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  • 251. Davidsson, Paul
    et al.
    Henesey, Lawrence
    Ramstedt, Linda
    Wernstedt, Fredrik
    Agent-Based Approaches to Transport Logistics2005In: Applications of Agent Technology in Traffic and Transportation, Whitestein Series in Software Agent Technologies / [ed] Klügl, Ana;; Ossowski, Franziska;; , Birkhäuser , 2005Chapter in book (Other academic)
  • 252. Davidsson, Paul
    et al.
    Holmgren, Johan
    Kyhlbäck, Hans
    Mengistu, Dawit
    Persson, Marie
    Applications of Agent Based Simulation2007Conference paper (Refereed)
    Abstract [en]

    This paper provides a survey and analysis of applications of Agent Based Simulation (ABS). A framework for describing and assessing the applications is presented and systematically applied. A general conclusion from the study is that even if ABS seems a promising approach to many problems involving simulation of complex systems of interacting entities, it seems as the full potential of the agent concept and previous research and development within ABS often is not utilized. We illustrate this by providing some concrete examples. Another conclusion is that important information of the applications, in particular concerning the implementation of the simulator, was missing in many papers. As an attempt to encourage improvements we provide some guidelines for writing ABS application papers.

  • 253.
    Davidsson, Paul
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Holmgren, Johan
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Persson, Jan A.
    Ramstedt, Linda
    Multi Agent Based Simulation of Transport Chains2008Conference paper (Refereed)
    Abstract [en]

    An agent-based tool for micro-level simulation of transport chains (TAPAS) is described. It is more powerful than traditional approaches as it is able to capture the interactions between individual actors of a transport chain, as well as their heterogeneity and decision making processes. Whereas traditional approaches rely on assumed statistical correlation between different parameters, TAPAS relies on causality, i.e., the decisions and negotiations that lead to the transports being performed. An additional advantage is that TAPAS is able to capture time aspects, such as, the influence of timetables, arrival times, and time-differentiated taxes and fees. TAPAS is composed of two layers, one layer simulating the physical activities taking place in the transport chain, e.g., production, storage, and transports of goods, and another layer simulating the different actors’ decision making processes and interaction. The decision layer is implemented as a multi-agent system using the JADE platform, where each agent corresponds to a particular actor. We demonstrate the use of TAPAS by investigating how the actors in a transport chain are expected to act when different types of governmental control policies are applied, such as, fuel taxes, road tolls, and vehicle taxes. By analyzing the costs and environmental effects, TAPAS provides guidance in decision making regarding such control policies. We argue that TAPAS may also complement existing approaches in different ways, for instance by generating input data such as transport demand. Since TAPAS models a larger part of the supply chain, the transport demand is a natural part of the output. Studies may concern operational decisions like choice of consignment size and frequency of deliveries, as well as strategic decisions like where to locate storages, terminals, etc., choice of producer, and adaptation of vehicle fleets.

  • 254. Davidsson, Paul
    et al.
    Jacobsson, Andreas
    Aligning Models of Normative Systems and Artificial Societies: Towards Normative Behavior in Virtual Enterprises2007Conference paper (Refereed)
  • 255. Davidsson, Paul
    et al.
    Johansson, Stefan J.
    On the Metaphysics of Agents2005Conference paper (Refereed)
  • 256.
    Davidsson, Paul
    et al.
    Blekinge Institute of Technology, School of Computing.
    Johansson, Stefan J.
    Blekinge Institute of Technology, School of Computing.
    On the Potential of Norm-Governed Behavior in Different Categories of Artificial Societies2006In: Computational and mathematical organization theory, ISSN 1381-298X, E-ISSN 1572-9346, Vol. 12, no 2-3, p. 169-80Article in journal (Refereed)
    Abstract [en]

    Based on a classification of artificial societies and the identification of four different types of stakeholders in such societies, we investigate the potential of norm-governed behavior in different types of artificial societies. The basis of the analysis is the preferences of the stakeholders and how they influence the state of the society. A general conclusion drawn is that the more open a society is the more it has to rely on agent owners and designers to achieve norm-governed behavior, whereas in more closed societies the environment designers and owners may control the degree of norm-governed behavior.

  • 257. Davidsson, Paul
    et al.
    Johansson, Stefan J.
    On the Potential of Norm-Governed Behavior in Different Categories of Artificial Societies2005Conference paper (Refereed)
    Abstract [en]

    Based on a classification of artificial societies and the identification of four different types of stakeholders in such societies, we investigate the potential of norm-governed behavior in different types of artificial societies. The basis of the analysis are the preferences of the stakeholders and how they influence the state of the society. A general conclusion drawn is that the more open a society is the more it has to rely on agent owners and designers to achieve norm-governed behavior, whereas in more closed societies the environment designers and owners may control the degree of norm -governed behavior.

