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  • 951.
    Krepper, Martin
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Reutermo, Anders
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Calculation program for timber connections2016Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Vi har skapat ett hjälpmedel som dimensionerar träbalk och infästningarna balksko och spikningsplåt, enligt eurokoderna. Det är programmerat i Visual-Basic och har ett enkelt användargränssnitt.

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  • 952.
    Krohn, Erik
    et al.
    Department of Computer Science, University of Wisconsin, Oshkosh, Oshkosh, WI, USA.
    Nilsson, Bengt J
    Department of Computer Science and Media Technology, Malmö University, Sweden.
    Schmidt, Christiane
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Opposing Half Guards2022In: 34th Canadian Conference on Computational Geometry, 2022Conference paper (Refereed)
    Abstract [en]

    We study the art gallery problem for opposing halfguards: guards that can either see to their left or to theirright only. We present art gallery theorems, show thatthe problem is NP-hard in monotone polygons, presentapproximation algorithms for spiral and staircase poly-gons, and show that the location of half guards in 2-guardable polygons is not restricted to extensions.

  • 953.
    Krus, Kristofer
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. 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.
    Polishchuk, Valentin
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Identifying Interesting Moments in Controllers Work Video via Dimensionality Reduction2020In: 2020 International Conference on Artificial Intelligence and Data Analytics for Air Transportation (AIDA-AT), 2020Conference paper (Refereed)
    Abstract [en]

    We explore use of machine learning in automating the discovery of meaningful time intervals in video data. We combine Convolutional Neural Networks and Principal Component Analysis in order to zoom-in on interesting moments in hours-long videos of air traffic controllers work. Experimental results for air traffic control tower at Stockholm Bromma airport confirm feasibility of our approach. The method may be consequently used to single out workload-influencing factors, incident investigation and other post-operational analysis of controllers performance.

  • 954.
    Kucher, Kostiantyn
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Engström, Nellie
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Axelsson, Wilma
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Savas, Berkant
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering. iMatrics AB.
    Kerren, Andreas
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering. Linnéuniversitetet, Institutionen för datavetenskap och medieteknik (DM).
    Visualization of Swedish News Articles: A Design Study2024In: Proceedings of the 19th International Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications (VISIGRAPP '24): Volume 1: GRAPP, HUCAPP and IVAPP / [ed] Thomas Bashford-Rogers, Daniel Meneveaux, Mounia Ziat, Mehdi Ammi, Stefan Jänicke, Helen Purchase, Kadi Bouatouch and A. Augusto Sousa, SciTePress , 2024, p. 670-677Conference paper (Refereed)
    Abstract [en]

    The amount of available text data has increased rapidly in the past years, making it difficult for many users to find relevant information. To solve this, natural language processing (NLP) and text visualization methods have been developed, however, they typically focus on English texts only, while the support for low-resource languages is limited. The aim of this design study was to implement a visualization prototype for exploring a large number of Swedish news articles (made available by industrial collaborators), including the temporal and relational data aspects. Sketches of three visual representations were designed and evaluated through user tests involving both our collaborators and end-users (journalists). Next, an NLP pipeline was designed in order to support dynamic and hierarchical topic modeling. The final part of the study resulted in an interactive visualization prototype that uses a variation of area charts to represent topic evolution. The prototype was evaluated thr ough an internal case study and user tests with two groups of participants with the background in journalism and NLP. The evaluation results reveal the participants’ preference for the representation focusing on top topics rather than the topic hierarchy, while suggestions for future work relevant for Swedish text data visualization are also provided.

  • 955.
    Kuiper, Erik
    et al.
    Saab Aeronautical, Linkoping, Sweden .
    Nadjm-Tehrani, Simin
    Linköping University, Department of Computer and Information Science, Software and 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.
    A framework for performance analysis of geographic delay-tolerant routing2012In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, no 184Article in journal (Refereed)
    Abstract [en]

