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  • 201.
    Bulusu, Vishwanath
    et al.
    University of California, Berkeley, USA.
    Polishchuk, Valentin
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Sengupta, Raja
    University of California, Berkeley, USA.
    Sedov, Leonid
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Capacity estimation for low altitude airspace2017In: 17th AIAA Aviation Technology, Integration, and Operations Conference, American Institute of Aeronautics and Astronautics , 2017, p. 1-15Conference paper (Refereed)
  • 202.
    Bulusu, Vishwanath
    et al.
    Univ Calif Berkeley, CA 94720 USA.
    Sedov, Leonid
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Polishchuk, Valentin
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Decentralized self-propagating ground delay for UTM: capitalizing on domino effect2017In: 2017 INTEGRATED COMMUNICATIONS, NAVIGATION AND SURVEILLANCE CONFERENCE (ICNS), IEEE , 2017Conference paper (Other academic)
    Abstract [en]

    n/a

  • 203.
    Bulusu, Vishwanath
    et al.
    Univ Calif Berkeley, CA 94720 USA.
    Sengupta, Raja
    Univ Calif Berkeley, CA 94720 USA.
    Polishchuk, Valentin
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Sedov, Leonid
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Cooperative and Non-Cooperative UAS Traffic Volumes2017In: 2017 INTERNATIONAL CONFERENCE ON UNMANNED AIRCRAFT SYSTEMS (ICUAS17), IEEE , 2017, p. 1673-1681Conference paper (Refereed)
    Abstract [en]

    We describe an analytical process to determine how much UAS traffic is feasible. The process is a simulator and data processing tools. The two are applied to the US San Francisco Bay Area and Norrkoping, Sweden. The amount of UAS traffic is measured in flights per day and simulated up to 200,000 flights. A UAS traffic volume is feasible if specified metrics meet operational requirements with high probability and are stable, in the sense of being below thresholds observed for monotone properties in random geometric graphs. We focus on conflict cluster size and argue for it as a fundamental safety metric worthy of extraordinary consideration.

  • 204.
    Burke, Kyle
    et al.
    Plymouth State University, NH, USA.
    Demaine, Erik D.
    Massachusetts Institute of Technology, MA, USA.
    Gregg, Harrison
    Bard Coll Simons Rock, MA, USA.
    Hearn, Robert A.
    Portola Valley, CA USA.
    Hesterberg, Adam
    Massachusetts Institute of Technology, MA, USA.
    Hoffmann, Michael
    Swiss Federal Institute Technology, Switzerland.
    Ito, Hiro
    The University of Electro-Communications, Chofu, Japan.
    Kostitsyna, Irina
    University of Iibre Bruxelles, Belgium.
    Leonard, Jody
    Bard Coll Simons Rock, MA, USA.
    Loeffler, Maarten
    University of Utrecht, Netherlands.
    Santiago, Aaron
    Bard Coll Simons Rock, MA, USA.
    Schmidt, Christiane
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering. University of Elect Communicat, Japan.
    Uehara, Ryuhei
    Japan Adv Institute Science and Technology, Japan.
    Uno, Yushi
    Osaka Prefecture University, Japan.
    Williams, Aaron
    Bard Coll Simons Rock, MA, USA.
    Single-Player and Two-Player Buttons & Scissors Games2016In: DISCRETE AND COMPUTATIONAL GEOMETRY AND GRAPHS, JCDCGG 2015 / [ed] Akiyama, J., Ito, H., Sakai, T., Uno, Y., SPRINGER INT PUBLISHING AG , 2016, Vol. 9943, p. 60-72Conference paper (Refereed)
    Abstract [en]

    We study the computational complexity of the Buttons amp; Scissors game and obtain sharp thresholds with respect to several parameters. Specifically we show that the game is NP-complete for C = 2 colors but polytime solvable for C = 1. Similarly the game is NP-complete if every color is used by at most F = 4 buttons but polytime solvable for F amp;lt;= 3. We also consider restrictions on the board size, cut directions, and cut sizes. Finally, we introduce several natural two-player versions of the game and show that they are PSPACE-complete.

  • 205.
    Bäckstrand, Jenny
    et al.
    Jönköping University, Sweden.
    Fredriksson, Anna
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    The potential of information sharing to improve supply chain performance inconstruction projects2018In: EurOMA 2018 Proceedings: To Serve, to Produce and to Servitize in the Era of Networks, Big Data, and Analytics, 2018Conference paper (Other academic)
    Abstract [en]

    The purpose is toexplore the potential of increased supply chain performance by improved informationsharing between suppliers and contractors in the construction supply chains.Six suppliers are included, representing different combinations of supplyingmaterials and tools for the product or services to support production as wellas few or continuous deliveries during the project. The study show that suppliersneed different information sharing practices if they continuously present atsite or have few deliveries. Based on this and information sharing literature,we have developed a model of what information different suppliers need, includinghow and when to exchange it.

  • 206.
    Bäckström, Gustav
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Wallberg, Sammy
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kvalitetskontroll och säkring av internationella byggprojekt2019Independent thesis Basic level (university diploma), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    The purpose and aim of this study are to examine how quality control and assurance is performed and how it varies in different regions around the world and strive towards international standardization of quality assurance. The foundation to the idea of this study is a Swedish company, called Runway Safe, working with international affairs regarding a safety solution for airport runways. To complete the study, cultural differences and structural differences in organizations comes to consideration.

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    Kvalitetskontroll och säkring av internationella byggprojekt
  • 207.
    Bång, Karl-Lennart
    et al.
    Kungliga Tekniska Högskolan, KTH, Stockhollm.
    Olstam, Johan
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering. Statens väg- och transportforskningsinstitut, Trafikanalys och logistik, TAL.
    Köhler, Joakim
    WSP, Parsons Brinckerhoff, UK.
    Wahlstedt, Johan
    Kungliga Tekniska Högskolan, KTH, Stockholm.
    Andersson, Jonas
    Tyréns AB, Stockholm.
    Handbok för kapacitetsanalys med hjälp av simulering2014Report (Other academic)
    Abstract [sv]

    Syftet med föreliggande handbok är att beskriva hur trafiksimulering kananvändas som en alternativ metod eller komplement till analytiska metoderför att bestämma kapacitet och framkomlighet. Liksom metodbeskrivningarnai TRV2013/64343 är beskrivningarna avsedda att kunna användas för att medhjälp av trafiksimulering uppskatta effekterna av en given utformning isamband med planering, konsekvensanalys, projektering och drift avvägtrafikanläggningar. Simulering kan användas som ett komplement till deanalytiska metoderna, eller som ersättning i fall som inte täcks av dessametoder. Härigenom minskas risken för onödiga kostnader förorsakade avsåväl över- som underkapacitet.

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    Handbok för kapacitetsanalys med hjälp av simulering
  • 208.
    Bång, Karl-Lennart
    et al.
    Kungliga Tekniska Högskolan, KTH, Stockholm.
    Olstam, Johan
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Köhler, Joakim
    WSP Sverige AB, Stockholm.
    Wahlstedt, Johan
    Kungliga Tekniska Högskolan, KTH, Stockholm.
    Andersson, Jonas
    Tyréns AB, Helsingborg .
    Tapani, Andreas
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Handbok för kapacitetsanalys med hjälp av simulering2014Report (Other academic)
    Abstract [sv]

    Syftet med föreliggande handbok är att beskriva hur trafiksimulering kan användas som en alternativ metod eller komplement till analytiska metoder för att bestämma kapacitet och framkomlighet. Liksom metodbeskrivningarna i TRV2013/64343 är beskrivningarna avsedda att kunna användas för att med hjälp av trafiksimulering uppskatta effekterna av en given utformning i samband med planering, konsekvensanalys, projektering och drift av vägtrafikanläggningar. Simulering kan användas som ett komplement till de analytiska metoderna, eller som ersättning i fall som inte täcks av dessa metoder. Härigenom minskas risken för onödiga kostnader förorsakade av såväl över- som underkapacitet.

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  • 209.
    Caap Hällgren, Eric
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Rescheduling blocked Vehicles at Daimler AG2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The purpose of this thesis is to develop a heuristic solution for the static problem of resequencing unblocked vehicles as a part of an ongoing research project at Daimler AG. The target client of this project is Mercedes-Benz Cars.

    An unblocked vehicle is defined as a vehicle that for some reason could not be processed in its given time slot but at a later point in time needs to be inserted into the production sequence. Work overload is defined as work that the worker is unable to finish prior to reaching the station border.

    The resequencing problem can be described as finding new positions for a set of unblocked vehicles in a sequence of previously not blocked vehicles, such that the new sequence containing the previously not blocked vehicles and the additional unblocked vehicles causes as little work overload as possible. A decision has to be made in real-time, forcing the solution method to return a solution within a cycle time.

    Today, Mercedes-Benz Cars uses the sequencing approach “car sequencing”. This approach relies on so called spacing constraints, which basically means, trying to distribute work intensive vehicles as evenly as possible over the planning horizon and thereby enabling a hopefully smooth production. The car sequencing approach needs limited information. The difficulty is to find spacing constraints that fits the high level of product customization characterizing a modern car manufacturer. To overcome these difficulties, a new approach is being considered, namely the mixed-model sequencing, which takes more detailed data into account than the car sequencing approach but on the other hand is more costly in terms of computation.

    To this end, a simple but promising tabu search scheme was developed, that for many instances was able to find the optimal solution in less than 30 seconds of computing time and that also clearly outperformed all benchmark heuristics.

