARE INTENSIVE SYSTEMS, PROCEEDINGS, 2008, p. 449-454Conference paper (Refereed)
    Abstract [en]

    A major issue in wireless sensor networks is to prolong network lifetime by efficient energy management. In this paper we present an initial study ofmaximum lifetime routing in sparse sensor networks. We have studied simulations of how different heuristic routing algorithms influence the energy consumption of individual sensor nodes, and thus the functional lifetime of a sparse sensor network. The functional lifetime of the sensornetwork can be either until the first node has run out of energy or until a certain threshold of nodes has demised. We have also compared themaximum lifetime of the heuristic algorithms to the maximum lifetime of an optimal routing solution. Our simulations with non-aggregated data indicates that using one of the presented heuristic routing algorithms are not enough to find a near optimal routing. Our study is made in the AROS framework.

  • 164.
    Hansson, Hans
    Mälardalen University, Department of Computer Science and Electronics.
    ARTES - A network for Real-Time research and graduate Education in Sweden 1997-20062006Collection (editor) (Other academic)
    Abstract [en]

    This book summarizes the results of the Swedish national real-time systems research initiative ARTES and provides a few representative examples of the science and scientific results that have emerged from ARTES.

    ARTES was supported by the Swedish Foundation for Strategic Research (SSF), with a total of 95 MSEK between 1998 and 2006. ARTES has unified and given strength to the Swedish real-time and embedded systems research community, and contributed substantially to advancing Sweden's international position in this area. ARTES has had a catalytic and coordinating effect for a total research effort extending far beyond the funding provided by SSF. It has created important synergies between disciplines, ensured industrial relevance in research, and facilitated important academic and industrial networking for approximately 100 senior researchers and some 200 post-graduate students.

  • 165.
    Hansson, Hans
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Åkerholm, Mikael
    Mälardalen University, Department of Computer Science and Electronics.
    Crnkovic, Ivica
    Mälardalen University, Department of Computer Science and Electronics.
    Törngren, Matrin
    KTH, Stockholm, Sweden .
    SaveCCM - a component model for safety-critical real-time systems2004In: Conference Proceedings of the EUROMICRO, Volume 30, 2004, 2004, p. 627-635Conference paper (Other academic)
    Abstract [en]

    Component-based development has proven effective in many engineering domains, and several general component technologies are available. Most of these are focused on providing an efficient software-engineering process. However for the majority of embedded systems, run-time efficiency and prediction of system behaviour are as important as process efficiency. This calls for specialized technologies. There is even a need for further specialized technologies adapted to different types of embedded systems, due to the heterogeneity of the domain and the close relation between the software and the often very application specific system. This paper presents the SaveCCM component model, intended for embedded control applications in vehicular systems. SaveCCM is a simple model in which flexibility is limited to facilitate analysis of real-time and dependability. We present and motivate the model, and provide examples of its use.

  • 166.
    Harnefors, Lennart
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Jansson, Magnus
    Mälardalen University, Department of Computer Science and Electronics.
    Ottersten, Rolf
    Chalmers University of Technology.
    Pietiläinen, Kai
    Mälardalen University, Department of Computer Science and Electronics.
    Unified Sensorless Vector Control of Synchronous and Induction Motors2003In: IEEE Transactions on Industrial Electronics, ISSN 0278-0046, Vol. 50, no 1, p. 153-160Article in journal (Refereed)
    Abstract [en]

    In this paper, a unified theory for sensorless flux estimation and vector control of induction motors and nonsalient permanent-magnet synchronousmotors (PMSMs) is developed. It is shown that an estimator and vector controller for one of the motor types can also be applied to the other, with only minor modifications necessary. Two candidate estimators are considered: a variant of the well-known "voltage model" (VM) and a phase-locked-loop-type speed and position estimator. These are applied to both motor types, and evaluated experimentally. For the nonsalient PMSM, an important result is that synchronization can be guaranteed from any initial rotor position.

  • 167.
    Hedelind, Mikael
    et al.
    ABB Automation Technologies AB, Sweden.
    Funk, Peter
    Mälardalen University, Department of Computer Science and Electronics.
    Milic, Milun
    ABB Automation Technologies AB, Sweden.
    Intelligent Buffer Storage System: Enabling Fast and Flexible Assembling with Industrial Robots2006In: Journal of Intelligent & Fuzzy Systems, ISSN 1064-1246, Vol. 17, no 4, p. 367-376Article in journal (Refereed)
    Abstract [en]

    Production cells usually require a continuous supply of parts to be assembled. Elaborate feeding mechanisms or a system of prepared pallets on which the parts have exact positions are expensive and if a variation of the product is to be produced, the feeding mechanism or pallets must be modified. Such solutions do not provide sufficient flexibility and increase production costs. Today's requirements for smaller series and customized orders have higher requirements on production cells.