    A major tool used for evaluating routing protocols in ad hoc and delay-tolerant networks is simulation. Whereas the results from simulations give good insights, they are limited to the specific scenario set-up that is used. If the scenario changes, new and often time-consuming simulations have to be run. Moreover, the simulation time in packet-level simulators with fairly realistic physical layer implementation, such as ns-2, generally grows rapidly in the number of nodes. This practically limits the number of nodes in a simulation, even if the limit can be extended by the use of simulation federations. Larger scenarios can also be facilitated by the use of more abstraction in the physical layer; abstractions that may impact the validity of the results. In this article, we present the forward-wait framework--a mathematical model describing the packet movements for opportunistic geographic delay-tolerant routing protocols. By describing packet movements as a sequence of alternating forwarding and waiting phases, the framework can accurately predict the routing performance. Key input parameters to the framework are random variables describing the forwarding and waiting phases. We show how the properties of the random variables can be derived, both via abstract modeling and small scale ns-2 simulation data. The model is then used to demonstrate the prediction capabilities of the framework in providing results that are close to the (much slower) packet-level simulations.

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  • 956.
    Kunclova, Tereza
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Application of Geofence for Safe Interaction with Emergency Vehicles2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of the thesis was to investigate if geofence instructions communicated via an in-vehicle human-machine interface (HMI) can have a positive impact on driver behavior when interacting with emergency vehicles. A total of n = 64 study participants were tested in a driving simulator on two different use cases without or with applied geofence instructions. The use cases were situated on an off-ramp and at an intersection. The results of the experiment demonstrated a statistically significant effect of the use of geofencing on the correct and timely reactions of drivers prior to the interaction with emergency vehicles. Furthermore, the use of geofencing indicated a potential to decrease collision risks and driving time of emergency vehicles. Although the HMI design needs to be improved for real-world geofence application, the study participants were positive about receiving the geofence instructions when interacting with emergency vehicles in their own vehicles in the future.

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  • 957.
    Kuusela, Matilda
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Sjöberg, Emma
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Kommunikation mellan yrkesarbetare och platschefer - Framgångsfaktorer för en lyckad kommunikation2020Independent thesis Basic level (university diploma), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [sv]

    Byggbranschen är en omtalad bransch i många avseenden. En gemensam nämnare för problem i branschen har visat sig vara bristande kommunikation mellan olika led i ett byggprojekt. (Svensk Byggtjänst, 2014).  Syftet med studien är att undersöka hur yrkesarbetare och platschefer upplever att kommunikationen idag fungerar ute i produktionen samt vad yrkesarbetare och platschefer kan göra för att bidra till en lyckad kommunikation. Studien avser att med hjälp av åsikter och tankar från yrkesarbetare och platschefer ta fram konkreta framgångsfaktorer för en lyckad kommunikation. Data har samlats in genom intervjuer med yrkesarbetare och platschefer. Respondenternas svar har därefter analyserats och jämförts med tidigare studier och teorier om kommunikation som ämne. Studiens resultat indikerar att yrkesarbetare och platschefer är eniga i hur kommunikationen sker idag men oeniga om hur välfungerande den är. Utifrån respondenternas svar är framgångsfaktorerna för en lyckad kommunikation i produktion engagemang, tydlighet, öppenhet, samarbete, återkoppling samt struktur och planering.

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  • 958.
    Kvarnbergs, Johan
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Petersson, Jerry
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Enhanced statistical anlysis to improve air safety; How to be proactive2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    LFV is Sweden‟s major provider of air navigation service. The organisation continuously strives towards providing better and safer air traffic control, and to minimize its part in incidents and accidents occurring. One part of the safety work is analysis of statistics, concerning different types of safety performance indicators; in other words, statistical analysis of occurrences. The numbers of occurrences in the investigated and monitored safety performance indicators are rising, and LFV therefore wants to find a way to use statistical analysis in a proactive way, instead of reactive as the use is today.

    We have identified the way LFV uses statistical analysis today, and compared it to alternative approaches. We will give suggestions to LFV on different approaches of statistical analysis, which can be used in a more proactive way compared with today. The information is collected through investigations of regulations, and of procedures at the organisations concerned by the Swedish occurrence reporting system. Experts from LFV have also been interviewed.

    We have, after discussions with LFV‟s experts, come up with an alternate approach to perform statistical analysis. The new approach is named 24 Hour Approach, and it sets the average statistics from a specific safety performance indicator for a specified period, in relation to the average amount of traffic for the same period. The occurrences are divided between the hours they took place during the day. We have also investigated the Alarm Model, an approach used by Transportstyrelsen.