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    Rescheduling blocked Vehicles at Daimler AG
  • 210.
    Cannon, Sarah
    et al.
    College of Computing, Georgia Institute of Technology, Atlanta, USA.
    Fai, Thomas
    Paulson School of Engineering and Applied Sciences, Harvard University, MA, USA.
    Iwerks, Justin
    Mathematics Department, The Spence School, NY, USA.
    Leopold, Undine
    Mathematics Department, Technische Universität Chemnitz, Germany.
    Schmidt, Christiane
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Combinatorics and complexity of guarding polygons with edge and point 2-transmitters2018In: Computational geometry, ISSN 0925-7721, E-ISSN 1879-081X, Vol. 68, p. 89-100Article in journal (Refereed)
    Abstract [en]

    We consider a generalization of the classical Art Gallery Problem, where instead of a light source, the guards, called k-transmitters, model a wireless device with a signal that can pass through at most k walls. We show it is NP-hard to compute a minimum cover of point 2-transmitters, point k-transmitters, and edge 2-transmitters in a simple polygon. The point 2-transmitter result extends to orthogonal polygons. In addition, we give necessity and sufficiency results for the number of edge 2-transmitters in general, monotone, orthogonal monotone, and orthogonal polygons.

  • 211.
    Capone, Antonio
    et al.
    Politecn Milan.
    Chen, Lei
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Gualandi, Stefano
    Politecn Milan.
    Yuan, Di
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Communications and Transport Systems.
    A New Computational Approach for Maximum Link Activation in Wireless Networks under the SINR Model2011In: IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, ISSN 1536-1276, Vol. 10, no 5, p. 1368-1372Article in journal (Refereed)
    Abstract [en]

    A fundamental and computationally challenging optimization task in wireless networks is to maximize the number of simultaneous transmissions, subject to signal-to-noise-and-interference ratio (SINR) requirements at the receivers. The conventional approach guaranteeing global optimality is to solve an integer programming model with explicit SINR constraints. These constraints are however numerically very difficult. We develop a new integer programming algorithm based on a much more effective representation of the SINR constraints. Computational experiments demonstrate that the new approach performs significantly better in proving optimality.

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  • 212.
    Capone, Antonio
    et al.
    Politecn Milan.
    Gualandi, Stefano
    Politecn Milan.
    Yuan, Di
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Communications and Transport Systems.
    Joint routing and scheduling optimization in arbitrary ad hoc networks: Comparison of cooperative and hop-by-hop forwarding2011In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 9, no 7, p. 1256-1269Article in journal (Refereed)
    Abstract [en]

    Cooperation schemes form a key aspect of infrastructure-less wireless networks that allow nodes that cannot directly communicate to exchange information through the help of intermediate nodes. The most widely adopted approach is based on hop-by-hop forwarding at the network layer along a path to destination. Cooperative relaying brings cooperation to the physical layer in order to fully exploit wireless resources. The concept exploits channel diversity by using multiple radio units to transmit the same message. The underlying fundamentals of cooperative relaying have been quite well-studied from a transmission efficiency point of view, in particular with a single pair of source and destination. Results of its performance gain in a multi-hop networking context with multiple sources and destinations are, however, less available. In this paper, we provide an optimization approach to assess the performance gain of cooperative relaying vis-a-vis conventional multi-hop forwarding under arbitrary network topology. The approach joint optimizes packet routing and transmission scheduling, and generalizes classical optimization schemes for non-cooperative networks. We provide numerical results demonstrating that the gain of cooperative relaying in networking scenarios is in general rather small and decreases when network connectivity and the number of traffic flows increase, due to interference and resource reuse limitations. In addition to quantifying the performance gain, our approach leads to a new framework for optimizing routing and scheduling in cooperative networks under a generalized Spacial Time Division Multiple Access (STDMA) scheme.

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  • 213.
    Capone, Antonio
    et al.
    Tech Univ Milan, Italy.
    Li, Yuan
    Natl Innovat Inst Def Technol, Peoples R China.
    Pioro, Michal
    Warsaw Univ Technol, Poland.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Minimizing end-to-end delay in multi-hop wireless networks with optimized transmission scheduling2019In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 89, p. 236-248Article in journal (Refereed)
    Abstract [en]

    The problem of transmission scheduling in single hop and multi-hop wireless networks has been extensively studied. The focus has been on optimizing the efficiency of transmission parallelization, through a minimum-length schedule that meets a given set of traffic demands using the smallest possible number of time slots. Each time slot is associated with a set of transmissions that are compatible with each other according to the considered interference model. The minimum-length approach maximizes the resource reuse, but it does not ensure minimum end-to-end packet delay for multiple source-destination pairs, due to its inherent assumption of frame periodicity. In the paper we study the problem of transmission scheduling and routing aiming at minimizing the end-to-end delay under the signal-to-interference-and-noise-ratio (SINR) model for multi-hop networks. Two schemes are investigated. The first scheme departs from the conventional scheduling approach, by addressing explicitly end-to-end delay and removing the restriction of frame periodicity. The second scheme extends the first one by featuring cooperative forwarding and forward interference cancellation. We study the properties of the two schemes, and propose novel mixed-integer programming models and solution algorithms. Extensive results are provided to gain insights on how the schemes perform in end-to-end delay. (C) 2019 Elsevier B.V. All rights reserved.

    The full text will be freely available from 2021-02-08 13:25
  • 214.
    Carlegrim, Sara
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    GIS analysis of walking and bicycle paths in the new city quarters of Östra Saltängen, Norrköping2014Independent thesis Basic level (university diploma), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Norrköpings kommun håller just nu på med ett stadsomvandlingsprojekt i Östra Saltängen. I dag bedrivs industri- och hamnverksamhet i området, vilka påverkas av de nya planerna och planerar flytten av sin verksamhet parallellt. Examensarbetets syfte var att planera och utforma GC-nätet för det nya området genom en GIS-modell, samt att analysera genhetskvoten från och till bostads- och målpunkter. GIS-modellen upprättades i programmet MapInfo Professional 12.0 där tilläggsprogrammet RouteFinder lades till för att utföra nätverksanalysen. Resultatet från nätverksanalysen användes sedan för att beräkna genhetkvoten. Fyra olika GC-nät togs fram för att analyseras i RouteFinder. Detta för att se vad nätens olika utformning hade för betydelse för genheten. JA bestod av ett GC-nät utifrån Norrköpings kommuns planskiss. UA1 bestod av ett GC-nät med normal maskvidd, UA2 av ett GC-nät med tät maskvidd och UA3 av ett GC-nät med dubbel diagonal. Därefter utfördes en tidsanalys och en diskussion kring broplacering. Till tiden från punkt A till B lades även en tidsrelaterad korsningsfördröjning på för att göra resultatet mera verklighetsbaserat. Diskussionen kring broplaceringen utfördes som en förbättringsåtgärd då en samverkan mellan broplacering och rutter med dålig genhetskvot upptäcktes. Resultatet av de olika analyserna är att en kombination av UA2 och UA3 är det bästa GC-nätet, med avseende på genhet- och tidsaspekten. Med avseende på broarna, bör Skeppsbron ersätta Hamnbron och ”GC-bro 2” byggas.

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  • 215.
    Carlo Cacciabue, Pietro
    et al.
    KITE Solut, Italy .
    Enjalbert, Simon
    University of Lille Nordic France, France .
    Soderberg, Hakan
    Chalmers, Sweden .
    Tapani, Andreas
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Unified Driver Model simulation and its application to the automotive, rail and maritime domains2013In: Transportation Research Part F: Traffic Psychology and Behaviour, ISSN 1369-8478, E-ISSN 1873-5517, Vol. 21, p. 315-327Article in journal (Refereed)
    Abstract [en]

    This paper describes the implementation of a model of a driver into a computerised numerical simulation. The model is developed to capture the essential characteristics and common aspects of cognition and behaviour of a human being in control of a "vehicle" in different surface transport systems, namely trains, cars and ships. The main functions of the simulation are discussed as well as the experiments carried out in different types of driving simulators to support the estimation of the parameters utilised in the numerical simulation. The validation processes carried out in the rail and maritime domains are also discussed together with a critical review of capacities and limitations of the proposed approach.

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  • 216.
    Carlsson, Arne
    et al.
    Statens väg- och transportforskningsinstitut,, VTI.
    Wiklund, Mats
    Statens väg- och transportforskningsinstitut,, VTI.
    Olstam, Johan
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Tapani, Andreas
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Metod för beräkning av fördröjningar på vägavsnitt utan omkörningsmöjlighet2013Report (Other academic)
    Abstract [en]

    This VTI report presents a method for calculating expected queue length and travel timedelay on one lane road sections without overtaking possibilities. The method wasdeveloped 2001 and presented in a working paper. The background for the modeldevelopment was that the Swedish Road Administration (now the Swedish TransportAdministration) planned to build so called 1+1 roads, i.e. roads with longer sectionswithout overtaking possibilities. The method developed has later on also shown to bevaluable for level of service calculations of 2+1 roads with varying share of two lanesections and for developing speed-flow relationships for the Administration’s ”Effectcalculations for road facilities”.The method uses section length, traffic flow, average speed and standard deviation asinput. The method is divided with respect to calculation of effects due to single slowrunningvehicles and effects at “normal” speed distribution. Since no data wereavailable when the model was developed, the model results were instead compared totraffic simulations with the microscopic traffic simulation model AIMSUN. The resultsshow a good correlation but the analytical model gives in general approximately 1.2 percent lower travel time delay. The differences can probably partly be explained by thestochastic parts of the simulation model. One should also remember that neither theanalytical model nor the simulation model has been calibrated and validated with realdata for this type of roads. Thus, the differences between the models do not necessaryimply that the analytical model is the one deviating from reality.

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    Metod för beräkning av fördröjningar på vägavsnitt utan omkörningsmöjlighet
  • 217.
    Carlsson, Axel
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Oxelbark, Eric
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Public Procurement - Pitfalls and Possibilities2015Independent thesis Basic level (university diploma), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Syftet med denna studie är att den ska lyfta fram problematiken byggföretagen upplever samt fungera som en fingervisning om i vilken riktigt eventuella förändringar i upphandlandets genomförande kan göras. Målet är att ta reda på vad branschen tycker om LOU och hur företagen förhåller sig till lagen. Vilka är dess problemområden som orsakar misstro och överklaganden? Undersökningens frågeställning: •Vad tycker entreprenörerna om tillvägagångssättet? •Vilken förändring skulle entreprenörerna vilja se?