    In this paper we show how flexible and adaptive production can be achieved, using methods and techniques from artificial intelligence by introducing an "autonomous" production cell, integrating and managing its own local buffer storage. The production cell is able to produce a number of variants of the product with no time delay between different configurations. The storage system, designated "Floating Storage", handles the local buffer storage and guides the industrial robots to use available floor-space as storage. The system also orders parts from the main storage as the buffer storage approaches depletion. The parts arrive to the cell in standard containers and a commercially available vision system is used to locate the material. The prototype has been introduced in an assembly line at ABB.

  • 168.
    Henriksson (Gunnarsson), Tommy
    Mälardalen University, Department of Computer Science and Electronics.
    Microwave Imaging of Biological Tissues: the current status in the research area2006Report (Other academic)
    Abstract [en]

    Microwave imaging is a non-ionizing method promising an ability of depth-scanning different biological bodies. The research in this area started in the late 70s and many contributions has been achieved by different groups until present, which has influenced and open up new possibilities of the technique. This document will review the historical work by the different groups to settle objectives of the research in microwave imaging at the Department of Computer Science and Electronics at Mälardalen University and the plan of the author’s Ph. D. studies. The planar 2.45 GHz microwave camera located at Supélec, France, may be a very useful platform in early studies of the three-dimensional properties of microwave imaging for breast tumor detection. By applying the developed Newton- Kantorovich algorithm to the planar camera a solid state of the art platform for quantitative reconstruction of inhomogeneous objects may be established. 

  • 169.
    Henriksson (Gunnarsson), Tommy
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Joachimowicz, Nadine
    SUPÉLEC, Département de Recherche en Electromagnétisme, France.
    Diet, Antonie
    SUPÉLEC, Département de Recherche en Electromagnétisme, France.
    Conessa, Cristophe
    SUPÉLEC, Département de Recherche en Electromagnétisme, France.
    Åberg, Denny
    Mälardalen University, Department of Computer Science and Electronics.
    Bolomey, Jean-Charles
    SUPÉLEC, Département de Recherche en Electromagnétisme, France.
    Quantitative Imaging Using a 2.45 GHz Planar Camera2007In: 5th World Congress in Industrial Process Tomography, 2007, p. 108-116Conference paper (Refereed)
    Abstract [en]

    Microwave imaging is recognized as an efficient diagnostic modality for non-invasively visualizing dielectric contrasts in non-metallic bodies. The usefulness of this modality results from the existing correlation between dielectric properties and quantities of practical relevance for industrial or biomedical applications. At the beginning of the 80s, Supélec developed a 2.45 GHz planar microwave camera and in the 90s, the group developed algorithms for quantitative microwave imaging. The purpose of this study is to investigate the capability of these existing materials, or an extended version of it, in terms of quantitative imaging of high contrast inhomogeneous object for application of breast cancer detection.

  • 170.
    Hessel, Anders
    et al.
    Uppsala University, Sweden.
    Pettersson, Paul
    Mälardalen University, Department of Computer Science and Electronics.
    A Global Algorithm for Model-Based Test Suite Generation2007In: Proceedings of the Third Workshop on Model Based Testing (MBT 2007), 2007, p. 47-59Conference paper (Refereed)
    Abstract [en]

    Model-based testing has been proposed as a technique to automatically

    verify that a system conforms to its specification. A popular approach is to

    use a model-checker to produce a set of test cases by formulating the test generation problem as a reachability problem. To guide the selection of test cases, a coverage criterion is often used. A coverage criterion can be seen as a set of items to be covered, called coverage items. We propose an on-the-fly algorithm

    that generates a test suite that covers all feasible coverage items. The algorithm returns a set of traces that includes a path fulfilling each item, without including redundant paths. The reachability algorithm explores a state only if it might increase the total coverage. The decision is global in the sense that it does not only regard each individual local search branch in isolation, but the total coverage in

    all branches together. For simpler coverage criteria as location of edge coverage, this implies that each model state is never explored twice.

    The algorithm presented in this paper has been implemented in the test generation tool UPPAAL CoVer. We present encouraging results from applying the tool to a set of experiments and in an industrial sized case study.

  • 171.
    Hessel, Anders
    et al.
    Uppsala University, Sweden.
    Pettersson, Paul
    Mälardalen University, Department of Computer Science and Electronics. Uppsala University, Sweden.
    Cover - A Test-Case Generation Tool for Timed Systems2007Conference paper (Refereed)
    Abstract [en]

    COVER is a new test-case generation tool for timed systems. It generates test cases from a timed automata model of a system to be tested, and a coverage criteria expressed in an observer language. In this paper, we describe the current architecture of the tool, its input languages, and a case study in which the tool has been applied in an industrial setting to test that a WAP gateway conform to its specification. 