  • 258. Davidsson, Paul
    et al.
    Johansson, Stefan J.
    Svahnberg, Mikael
    Characterization and Evaluation of Multi-Agent System Architectural Styles2006In: Software Engineering for Multi-Agent Systems IV, Springer , 2006, p. 179-188Chapter in book (Other academic)
  • 259. Davidsson, Paul
    et al.
    Johansson, Stefan J.
    Svahnberg, Mikael
    Characterization and Evaluation of Multi-Agent System Architectural Styles2005Conference paper (Refereed)
  • 260. Davidsson, Paul
    et al.
    Johansson, Stefan J.
    Svahnberg, Mikael
    Using the Analytic Hierarchy Process for Evaluating Multi-Agent System Architecture Candidates2006In: Agent-Oriented Software Engineering VI: 6th Internaitonal Workshop, AOSE 2005, Revised and Invited Papers, 2006, p. 205-217Chapter in book (Other academic)
    Abstract [en]

    Although much effort has been spent on suggesting and implementing new architectures of Multi-Agent Systems (MAS), the evaluation and comparison of these has often been done in a rather ad-hoc fashion. We believe that the time has come to start doing this in a more systematic way using established methods. For instance, we argue that it is important to evaluate the architecture candidates for a particular application according to several quality attributes relevant to that application. The architecture that provides the most appropriate balance between these attributes should then be selected. As a case study we investigate the problem of load balancing and overload control of Intelligent Networks and present four MAS architectures that can be used to handle this task. We instantiate each of these and define metrics for the selected quality attributes. The instantiations are studied in simulation experiments and measurements of the metrics are recorded. The measurements are then analyzed using the Analytic Hierarchy Process, which is a basic approach to select the most suitable alternative from a number of alternatives evaluated with respect to several criteria. We illustrate how such analyzes can be used for deciding which architecture candidate is the most appropriate in different situations.

  • 261. Davidsson, Paul
    et al.
    Johansson, Stefan J.
    Svahnberg, Mikael
    Using the Analytic Hierarchy Process for Evaluating Multi-Agent System Architecture Candidates2005Conference paper (Refereed)
  • 262. Davidsson, Paul
    et al.
    Logan, BrianTakadama, Keiki
    Multi-Agent and Multi-Agent Based Simulation2005Collection (editor) (Other academic)
  • 263. Davidsson, Paul
    et al.
    Persson, Jan A.
    Holmgren, Johan
    On the Integration of Agent-Based and Mathematical Optimization Techniques2007In: 1st KES International Symposium on Agent and Multi-Agent Systems: Technologies, SPRINGER-VERLAG BERLIN , 2007, p. 1-10Chapter in book (Refereed)
    Abstract [en]

    The strengths and weaknesses of agent-based approaches and classical optimization techniques are compared. Their appropriateness for resource allocation problems were resources are distributed and demand is changing is evaluated. We conclude that their properties are complementary and that it seems beneficial to combine the approaches. Some suggestions of such hybrid systems are sketched and two of these are implemented and evaluated in a case study and compared to pure agent and optimization-based solutions. The case study concerns allocation of production and transportation resources in a supply chain. In one of the hybrid systems, optimization techniques were embedded in the agents to improve their decision making capability. In the other system, optimization was used for creating a long-term coarse plan which served as input the agents that adapted it dynamically. The results from the case study indicate that it is possible to capitalize both on the ability of agents to dynamically adapt to changes and on the ability of optimization techniques for finding high quality solutions.

  • 264. Davidsson, Paul
    et al.
    Ramstedt, Linda
    Törnquist, Johanna
    Inter-Organization Interoperability in Transport Chains Using Adapters Based on Open Source Freeware2005Conference paper (Refereed)
    Abstract [en]

    The significance of electronic information exchange in transport chains and its influence on the performance of the logistics processes is well known. While much focus is still on the various techniques for information exchange, many SMEs experience problems that are not primarily caused by an absence of technology. Several advanced solutions exist but investment possibilities within many SMEs are very limited while their needs for electronic data exchange may be very similar as for the large companies. We describe a general “adapter” solution based on open source freeware that make it possible (in principle) for any business system to exchange information with any other business system. It has been successfully applied in a pilot study involving two companies (the transport operator being an SME) using different business systems (Hogia Mobilast and Movex). The solution was evaluated with the result that it met the requirements of the companies and is now planned to be used for future data exchange between the companies.

  • 265. Davidsson, Paul
    et al.
    Wernstedt, Fredrik
    A Framework for Evaluation of Multi-Agent System Approaches to Logistics Network Management2004In: An Application Science for Multi-Agent Systems, Kluwer , 2004, p. 27-40Chapter in book (Other academic)
    Abstract [en]

    We study the applicability of multi-agent systems (MAS) to production and logistics network management. The goal is to create and evaluate sets of intelligent agents that can cooperatively support production and logistics network decisions, as well as to compare their performance to other more traditional methods. A short description of supply chains is given, as well as a formal characterization of the problem space under investigation. We outline a general simulator that allows for a systematic evaluation of different multi-agent approaches across the different parts of this problem space. This is illustrated by a case study on district heating systems. A major concern in this domain is how to cope with the uncertainty caused by the discrepancies between the estimated and the actual customer demand. Another concern is the temporal constraints imposed by the relatively long production and/or distribution times. In the case study we show how to lessen the impact of these problems by the usage of agent clusters and redistribution of resources.

  • 266. Davidsson, Paul
    et al.
    Wernstedt, Fredrik
    Embedded Agents for District Heating Management2004Conference paper (Refereed)
    Abstract [en]

    We investigate the applicability of multi-agent systems as a control approach for district heating systems. The consumers, i.e., the heat exchange systems, in current district heating systems are purely reactive devices without communication capabilities. In this work, the possibilities of a new type of heat exchanger system that has an open software environment and communication capabilities are explored. Operators of district heating systems have several, often conflicting, goals, e.g., to satisfy the demand of the customers and to minimize production costs. Our approach is to embed a cooperative agent in each consumer. Results from a simulation study indicate that the approach makes it possible to reduce production while maintaining the quality of service. In another experiment in a controlled physical environment, two agent-based approaches are evaluated and compared to existing technologies. The experiment shows that it is possible to automatically load balance a small district heating network using agent technology.