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  • 218.
    Carlsson, Niklas
    et al.
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Eager, Derek
    University of Saskatchewan, Canada.
    Krishnamoorthi, Vengatanathan
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Polishchuk, Tatiana
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Optimized Adaptive Streaming of Multi-video Stream Bundles2017In: IEEE transactions on multimedia, ISSN 1520-9210, E-ISSN 1941-0077, Vol. 19, no 7, p. 1637-1653Article in journal (Refereed)
    Abstract [en]

    In contrast to traditional video, multi-view video streaming allows viewers to interactively switch among multiple perspectives provided by different cameras. One approach to achieve such a service is to encode the video from all of the cameras into a single stream, but this has the disadvantage that only a portion of the received video data will be used, namely that required for the selected view at each point in time. In this paper, we introduce the concept of a multi-video stream bundle that consists of multiple parallel video streams that are synchronized in time, each providing the video from a different camera capturing the same event or movie. For delivery we leverage the adaptive features and time-based chunking of HTTP-based adaptive streaming, but now employing adaptation in both content and rate. Users are able to change their viewpoint on-demand and the client player adapts the rate at which data are retrieved from each stream based on the users current view, the probabilities of switching to other views, and the users current bandwidth conditions. A crucial component of such a system is the prefetching policy. For this we present an optimization model as well as a simpler heuristic that can balance the playback quality and the probability of playback interruptions. After analytically and numerically characterizing the optimal solution, we present a prototype implementation and sample results. Our prefetching and buffer management solution is shown to provide close to seamless playback switching when there is sufficient bandwidth to prefetch the parallel streams.

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  • 219.
    Cederborg, Ola
    et al.
    Linköping University, Department of Management and Engineering, Production Economics. Linköping University, The Institute of Technology.
    Rudberg, Martin
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Customer Segmentation and Capable-to-promise in a Capacity Constrained Manufacturing Environmen2009In: Proceedings of the 16th EurOMA Conference, 2009, 2009Conference paper (Other academic)
    Abstract [en]

    The purpose of this study is to analyse customer segmentation and capable-to-promise functionality in a demand fulfilment process. This is done through a literature review and a case study, the case showing that the company has experienced good results from using an advanced planning system based on customer segmentation and capable-to-promise functionality.

  • 220.
    Cen, Song
    et al.
    Xi An Jiao Tong Univ, Peoples R China.
    Zhang, Xingjun
    Xi An Jiao Tong Univ, Peoples R China.
    Lei, Ming
    Xi An Jiao Tong Univ, Peoples R China.
    Fowler, Scott
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Dong, Xiaoshe
    Xi An Jiao Tong Univ, Peoples R China.
    Stochastic geometry modeling and energy efficiency analysis of millimeter wave cellular networks2018In: Wireless networks, ISSN 1022-0038, E-ISSN 1572-8196, Vol. 24, no 7, p. 2565-2578Article in journal (Refereed)
    Abstract [en]

    Current wireless networks face unprecedented challenges because of the exponentially increasing demand for mobile data and the rapid growth in infrastructure and power consumption. This study investigates the optimal energy efficiency of millimeter wave (mmWave) cellular networks, given that these networks are some of the most promising 5G-enabling technologies. Based on the stochastic geometry, a mathematical framework of coverage probability is proposed and the optimal energy efficiency is obtained with coverage performance constraints. Numerical results show that increasing the base station density damages coverage performance exceeding the threshold. This work demonstrates an essential understanding of the deployment and dynamic control of energy-efficient mmWave cellular networks.

  • 221.
    Chapko, R.
    et al.
    Ivan Franko National University of Lviv, Ukraine .
    Johansson, B.Tomas
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology. EAS, Aston University, Birmingham, UK.
    Vavrychuk, V.
    Ivan Franko National University of Lviv, Ukraine .
    Numerical solution of parabolic Cauchy problems in planar corner domains2014In: Mathematics and Computers in Simulation, ISSN 0378-4754, E-ISSN 1872-7166, Vol. 101, p. 1-12Article in journal (Refereed)
    Abstract [en]

    An iterative method for the parabolic Cauchy problem in planar domains having a finite number of corners is implemented based on boundary integral equations. At each iteration, mixed well-posed problems are solved for the same parabolic operator. The presence of corner points renders singularities of the solutions to these mixed problems, and this is handled with the use of weight functions together with, in the numerical implementation, mesh grading near the corners. The mixed problems are reformulated in terms of boundary integrals obtained via discretization of the time-derivative to obtain an elliptic system of partial differential equations. To numerically solve these integral equations a Nystrom method with super-algebraic convergence order is employed. Numerical results are presented showing the feasibility of the proposed approach.

  • 222.
    Chapko, Roman
    et al.
    Ivan Franko National University of Lviv, Ukraine .
    Johansson, Tomas
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Savka, Yuriy
    Ivan Franko National University of Lviv, Ukraine .
    On the use of an integral equation approach for the numerical solution of a Cauchy problem for Laplace equation in a doubly connected planar domain2014In: Inverse Problems in Science and Engineering, ISSN 1741-5977, E-ISSN 1741-5985, Vol. 22, no 1, p. 130-149Article in journal (Refereed)
    Abstract [en]

    We consider the Cauchy problem for the Laplace equation, i.e. the reconstruction of a harmonic function from knowledge of the value of the function and its normal derivative given on a part of the boundary of the solution domain. The solution domain considered is a bounded smooth doubly connected planar domain bounded by two simple disjoint closed curves. Since the Cauchy problem is ill-posed, as a regularizing method we generalize the novel direct integral equation approach in [1], originally proposed for a circular outer boundary curve, to a more general simply connected domain. The solution is represented as a sum of two single-layer potentials defined on each of the two boundary curves and in which both densities are unknown. To identify these densities, the representation is matched with the given Cauchy data to generate a system to solve for the densities. It is shown that the operator corresponding to this system is injective and has dense range, thus Tikhonov regularization is applied to solve it in a stable way. For the discretisation, the Nystrom method is employed generating a linear system to solve, and via Tikhonov regularization a stable discrete approximation to these densities are obtained. Using these one can then find an approximation to the solution of the Cauchy problem. A numerical example is included and we compare with other regularizing methods as well (implemented via integral methods). These results show that the proposed direct method gives accurate reconstructions with little computational effort (the computational time is of order of seconds). Moreover, the obtained approximation can be used as an initial guess in more involved regularizing methods to further improve the accuracy.

  • 223.
    Chapko, Roman
    et al.
    Ivan Franko National University of Lviv, Ukraine .
    Johansson, Tomas
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Nephrology.
    Vavrychuk, Vasyl
    Ivan Franko National University of Lviv, Ukraine .
    A projected iterative method based on integral equations for inverse heat conduction in domains with a cut2013In: Inverse Problems, ISSN 0266-5611, E-ISSN 1361-6420, Vol. 29, no 6, p. 065003-Article in journal (Refereed)
    Abstract [en]

    The Cauchy problem for the parabolic heat equation, consisting of the reconstruction of the solution from knowledge of the temperature and heat flux on a part of the boundary of the solution domain, is investigated in a planar region containing a cut. This linear inverse ill-posed problem is numerically solved using an iterative regularization procedure, where at each iteration step mixed Dirichlet-Neumann problems for the parabolic heat equation are used. Using the method of Rothe these mixed problems are reduced to a sequence of boundary integral equations. The integral equations have a square root singularity in the densities and logarithmic and hypersingularities in the kernels. Moreover, the mixed parabolic problems have singularities near the endpoints of the cut. Special techniques are employed to handle each of these (four) types of singularities, and analysis is performed in weighted spaces of square integrable functions. Numerical examples are included showing that the proposed regularizing procedure gives stable and accurate approximations.

  • 224.
    Chen, Bolin
    et al.
    Department of Electronic and Electrical Engineering, The University of Sheffield, Sheffield, UK.
    Chen, Zheng
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Zhang, Jie
    Department of Electronic and Electrical Engineering, The University of Sheffield, Sheffield, UK.
    Modeling and Analysis of MPTCP Proxy-based LTE-WLAN Path Aggregation2017In: 2017 IEEE Global Communications Conference (GLOBECOM), Proceedings Singapore 4 – 8 December 2017, IEEE Communications Society, 2017, p. 1-7Conference paper (Refereed)
    Abstract [en]

    Long Term Evolution (LTE)-Wireless Local Area Network (WLAN) Path Aggregation (LWPA) based on Multi- path Transmission Control Protocol (MPTCP) has been under standardization procedure as a promising and cost-efficient solution to boost Downlink (DL) data rate and handle the rapidly increasing data traffic. This paper aims at providing tractable analysis for the DL performance evaluation of large-scale LWPA networks with the help of tools from stochastic geometry. We consider a simple yet practical model to determine under which conditions a native WLAN Access Point (AP) will work under LWPA mode to help increasing the received data rate. Using stochastic spatial models for the distribution of WLAN APs and LTE Base Stations (BSs), we analyze the density of active LWPA- mode WiFi APs in the considered network model, which further leads to closed-form expressions on the DL data rate and area spectral efficiency (ASE) improvement. Our numerical results illustrate the impact of different network parameters on the performance of LWPA networks, which can be useful for further performance optimization. 