    We discuss the Human Factors Analysing and Classification System (HFACS) as a proposal to future development. It is an approach towards the reports for the occurrences. By classifying the reports with the human factors involved with the occurrences, statistical analyses can be made on the causal factors involved. LFV have started to introduce human factors in LFV‟s occurrence reporting system, which will give the possibly to combine different occurrences (runway incursion, airspace infringement, clearance bust, etc.) within the same safety performance indicator, thus performing statistical analyses on causal factors instead of occurrences.

    We conclude and recommend LFV to use the provided 24 Hour Approach on its statistics. LFV is also recommended to keep up the on-going work with integrating human factors into the Synergi system, and to adapt the Risk Analysis Tool provided by EUROCONTROL.

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  • 959.
    Källstrand, Ellen
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Pucar, Nina
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Comparison of various wooden facades2017Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Gran och tall är de vanligaste barrträden i Sverige. Tack vare import från andra länder har kontakt med andra träslag som inte växer i Sverige uppstått. Dessa nya träslag väcker ett intresse att vilja skapa fasader med de nya träslagen. Studiens syfte är att jämföra behandlade träfasader med två obehandlade ädelträslag gällande kostnad och beständighet. Behandlingarna som har studerats är järnvitriol samt akrylatfärg och ädelträslagen som valts är jättetuja (Thuja Plicata) och sibirisk lärk (Larix Sibirica). Då det vanligaste underlaget för akrylatfärg är gran och furu har även dessa träslag behandlats i rapporten. Målet är att komma fram till vilket ädelträ som är mest lämpligt i förhållande till en behandlad fasad. Studien har genomförts genom att studera litteratur och dokument samt intervjua en arkitekt, en bebyggelseantikvarie, en forskare, en färghandlare och en produktchef från en träleverantör. Respondenternas svar vid intervjuerna behandlar bland annat osäkerheten vid att använda ett relativt nytt träslag i Sverige som fasad. Flera av dem tar även upp att en obehandlad träfasad kommer att få färgförändringar med tiden och det är svårt på att förhand veta vilken färg fasaden kommer att anta och om den åldras jämnt. Järnvitriol är en behandling som ger träet ett väderpinat uttryck snabbare än den naturliga patineringen. Dock skyddar behandlingen inte träet till skillnad från akrylatfärgen som ger träet ett extra skydd mot yttre påverkan. Skillnaden mellan ceder och lärk är stor i vissa avseenden, bland annat är det ena träslaget mer sprickbenäget och har kortare livslängd. Fördelen med en obehandlad träfasad, jämfört med en fasad målad med akrylatfärg, är att en rätt konstruerad obehandlad träfasad kräver väldigt lite underhåll till skillnad från akrylatfärgens underhållsintervall på 10–15 år. Kostnadsmässigt är det ganska stor skillnad beroende på vilken typ av fasad som väljs. Det viktiga för en träfasad är att den får möjlighet att torka ut ordentligt efter nederbörd. Ett takutsprång är även en fördel både vad gäller en behandlad och obehandlad fasad. Träslagen rapporten behandlar är alla lämpliga att använda som fasad men då de har olika egenskaper passar behandlingarna olika bra med respektive träslag.

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    Comparison of various wooden facades
  • 960.
    Kågesten, Owe
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Engelbrecht, Johann
    University of Pretoria.
    Student group presentations: A learning instrument in undergraduate mathematics for engineering students2007In: European Journal of Engineering Education, ISSN 0304-3797, E-ISSN 1469-5898, Vol. 32, no 3, p. 303-314Article in journal (Refereed)
    Abstract [en]

    In this study we created an environment for peer learning, where students teach students by making oral presentations in groups about solving mathematical problems and explaining theoretical background in mathematics, during the first year of an undergraduate engineering programme at the Norrköping campus of the Linköping University. In order to strengthen the students' understanding and perception of central mathematical concepts, the study was designed to take the students through five different learning experiences, preparing the presentation, presenting the mathematics, listening to others presenting, discussion by all students after the presentation and feedback by the teacher to the small group of students separate from the other students. We study how oral presentations work as a learning and assessment method. The study consisted of three stages.  After a first run of the presentations as a learning instrument, three guidebooks with recommendations to students and teachers were developed in order to assist students as well as teachers about their role in this learning environment. Students’ and teachers’ views on the student presentations as learning instrument were surveyed before and after the intervention.  In stage three, students were interviewed individually to ascertain the relevant success of the different learning experiences.