  • 267. Davis, Alan
    et al.
    Low, Siow Yong
    Nordholm, Sven
    Grbic, Nedelko
    A subband space constrained beamformer incorporating voice activity detection2005Conference paper (Refereed)
    Abstract [en]

    This paper introduces a new subband adaptive space constrained beamforming structure for use in hands-free speech enhancement applications. The scheme incorporates a space constrained source model and voice activity information through the integration of a voice activity detector (VAD). The VAD information is used to estimate noise covariance information during non-speech periods and to optimally estimate the source power spectral density (PSD), which is used to provide a spectrally optimized constraint on the source. The proposed structure is evaluated in a real car environment, yielding results which compare well to the optimal Wiener solution where full knowledge of the source is known. ©2005 IEEE.

  • 268.
    Dernaika, Ghina
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Telecommunication Systems.
    Khavtasi, Sophia
    Blekinge Institute of Technology, School of Engineering, Department of Telecommunication Systems.
    Multimedia Codec Evaluation and Overview2007Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    Movies, songs, conferences, video streams and other multimedia services are spreading in everybody’s life, needs and work. Different types of audio and video codecs of various qualities appear to be used for different purposes. However, each codec can be suitable for a special usage, as for example a codec that can be use for high quality film may not be suitable for streaming it into network. The main purpose of this thesis is to compare the performance of different codecs in one particular scenario and indicate which codec performance is the best. The thesis work includes the investigation of several codec aspects (audio and video) and problems related to choosing a multimedia codec (coder/decoder) suitable for large-scale multimedia distribution over the Internet. More specifically, the work focuses on various features of modern media codecs, compares them and finds the best application for each of them. Furthermore, the thesis provides an overview of available research results related to this work and codec comparison tables for codecs and their features. Additionally, as part of this work, a testbed was developed to measure the performance of codecs when used to stream media over a network. The testbed enabled the collection of various QoS parameters, such as bandwidth usage and burst, size for each codec considered in this thesis.

  • 269. DeVogeleer, Karel
    et al.
    Erman, David
    Popescu, Adrian
    Simulating BitTorrent2008Conference paper (Refereed)
    Abstract [en]

    IP Television (IPTV) and other media distribution applications are expected to be one of the next Internet killer applications. One indication of this is the corporate backing that the IP Multimedia Subsystem (IMS) is getting. However, the bandwidth utilization of these applications is still an issue, as the volume of multimedia grows due to larger image resolution and higher bitrate audio. One way of managing this increase in bandwidth requirements is to use existing endhost bandwidth to decrease the load on the content server in a Peer-to-Peer (P2P) fashion. One of the most successful P2P applications is BitTorrent (BT), a swarming file transfer system. This paper presents an implementation of a BT simulator intended for future use in investigating modifications to the BT system to provide streaming media capabilities. The simulator is validated against real-world measurements and a brief performance analysis is provided.

  • 270.
    Dielewicz, Jan
    Blekinge Institute of Technology, School of Engineering, Department of Systems and Software Engineering.
    Sample Solutions as First Step to Knowledge Management2007Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    Knowledge Management and Customer Care are regarded to be able to strengthen the competitive capability of a company. Knowledge Management is supposed to increase the innovative power for problem solving whereas Customer Relationship Management is supposed to increase the customer satisfaction and thereby the customer loyalty. This case study followed a mixed approach to combine aspects from the Knowledge Management and the Customer Relationship Management. Matter of this study was a small-size organization that had a demand for a ticket system for the 2nd and 3rd level support as part of their customer service. Because of an increasing volume of incoming requests, it was necessary to change the system from e-mail clients to a ticket system. Additionally, the company wanted to assure that all agents are able to process all types of requests in order to keep up good service quality even if the experts are not available. For this reason, the concept of this study was not only to introduce a ticket system, but also to implement a Knowledge Base storing the knowledge how to solve the requests in shape of sample solutions. The aim of the study was to find out whether such an approach would be possible, what the success influencing factors would be and what effect such an approach would have on the overall Knowledge Management practices. For this purpose the study made use of qualitative research methods, like interviews and observations, throughout the whole project’s duration. As a result, the project was not able to deliver the desired insights completely. The introduction of the pure ticket system was very successful as the employees reported an improvement of their working processes. The Knowledge Base however was not used during the observation period at all. As a standard risk for projects, late hardware delivery, turned into a problem and used up the planed buffers, the remaining time for observation, whether the Knowledge Base would be used or not, was too short. Therefore, it is necessary to do a follow-up study and assess whether the effect only is late or there is no effect. It might even be necessary to prove the approach in another environment, as the studied company very much relies on the personalization approach for Knowledge Management. Because of the well developed communication culture at the studied company, the employees prefer direct communication for knowledge sharing and knowledge transfer. That inhibits knowledge codification as a Knowledge Management approach. This itself, of course is a valuable insight.

  • 271. Diestelkamp, Wolfgang
    On Design Methodology for Flexible Systems2002Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In software architecture, two seemingly contradicting goals are to be considered when designing systems, namely maintainability and performance aspects. It seems to be commonly accepted that systems can be designed either for flexibility and thus easily be maintained, or for performance, but generally not both at the same time. In this thesis we dexcribe blexibility and resulting maintainabiltiy from different aspects and show how it can eventually be achieved togehter with acceptable performance.