  • 172.
    Hjertström, Andreas
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Nyström, Dag
    Mälardalen University, Department of Computer Science and Electronics.
    Åkerholm, Mikael
    Mälardalen University, Department of Computer Science and Electronics.
    Sjödin, Mikael
    Mälardalen University, Department of Computer Science and Electronics.
    INCENSE: Information-Centric Run-Time Support for Component-Based Embedded Real-Time Systems2007In: Proceedings of the Work-In-Progress (WIP) session, 14th IEEE Real-Time and Embedded Technology and Applications Symposium, Seattle, United States, 2007, p. 4-Conference paper (Refereed)
    Abstract [en]

    In this paper we present a technique to allow the use of

    real-time database management together with componentbased

    software development, to achieve an information centric

    run-time platform for the development of embedded

    real-time systems. The technique allows components to

    benefit from the advantages of a real-time database management

    system while still retaining desirable component

    properties, such as isolation and a high level of reusability.

    We propose that a database is integrated in the component

    framework, and introduce the concept of database

    proxies to decouple components from the database schema.

    The resulting system fully benefits from the advantages of

    component-based software development, such as reusability,

    all component interaction through interfaces, etc, combined

    with the advantages of a real-time database management

    system, i.e., system openness, controlled data access,

    and dynamic query language capabilities.

  • 173. Holmberg, J.
    et al.
    Harnefors, L.
    Landernäs, K.
    Mälardalen University, Department of Computer Science and Electronics.
    Signell, S.
    LDI/LDD Lattice FiltersManuscript (Other academic)
  • 174.
    Huselius, Joel
    Mälardalen University, Department of Computer Science and Electronics.
    Preparing for replay2003Licentiate thesis, comprehensive summary (Other scientific)
  • 175.
    Huselius, Joel
    Mälardalen University, Department of Computer Science and Electronics.
    Reverse Engineering of Legacy Real-Time Systems: An Automated Approach Based on Execution-Time Recording2007Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    Many real-time systems have significant value in terms of legacy, since large efforts have been spent over many years to ensure their proper functionality. Examples can be found in, e.g., telecom and automation-industries. Maintenance consumes the major part of the budget for these systems. As each system is part of a dynamically changing larger whole, maintenance is required to modify the system to adapt to these changes. However, due to system complexity, engineers cannot be assumed to understand the system in every aspect, making the full range of effects of modifications on the system difficult to predict. Effect prediction would be useful, for instance in early discovery of unsuitable modifications. Accurate models would be useful for such prediction, but are generally non-existent.

    With the introduction of a method for automated modeling, this thesis applies an industrial perspective to the problem of obtaining models of legacy real-time systems. The method generates a model of the system as it behaved during the executions. The recordings cover system level events such as context switches and communication, and may optionally cover data manipulations on task level, which allows modeling of causal relations. As means of abstraction, the models can contain probabilistic selections and execution time requirements. The method also includes automatic validation of the generated model, in which the model is compared to the system behavior. Our method has been implemented and has been evaluated in both an industrial case-study and in a controlled experiment. For the controlled experiment, we have developed a framework for automatic evaluation of (automated) modeling methods.

    Using the models generated with our method, engineers can prototype designs of modifications, which allows for early rejection of unfeasible designs. The earlier such rejection is performed, the more time and resources are freed for other activities.

  • 176.
    Huselius, Joel
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Andersson, Johan
    Mälardalen University, Department of Computer Science and Electronics.
    Hansson, Hans
    Mälardalen University, Department of Computer Science and Electronics.
    Punnekkat, Sasikumar
    Mälardalen University, Department of Computer Science and Electronics.
    Automatic Generation and Validation of Models of Legacy Software2006In: Proceedings of the 12:th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications (RTCSA), Sydney, Australia, 2006, p. 342-349Conference paper (Refereed)
    Abstract [en]

    The modeling approach is not used to its full potential in maintenance of legacy systems. Often, models do not even exist. The main reasons being that the economic implications and practical hurdles in manually maintaining models of in-use legacy systems are considered too high by the industry. In this paper, we present a method for automated validation of models automatically generated from recordings of executing real-time embedded systems. This forms an essential constituent of a unified process for the automatic modeling of legacy software. We also present a study in which we automatically model a state-of-practice industrial robot control system, the results of which are clearly positive indicators of the viability of our approach.

  • 177.
    Huselius, Joel
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Kraft, Johan
    Mälardalen University, Department of Computer Science and Electronics.
    Hansson, Hans
    Mälardalen University, Department of Computer Science and Electronics.
    Punnekkat, Sasikumar
    Mälardalen University, Department of Computer Science and Electronics.
    Evaluating the Quality of Models Extracted from Embedded Real-Time Software2007In: Proceedings of the International Symposium and Workshop on Engineering of Computer Based Systems, 2007, p. 577-585Conference paper (Refereed)
    Abstract [en]

    Due to the high cost of modeling, model-based techniques are yet to make their impact in the embedded systems industry, which still persist on maintaining code-oriented legacy systems. Re-engineering existing code-oriented systems to fit model-based development is a risky endeavor due to the cost and efforts required to maintain correspondence between the code and model. We aim to reduce the cost of modeling and model maintenance by automating the process, thus facilitating model-based techniques. We have previously proposed the use of automatic model extraction from recordings of existing embedded real-time systems. To estimate the quality of the extracted models of timing behavior, we need a framework for objective evaluation. In this paper, we present such a framework to empirically test and compare extracted models, and hence obtain an implicit evaluation of methods for automatic model extraction. We present a set of synthetic benchmarks to be used as test cases for emulating timing behaviors of diverse systems with varying architectural styles, and extract automatic models out of them. We discuss the difficulties in comparing response time distributions, and present an intuitive and novel approach along with associated algorithms for performing such a comparison. Using our empirical framework, and the comparison algorithms, one could objectively determine the correspondence between the model and the system being modeled.