    Download full text (pdf)
    Modeling and Analysis of MPTCP Proxy-based LTE-WLAN Path Aggregation
  • 225.
    Chen, Bolin
    et al.
    Univ Sheffield, England.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Chen, Zheng
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Zhang, Jie
    Univ Sheffield, England.
    LTE-WLAN Aggregation with Bursty Data Traffic and Randomized Flow Splitting2019In: ICC 2019 - 2019 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC), IEEE , 2019Conference paper (Refereed)
    Abstract [en]

    We investigate the effect of bursty traffic in an LTE and Wi-Fi aggregation (LWA)-enabled network, where part of the LTE traffic is offloaded to Wi-Fi access points (APs) to boost the performance of LTE networks. A Wi-Fi AP maintains two queues containing data intended for the LWA-mode user and the native Wi-Fi user, and it is allowed to serve them simultaneously by using superposition coding (SC). With respect to the existing works on LWA, the novelty of our study consists of a random access protocol allowing the Wi-Fi AP to serve the native Wi-Fi user with probabilities that depend on the queue size of the LWA-mode data. We analyze the throughput of the native Wi-Fi network, accounting for different transmitting probabilities of the queues, the traffic flow splitting between LTE and Wi-Fi, and the operating mode of the LWA user with both LTE and Wi-Fi interfaces. Our results provide fundamental insights in the throughput behavior of such aggregated systems, which are essential for further investigation in larger topologies.

  • 226.
    Chen, Bolin
    et al.
    Univ Sheffield, England.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Chen, Zheng
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Zhang, Jie
    Univ Sheffield, England.
    Throughput and Delay Analysis of LWA With Bursty Traffic and Randomized Flow Splitting2019In: IEEE Access, E-ISSN 2169-3536, Vol. 7, p. 24667-24678Article in journal (Refereed)
    Abstract [en]

    We investigate the effect of bursty traffic in a long term evolution (LTE) and Wi-Fi aggregation (LWA)-enabled network. The LTE base station routes packets of the same IP flow through the LIE and Wi-Fi links independently. We motivate the use of superposition coding at the LWA-mode Wi-Fi access point (AP) so that it can serve LWA users and Wi-Fi users simultaneously. A random access protocol is applied in such system, which allows the native-mode AP to access the channel with probabilities that depend on the queue size of the LWA-mode AP to avoid impeding the performance of the LWA-enabled network. We analyze the throughput of the native Wi-Fi network and the delay experienced by the LWA users, accounting for the native-mode AP access probability, the traffic flow splitting between LTE and Wi-Fi, and the operating mode of the LWA user with both LIE and Wi-Fi interfaces. Our results show some fundamental tradeoffs in the throughput and delay behavior of LWA-enabled networks, which provide meaningful insight into the operation of such aggregated systems.

    Download full text (pdf)
    fulltext
  • 227.
    Chen, Bolin
    et al.
    Univ Sheffield, England.
    You, Lei
    Uppsala Univ, Sweden.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Zhang, Jie
    Univ Sheffield, England.
    Resource Optimization for Joint LWA and LTE-U in Load-Coupled and Multi-Cell Networks2019In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 23, no 2, p. 330-333Article in journal (Refereed)
    Abstract [en]

    We consider the performance optimization of multi-cell networks with LTE and Wi-Fi aggregation (LWA) and LTE-unlicensed (LTE-U) with sharing of the unlicensed band. Theoretical results are derived to enable an algorithm to approach the optimum. Numerical results show the algorithms effectiveness and benefits of joint use of LWA and LTE-U.

    Download full text (pdf)
    fulltext
  • 228.
    Chen, Lei
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Coverage Planning and Resource Allocation in Broadband Cellular Access: Optimization Models and Algorithms2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The last two decades have witnessed a booming in the use of cellular communication technologies. Billions of people are now enjoying the benefits of mobile communications. This thesis deals with planning and optimization of broadband cellular access network design and operation. The problem types considered include coverage planning, power optimization, and channel assignment. Mathematical modeling and optimization methods have been used to approach the problems.

    Coverage planning is a classical problem in cellular network deployment. A minimum-power covering problem with overlap constraints between cell pairs is considered. The objective is to minimize the total power consumption for coverage, while maintaining a necessary level of overlap to facilitate handover. For this coverage planning problem, the thesis develops two integer programming models and compares the models' strength in approaching global optimality. In addition, a tabu search algorithm has been developed for solving the problem in large-scale networks.

    For High Speed Downlink Packet Access (HSDPA) networks, transmission power is a crucial factor to performance. Minimizing the power allocated for coverage enables significant power saving that can be used for HSDPA data transmission, thus enhancing the HSDPA performance. Exploring this potential power saving, a mathematical model targeting cell-edge HSDPA performance has been developed. In determining the optimal coverage pattern for maximizing power saving, the model also allows for controlling the degree of soft handover for Universal Mobile Telecommunications System (UMTS) Release 99 services. In addition to the mathematical model, heuristic algorithms based on local search and repeated local search are developed.

    For Orthogonal Frequency Division Multiple Access (OFDMA), which is used in Long Term Evolution (LTE) networks, inter-cell interference control is a key performance engineering issue. The aspect is of particular importance to cell-edge throughput. Frequency reuse schemes for mitigating inter-cell interference at cell-edge areas have received an increasing amount of research attention. In the thesis, a generalization of the standard Fractional Frequency Reuse (FFR) scheme is introduced. The generalization addresses OFDMA networks with irregular cell layout.  Optimization algorithms using local search have been proposed to find the frequency reuse pattern of generalized FFR that maximizes the cell-edge area performance.

    For the problems considered in the thesis, computational experiments of the optimization models and algorithms using data sets representing realistic planning scenarios have been carried out. The experimental results demonstrate the effectiveness of the proposed solution approaches.

    List of papers
    1. Solving a minimum-power covering problem with overlap constraint for cellular network design
    Open this publication in new window or tab >>Solving a minimum-power covering problem with overlap constraint for cellular network design
    2010 (English)In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 203, no 3, p. 714-723Article in journal (Refereed) Published
    Abstract [en]

    We consider a type of covering problem in cellular networks. Given the locations of base stations, the problem amounts to determining cell coverage at minimum cost in terms of the power usage. Overlap between adjacent cells is required in order to support handover. The problem we consider is NP-hard. We present integer linear models and study the strengths of their continuous relaxations. Preprocessing is used to reduce problem size and tighten the models. Moreover, we design a tabu search algorithm for finding near-optimal solutions effectively and time-efficiently. We report computational results for both synthesized instances and networks originating from real planning scenarios. The results show that one of the integer models leads to tight bounds, and the tabu search algorithm generates high-quality solutions for large instances in short computing time.

    Keywords
    OR in telecommunications; Cellular networks; Covering; Integer programming; Tabu search
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-52895 (URN)10.1016/j.ejor.2009.09.018 (DOI)
    Note
    Original Publication: Lei Chen and Di Yuan, Solving a minimum-power covering problem with overlap constraint for cellular network design, 2010, European Journal of Operational Research, (203), 3, 714-723. http://dx.doi.org/10.1016/j.ejor.2009.09.018 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/Available from: 2010-01-13 Created: 2010-01-12 Last updated: 2017-12-12
    2. Coverage Planning for Optimizing HSDPA Performance and Controlling R99 Soft Handover
    Open this publication in new window or tab >>Coverage Planning for Optimizing HSDPA Performance and Controlling R99 Soft Handover
    2012 (English)In: Telecommunications Systems, ISSN 1018-4864, E-ISSN 1572-9451, Vol. 51, no 1, p. 53-64Article in journal (Refereed) Published
    Abstract [en]

    Coverage planning is an important engineering task in deploying UMTSnetworks implementing both high speed downlink packet access (HSDPA)and Release 99 (R99) services.  Coverage planning amounts todetermining the cell coverage pattern by means of setting the commonpilot channel (CPICH) power of the cells. A conventional strategy isto uniformly allocate a proportion of the total power to CPICH. Inthis paper, we develop mathematical modeling and optimizationapproaches to bring the benefit of power saving enabled by optimizingnon-uniform CPICH to enhance HSDPA performance, while preserving adesired degree of soft handover (SHO) for R99.  The studyfocuses on HSDPA performance at cell edges, where data throughput istypically low.  An integer linear programming model is developed forthe resulting optimization problem.  The model admits optimal ornear-optimal planning solutions for relatively small networks.Solution algorithms based on local search and repeated localsearch are developed.  These algorithms are able to perform theoptimization for large-scale networks time-efficiently.  Experimentalresults for both synthesized networks as well as instances originatingfrom real planning scenarios demonstrate the benefit of ouroptimization approach.

    Place, publisher, year, edition, pages
    Springer, 2012
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-62761 (URN)10.1007/s11235-010-9414-z (DOI)000311517300006 ()
    Note

    funding agencies|CENIIT||Linkoping Institute of Technology, Sweden||Swedish Research Council (Vetenskapsradet)||ELLIIT network||

    Available from: 2010-12-03 Created: 2010-12-03 Last updated: 2017-12-12
    3. Generalizing and Optimizing Fractional Frequency Reuse in Broadband Cellular Radio Access Networks
    Open this publication in new window or tab >>Generalizing and Optimizing Fractional Frequency Reuse in Broadband Cellular Radio Access Networks
    2012 (English)In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 230Article in journal (Refereed) Published
    Abstract [en]

    For broadband cellular access based on orthogonal frequency divisionmultiple access (OFDMA), fractional frequency reuse (FFR) is one ofthe key concepts for mitigating inter-cell interference and therebyoptimizing cell-edge performance. In standard FFR, the number of OFDMAsub-bands and the reuse factor are both fixed. Whereas this works wellfor an idealized cell pattern, it is neither directly applicable noradequate for real-life networks with very irregular cell layouts. Inthis paper, we generalize the standard FFR to allow for flexibilities inthe total number of sub-bands as well as the number of sub-bands ineach cell-edge zone, enabling network-adaptive FFR. Two powerassignment strategies that use fixed power per sub-band prior tosub-band allocation and apply cell-specific power derived from thenumber of sub-bands allocated to each cell-edge zone, respectively,are investigated. Optimization algorithms based on local search aredeveloped for sub-band allocation to maximize the cell-edgethroughput. Evaluations using networks with realistic radiopropagation conditions demonstrate the applicability of the generalizedand optimized FFR in performance engineering of OFDMA networks.