  • 272. Diestelkamp, Wolfgang
    et al.
    Lundberg, Lars
    Performance tuning a generic database system by data striping2000Conference paper (Refereed)
    Abstract [en]

    In this paper we briefly present an existing database system with its advantages and disadvantages. The system uses an approach that significantly improves flexibility and maintainability. A performance model has been developed for the system, thus making it possible to quantitatively compare the performance reduction caused by the increased maintainability. Validations using real-world scenarios and data show that the performance model is very accurate. The model and validation show that the performance loss of using the flexible approach is substantial. Based on insights gained from the performance model, we improve performance by using different data-striping techniques. We show the effect of standard RAID 0 striping, and then further improve our results by using range partitioning.

  • 273. Dittrich, Yvonne
    et al.
    Eriksén, Sara
    Wessels, Bridgette
    From Knowledge Transfer to Situated Innovation: Cultivating spaces for co-operation in innovation and design between academics, user-groups and ICT providers2009Report (Other academic)
    Abstract [en]

    Innovation systems, ‘triple helix’, and similar expressions, are used to conceptualise the growing need for more integrated forms of co-operation between academia and other societal actors, such as governmental agencies and industry, in order to produce knowledge relevant for society. However, there is as yet little reported experience from such recent and on-going co-operative projects of how research changes when it becomes involved in practices it is meant to contribute to. In this paper, the authors report about three different research projects where researchers co-operated with governmental agencies and industry around the development of ICT. Evidence from three domains, namely e-government, telecommunications and welfare services, indicates the need for problematising current mainstream understandings of innovation. Innovation, as we see it, is occurring through configurations of designers, developers and domain experts that form constituencies and where scientific knowledge is confronted by requirements, constraints and possibilities of the specific situation. In this context innovation of, or involving, ICT requires a significant amount of imagination, represents a relatively sharp break with established ways of doing things, and requires artful integration of different professional practices, communities, and technologies. We define these creative processes of co-development of work practices, organisations and technology as ‘situated innovation’.

  • 274. Dittrich, Yvonne
    et al.
    Rönkkö, Kari
    Eriksson, Jeanette
    Hansson, Christina
    Lindeberg, Olle
    Cooperative method development: Combining qualitative empirical research with method, techniqueand process improvement2008In: Empirical Software Engineering, ISSN 1382-3256, 1573-7616, Vol. 13, no 3, p. 231-260Article in journal (Refereed)
    Abstract [en]

    The development of methods tools and process improvements is best to be based on the understanding of the development practice to be supported. Qualitative research has been proposed as a method for understanding the social and cooperative aspects of software development. However, qualitative research is not easily combined with the improvement orientation of an engineering discipline. During the last 6 years, we have applied an approach we call ‘cooperative method development’, which combines qualitative social science fieldwork, with problem-oriented method, technique and process improvement. The action research based approach focusing on shop floor software development practices allows an understanding of how contextual contingencies influence the deployment and applicability of methods, processes and techniques. This article summarizes the experiences and discusses the further development of this approach based on several research projects in cooperation with industrial partners.

  • 275. Dittrich, Yvonne
    et al.
    Rönkkö, Kari
    Lindeberg, Olle
    Eriksson, Jeanette
    Hansson, Christina
    Co-Operative Method Development revisited2005Conference paper (Refereed)
    Abstract [en]

    During the last five years, we applied a research approach we call 'Co-operative Method Development' formulated on first experience with empirical research focusing especially on the social side of software engineering. This position paper summarizes the experiences and discusses the improvement and further development of this research approach based on our experiences in different research projects in co-operation with industrial partners.

  • 276.
    Dobrzanski, Lukasz
    Blekinge Institute of Technology, School of Engineering, Department of Systems and Software Engineering.
    UML Model Refactoring: Support for Maintenance of Executable UML Models2005Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    One of the inevitable negative effects of software evolution is design erosion. Refactoring is a technique that aims at counteracting this phenomenon by successively improving the design of software without changing its observable behaviour. Design erosion occurs also in the context of executable UML models, i.e. models that are detailed enough to be automatically compiled to executable applications. This thesis presents results of a study on applying refactoring to the area of maintenance of executable UML models. It contains an overview of recent approaches to UML model refactoring and to executable modelling, followed by identification of refactoring areas in models built in Telelogic TAU, a state-of-the art UML CASE tool. It proposes a systematic approach to specification of both executable UML model refactorings as well as associated bad smells in models. Additionally, it shows how refactorings can be implemented in Telelogic TAU.

  • 277. Dobrzanski, Lukasz
    et al.
    Kuzniarz, Ludwik
    An Approach to Refactoring of Executable UML Models2006Conference paper (Refereed)
  • 278.
    Dogs, Carsten
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Systems and Software Engineering.
    Klimmer, Timo
    Blekinge Institute of Technology, School of Engineering, Department of Systems and Software Engineering.
    An Evaluation of the Usage of Agile Core Practices: How they are used in industry and what we can learn from their usage2004Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    In this thesis we investigate the usage of several agile software development methods as well as the usage of certain agile core practices. By conducting a web survey, we examine what makes these practices beneficial and what tends to make them rather less suitable for certain situations. Based on the results, we finally set up some recommendations for practitioners to reflect upon and improve their own software development process. Concerning these recommendations as well as the list of the investigated practices, we hope (and are almost sure) that there are some practices or ideas contained which are worth at least thinking about. The main findings of this thesis are: - Agile software development methods have already entered the professional market but they are still no cure-all. In many cases they also produce only middle-quality software. Nevertheless, there is – even if only little – evidence that at least XP projects meet the requirements of the customer better than traditional, non-agile methods. - For a successful software development project it is important that it has a suitable requirements engineering process, that the produced software is tested sufficiently (using automated regression testing among other types of testing), that there is a good communication between the customer and the developer side, that the risks of the project are considered, that the pros and cons of practices are considered and that processes are improved continuously. - Besides, it is important to consider the whole context when implementing a certain practice. For some contexts, certain practices do not fit for their purpose and this has to be realized. However, certain shortcomings of a specific practice might be reduced or even eliminated if implemented in combination with other practices.