  • 178.
    Hänninen, Kaj
    Mälardalen University, Department of Computer Science and Electronics.
    Introducing a Memory Efficient Execution Model in a Tool-Suite for Real-Time Systems2006Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis shows how development of embedded real-time systems can be made more efficient by introduction of an memory efficient execution model in a commercial development suite. To identify the need of additional support for execution models in development tools, the thesis investigate by a series of interviews, the common requirements in development of industrial embedded real-time systems. The results indicate that there exist functionality in industrial systems that could be more efficiently implemented in other execution models than the currently supported ones. The thesis then presents how use of multiple execution models (hybrid scheduling) can reduce processor utilization in real-world applications. Furthermore, the thesis presents an integration of an memory efficient execution model in an industrially used real-time operating system. In addition, the thesis describes an efficient technique to analyze memory consumptions of functionality executing under the introduced execution model.

    Embedded computers play an important role in peoples everyday life. Nowadays, we can find computers in product such as microwave ovens, washing machines, DVD players, cellular phones and cars, to mention a few examples. For example, a modern car may have more than 70 embedded control units handling functionality such as airbags, anti-lock braking, traction control etc. In addition, there is a clear trend indicating that the amount of computer controlled functionality in products will continue to increase. Many of today’s embedded systems are resource constrained and the software for them is developed for a few execution models. Even though researchers has proposed a numerous number of different execution models for embedded real-time systems, in practice however, only a few of the proposed execution models are supported in industrial development tools. This implies that developers often force fit functionality to be executed under these models, resulting in poor resource utilization and increasing complexity in software.

  • 179.
    Hänninen, Kaj
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Mäki-Turja, Jukka
    Mälardalen University, Department of Computer Science and Electronics.
    Bohlin, Markus
    Mälardalen University, Department of Computer Science and Electronics.
    Carlson, Jan
    Mälardalen University, Department of Computer Science and Electronics.
    Sjödin, Mikael
    Mälardalen University, Department of Computer Science and Electronics.
    Analysing Stack Usage in Preemptive Shared Stack Systems2006Report (Other academic)
    Abstract [en]

    This paper presents a novel method to determine the maximum stack memory used in preemptive, shared stack, real-time systems. We provide a general and exact problem formulation applicable for any preemptive system model based on dynamic (run-time) properties. We also show how to safely approximate the exact stack usage by using static (compile time) information about the system model and the underlying run-time system on a relevant and commercially available system model: A hybrid, statically and dynamically, scheduled system. Comprehensive evaluations show that our technique significantly reduces the amount of stack memory needed compared to existing analysis techniques. For typical task sets a decrease in the order of 70% is typical.

  • 180.
    Hänninen, Kaj
    et al.
    Mälardalen University, Department of Computer Science and Electronics. Arcticus Systems, Järfälla, Sweden.
    Mäki-Turja, Jukka
    Mälardalen University, Department of Computer Science and Electronics.
    Bohlin, Markus
    Mälardalen University, Department of Computer Science and Electronics. Swedish Institute of Computer Science, Kista, Sweden.
    Carlson, Jan
    Mälardalen University, Department of Computer Science and Electronics.
    Sjödin, Mikael
    Mälardalen University, Department of Computer Science and Electronics. CC Systems, Uppsala, Sweden .
    Determining Maximum Stack Usage in Preemptive Shared Stack Systems2007In: Proceedings of the 9th Real-Time in Sweden (RTiS'07), Västerås, Sweden, 2007, p. 118-126Conference paper (Refereed)
    Abstract [en]

    This paper presents a novel method to determine the

    maximum stack memory used in preemptive, shared stack,

    real-time systems. We provide a general and exact problem

    formulation applicable for any preemptive system model

    based on dynamic (run-time) properties.

    We also show how to safely approximate the exact stack

    usage by using static (compile time) information about the

    system model and the underlying run-time system on a relevant

    and commercially available system model: A hybrid,

    statically and dynamically, scheduled system.

    Comprehensive evaluations show that our technique significantly

    reduces the amount of stack memory needed compared

    to existing analysis techniques. For typical task sets

    a decrease in the order of 70% is typical.