    Keywords
    orthogonal frequency division multiple access; fractional frequency reuse; optimization; local search.
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-62762 (URN)10.1186/1687-1499-2012-230 (DOI)000315038300001 ()
    Available from: 2010-12-03 Created: 2010-12-03 Last updated: 2017-12-12Bibliographically approved
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    Coverage Planning and Resource Allocation in Broadband Cellular Access : Optimization Models and Algorithms
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    Cover
  • 229. Order onlineBuy this publication >>
    Chen, Lei
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Performance Engineering of Mobile Broadband: Capacity Analysis, Cellular Network Optimization, and Design of In-Building Solutions2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The rapid evolution of mobile communication technologies is making mobile broadband a reality. With over 6 billion cellular connections and the booming of mobile data, mobile broadband leads the technology and service innovation within the domain of information and communication technologies. The thesis deals with performance engineering of mobile broadband. The problems investigated range from fundamental capacity analysis, resource planning and optimization of broadband cellular networks, to design of in-building solutions based on distributed antenna systems. Mathematical modeling and optimization methods have been used to approach the problems.

    The first three papers address capacity analysis in wireless communications, where the establishment of any communication link is subject to the Signal to Interference plus Noise Ratio (SINR) threshold. Paper I addresses the maximum link activation problem. The paper introduces a new exact algorithm by reformulating the SINR constraints with equivalent but numerically more effective inequalities, leading to an approach performing significantly better in proving optimality in comparison to the conventional algorithm. Paper II explores the notion of collaborative rate selection for Interference Cancellation (IC) to maximize the transmission rate in wireless networks. The paper analyzes the problem complexity and develops integer programming models for both single stage single-link IC and single stage parallel IC. Paper III studies the performance gain of single-stage and multi-stage IC to optimal link activation. Compact integer programming formulations have been developed and a thorough numerical study is performed.

    The next three papers are devoted to planning and optimization of radio resources in cellular mobile broadband networks. Paper IV considers a minimum-power coverage problem with overlap requirements between cell pairs. The paper develops two integer programming models and compares their strength in approaching global optimality. A tabu search algorithm has been developed for large-scale networks. Paper V deals with transmission power planning and optimization in High Speed Downlink Packet Access (HSDPA) networks. A method for enhancing the HSDPA performance by minimizing the power for coverage and reallocating the power to data transmission has been considered. A mathematical model targeting cell-edge HDSPA performance and accounting for soft handover in Universal Mobile Telecommunications System (UMTS) has been developed. In addition, heuristic algorithms based on local search and repeated local search are developed. Paper VI focuses on frequency planning for inter-cell interference mitigation in Orthogonal Frequency Division Multiple Access (OFDMA) networks. The paper generalizes the standard Fractional Frequency Reuse (FFR) concept and addresses its performance for networks with irregular topology. Optimization algorithms using local search have been proposed to find the frequency reuse pattern of generalized FFR for maximizing the edge-user performance. The investigations in Papers IV-VI base the experiments on data sets representing realistic planning scenarios to demonstrate the effectiveness of the proposed approaches.

    To face the challenge of in-building mobile broadband service, In-Building Distributed Antennas Systems (IB-DAS) has been proposed. Paper VII tackles the problem of optimal topology design of IB-DAS systems, where a number of in-building distributed antennas are connected to a base station via coaxial cables and power equipments. The paper develops efficient mathematical models for topology design as well as equipment selection, and presents case studies of realistic IB-DAS deployment scenarios.

    List of papers
    1. A New Computational Approach for Maximum Link Activation in Wireless Networks under the SINR Model
    Open this publication in new window or tab >>A New Computational Approach for Maximum Link Activation in Wireless Networks under the SINR Model
    2011 (English)In: IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, ISSN 1536-1276, Vol. 10, no 5, p. 1368-1372Article in journal (Refereed) Published
    Abstract [en]

    A fundamental and computationally challenging optimization task in wireless networks is to maximize the number of simultaneous transmissions, subject to signal-to-noise-and-interference ratio (SINR) requirements at the receivers. The conventional approach guaranteeing global optimality is to solve an integer programming model with explicit SINR constraints. These constraints are however numerically very difficult. We develop a new integer programming algorithm based on a much more effective representation of the SINR constraints. Computational experiments demonstrate that the new approach performs significantly better in proving optimality.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers, 2011
    Keywords
    Wireless networks, optimization, link activation, SINR, integer programming
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-68909 (URN)10.1109/TWC.2011.030311.100777 (DOI)000290992300005 ()
    Note
    ©2011 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. Antonio Capone, Lei Chen, Stefano Gualandi and Di Yuan, A New Computational Approach for Maximum Link Activation in Wireless Networks under the SINR Model, 2011, IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, (10), 5, 1368-1372. http://dx.doi.org/10.1109/TWC.2011.030311.100777Available from: 2011-06-10 Created: 2011-06-10 Last updated: 2013-03-04
    2. Optimal and Collaborative Rate Selection for Interference Cancellation in Wireless Networks
    Open this publication in new window or tab >>Optimal and Collaborative Rate Selection for Interference Cancellation in Wireless Networks
    2011 (English)In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 15, no 8, p. 819-821Article in journal (Refereed) Published
    Abstract [en]

    Analysis of wireless systems commonly assumes single-user detection at the receivers. Interference is typically treated as noise. On the other hand, multiuser detection has long been taking advantage of interference cancellation (IC) to increase capacity. We exploit IC by optimal rate selection. Transmission rates are collaboratively optimized to maximize the benefit of IC. A link reduces its rate, if that enables IC to significantly boost the SINR on other links. We provide a complexity analysis and an integer programming model to find the optimal IC pattern. Simulation results indicate that throughput improvement is over 30% in low SINR regimes.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2011
    Keywords
    Interference cancellation, rate selection, optimization, wireless communications
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-70529 (URN)10.1109/LCOMM.2011.062711.110561 (DOI)000294133000012 ()
    Available from: 2011-09-12 Created: 2011-09-12 Last updated: 2017-12-08
    3. On Optimal Link Activation with Interference Cancelation in Wireless Networking
    Open this publication in new window or tab >>On Optimal Link Activation with Interference Cancelation in Wireless Networking
    Show others...
    2013 (English)In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 62, no 2, p. 939-945Article in journal (Refereed) Published
    Abstract [en]

    A fundamental aspect in performance engineering of wireless networks is optimizing the set of links that can be concurrently activated to meet given signal-to-interference-and-noise ratio (SINR) thresholds. The solution of this combinatorial problem is the key element in scheduling and cross-layer resource management. In this paper, we assume multiuser decoding receivers, which can cancel strongly interfering signals. As a result, in contrast to classical spatial reuse, links being close to each other are more likely to be active concurrently. Our focus is to gauge the gain of successive interference cancellation (SIC), as well as the simpler, yet instructive, case of parallel interference cancellation (PIC), in the context of optimal link activation. We show that both problems are NP-hard and develop compact integer linear programming formulations that enable to approach global optimality. We provide an extensive numerical performance evaluation, indicating that for low to medium SINR thresholds the improvement is quite substantial, especially with SIC, whereas for high SINR thresholds the improvement diminishes and both schemes perform equally well.

    Keywords
    Integer linear programming, interference cancellation, link activation, multiuser decoding, optimization, wireless networks
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-81933 (URN)10.1109/TVT.2012.2222683 (DOI)000318515100045 ()
    Available from: 2012-09-25 Created: 2012-09-25 Last updated: 2017-12-07
    4. Solving a minimum-power covering problem with overlap constraint for cellular network design
    Open this publication in new window or tab >>Solving a minimum-power covering problem with overlap constraint for cellular network design
    2010 (English)In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 203, no 3, p. 714-723Article in journal (Refereed) Published
    Abstract [en]

    We consider a type of covering problem in cellular networks. Given the locations of base stations, the problem amounts to determining cell coverage at minimum cost in terms of the power usage. Overlap between adjacent cells is required in order to support handover. The problem we consider is NP-hard. We present integer linear models and study the strengths of their continuous relaxations. Preprocessing is used to reduce problem size and tighten the models. Moreover, we design a tabu search algorithm for finding near-optimal solutions effectively and time-efficiently. We report computational results for both synthesized instances and networks originating from real planning scenarios. The results show that one of the integer models leads to tight bounds, and the tabu search algorithm generates high-quality solutions for large instances in short computing time.

    Keywords
    OR in telecommunications; Cellular networks; Covering; Integer programming; Tabu search
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-52895 (URN)10.1016/j.ejor.2009.09.018 (DOI)
    Note
    Original Publication: Lei Chen and Di Yuan, Solving a minimum-power covering problem with overlap constraint for cellular network design, 2010, European Journal of Operational Research, (203), 3, 714-723. http://dx.doi.org/10.1016/j.ejor.2009.09.018 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/Available from: 2010-01-13 Created: 2010-01-12 Last updated: 2017-12-12
    5. Coverage Planning for Optimizing HSDPA Performance and Controlling R99 Soft Handover
    Open this publication in new window or tab >>Coverage Planning for Optimizing HSDPA Performance and Controlling R99 Soft Handover
    2012 (English)In: Telecommunications Systems, ISSN 1018-4864, E-ISSN 1572-9451, Vol. 51, no 1, p. 53-64Article in journal (Refereed) Published
    Abstract [en]

    Coverage planning is an important engineering task in deploying UMTSnetworks implementing both high speed downlink packet access (HSDPA)and Release 99 (R99) services.  Coverage planning amounts todetermining the cell coverage pattern by means of setting the commonpilot channel (CPICH) power of the cells. A conventional strategy isto uniformly allocate a proportion of the total power to CPICH. Inthis paper, we develop mathematical modeling and optimizationapproaches to bring the benefit of power saving enabled by optimizingnon-uniform CPICH to enhance HSDPA performance, while preserving adesired degree of soft handover (SHO) for R99.  The studyfocuses on HSDPA performance at cell edges, where data throughput istypically low.  An integer linear programming model is developed forthe resulting optimization problem.  The model admits optimal ornear-optimal planning solutions for relatively small networks.Solution algorithms based on local search and repeated localsearch are developed.  These algorithms are able to perform theoptimization for large-scale networks time-efficiently.  Experimentalresults for both synthesized networks as well as instances originatingfrom real planning scenarios demonstrate the benefit of ouroptimization approach.