  • 279.
    Drincic, Samir
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Systems and Software Engineering.
    Dedic, Asim
    Blekinge Institute of Technology, School of Engineering, Department of Systems and Software Engineering.
    Evolving test-case selection at a large scale company2007Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    This paper presents a possible solution for selection of test-cases that should be executed to provide good coverage and quality at UIQ Technologies. It describes how the company can sort and prioritize their test-cases, so that quality is maintained while having controlled amount of test-cases. The idea behind the proposed method is to prioritize the test-cases and execute those that received highest prioritization first and thereby ensuring that all high-risk defects are found first. We have created a model that performs those tasks and we have also executed it on an ongoing project at UIQ Technology to provide data for comparison with the currently used model. We also make a comparison proving that our proposed method is more effective then the current method. We have emphasized adaptability and changeability of the model so that UIQ Technology easily can modify and adapt the model later on.

  • 280. Duong, Quang Trung
    Exact Closed-Form Expression for Average Symbol Error Rate of MIMO-MRC Systems2008Conference paper (Refereed)
    Abstract [en]

    In this paper, we derive closed-form expressions for exact average symbol error rate (SER) of multiple-input multiple-output (MIMO)-maximum ratio combining (MRC) systems with M-ary modulations. We obtain the tractable compact closed-form expressions for the average SER in terms of the Gauss and Appell hypergeometric functions which are provided as library functions in common mathematical softwares such as MAPLE and MATHEMATICA. The analysis is validated by comparing with Monte-Carlo simulations and we further show that our general SER expressions reduce to the previous known results for binary signals (M=2) as a special case. Applying the series representation of the Gauss and Appell hypergeometric function, we derive a very tight approximation for the average SER

  • 281. Duong, Quang Trung
    et al.
    Bao, Vo Nguyen Quoc
    Performance Analysis of Selection Decode-and-Forward Relay Networks2008In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 44, no 20, p. 1206-07Article in journal (Refereed)
    Abstract [en]

    The performance of decode-and-forward (DF) cooperative networks with relay selection is presented. Specifically, we derive closed-form expressions for symbol error probability (SEP), bit error rate (BER), and achievable spectral efficiency of DF relay selection system in independent but not identically distributed (i.n.i.d.) Rayleigh fading channels taking into account the incapability of decoding the received signals' cyclic redundancy code (CRC) at the relays. We also perform Monte-Carlo simulations to validate the analysis.

  • 282. Duong, Quang Trung
    et al.
    Bao, Vo Nguyen Quoc
    Tran, Nguyen Nam
    Ergodic Capacity of Cooperative Networks Using Adaptive Transmission and Selection Combining2009Conference paper (Refereed)
    Abstract [en]

    Closed-form expressions for channel capacity of repetition-based cooperative networks under adaptive transmission with selection combining are presented under the assumption of independent Rayleigh fading. Specifically, three different adaptive techniques are investigated: optimal simultaneous power and rate adaptation (OPRA), constant power with optimal rate adaptation (OPA) and channel inversion with fixed rate (TIFR). Among them, for an arbitrary number of relays, TIFR gives the worst channel capacity; OPRA gives the best channel capacity and ORA has a channel capacity quality in between the others. The analysis results, based on the upper and lower bound of the end-to-end SNR, agree very well with the simulated results and definitely show the impact of selection combining on the calculated channel capacity per unit bandwidth

  • 283. Duong, Quang Trung
    et al.
    Bao, Vo Nguyen Quoc
    Zepernick, Hans-Jürgen
    On the Performance of Selection Decode-and-Forward Relay Networks over Nakagami-m Fading Channels2009In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 13, no 3, p. 172-174Article in journal (Refereed)
    Abstract [en]

    In this paper, we present the performance of fixed decode-and-forward cooperative networks with relay selection over independent but not identically distributed Nakagamim fading channels, with integer values of the fading severity parameter m. Specifically, closed-form expressions for the symbol error probability and the outage probability are derived using the statistical characteristic of the signal-to-noise ratio. We also perform Monte-Carlo simulations to verify the analytical results

  • 284. Duong, Quang Trung
    et al.
    Engelke, Ulrich
    Zepernick, Hans-Jürgen
    Unequal Error Protection for Wireless Multimedia Transmission in Decode-and-Forward Relay Networks2009Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose an unequal error protection (UEP) scheme for multimedia transmission over wireless decode-and-forward (DF) relay networks. We prove that relay selection combining (R-SC) mode yields a better error rate performance than all-participate relays, i.e., distributed spacetime codes (DSTC) and orthogonal transmission with maximum ratio combining (OT-MRC) at the destination. Hence, we apply the R-SC scheme for transmitting bit sequence with high priority while the cooperative spatial multiplexing scheme is employed for the bit-stream with low priority. With this strategy, we achieve the maximum spatial diversity gain for high priority data and a high spatial multiplexing gain for low priority data. Monte- Carlo simulations and analytical results are shown to validate the proposed UEP scheme.