  • 961.
    Ladekrans, Christian
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Leinmark, Niclas
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Analysis of tied up capital at Rejmes Lastvagnar2017Independent thesis Basic level (degree of Bachelor), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Detta examensarbete har utförts vid Linköpings Tekniska Högskola och Tage Rejmes Lastvagnar AB i Norrköping under vårterminen 2016. Tage Rejmes Lastvagnar AB säljer och reparerar lastvagnar och bussar samt erbjuder leasing från företagets lokaler i Butängen, Norrköping. Branschen ställer höga krav på servicenivåer och flexibilitet kopplat till verksamhetens reparation och service av lastbilar, varpå behov av lagerhållna artiklar uppstår för företaget. Majoriteten av dessa artiklar köps in från en enskild leverantör som ensamt styr prognostisering av efterfrågan och inköpskvantiteter. Förändringar i företagets omsättning och förändringar i leverantörens beställningssystem har skapat en ökad kapitalbindning på Tage Rejmes Lastvagnar AB’s lager under de senaste åren. Denna studie har därför genom datainsamling, observationer och intervjuer jämfört det nuvarande beställningssystemet med teoretiska modeller, och genom artikelklassificering föreslagit alternativa tillvägagångssätt för företagets lagerstyrning. Resultatet av ABC-klassificeringen som utförts har kategoriserat företagets artiklar baserat på dess efterfrågan och volymvärde, varpå en differentiering av servicenivån för dessa kategorier gör att kapitalbindningen kan sänkas. Artiklar med låg efterfrågan och höga priser blir i det nya systemet beställningsvaror till priset av en sänkt servicenivå. Studiens analys visar dock att förändrade partiformningar kan öka det totala antalet transporter från beställaren, vilket i sig kan resultera i både en ökad miljöpåverkan och förhöjda orderkostnader.

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  • 962.
    Lagervall, Malin
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Samuelsson, Sandra
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Microscopic Simulation of Pedestrian Traffic in a Station Environment: A Study of Actual and Desired Walking Speeds2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In order to attract pedestrians to travel with public transport instead of private cars, the layout of interchange stations is important and should be designed in an effective way. Microscopic simulation of pedestrians can be used to evaluate different layout scenarios or a future increase in flow. The simulation software Viswalk was investigated, where the movements of pedestrians are based on a social force model,. The purpose of this thesis was to investigate simulated walking speeds for different flow levels and to investigate the effects of dividing pedestrians into types with different desired speeds. The aim was to find a desired speed distribution that can be used for different flow levels. Field studies have been performed to collect pedestrian traffic data with a video camera at Stockholm Central Station. Two disjoint flow levels were identified and used to investigate if the same desired speed distribution could be used for different flow levels. The average observed walking speed was 1.33 metres per second at the low flow level and 1.25 metres per second at the high flow level. The error was 4.5 percent between the average observed walking speed and the average simulated walking speed when the optimal desired speed distribution at the low flow level was used at the high flow level. Effects of using different desired speed distributions for different pedestrian types have also been investigated. The error between the average of the observed and the simulated walking speeds varies between 2.3 and 4.1 percent when dividing pedestrians into different types when the optimal desired speed distributions at the low flow level are used at the high flow level. A sensitivity analysis of some parameters of the social force model in Viswalk has also been performed. Several adjustments of the parameters show that some parameters had great impact of the simulated walking speeds. The final conclusion is that the parameter configuration and how the pedestrians are divided into different types affect the average simulated walking speed.

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  • 963.
    Lagg, David
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Waldt, Niklas
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    An analysis of wastes in the construction industry - a case study of Ebbepark2020Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    Inefficient use of resources occurs in many industries, including both time and materials being wasted. A theory which has been used for a long time to reduce waste of resources in all supply chains is the SCM theory. The aim of SCM is mainly to guide the different components of a supply chain, so at the end of the process generate a value for the end-customer as great as possible. An important aspect of SCM is logistics, which to some extent relates to managing and making the usage of resources more efficient, with the goal of reducing waste. The construction industry has previously been under scrutiny for their lack of ambition regarding the improvement of the current course of action, and implementation of well-functioning logistics in their activities. One solution which has been used is Lean Construction, a branch of Toyota’s Lean-theory. 