  • 181.
    Hänninen, Kaj
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Mäki-Turja, Jukka
    Mälardalen University, Department of Computer Science and Electronics.
    Bohlin, Markus
    Mälardalen University, Department of Computer Science and Electronics.
    Carlson, Jan
    Mälardalen University, Department of Computer Science and Electronics.
    Sjödin, Mikael
    Mälardalen University, Department of Computer Science and Electronics.
    Determining Maximum Stack Usage in Preemptive Shared Stack Systems2006In: Proceedings - Real-Time Systems Symposium, 2006, p. 445-453Conference paper (Refereed)
    Abstract [en]

    This paper presents a novel method to determine the maximum stack memory used in preemptive, shared stack, real-time systems. We provide a general and exact problem formulation applicable for any preemptive system model based on dynamic (run-time) properties. We also show how to safely approximate the exact stack usage by using static (compile time) information about the system model and the underlying run-time system on a relevant and commercially available system model: A hybrid, statically and dynamically, scheduled system.

    Comprehensive evaluations show that our technique significantly reduces the amount of stack memory needed compared to existing analysis techniques. For typical task sets a decrease in the order of 70% is typical.

  • 182.
    Hänninen, Kaj
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Mäki-Turja, Jukka
    Mälardalen University, Department of Computer Science and Electronics.
    Sjödin, Mikael
    Mälardalen University, Department of Computer Science and Electronics.
    Present and Future Requirements in Developing Industrial Embedded Real-Time Systems - Interviews with Designers in the Vehicle Domain2006In: 13th Annual IEEE International Conference and Workshop on the Engineering of Computer Based Systems (ECBS), Potsdam, Germany, 2006, p. 139-147Conference paper (Refereed)
    Abstract [en]

    In this paper, we aim at capturing the industrial viewpoint of todays and future requirements in development of embedded real-time systems. We do this by interviewing ten senior designers at four Swedish companies, developing embedded applications in the vehicle domain.

    This study shows that reliability and safety are the main properties in focus during development. It also shows that the amount of functionality has been increasing in the examined systems. Still the present requirements are fulfilled using considerably homogenous development methods.

    The study also shows that, in the future, there will be even stronger requirements on dependability and control performance at the same time as requirements on more softer and resource demanding functionality will continue to increase. Consequently, the complexity will increase, and with diverging requirements, more heterogeneous development methods are called for to fulfil all application specific requirements.

  • 183.
    Håkansson, John
    et al.
    Uppsala University, Sweden.
    Pettersson, Paul
    Mälardalen University, Department of Computer Science and Electronics.
    Partial Order Reduction for Verification of Real-Time Components2007In: Proceedings of the 5th International Conference on Formal Modelling and Analysis of Timed Systems, Lecture Notes in Computer Science 4763, 2007, p. 211-226Conference paper (Refereed)
    Abstract [en]

    We describe a partial order reduction technique for a real-time component model. Components are described as timed automata with data ports, which can be composed in static structures of unidirectional control and data flow. Compositions can be encapsulated as components and used in other compositions to form hierarchical models. The proposed partial order reduction technique uses a local time semantics for timed automata, in which time may progress independently in parallel automata which are resynchronized when needed. To increase the number of independent transitions and to reduce the problem of re-synchronizing parallel automata we propose, and show how, to use information derived from the composition structure of an analyzed model. Based on these ideas, we present a reachability analysis algorithm that uses an ample set construction to select which symbolic transitions to explore. The algorithm has been implemented as a prototype extension of the real-time model-checker UPPAAL. We report from experiments with the tool that indicate that the technique can achieve substantial reduction in the time and memory needed to analyze a real-time system described in the studied component model

  • 184.
    Isovic, Damir
    Mälardalen University, Department of Computer Science and Electronics.
    A Web-based Platform for Distance Education2006In: Proceedings of the 4th IEEE CeTUSS Workshop, Uppsala, Sweden, 2006Conference paper (Refereed)
    Abstract [en]

    We have developed a web-based platform for distance education. The platform supports efficient creation and maintenance of online distance courses, only requiring an Internet connection and a web browser from teachers and students. All tools that are necessary to run a distance course are integrated in the platform and accessible via a regular web browser, such as such as Internet Explorer, or Mozilla Firefox. This means that students and teachers can access the course from any computer with Internet connection, just as any other regular web page.

    <p>

    After logging in to the course home page, teachers can easily create student accounts, upload their learning material, add course assignments, correct turned assignments, add news and FAQs, and much more, just by using a regular web browser, no other tools are needed. The similar applies for the students; they log in to their personal course account via the course home page, and once logged in, they can turn in their solutions to the course assignments and find corrected reports with grades and corrections done by the teacher.

    </p>

    The platform has been successfully used in several courses at the Malardalen University. Its functions are continuously extended to cover diverse user's requirements.