    Place, publisher, year, edition, pages
    Springer, 2012
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-62761 (URN)10.1007/s11235-010-9414-z (DOI)000311517300006 ()
    Note

    funding agencies|CENIIT||Linkoping Institute of Technology, Sweden||Swedish Research Council (Vetenskapsradet)||ELLIIT network||

    Available from: 2010-12-03 Created: 2010-12-03 Last updated: 2017-12-12
    6. Generalizing and Optimizing Fractional Frequency Reuse in Broadband Cellular Radio Access Networks
    Open this publication in new window or tab >>Generalizing and Optimizing Fractional Frequency Reuse in Broadband Cellular Radio Access Networks
    2012 (English)In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 230Article in journal (Refereed) Published
    Abstract [en]

    For broadband cellular access based on orthogonal frequency divisionmultiple access (OFDMA), fractional frequency reuse (FFR) is one ofthe key concepts for mitigating inter-cell interference and therebyoptimizing cell-edge performance. In standard FFR, the number of OFDMAsub-bands and the reuse factor are both fixed. Whereas this works wellfor an idealized cell pattern, it is neither directly applicable noradequate for real-life networks with very irregular cell layouts. Inthis paper, we generalize the standard FFR to allow for flexibilities inthe total number of sub-bands as well as the number of sub-bands ineach cell-edge zone, enabling network-adaptive FFR. Two powerassignment strategies that use fixed power per sub-band prior tosub-band allocation and apply cell-specific power derived from thenumber of sub-bands allocated to each cell-edge zone, respectively,are investigated. Optimization algorithms based on local search aredeveloped for sub-band allocation to maximize the cell-edgethroughput. Evaluations using networks with realistic radiopropagation conditions demonstrate the applicability of the generalizedand optimized FFR in performance engineering of OFDMA networks.

    Keywords
    orthogonal frequency division multiple access; fractional frequency reuse; optimization; local search.
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-62762 (URN)10.1186/1687-1499-2012-230 (DOI)000315038300001 ()
    Available from: 2010-12-03 Created: 2010-12-03 Last updated: 2017-12-12Bibliographically approved
    7. Mathematical Modeling for Optimal Design of In-Building Distributed Antenna Systems
    Open this publication in new window or tab >>Mathematical Modeling for Optimal Design of In-Building Distributed Antenna Systems
    2013 (English)In: Computer Networks, ISSN 1389-1286, E-ISSN 1872-7069, Vol. 57, no 17, p. 3428-3445Article in journal (Refereed) Published
    Abstract [en]

    In-building Distributed Antenna System (IB-DAS) has proven to be one of the most promising In-Building Solutions (IBS) to provide coverage and capacity for indoor users. We consider optimal deployment of the passive IB-DAS, focusing on mathematical optimization models based on integer programming, for the topology design and optimal equipment selection of IB-DAS. The models minimize the cable cost and keep the transmit power at each antenna within a pre-defined interval, thus guaranteeing the quality of service. The models can deliver optimal solutions to systems of which the size is of practical relevance. To improve the time efficiency, we develop preprocessing techniques that integrate the building layout data into the system modeling. Application of the models to realistic IB-DAS deployment demonstrates the effectiveness of the models.

    Place, publisher, year, edition, pages
    Elsevier, 2013
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-89716 (URN)10.1016/j.comnet.2013.07.027 (DOI)000328295600012 ()
    Available from: 2013-03-04 Created: 2013-03-04 Last updated: 2017-12-06
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    Performance Engineering of Mobile Broadband: Capacity Analysis, Cellular Network Optimization, and Design of In-Building Solutions
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  • 230.
    Chen, Lei
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Song, Hui
    Ranplan Wireless Network Design, Ltd, UK.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Zhang, Jie
    University of Sheffield, UK.
    Mathematical Modeling for Optimal Deployment of In-Building Distributed Antenna Systems2012In: Communications in China (ICCC), 2012, IEEE , 2012, p. 786-791Conference paper (Refereed)
    Abstract [en]

    In-building Distributed Antenna System (IB-DAS) has been proved to be one of the most efficient methods to provide sufficient coverage and capacity for indoor users. The target of a successful IB-DAS deployment is to guarantee the coverage as well as the capacity of the in-building areas with minimum deployment cost. We consider the optimaldeployment of the IB-DAS based on passive DAS in this paper. Mixed Integer Programming model has been developed forthe topology design of IB-DAS through the optimal installation of power splitters in order to connect all the antennas with minimum cable cost, meanwhile, the transmit power at each antenna are kept within the satisfied level for the service guarantee. The model can deliver optimal solutions to systems with a practical size where passive DAS is commonly deployed. To improve the time efficiency, preprocessing has been done to integrate the building layout data into themodeling. Application of the model over realistic IB-DAS deployment has been conducted, which demonstrates the effectiveness of the model.

  • 231.
    Chen, Lei
    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.
    Achieving higher HSDPA performance and preserving R99 soft handover control by large scale optimization in CPICH coverage planning2009In: Proceedings of IEEE Wireless Telecommunications Symposium (WTS) 2009, Piscataway, NJ, USA: IEEE , 2009, p. 39-44Conference paper (Refereed)
    Abstract [en]

    Common Pilot Channel (CPICH) power is a crucial parameter in coverage planning of todays UMTS networks that implement both HSDPA and R99 services. Adopting a non-uniform allocation of cell CPICH power and minimizing its amount necessary for coverage, the resulting power saving significantly improves HSDPA performance. At the same time, it is vital to have the desired level R99 soft handover which is heavily influenced by CPICH. In this paper, we demonstrate how large scale optimization can deal with both tasks. Our approach focuses on enhancing cell-edge HSDPA data rate, subject to requirements of CPICH coverage and the level of R99 soft(-er) handover We present a solution algorithm that optimizes CPICH allocation for HSDPA performance, and, in parallel, offers accurate control of R99 soft handover Experimental results for large and realistic network planning scenarios demonstrate the benefit of our optimization approach.

  • 232.
    Chen, Lei
    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.
    Automated Planning of CPICH Power for enhancing HSDPA Performance at Cell Edges with Preserved Control of R99 Soft Handover2008In: IEEE International Conference on Communications, 2008. ICC '08., Piscataway, NJ, USA: IEEE , 2008, p. 2936-2940Conference paper (Refereed)
    Abstract [en]

    We present and demonstrate a novel approach for automated planning of common pilot channel (CPICH) power in mobile networks with co-existing HSDPA and R99 services. CPICH power allocation greatly influences the cell coverage pattern. A conventional strategy is to uniformly allocate a constant proportion of the total power to CPICH. We study non-uniform CPICH and optimize its allocation for enhancing HSDPA performance. We focus on HSDPA performance at cell edges, where user throughput is typically very low. Our approach is based on a linear-integer mathematical model; solving the model results in a power allocation that both ensures CPICH coverage and optimizes HSDPA performance at cell edges. Moreover, the model allows for precise control of soft handover (SHO) regions for R99 service. Experimental results show that our approach yields significant enhancement of HSDPA performance at cell edges with preserved R99 SHO control.

  • 233.
    Chen, Lei
    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.
    Beyond Conventional Fractional Frequency Reuse for Networks with Irregular Cell Layout: An Optimization Approach and Performance Evaluation2010In: Proceedings of the 5th Annual International Wireless Internet Conference (WICON), IEEE , 2010Conference paper (Refereed)
    Abstract [en]

    Fractional frequency reuse (FFR) is one of the key concepts for interference mitigation in OFDMA networks. Previous work on FFR has focused on networks of relatively small size and standard hexagon-shaped cell layout. For real-life networks with very irregular cell layout and high variation in radio propagation, standard reuse schemes (e.g., reuse with a factor three) are inadequate; applying a standard scheme, if possible at all, is far from optimal due to the irregularity. We present an approach based on large-scale optimization to study FFR in networks with irregular cell layout. The approach goes beyond the conventional reuse schemes by optimizing the allocation of the cell-edge sub-band of every cell, taking into account the interference caused by the sub-band allocation of all other cells. What's more, whereas the conventional FFR scheme uses three sub-bands, our optimization process allows for considering the number of subbands as a parameter, and enables the analysis of the impact of this parameter on FFR performance. Performance evaluation for networks with realistic radio propagation conditions shows that the approach enables significant throughput improvement at cell-edge zones, and sometimes it is optimal to split the cell-edge band into more than the standard three sub-bands. These results along with the analysis demonstrate the potential benefits of the proposed approach in practicing FFR for large-scale networks, and illustrate the performance trade-off between the cell-edge and cell-center zones.