    This report has been written with the study conducted by Josephson and Saukkoriipi as a benchmark. Josephson and Saukkoriipi studied potential wastes in the construction industry by utilizing field research. The target for this case study is Ebbepark in Linköping, a construction site for a new district in the city. The district contains a variety of buildings, including private housing and schools. The project group has chosen to make a follow up study of Josephson and Saukkoriipi’s research with the goal of identifying waste of resources and their potential effects on Ebbepark, as well as propose solutions. To establish areas of improvement, the study was done in three steps by using surveys, observations and interviews, as inspired by Josephson and Saukkoriipi’s methods. These particular steps were used since they complement each other well, to create a broader view of how the construction site works. The data extracted from these three methods were then examined using literature to find potential solutions for reducing wastes at Ebbepark. 

    In the sense that Josephson and Saukkoriipi’s report represents the construction industry as it was in 2005, clear improvements have been observed in this case. E.g., in the matter of the construction workers' hours, the number of wasteful activities has been reduced from 33% to 13%. Although there were clear improvements, there were still some areas where waste could be identified. E.g., large volumes of material were stored at the construction site, which might lead to increased workload and risk of damaged material. Fill rate during transport was low, as well as breaks being lengthy. The study concluded with the recommendation that improvements could be made using different aspects of Lean construction and SCM.

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  • 964.
    Lambrix, Patrick
    et al.
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Göthe Lundgren, Maud
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kamkar, Mariam
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Computer science as an integrated part of engineering education1997In: Proceedings of the ACM SIGCSE/SIGCUE Conference on Integrating Technology into Computer Science Education, 1997, p. 151-Conference paper (Refereed)
  • 965.
    Lantto, Johanna
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Wiholm, Willie
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Innovative communication strategies and modelling of robust sensor functions2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this thesis was to create a resilient network, capable of handling link failures without affecting the data flow. This was done by using graph theory and three mathematical models. A generic system was created, on which the models were applied on. The mathematical models were path diversity, edge protection and path restoration. These models were tested to evaluate if they could create a robust system. The models were also compared with each other to obtain the best performing one. It was concluded that it was possible to construct a resilient network using these types of mathematical modelling. It was also concluded that the models provided different results in terms of cost and robustness. The report ends with suggestions on future work of how studies can be conducted to create realistic systems.

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  • 966.
    Larsson, Agneta
    et al.
    Chalmers Tekniska Högskola, Gothenburg, Sweden.
    Fredriksson, Anna
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Capacity Planning at a Tactical Level in Hospital Departments2014In: ADVANCES IN PRODUCTION MANAGEMENT SYSTEMS: INNOVATIVE AND KNOWLEDGE-BASED PRODUCTION MANAGEMENT IN A GLOBAL-LOCAL WORLD, APMS 2014, PT II, 2014, Vol. 439, p. 535-547Conference paper (Refereed)
    Abstract [en]

    The purpose is to describe the essential components and output of the tactical planning process and to explore context-related variations in the applicability of the planning process for hospital departments. The paper is based on a multiple-case study of three hospital departments’ planning processes at a tactical level, wherein the department manager’s[1]support of the planning process was found to be essential. This study illustrates how an active tactical planning process can provide for numerous potential measures to adjust capacity and how they may vary in different contexts. An active tactical planning process provides the ability to move from current short-term, costly fire-fighting measures to more proactive capacity adjustments within hospital departments, which allow the department to stay under budget while keeping waiting times and queues within limits.

    [1] The department manager is responsible for the provision of hospital specialty care. In this paper, the relevant individuals manage the Urology, Cardiology and Psychiatry (affectionate disorders) departments.

  • 967.
    Larsson, Agneta
    et al.
    Chalmers Univ Technol, Sweden.
    Fredriksson, Anna
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Tactical capacity planning in hospital departments2019In: International Journal of Health Care Quality Assurance, ISSN 0952-6862, E-ISSN 1758-6542, Vol. 32, no 1, p. 233-245Article in journal (Refereed)
    Abstract [en]