  • 185.
    Isovic, Damir
    Mälardalen University, Department of Computer Science and Electronics.
    Flexible Media Processing in Resource Constrained Real-Time Systems2006In: Proceedings of the Eighth IEEE International Symposium on Multimedia (ISM 2006), San Diego, California, USA, 2006, p. 363-370Conference paper (Refereed)
    Abstract [en]

    In this paper we propose real-time methods for flexible processing of MPEG-2 video in resource constrained systems. The video stream is adapted to resource fluctuations by using a quality-aware frame skipping approach which keeps the video frames that have the most impact on the overall video quality. Real-time admission control and resource reservation mechanisms ensure that video processing applications adapt Quality-of-Service at run-time according to current state of the system, while fully utilizing the available resources.

  • 186.
    Isovic, Damir
    Mälardalen University, Department of Computer Science and Electronics.
    Flexible Scheduling for Media Processing in Resource Constrained Real-Time Systems2004Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    The MPEG-2 standard for video coding is predominant in consumer electronics for DVD players, digital satellite receivers, and TVs today. MPEG-2 processing puts high demands on audio/video quality, which is achieved by continuous and synchronized playout without interrupts. At the same time, there are restrictions on the storage media, e.g.., limited size of a DVD disc, communication media, e.g., limited bandwidth of the Internet, display devices, e.g., the processing power, memory and battery life of pocket PCs or video mobile phones, and finally the users, i.e., humans ability of perceiving motion. If the available resources are not sufficient to process a full-size MPEG-2 video, then video stream adaptation must take place. However, this should be done carefully, since in high quality devices, drops in perceived video quality are not tolerated by consumers.

    We propose real-time methods for resource reservation of MPEG-2video stream processing and introduce flexible scheduling mechanisms for video decoding. Our method is a mixed offline and online approach for scheduling of periodic, aperiodic and sporadic tasks, based on slot shifting. We use the offline part of slot shifting to eliminate all types of complex task constraints before the runtime of the system. Then, we propose an online guarantee algorithm for dealing with dynamically arriving tasks. Aperiodic and sporadic tasks are incorporated into the offline schedule by making use of the unused resources and leeways in the schedule. Sporadic tasks are guaranteed offline for the worst-case arrival patterns and scheduled online, where an online algorithm keeps track of arrivals of instances of sporadic tasks to reduce pessimism about future sporadic arrivals and improve response times and acceptance of firm aperiodic tasks. At runtime, our mechanism ensures feasible execution of tasks with complex constraints in the presence of additional tasks or overloads.

    We use the scheduling and resource reservation mechanism above to flexibly process MPEG-2 video streams. First, we present results from a study of realistic MPEG-2 video streams to analyze the validity of common assumptions for software decoding and identify a number of misconceptions. Then, we identify constraints imposed by frame buffer handling and discuss their implications on the decoding architecture and timing. Furthermore, we propose realistic timing constraints demanded by high quality MPEG-2 software video decoding. Based on these, we present a MPEG-2 video frame selection algorithm with focus on high video quality perceived by the users, which fully utilize limited resources. Given that not all frames in a stream can be processed, it selects those which will provide the best picture quality while matching the available resources, starting only such decoding, which is guaranteed to be completed. As a final result, we provide a real-time method for flexible scheduling of media processing in resource constrained system. Results from study based on realistic MPEG-2 video underline the effectiveness of our approach.

  • 187.
    Isovic, Damir
    Mälardalen University, Department of Computer Science and Electronics.
    Temporal impact of high-level resources on end-to-end timing of video streaming2006Report (Other academic)
    Abstract [en]

    Processing of high-quality streams is quite computationally expensive at the same time as video processing applications are more and more deployed in small embedded systems that traditionally exhibit limited processing and network resources, e.g. set top boxes, mobile phones or PDAs. Hence, for some combinations of streams and devices, the timing constraints on stream processing within a functional component will not automatically be met.

    This paper analyses the functional components of a video stream processing and transmission with respect to their impact on the timing of end-to-end delivery chain processing. In particular it identifies parameters at a high level of abstraction, i.e., hiding the full internal details. The results can be used to make trade-offs between timeliness, resource usage and energy consumption at system design time.

  • 188.
    Jansson, Magnus
    Mälardalen University, Department of Computer Science and Electronics.
    On Stabilization of Sensorless Synchronous Motor Drives and Traction Converters2005Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In this thesis we discuss and analyze aspects and methods for low-speed poeration, startup, and particularly rotational reversal for sensorless control of non-salient permanent-magnet synchronous motors (PMSMs), i.e., stabilization in the low-speed region. Furtermore, a speed and position estimation algorithm for speed-sensorless control of electrically excited synchronous machines (EESMs) with damper windings is developed. For EESM drives, an initial rotor position estimation algorithm is also developed. Regarding the PMSM drives, it is shown that the sensorless drive synchronizes from any initial rotor position, recovers from initial rotation in the wrong direction, and also reverses rotation without lockup or instability phenomena.

    The result regarding sensorless control and preformance in the low-speed region are simulated and experimentally verified, which indicates that the proposed estimator is effective. An additional subject in this thesis is control traction converters. One major problem is that trains with pulse-width-modulation (PWM) converters have active input impedance; thus the phase shift between the input current and voltage is greater than +90 degrees or less than -90 degrees for a certain ferquency region. This may result in poor damping and in worst case unstable operation. Here, it is shown that via sophisticated current control and improved feed-forward, one may stabilize the system with respect to passivity.