  • 234.
    Chen, Lei
    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.
    Coverage Planning for Optimizing HSDPA Performance and Controlling R99 Soft Handover2012In: Telecommunications Systems, ISSN 1018-4864, E-ISSN 1572-9451, Vol. 51, no 1, p. 53-64Article in journal (Refereed)
    Abstract [en]

    Coverage planning is an important engineering task in deploying UMTSnetworks implementing both high speed downlink packet access (HSDPA)and Release 99 (R99) services.  Coverage planning amounts todetermining the cell coverage pattern by means of setting the commonpilot channel (CPICH) power of the cells. A conventional strategy isto uniformly allocate a proportion of the total power to CPICH. Inthis paper, we develop mathematical modeling and optimizationapproaches to bring the benefit of power saving enabled by optimizingnon-uniform CPICH to enhance HSDPA performance, while preserving adesired degree of soft handover (SHO) for R99.  The studyfocuses on HSDPA performance at cell edges, where data throughput istypically low.  An integer linear programming model is developed forthe resulting optimization problem.  The model admits optimal ornear-optimal planning solutions for relatively small networks.Solution algorithms based on local search and repeated localsearch are developed.  These algorithms are able to perform theoptimization for large-scale networks time-efficiently.  Experimentalresults for both synthesized networks as well as instances originatingfrom real planning scenarios demonstrate the benefit of ouroptimization approach.

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  • 235.
    Chen, Lei
    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.
    CPICH Power Planning for Optimizing HSDPA and R99 SHO Performance: Mathematical Modelling and Solution Approach2008In: 1st IFIP Wireless Days, 2008. WD '08., Piscataway, NJ, USA: IEEE , 2008, p. 1-5Conference paper (Refereed)
    Abstract [en]

    We present and demonstrate mathematical modelling and optimization algorithm for enhancing HSDPA performance by automatically linking Common Pilot Channel (CPICH) power to HSDPA transmit power. Our approach uses non-uniformly allocated CPICH power and focuses on HSDPA performance with the side constraint of R99 soft handover. Solving the mathematical model gives the optimal CPICH allocation for small networks. The optimization algorithm demonstrates itself very time efficient in dealing with large scale networks which might have hundreds of cells and tens of thousands of users. A case study of realistic network planning scenario for Berlin shows significant CPICH power saving and HSDPA performance improvement.

  • 236.
    Chen, Lei
    et al.
    Viktoria Swedish ICT, Sweden.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Design of in-building distributed antenna systems: mathematical models and efficient algorithms2015In: 2015 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATION WORKSHOP, IEEE , 2015, p. 1497-1502Conference paper (Refereed)
    Abstract [en]

    In order to provide sufficient coverage and capacity for indoor users, in-building distributed antenna system (IB-DAS) has been considered. A passive IB-DAS deploys distributed antennas inside the building and connects the antennas to a base station (BS) through coaxial cables and power equipment. Power is distributed from the BS to each of the antennas. We consider an optimal design of passive IB-DAS with the target to minimize the cable usage, together with the consideration of power distribution. We decompose the problem into two sub-problems, namely the topological design and the equipment selection. Mixed integer linear models are developed for solving the sub-problems. Local search is designed to combine the sub-problems and balance their objectives. Application over realistic IB-DAS deployment and comparison with previous studies demonstrate the effectiveness of the algorithm.

  • 237.
    Chen, Lei
    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.
    Enhanced Fractional Frequency Reuse for large-scale OFDMA networks with heterogeneous cell layout: Optimization and performance evaluation2010In: Communication Systems (ICCS), 2010, IEEE , 2010, p. 279-283Conference paper (Refereed)
    Abstract [en]

    Fractional Frequency Reuse (FFR) is one of the key concepts for mitigating inter-cell interference and improving cell-edge performance in OFDMA networks. The standard FFR scheme is intuitive and optimal for the hexagon-shaped cell pattern. In contrast, real-life OFDMA systems have very irregular cell layout, thus the number of surrounding cells and their respective interference vary significantly over the network. For such scenarios, the standard scheme, if applicable at all, is inadequate because the number of sub-bands and the reuse factor are fixed. To overcome the limitations, we present enhanced FFR (EFFR) that allows for high flexibility in the total number of sub-bands as well as the allocation of sub-bands in edge zones. An optimization algorithm is developed to determine sub-band allocation to maximize the cell-edge throughput. Hence EFFR adapts the allocation and reuse pattern to the irregularity of each individual network. Evaluations based on networks with realistic radio propagation conditions show the high performance of EFFR in improving cell-edge throughput. The improvement allows for better trade-off between cell-center and cell-edge throughput. These results along with the analysis demonstrate the benefits of EFFR to performance engineering of OFDMA networks.

  • 238.
    Chen, Lei
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Yuan, Di
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Communications and Transport Systems.
    Fast Algorithm for Large-scale UMTS Coverage Planning with Soft Handover Consideration2009In: Proceedings of the 2009 International Conference on Wireless Communications and Mobile Computing: Connecting the World Wirelessly, New York, NY, USA: ACM , 2009, p. 1488-1492Conference paper (Refereed)
    Abstract [en]

    Coverage planning by means of controlling cell Common Pilot Channel (CPICH) power is an important task in deploying UMTS networks. In addition to determining coverage, CPICH power heavily influences the amount of Soft Handover (SHO). Non-uniform cell CPICH power allows for significant power saving and thereby higher capacity for traffic channels. However, optimizing non-uniform CPICH is challenging in terms of computational effort, if the resulting coverage pattern is required to satisfy a desired level of SHO. We present a very fast algorithm for this planning problem. The algorithm has utilized the fact that SHO is strongly correlated with cell overlap. Using overlap as a very good approximation of SHO, the algorithm can compute a near optimal coverage pattern within a few seconds even for large networks. Next, the solution is further polished to deal with SHO accurately. Simulation results show that our solution strategy is able to perform non-uniform CPICH optimization very time-efficiently, making it possible to tackle large scale UMTS coverage planning under SHO consideration.

  • 239.
    Chen, Lei
    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.
    Generalized Frequency Reuse Schemes for OFDMA Networks: Optimization and Comparison2010In: IEEE 71st Vehicular Technology Conference (VTC 2010-Spring), 2010, Piscataway, NJ, USA: IEEE , 2010Conference paper (Refereed)
    Abstract [en]

    Frequency reuse is a key concept for interference mitigation and thereby enhancing cell-edge performance in OFDMA networks. Two representative strategies are Fractional Frequency Reuse (FFR) and Soft Frequency Reuse (SFR). Both divide a cell into a center zone and an edge zone, and differentiate their levels of frequency reuse. Previous work on FFR and SFR has focused on networks of relatively small size with standard hexagon-shaped cells. And dividing the cell edge frequency band into three parts has been a common practice so far. However, for real-life networks, this is inadequate because of the irregular cell layout. We consider generalized FFR and SFR schemes, where the number of sub-bands is not restricted to three, and for SFR the power ratio is variable. To find optimal sub- band allocation for the generalized schemes, we present an approach based on large-scale optimization to deal with networks with irregular cell layout. The optimization process allows us to analyze the impact of the number of sub-bands and the SFR power ratio on cell-edge performance, and thereby compare the reuse schemes. We conduct experiments on large networks with realistic radio propagations and present a thorough numerical comparison.

  • 240.
    Chen, Lei
    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.
    Generalizing and Optimizing Fractional Frequency Reuse in Broadband Cellular Radio Access Networks2012In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 230Article in journal (Refereed)
    Abstract [en]

    For broadband cellular access based on orthogonal frequency divisionmultiple access (OFDMA), fractional frequency reuse (FFR) is one ofthe key concepts for mitigating inter-cell interference and therebyoptimizing cell-edge performance. In standard FFR, the number of OFDMAsub-bands and the reuse factor are both fixed. Whereas this works wellfor an idealized cell pattern, it is neither directly applicable noradequate for real-life networks with very irregular cell layouts. Inthis paper, we generalize the standard FFR to allow for flexibilities inthe total number of sub-bands as well as the number of sub-bands ineach cell-edge zone, enabling network-adaptive FFR. Two powerassignment strategies that use fixed power per sub-band prior tosub-band allocation and apply cell-specific power derived from thenumber of sub-bands allocated to each cell-edge zone, respectively,are investigated. Optimization algorithms based on local search aredeveloped for sub-band allocation to maximize the cell-edgethroughput. Evaluations using networks with realistic radiopropagation conditions demonstrate the applicability of the generalizedand optimized FFR in performance engineering of OFDMA networks.

    Download full text (pdf)
    fulltext
  • 241.
    Chen, Lei
    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.
    Generalizing FFR by Flexible Sub-Band Allocation in OFDMA Networks with Irregular Cell Layout2010In: IEEE Wireless Communications and Networking Conference Workshops (WCNCW), 2010, IEEE , 2010Conference paper (Refereed)
    Abstract [en]

    Fractional Frequency Reuse (FFR) is one of the key concepts for enhancing cell-edge performance of OFDMA networks. Standard FFR allows one sub-band to be allocated for each cell. This limits the performance improvement of cell edge users, especially those bandwidth-sensitive users. With flexible sub-band allocation, cell edge can be allocated more than one sub-band, thereby performance can be improved largely. Furthermore, previous work on FFR has focused on networks of relatively small size and with standard hexagon- shaped cells.For real-life networks with a very irregular cell layout, these results are inadequate. In this paper, we present the idea of Flexible FFR (FFR-F) which allows more than one sub-band to be allocated to cell edges. Meanwhile, an optimization algorithm based on local search is present for FFR-F planning in large-scale networks with irregular cell layout. Sub-band allocation scheme which maximizes the cell-edge throughput can be found time efficiently. Results from networks with realistic radio propagation conditions show that FFR-F enables significant throughput improvement at cell edges. These results along with the analysis demonstrate the potential benefits of FFR-F and the proposed approach for planning of real-life OFDMA networks.

