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  • 1.
    Modarres Razavi, Sara
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Gunnarsson, Fredrik
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Moe, Johan
    Linköping University, Department of Computer and Information Science, PELAB - Programming Environment Laboratory. Linköping University, The Institute of Technology.
    Dynamic Tracking Area List configuration and performance evaluation in LTE2010Conference paper (Refereed)
    Abstract [en]

    Reducing the signaling overhead for tracing user equipment (UE), while maintaining the improved performance over time despite the changes in UE location and mobility patterns, is a challenging issue in the area of mobility management. Flexibility and automatic reconfiguration are two significant features in Long Term Evolution (LTE) systems. The Tracking Area List (TAL) is a novel concept in LTE systems, which allows a more flexible configurations, expecting to reduce the overall signaling overhead. In this paper, we first present a ”rule of thumb” method to allocate and assign TALs for a network. The easily applied approach does not require any data other than what is available for conventional TA design. Second we compare the performance of an optimum conventional TA design with the suggested TAL design for a large scale network in Lisbon, Portugal. A thorough computation is done to make a justified evaluation. We follow the comparison during specific time intervals for one complete day, and we illustrate the performance of reconfiguration for each approach. The results clearly demonstrate the ability of dynamic TAL in reducing the signaling overhead and maintaining a good performance due to reconfiguration compared to the conventional TA design.

  • 2.
    Modarres Razavi, Sara
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Gunnarsson, Fredrik
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Moe, Johan
    Linköping University, Department of Computer and Information Science, PELAB - Programming Environment Laboratory. Linköping University, The Institute of Technology.
    Exploiting Tracking Area List for Improving Signaling Overhead in LTE2010In: Proceedings of IEEE 71st Vehicular Technology Conference (VTC 2010-Spring), IEEE , 2010, p. 1-5Conference paper (Refereed)
    Abstract [en]

    Reducing the overhead required for tracing mobile devices is one of the major aspects in the study of mobility management of a cellular network. The Long Term Evolution (LTE) systems give a more flexible configuration of Tracking Area (TA) design by means of Tracking Area List (TAL). Being a novel concept, TAL goes beyond the capability of the conventional TA approach. Although TAL is expected to be able to reduce the overall signaling overhead by overcoming a couple of major limitations of the conventional TA concept, how to apply TAL in large scale networks, remains unexplored. In this paper, we present a novel approach for allocating and assigning TA lists. The approach does not require any data other than what is needed for conventional TA design. We present numerical results to illustrate the approach for a realistic network of Lisbon city. The experiments demonstrate the ability of TAL in reducing the signaling overhead compared to the conventional TA concept.

  • 3.
    Modarres Razavi, Sara
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Gunnarsson, Fredrik
    Ericsson Research, Ericsson AB, Sweden.
    Moe, Johan
    Ericsson Research, Ericsson AB, Sweden.
    Performance and Cost Trade-off in Tracking Area Reconfiguration: A Pareto-optimization Approach2012In: Computer Networks, ISSN 1389-1286, E-ISSN 1872-7069, Vol. 56, no 1, p. 157-168Article in journal (Refereed)
    Abstract [en]

    Tracking Area (TA) design is one of the key tasks in location management of Long Term Evolution (LTE) networks. TA enables to trace and page User Equipments (UEs). As UEs distribution and mobility patterns change over time, TA design may have to undergo revisions. For revising the TA design, the cells to be reconfigured typically have to be temporary torn down. Consequently, this will result in service interruption and “cost”. There is always a trade-off between the performance in terms of the overall signaling overhead of the network and the reconfigurationcost. In this paper, we model this trade-off as a bi-objective optimization problem to which the solutions are characterized by Pareto-optimality. Solving the problem delivers a host of potential trade-offs among which the selection can be based on the preferences of a decision maker. An integer programming model has been developed and applied to the problem. Solving the integer programming model for various cost budget levels leads to an exact scheme for Pareto-optimization. In order to deliver Pareto-optimal solutions for large networks in one single run, a Genetic Algorithm (GA) embedded with Local Search (LS) is applied. Unlike many commonly adopted approaches in multi-objective optimization, our algorithm does not consider any weighted combination of the objectives. Comprehensive numerical results are presented in this study, using large-scale realistic or real-life network scenarios. The experiments demonstrate the effectiveness of the proposed approach.