  • 285. Duong, Quang Trung
    et al.
    Ha, Dac-Binh
    Tran, Hoai-An
    Vo, Nguyen-Son
    Symbol Error Probability of Distributed-Alamouti Scheme in Wireless Relay Networks2008Conference paper (Refereed)
    Abstract [en]

    In this paper, we analyze the maximum likelihood decoding performance of non-regenerative cooperation employing Alamouti scheme. Specifically, we derive two closed-form expressions for average symbol error probability (SEP) when the relays are located near by the source or destination. The analytical results are obtained as a single integral with finite limits and an integrand composed solely of trigonometric functions. Assessing the asymptotic (high signal-to-noise ratio) behavior of SEP formulas, we show that the distributed-Alamouti codes achieves a full diversity order. We also perform Monte-Carlo simulations to validate the analysis.

  • 286. Duong, Quang Trung
    et al.
    Ha, Dac-Binh
    Tran, Hoai-An
    Vo, Nguyen-Son
    Haroon, Ahsan
    On The Symbol Error Probability of Distributed-Alamouti Scheme2009In: Journal of Communications, ISSN 1796-2021, E-ISSN 1796-2021, Vol. 4, no 7, p. 437-444Article in journal (Refereed)
    Abstract [en]

    Taking into account the relay’s location, we analyze the maximum likelihood (ML) decoding performance ofdualhop relay network, in which two amplify-and-forward (AF) relays employ the Alamouti code in a distributed fashion. In particular, using the well-known moment generating function (MGF) approach we derive the closed-form expressions of the average symbol error probability (SEP) for M-ary phase-shift keying (M-PSK) when the relays are located nearby either the source or destination. The analytical result is obtained as a single integral with finite limits and the integrand composed solely of trigonometric functions. Assessing the asymptotic characteristic of SEP formulas in the high signal-to-noise ratio regime, we show that the distributed-Alamouti protocol achieves a full diversity order. We also perform the Monte-Carlo simulations to validate our analysis. In addition, based on the upper bound of SEP we propose an optimal power allocation between the first-hop (the source-to-relay link) and second-hop (the relay-to-destination link) transmission. We further show that as the two relays are located nearby the destination most of the total power should be allocated to the broadcasting phase (the first-hop transmission). When the two relays are placed close to the source, we propose an optimal transmission scheme which is a non-realtime processing, hence, can be applied for practical applications. It is shown that the optimal power allocation scheme outperforms the equal power scheme with a SEP performance improvement by 2-3 dB.

  • 287. Duong, Quang Trung
    et al.
    Nguyen, Ngoc-Tien
    Hoang, Trang
    Nguyen, Viet-Kinh
    Pairwise Error Probability of Distributed Space--Time Coding Employing Alamouti Scheme in Wireless Relays Networks2009In: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 51, no 2, p. 231-244Article in journal (Refereed)
    Abstract [en]

    In this paper, we analyze the pairwise error probability (PEP) of distributed space-time codes, in which the source and the relay generate Alamouti space--time code in a distributed fashion. We restrict our attention to the space-time code construction for Protocol III in [1]. In particular, we derive two closed-form approximations for PEP when the relay is either close to the destination or source and an upper bound for any position of the relay. Using the alternative definition of $Q$-function, we can express these PEPs in terms of finite integral whose integrand is composed of trigonometric functions. We further show that with only one relay assisted source-destination link, system still achieves diversity order of two, assuming single-antenna terminals. We also perform Monte-Carlo simulations to verify the analysis.

  • 288. Duong, Quang Trung
    et al.
    Tran, Hoai-An
    Distributed Space-Time Block Codes with Amicable Orthogonal Designs2008Conference paper (Refereed)
    Abstract [en]

    In this paper, we generalize the construction of distributed space–time block codes (DSTBCs) using amicable orthogonal designs which are originally applied to co-located multiple-antenna systems. We also derive the closed-form expression of average symbol error probability (SEP). The result is obtained in the form of single finite-range integral whose integrand contains only the trigonometric functions. Using the asymptotic (high signal-to-noise ratio) SEP formulas we show that the orthogonal DSTBCs achieve full diversity order. We also perform Monte-Carlo simulation to validate the analysis.

  • 289.
    Duong, Quang Trung
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Signal Processing.
    Yeoh, Phee Lep
    Vo, Nguyen Quoc Bao
    Elkashlan, Maged
    Yang, Nan
    Cognitive Relay Networks With Multiple Primary Transceivers Under Spectrum-Sharing2012In: IEEE Signal Processing Letters, ISSN 1070-9908, E-ISSN 1558-2361, Vol. 19, no 11, p. 741-744Article in journal (Refereed)
    Abstract [en]

    We examine the impact of multiple primary transmitters and receivers (PU-TxRx) on the outage performance of cognitive decode-and-forward relay networks. In such a joint relaying/spectrum-sharing arrangement, we address fundamental questions concerning three key power constraints: 1) maximum transmit power at the secondary transmitter (SU-Tx), 2) peak interference power at the primary receivers (PU-Rx), and 3) interference power at SU-Rx caused by the primary transmitter (PU-Tx). Our answers to these are given in new analytical expressions for the exact and asymptotic outage probability of the secondary relay network. Based on our asymptotic expressions, important design insights into the impact of primary transceivers on the performance of cognitive relay networks is reached. We have shown that zero diversity order is attained when the peak interference power at the PU-Rx is independent of the maximum transmit power at the SU-TX.