  • 189.
    Jansson, Magnus
    Mälardalen University, Department of Computer Science and Electronics.
    Sensorless Control of Electrically Excited Synchronous MachinesManuscript (Other academic)
  • 190.
    Jansson, Magnus
    Mälardalen University, Department of Computer Science and Electronics.
    Stable and Passive TractionManuscript (Other academic)
  • 191.
    Jansson, Magnus
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Harnefors, Lennart
    Pietiläinen, Kai
    Guaranteed Synchronization of Sensorless Non-Salient PMSM Drives2003In: Proc. Eur. Conf. on Power Electron. and Applicat., 2003Chapter in book (Other academic)
  • 192.
    Jansson, Magnus
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Harnefors, Lennart
    Wallmark, Oskar
    Leksell, Mats
    Synchronization at Startup and Stable Rotation Reversal of Sensorless Nonsalient PMSM Drives2006In: IEEE Transactions on Industrial Electronics, ISSN 0278-0046, Vol. 53, no 2, p. 379-387Article in journal (Refereed)
    Abstract [en]

    In this paper, a variant of the well-known "voltage model" is applied to rotor position estimation for sensorless control of nonsalient permanent-magnet synchronous motors (PMSMs). Particular focus is on a low-speed operation. It is shown that a guaranteed synchronization from any initial rotor position and stable reversal of rotation can be accomplished, in both cases under load. Stable rotation reversal is accomplished by making the estimator insensitive to the stator resistance. It is also shown that the closed-loop speed dynamics are similar to those of a sensored drive for speeds above approximately 0.1 per unit, provided that the model stator inductance is underestimated. Experimental results support the theory.

  • 193.
    Johnson, Tord
    Mälardalen University, Department of Computer Science and Electronics.
    Design and Analysis of Charge-Pump Bases Frequency Synthsizers2005Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    Most telecommunication systems employ modulation techniques that require the transceiver to be capable of accurately estimating the phase of the transmission signal. The frequency synthesizer is a key element and extensively utilized to synthesize frequencies for such radio-frequency communication systems. A common topology for the frequency synthesizer is the charge-pump based phase-locked loop. The development and design of frequency synthesizer is known to be a complex and time-consuming task, aggravated by the vast difference in frequencies between the output and the internal signals. It is often necessary to perform long transient simulations with short time steps to achieve reliable results. This thesis will treat these difficulties and propose solutions to some of the design issues that concerns the frequency synthesizer. In most modern frequency synthesizers the phase detection circuits are capable of detecting both the frequency and phase difference. Such phase detectors are collectively known as phase-frequency detectors and generally employ some kind of memory functionality. The inherited memory in the phase-frequency detectors rouse the need for new models describing the synthesizer. Throughout this thesis the dynamic and noise behavior in the presence of phase-frequency detector are especially investigated. The derived theory and conclusions are validated through earlier presented research as well as simulations of both the phase-frequency detector and the frequency synthesizer. A high reference frequency is often sought after in frequency synthesizers, since it then becomes possible to lower the division ratio in the frequency synthesizer. This will in turn lower the close-in phase noise of the synthesizer as well as decrease the power consumption of the divider chain. Unfortunately, it has also been shown that the size of the phase-frequency detectors blind-zone is directly proportional to the reference input frequency. Consequently, frequency synthesizers, utilizing high reference frequencies, will also have to include the effects of the phase-frequency detector's blind zone to accurately estimate the frequency synthesizer behavior. The blind-zone effect will become even more important as the tendency for high reference frequencies is further pursued. This thesis, therefore, investigates the influence of the phase-frequency detector blind zone. The results from these investigations have shown that a large blind zone is deteriorative for the settling time, but has little influence on the synthesizer noise performance. However, for an exceptional large blind zone there is the possibility that noise, present in the circuit, will force the synthesizer out of the locked condition. Nonlinear models are developed and utilized to fully capture the frequency synthesizer's dynamic behavior both in the locked and out-of-locked condition. The models are presented in the state-space form to facilitate simulations and to describe the internal variables within the synthesizer. Two different closed formulas for the settling time are given for a synthesizer with and without a phase-frequency detector exhibiting blind zone. For the phase noise performance in the frequency synthesizer the nonlinear state-space model has been expanded with time-domain noise sources correlated according to the input noise sources. The linearized phase-domain noise model is compared to the state-space model. The comparison shows that the phase-domain model describes the phase noise property of the synthesizer well below the loops bandwidth. However, for offsets larger than the loop bandwidth the linearized phase-domain is insufficient.