  • 242.
    Chen, Lei
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Communications and Transport Systems.
    Yuan, Di
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Communications and Transport Systems.
    Performance Evaluation of Soft Frequency Reuse in Large Networks with  Irregular Cell Pattern: How Much Gain To Expect?2009In: Proceedings of IEEE PIMRC 2009, 2009Conference paper (Refereed)
  • 243.
    Chen, Lei
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Yuan, Di
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Communications and Transport Systems.
    Solving a minimum-power covering problem with overlap constraint for cellular network design2010In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 203, no 3, p. 714-723Article in journal (Refereed)
    Abstract [en]

    We consider a type of covering problem in cellular networks. Given the locations of base stations, the problem amounts to determining cell coverage at minimum cost in terms of the power usage. Overlap between adjacent cells is required in order to support handover. The problem we consider is NP-hard. We present integer linear models and study the strengths of their continuous relaxations. Preprocessing is used to reduce problem size and tighten the models. Moreover, we design a tabu search algorithm for finding near-optimal solutions effectively and time-efficiently. We report computational results for both synthesized instances and networks originating from real planning scenarios. The results show that one of the integer models leads to tight bounds, and the tabu search algorithm generates high-quality solutions for large instances in short computing time.

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  • 244.
    Chen, Ting
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Energy-Efficient Resource Allocation in OFDMA Systems2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis, a resource allocation problem in OFDMA is studied for the energy efficiency of wireless network. The objective is to minimize the total energy consumption which includes transmission energy consumption, and circuit energy consumption at both transmitter and receiver with required per user’s rate constraint. For problem solution, a heuristic algorithm with low computational complexity and suboptimal solution is proposed, developed in two steps with an increasing order of complexity. Besides, a bounding scheme based on model linearization of formulated nonlinear system model is also proposed to give lower and upper bounds for both small- and large-scale OFDMA network for further algorithm performance evaluation, while the implemented exhaustive search is only capable to provide the optimal solution for small-scale instance for algorithm performance evaluation. Numerical results show that the proposal heuristic algorithm can achieve near-optimal performance with applicable computational complexity even for large-scale networks, and that the bounds from the bounding scheme are very tight for both small- and large-scale OFDMA networks.

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    fulltext
  • 245.
    Chen, Zheng
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Age of Information in a Multiple Access Channel with Heterogeneous Traffic and an Energy Harvesting Node2019In: IEEE CONFERENCE ON COMPUTER COMMUNICATIONS WORKSHOPS (IEEE INFOCOM 2019 WKSHPS), IEEE , 2019, p. 662-667Conference paper (Refereed)
    Abstract [en]

    Age of Information (AoI) is a newly appeared concept and metric to characterize the freshness of data. In this work, we study the delay and AoI in a multiple access channel (MAC) with two source nodes transmitting different types of data to a common destination. The first node is grid-connected and its data packets arrive in a bursty manner, and at each time slot it transmits one packet with some probability. Another energy harvesting (EH) sensor node generates a new status update with a certain probability whenever it is charged. We derive the delay of the grid-connected node and the AoI of the EH sensor as functions of different parameters in the system. The results show that the mutual interference has a non-trivial impact on the delay and age performance of the two nodes.

  • 246.
    Chen, Zheng
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Mathematical and Algorithmic Sciences Lab, France Research Center, Huawei Technologies France SASU, Boulogne-Billancourt, France.
    Energy Harvesting in Delay-Aware Cognitive Shared Access Networks2017In: IEEE Workshop on Emerging Energy Harvesting Solutions for 5G Networks (5G-NRG): May 2017, Paris, France., IEEE Press, 2017, p. 168-173Conference paper (Refereed)
    Abstract [en]

    In this work, we study the effect of energy harvesting in a cognitive shared access network with delay constraints on the primary user. We model the distribution of secondary nodes by a homogeneous Poisson point process (PPP), while the primary user is located at fixed location. The secondary users are assumed to have always packets to transmit whilst the primary transmitter has bursty traffic. We assume an energy harvesting zone around the primary transmitter and a guard zone around the primary receiver. The secondary users are transmitting in a random access manner, however, transmissions of secondary nodes are restricted by their battery status and location. Targeting at achieving the maximum secondary throughput under primary delay constraints, we analyze the impact of various parameters on the performance of the considered network. Our results provide insights into the optimization of access protocol parameters for the energy harvesting-based cognitive shared access network with delay constraints.

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  • 247.
    Chen, Zheng
    et al.
    University of Paris Sud, France.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Huawei Technology Co Ltd, France.
    Probabilistic Caching in Wireless D2D Networks: Cache Hit Optimal Versus Throughput Optimal2017In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 21, no 3, p. 584-587Article in journal (Refereed)
    Abstract [en]

    Departing from the conventional cache hit optimization in cache-enabled wireless networks, we consider an alternative optimization approach for the probabilistic caching placement in stochastic wireless D2D caching networks taking into account the reliability of D2D transmissions. Using tools from stochastic geometry, we provide a closed-form approximation of cache-aided throughput, which measures the density of successfully served requests by local device caches, and we obtain the optimal caching probabilities via numerical optimization. Compared with the cache-hit-optimal case, the optimal caching probabilities obtained by cache-aided throughput optimization show notable gain in terms of the density of successfully served user requests, particularly in dense user environments.

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    fulltext
  • 248.
    Chen, Zheng
    et al.
    University of Paris Sud, France.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Huawei Technology Co Ltd, Peoples R China.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Throughput Analysis of Smart Objects with Delay Constraints2016In: 2016 IEEE 17TH INTERNATIONAL SYMPOSIUM ON A WORLD OF WIRELESS, MOBILE AND MULTIMEDIA NETWORKS (WOWMOM), IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    In this paper, we analyze a shared access network with one primary device and randomly distributed smart objects with secondary priority. Assuming random traffic at the primary device and saturated queues at the smart objects with secondary priority, an access protocol is employed to adjust the random access probabilities of the smart objects depending on the congestion level of the primary. We characterize the maximum throughput of the secondary network with respect to delay constraints on the primary. Our results highlight the impact of system design parameters on the delay and throughput behavior of the shared access network with massive number of connected objects.

  • 249.
    Chen, Zheng
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Huawei Technol Co Ltd, France.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Throughput With Delay Constraints in a Shared Access Network With Priorities2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 9, p. 5885-5899Article in journal (Refereed)
    Abstract [en]

    In this paper, we analyze a shared access network with a fixed primary node and randomly distributed secondary nodes whose spatial distribution follows a poisson point process. The secondary nodes use a random access protocol allowing them to access the channel with probabilities that depend on the queue size of the primary node. Assuming a system with multipacket reception receivers, having bursty packet arrivals at the primary and saturated traffic at the secondary nodes, our protocol can be tuned to alleviate congestion at the primary. We analyze the throughput of the secondary network and the primary average delay, as well as the impact of the secondary node access probability and transmit power. We formulate an optimization problem to maximize the throughput of the secondary network under delay constraints for the primary node; in the case of no congestion control, the optimal access probability can be provided in closed form. Our numerical results illustrate the effect of network operating parameters on the performance of the proposed priority-based shared access protocol.

  • 250.
    Collin, Rebecka
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Druskic, Ilda
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    En nyckeltalsanalys för SAS schemaläggning av flygbesättningen2019Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    Flygbranschen besitter stora innovativa kunskaper och är dessutom en väsentlig bransch för framtidens tekniska utveckling. För att flygbolagen ska kunna bedriva sin verksamhet finns det tre huvudaspekter som måste planeras och övervakas för att uppnå en operativ effektivitet. De tre aspekterna är: flygbesättning, flygplan och passagerare. Den näst största kostnaden för majoriteten av flygbolagen är besättningen, därför är planering av effektiva och robusta scheman en viktig del för lönsamheten hos flygbolaget. Ett gynnsamt schema för flygbesättningen ska minimera kostnaden för personalen och samtidigt vara robust. Scandinavian Airlines (SAS) är ett skandinaviskt flygbolag som i nuläget använder sig av optimeringsverktyget Crew management system (CMS) för att schemalägga flygbesättningen på samtliga flygningar. Crew Planning-avdelningen är den övergripande avdelningen där all schemaläggning av flygbesättningen sker. Inom Crew Planning finns avdelningen Crew Optimization som skapar månatliga scheman för 5000 piloter och Cabin Crew som varje månad bemannar över 24 000 flygningar. Syftet med examensarbetet är att framställa en metodik för att jämföra flera nyckeltal samtidigt. Nyckeltalen utvärderar schemats prestanda och ger schemaläggaren en inblick i dess styrkor och svagheter. SAS intresserar sig av att veta vart trade-off punkterna ligger för dessa nyckeltal inklusive att finna punkten som är optimal. Punkten som anses vara optimal har en parameterinställning där samtliga nyckeltal har ett så förmånligt värde som möjligt. Resultatet av jämförelsen ska förevisa om modellen är optimalt inställd utefter dessa preferenser. I studien inkluderas en regressionsanalys och en nyckeltalsanalys som studerar de utvalda nyckeltalen Duty days som innefattar produktionsdagar, Absolute Fatigue Risk som innebär risken för utmattning och Aircraft changes som mäter antal flygplansbyten. För att möjliggöra analysen har parametrarna Fatigue penalty och Aircraft changes penalty valts ut för att studera effekten på de olika nyckeltalen när inställningen på parametrarna förändras. Varje nyckeltal är sammankopplat med en parameter i CMS. Schemaläggning är en komplex uppgift att genomföra då robusta scheman inte alltid är de mest kostnadseffektiva. Vad som då uppstår mellan de olika faktorerna är trade-off punkter. Trade-off punkt är den punkt där båda nyckeltalen har ett så gynnsamt värde som möjligt innan ett av nyckeltal börjar påverkas negativt av de andra nyckeltalets positiva utveckling. För att jämföra de tre nyckeltalen samtidigt har olika körningar i optimeringsverktyget CMS genomförts med olika inställningar på de utvalda parametrarna. Utdata från nyckeltalen har standardiserats och sedan tillämpades Pythagoras sats för att lokalisera den optimala punkten. Det rekommenderas att SAS framställer ett nyckeltal för robusthet och undersöker möjligheten att mäta nyckeltalen i en form av en kostnad.

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    En nyckeltalsanalys för SAS schemaläggning av flygbesättningen
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