  • 290. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Adaptive Transmission Scheme for Wireless Cooperative Communications2009Conference paper (Refereed)
    Abstract [en]

    An adaptive transmission scheme for cooperative communications is proposed in this paper. Communication protocols with amplify-and-forward relays based on the distributed-Alamouti space-time code (achieving spatial diversity gain) and cooperative spatial multiplexing (C-SM) (pertaining spatial multiplexing gain) are considered. Specifically, under a fix transmission rate, we use adaptively the cooperative diversity (C-DIV) and C-SM according to channel conditions. With this strategy, either C-DIV with higher order modulation or C-SM with lower order modulation can be properly selected to enhance the error rate performance. The proposed adaptive protocol is shown to provide superior performance compared to C-DIV and C-SM.

  • 291. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Exact Average Symbol Error Rate of Cooperative Spatial Multiplexing in Composite Channels2008Conference paper (Refereed)
    Abstract [en]

    Performance of cooperative spatial multiplexing systems over composite channels is presented. In particular, we derive the exact closed-form average symbol error rate (SER) expressions for cooperative spatial multiplexing systems with linear equalization receiver (e.g., Zero-Forcing) and M-ary modulation scheme in the composite channel of log-normal shadowing and Rayleigh fading. Using the Gauss-Hermite quadrature integration, the average SER is expressed in the forms of Appell hypergeometric function. Applying the series representation of Appell hypergeometric function, we derive a very tight approximation for the average SER. We also perform Monte-Carlo simulations to validate our analysis.

  • 292. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Hybrid Decode-Amplify-Forward Cooperative Communications with Multiple Relays2009Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate the performance gain of hybrid decode-amplify-forward (HDAF) relay protocol over the two conventional ones: the adaptive decode-forward (ADF) and amplify-forward (AF) in dual-hop multiple-relay networks. We analyze the performance gain in terms of the symbol error probability (SEP) in the high signal-to-noise ratio (SNR) regime. Similarly as in the single relay case [1], under a specific modulation scheme, these gains only depend on the ratio of channel mean power between the first-hop and second-hop transmission. In particular, we show that the HDAF protocol obtains a large gain, medium gain, and small gain over ADF, AF as the relays are placed close to the destination, half-way between the source and destination (symmetric case), and nearby the source, respectively. In contrast to the single-relay case in which the HDAF scheme has no benefit compared to ADF and AF as the relay is located close to the source [1], HDAF still achieves a small gain with multiple relays. Interestingly, we further show that for all cases the performance gains are saturated as the number of relays is large.

  • 293. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    On the Ergodic Capacity of Cooperative Spatial Multiplexing Systems in Composite Channels2009Conference paper (Refereed)
    Abstract [en]

    The ergodic capacity of cooperative spatial multiplexing systems over composite channels is presented. Specifically, we derive the exact closed-form expressions for ergodic capacity of cooperative spatial multiplexing systems with linear receiver in the composite channel of log-normal shadowing and Rayleigh fading. Using the Gauss-Hermite quadrature integration, the final analytical result of ergodic capacity is described in a closed-form expression. We also perform Monte-Carlo simulations to validate our analysis. Subsequently, we apply the obtained analytical expression to evaluate some representative scenarios regarding to spatial multiplexing gain in relay composite channels

  • 294. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    On the Performance Gain of Hybrid Decode-Amplify-Forward Cooperative Communications2009In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 2009Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate the performance of adaptive decode-forward (ADF), amplify-forward (AF), and hybrid decode-amplify-forward (HDAF) relaying protocol. In particular, we derive the closedform expression of symbol error probability (SEP) for these three relaying protocols. For the AF protocol, we derive a simpler and more tractable final result than previously published work [1]. Furthermore, analyzing the high signal-to-noise ratio (SNR) regime, we derive an asymptotically tight approximation for SEP. Especially, for the AF protocol, our SEP approximation is tighter than the result in [2]. The SEP approximation is used to assess an important aspect between the three different relaying protocols, i.e., the SEP performance gain of HADF over the two conventional relaying schemes ADF and AF. It is shown that the performance gain of HDAF over ADF and AF significantly depends on the relative value of channel conditions between source-to-relay and relay-to- estination link (relay channels). Interestingly, it is shown that the HDAF protocol has no benefit compare to the two others if the relay is located close to the source. In contrast, the performance gains of HDAF over the ADF and AF scheme are remarkably large as the relay moves nearby the destination. Specifically, the numerical results given as well as our analysis indicate that for QPSK modulation, HDAF outperforms ADF and AF with a performance improvement by 5 dB and 6 dB, respectively.

  • 295. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    On the Performance of ROI-Based Image Transmission Using Cooperative Diversity2008Conference paper (Refereed)
    Abstract [en]

    In this paper, we examine the spatial diversity of cooperative communications for image transmission without deploying multiple antennas at the transmitter. We propose a novel region of interest (ROI)-based scheme for image transmission over wireless cooperative/relay fading channels. By having the relay terminal assist the direct communications, we can increase the resilience for ROI against the error-prone fading channels. Our proposed scheme significantly improves the performance of ROI compared to the direct communications (no-cooperation) and conventional relay networks without performing any forward error correction. Although we focus on the adaptive decode-forward (ADF) relay protocol, our proposed scheme can be easily adopted to any other relaying protocol such as fixed decode-forward (FDF), amplify-forward (AF), hybrid decode-amplify-forward (HDAF), and distributed-Alamouti space--time coding. Simulation results show that under the the same total transmit power constraint our proposed scheme significant outperforms the conventional ones in terms of bit error rate (BER) and peak signal-to-noise ratio (PSNR).