  • 194. Johnson, Tord
    et al.
    Fard, Ali
    Mälardalen University, Department of Computer Science and Electronics.
    Åberg, Denny
    A High-Performance 1V Dead-Zone Free Phase-Frequency Detector with Minimized Blind-zone2004In: Proceedings of Swedish System-on-Chip Conference (SSoC), 2004Conference paper (Other academic)
  • 195.
    Johnson, Tord
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Fard, Ali
    Mälardalen University, Department of Computer Science and Electronics.
    Åberg, Denny
    Mälardalen University, Department of Computer Science and Electronics.
    An Improved Phase-Frequency Detector with Extended Frequency Capability2004In: Midwest Symposium on Circuits and SystemsVolume 1, 2004, 2004, p. 181-184Conference paper (Other academic)
    Abstract [en]

    An improved high-performance dynamic-logic tri-state phase-frequency detector architecture is derived through extensive time domain analysis. In particular, the impact of the reset time's on the maximum operating frequency and phase characteristics of the phase-frequency detector is discussed. The analysis is verified for the presented improved architecture and excellent agreement between theory and simulation is observed. The phase-frequency detector architecture is proven to function for supply voltages below 1 V and has an increased frequency capability of more than 20% with a power consumption of 10 μW at 500 MHz input frequency.

  • 196.
    Johnsson, Andreas
    Mälardalen University, Department of Computer Science and Electronics.
    A doctoral thesis proposal: Implementation, Evaluation and Modeling of IP Network Bandwidth Measurement Methods2006Other (Other academic)
  • 197.
    Johnsson, Andreas
    Mälardalen University, Department of Computer Science and Electronics.
    Modeling, Implementation and Evaluation of IP Network Bandwidth Measurement Methods2007Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Internet has gained much popularity among the public since the mid 1990's and is now an integrated part of our society. A large range of high-speedbroadband providers and the development of new and more efficient Internet applications increase the possibilities to watch movies and live TV, use IP-telephony and share files over the Internet. Such applications demand high data transmission rates, which in turn consume network bandwidth. Since several users must share the common bandwidth capacity on the Internet, there will be locations in the network where the demand is higher than the capacity. This causes network congestion, which has negative impact on both the data transmission rate and transmission quality.

    This thesis is about methods for measuring the available bandwidth of a network path between two computers. The available bandwidth can be interpreted as the maximum transfer rate possible without causing congestion. By deploying the methods studied in this thesis the available bandwidth can be measured without previous knowledge of the network topology. When an estimate of the available bandwidth is obtained, the transfer rate when sending messages between computers can be set to the measured value in order to avoid congestion.

    In the thesis an active end-to-end available bandwidth measurement method called "Bandwidth Available in Real Time" (BART for short) is evaluated. BART measures the available bandwidth by injecting probe packets into the network at a given rate and then analysing how this rate has changed on the receiving side. A Kalman filter is used to update the current estimate of the available bandwidth using the new measurement sample.

    The focus of the thesis is on how methods, such as BART, function in wireless 802.11 networks, which are very popular in work as well as in home environments. Wireless networks have a different construction compared to many other types of networks and this can affect the accuracy of the measurement methods discussed in this thesis. The effects must be analyzed and understood in order to obtain accurate available bandwidth estimates. Since wireless links are often parts of the network path between a sender and a receiver on the Internet, it is important to study how these links affect the estimates of the available bandwidth.

  • 198.
    Johnsson, Andreas
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Björkman, Mats
    Measuring the Impact of Active Probing on TCP2006Conference paper (Other academic)
    Abstract [en]

    Available bandwidth measurement methods have be- ome more and more a epted to be used when seeking the status of a network path. To measure the end-toend available bandwidth without a ess to the path routers, these methods inje t UDP based probe pa kets into the network path. The probe-pa ket load an transiently be high and thus it is important to study the impa t on the existing network ows. In this paper, we show and dis uss our simulation results on how the TCP ows are ae ted when inje ting probe pa kets with dierent ight patterns into the network path. We investigate the relation between the amount of inje ted probe pa kets and the redu tion in TCP performan e. Further, we suggest a quantitative denition of the term network friendly probing.

  • 199.
    Johnsson, Andreas
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Björkman, Mats
    Mälardalen University, Department of Computer Science and Electronics.
    Measuring the Impact of Active Probing on TCP2006Conference paper (Refereed)
    Abstract [en]

    Available bandwidth measurement methods have become more and more accepted to be

    used when seeking the status of a network path. To measure the end-to-end available bandwidth without access to the path routers, these methods inject probe packets into the network path. The probe-packet load can transiently be high and thus it is important to study the impact on the existing TCP flows.

    In this paper, we show and discuss our simulation results on how the TCP flows are affected when injecting probe packets with different flight patterns into the network path. We also investigate the relation between the amount of injected probe packets and the reduction in TCP performance. Finally we suggest and discuss a quantitative definition of the term ``network friendly probing''.

  • 200.
    Johnsson, Andreas
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Björkman, Mats
    On measuring the available bandwidth in wireless 802.11b networksManuscript (Other academic)
1234567 151 - 200 of 388
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