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  • 4.
    Moe, Johan
    Linköping University, Department of Computer and Information Science, PELAB - Programming Environment Laboratory. Linköping University, The Institute of Technology.
    Execution tracing of large distributed systems2001Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Understanding the dynamic properties of a large distributed software system is most challenging. Knowledge of a system's dynamics is a prerequisite for the design of viable solutions for both coding and testing. Taking the perspective of a maintainer of the system, we have focused on how execution trace data generated from object interaction during execution can be used in maintenance.

    A practical method for improving a system (by increased understanding) is a contribution of this research. The result increases our understanding of how information based on execution tracing can be derived and used. To support the method we developed a toolbox consisting of CORBA-based systems comprising trace collection, information building and visualisation. In short, trace collection is performed by observing the messages sent over the CORBA layer, thus no instrumentation of source code is needed. Information building consists of pattern matching and statistical analysis. Visualisation is performed with the Spotfire.netTM tool.

    The method has been examined during a case study with software optirnising operation of a network for GSM. Trace data were collected during both testing, and operation at a customer site. By feeding back generated information to the design organisation several positive results have been noted. For example, performance tuning has become a natural activity amongst designers, as the system behaviour is better understood from information building on both testing and normal operation. In the actual case we were able to suggest nine improvements based on unexpected use and non-use of the systems parts.

    The conclusion is that we have found a practically relevant area, where only little information has been published. For the future, we are keen on generalising the findings with more studies and to increase the technical sophistication and theoretical foundation of the toolbox.

  • 5.
    Moe, Johan
    Linköping University, Department of Computer and Information Science. Linköping University, The Institute of Technology.
    Observing the dynamic behaviour of large distributed systems to improve development and testing: an empirical study in software engineering2003Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Knowledge about software systems' dynamics is a prerequisite for the successful design, testing and maintenance of viable products. This work has evolved a number of tools based on observation of software system dynamics in a commercial environment, resulting in a method and a toolbox that can be used by testers and maintainers to improve both the system and its test environment.

    The toolbox uses interceptors to observe the object interaction on the CORBA level during execution. With interceptors it is possible to intercept object communication without the need of the source code and with low impact on system performance. Intercepting a series of messages between the various objects can create an image of specific dynamic aspects of a running system. Observation can also be combined with simulation via active probing. Here active probing denote delays in communication and other simulated resource limitations that can be injected into the system for capacity testing purposes.

    The method conceptually supports plan-do-study-act promoted by Shewhart. The method is created to handle at least four different development activities: system tuning, testing, test evaluation, usage evaluation and increasing software understanding in general. System tuning can be activities such as performance enhancements or load balancing. The method also serves user profiling if it can run at a customer site. With coverage measurements, for example, how each internal function is covered during testing, one gets a measure of test quality and a way to specify goals for testing. With active probing, it will be possible to effect execution of a program. This can be used for system-robustness testing or as an oracle as how the system will react in different real-life situations. The need of a general understanding is documented with an interview series of software professionals. Yet another interview series with professionals using the tool shows how understanding can be enhanced.

    The method has been developed and evaluated in several case studies at different branches of ERICSSON AB in Linköping and Stockholm, Sweden. It is planned to become an integrated part of ERICSSON's O&M platform from 2004. 

  • 6.
    Moe, Johan
    et al.
    Linköping University, Department of Computer and Information Science, PELAB - Programming Environment Laboratory. Linköping University, The Institute of Technology.
    Carr, David
    Linköping University, Department of Computer and Information Science, ASLAB - Application Systems Laboratory. Linköping University, The Institute of Technology.
    Patel, Mikael
    Ericsson AB.
    Using Observation and Refinement to Improve Distributed System Test2003In: Proceedings of the 7th European Conference on Software Maintenance and Reengineering (CSMR 2003), 2003Conference paper (Refereed)
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