  • 296. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Robust EZW Image Transmission Scheme Using Distributed-Alamouti Codes in Relay Networks2008Conference paper (Refereed)
    Abstract [en]

    A robust image transmission scheme deploying distributed-Alamouti space-time code (STC) over wireless relay networks is proposed. Specifically, we propose a cross-layer design combining application, networking, and physical layer to enhance the quality of multimedia data over error-prone wireless channels. At the application layer, a coded image sequence based on the wavelet transform is divided into two priorities. The higher priority contains the most significant information of image and the lower priority conveys less important information. At the physical layer, two pre-assigned relays cooperate to form a distributed-Alamouti code which help the source to transmit the low priority sequence of the image over error-prone wireless channels. At the networking layer, among the whole relay nodes in the networks we select two relay nodes which provides the maximum signal-to-noise ratio to convey the higher priority. With this strategy, we implicitly achieve unequal error protection for image transmission without controlling power or varying modulation and coding at the transmitter at the expense of increasing network's overhead (i.e. feedback information). The selection of relays needs limited feedback, hence, enabling our proposed scheme feasible in practical applications. Analytical and simulation results are provided to verify our proposal. It has been shown that the image quality is remarkably enhanced in terms of objective quality using the proposed scheme compared to the conventional transmission schemes.

  • 297. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Bao, Vo Nguyen Quoc
    Symbol error probability of hop-by-hop beamforming in Nakagami-m fading2009In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 45, no 20, p. 1042-1044Article in journal (Refereed)
    Abstract [en]

    The symbol error probability (SEP) of amplify-and-forward(AF) multiple-input multiple-output (MIMO) cooperative networks where beamforming is adopted at both the source and destination is investigated. In particular, the tight lower bound for SEP of AF MIMO relay systems is presented with hop-by-hop beamforming over independent, but not necessarily identically distributed, Nakagami-m fading channels. Furthermore, assessing the high SNR, an asymptotic SEP expression is derived which reveals the array and diversity gain. Numerical results are shown to verify the analysis in some representative scenarios.

  • 298. Duursma, Rick
    et al.
    Fiedler, Markus
    Iterative computations of bit rate summary statistics at inlet and outlet of a discrete time fluid queue2006Conference paper (Refereed)
    Abstract [en]

    Network performance management is facing the challenge of provisioning advanced services with stringent delay and throughput requirements. For this reason, shortage of network capacity implying delay or loss, so-called bottlenecks, have to be identified and to be classified. The latter tasks imply the need for tractable analytical performance models. As we are particularly interested in the traffic flow properties, we focus on a discrete-time fluid flow traffic model. The fluid model considers averages of bit rates on small time scales. These averages can easily be measured, and thus, bit rate statistics for data streams entering and leaving a bottleneck can be obtained. The fluid flow model helps us to obtain analytical estimates on the impact of network entities on data streams and their statistics, i.e., efficiently predict the effects of bottlenecks on data streams. In this work we derive formulae for an iterative calculation of summary statistics such as the bit rate distribution and autocorrelation function. In addition, a corresponding simulation has been implemented, and the simulation results agree closely with the exact solutions. With the aid of the derived formulae we are able to match the model to observations.

  • 299. Dzamashvili-Fogelström, Nina
    et al.
    Gorschek, Tony
    Test-case Driven versus Checklist-based Inspections of Software Requirements – An Experimental Evaluation2007Conference paper (Refereed)
    Abstract [en]

    Software inspections have proved to be an effective means to find faults in different software artifacts, and the application of software inspections on requirements specifications is believed to give a high return on investment as problems are caught early. However, despite the existing evidence of positive effects requirements inspections are not a common practice in industry. The reason is believed to be the cost associated with inspections as a technology. This paper presents an evaluation of test-case driven inspections (TCD) - an emerging inspection technique that aims to cut costs associated with traditional requirements inspections. To formally test the efficiency and effectiveness of TCD inspections an experiment was conducted, in a controlled environment, where checklist based inspections was used as a point of reference. The experiment results indicate that TCD inspections perform better when it comes to effectiveness in finding major faults in a requirements specification.

  • 300. Dzamashvili-Fogelström, Nina
    et al.
    Gorschek, Tony
    Svahnberg, Mikael
    Needs Oriented Framework for Producing Requirements Decision Material: NORM2008Conference paper (Refereed)
    Abstract [en]

    The need of understanding and supporting requirements engineering decisions in market-driven product development is motivated by the complexity and economical impact of these decisions. While being a key for success, correct and timely decisions are dependent on the availability and the quality of decision material (requirements, business cases, costvalue estimations etc). This paper presents a needsoriented framework (NORM) for identifying and assuring the creation of appropriate decision material for RE decisions. NORM is based on analysis of the applied RE process and characteristics of separate RE decisions, focusing mainly on pre-project activities. The framework is developed in close cooperation with industry with the intention to ensure that resources are spent on producing just-the-necessary information at the right time and to be able to monitor and control this production effort.

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