    Purpose The purpose of this paper is to explore tactical planning potential within hospital departments. The study had two objectives: first, to develop a framework for tactical capacity planning in healthcare departments by identifying and structuring essential components for healthcare capacity management; and, second, to identify context-specific requirements and functionality demands on tactical planning processes within healthcare. Design/methodology/approach A framework for tactical capacity planning was developed through a literature review. Additionally, an exploratory multiple-case study was performed, with cases from three Swedish hospital departments, which provide the opportunity to study framework applicability in its natural context. Findings Findings illustrate how an active tactical planning process can facilitate adjustments to capacity. However, the multiple-case study shows that there are contextual differences between departments, depending on available treatments and resources that affect capacity adjustments, and how the planning process activities should be structured. Originality/value This project develops a framework for a tactical capacity-planning process adapted to healthcare provider contexts. By developing the framework, based on the literature and tactical level planning processes within three Swedish hospital case studies, the authors bridge gaps between theory and application regarding healthcare capacity planning.

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  • 968.
    Larsson, Annika
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Lundqvist, Desireé
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Designdialog som arbetssätt - En fallstudie kring Bärstadsskolans utformning2015Independent thesis Basic level (university diploma), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    I byggbranschen är tidiga skeden ett vanligt begrepp. Alltför ofta hinner brukarna inte reflektera över sina behov, krav och önskemål och entreprenörerna ges för lite tid att bidra med sina kompetenser. Denna rapport beskriver vikten av att tidigt involvera viktiga intressenter i en dialog för att samverka och därmed undvika onödiga revideringar senare i processen. Arkitektens betydande roll att tolka och översätta brukarnas bild av verksamheten till byggprocessens språk, framgår också. Rapporten lyfter fram designdialogen som ett designmässigt arbetssätt som stödjer behovsanalys och idéskapande. Dialogen bygger på en serie workshops vilka ger förutsättningar för ett kreativt arbetssätt som skapar engagemang och delaktighet. Efter en teoretisk datainsamling gjordes en empirisk fallstudie på projektet Bärstadsskolan i Karlstad med stöd från Sweco Architects. Studien syftar till att åskådliggöra arkitektens roll i dialogen och visa fördelar och risker med arbetssättet.

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  • 969.
    Larsson, Felix
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Linna, Robin
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    An Analysis of Passenger Demand Forecast Evaluation Methods2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In the field of aviation forecasting is used, among other things, to determine the number of passengers to expect for each flight. This is beneficial in the practice of revenue management, as the forecast is used as a base when setting the price for each flight. In this study, a forecast evaluation has been done on seven different routes with a total of 61 different flights, using four different methods. These are: Mean Absolute Scaled Error (MASE), Mean Absolute Percentage Error (MAPE), Tracking Signal, and a goodness of fit test to determine if the forecast errors are normally distributed. The MASE has been used to determine if the passenger forecasts are better or worse than a naïve forecast, while the MAPE provides an error value for internal comparisons between the flights. The Tracking Signal and the normal distribution test have been used in order to determine whether a flight has bias or not towards under- or overforecasting. The results point towards a general underforecast across all studied flights. A total of 89 % of the forecasts perform better than the naïve forecast, with an average MASE value of 0,78. As such, the forecast accuracy is better than that of the naïve forecast. There are however large error values among the observed flights, affecting the MAPE average. The MAPE average is 38,53 % while the median is 30,60 %. The measure can be used for internal comparisons, and one such way is to use the average value as a benchmark in order to focus on improving those forecasts with a higher than average MAPE. The authors have found that the MASE and MAPE are useful in measuring forecast accuracy and as such the recommendation of the authors is that these two error measures can be used together to evaluate forecast accuracy at frequent intervals. In addition to this there is value in examining the error distribution in conjunction with the Mean Error when searching for bias, as this will indicate if there is systematic error present.

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  • 970.
    Larsson, Hanna
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Tica, Selma
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    A study of the order picking process at PostNord Logistic - improving the picking process by identifying factors that inhibit the prodctivity2017Independent thesis Basic level (degree of Bachelor), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The goal of this study was to find factors affecting the pickers’ productivity negatively, in the order picking process, and to suggest a change that can increase the pickers’ productivity. By a qualitative approach the initial situation at PostNord was studied. The obtained results, after analyzing the initial situation, showed various factors that affect the pickers’ productivity negatively. All these contributed to waste, meaning that the picker did not use its time correctly according to Lean theory. These factors were analyzed and categorized into four problem areas, which are quality of tools, standardization of routines and leadership, article placement and jam in the corridors. Possible suggestions to improve the situation can be done with smaller or bigger changes. One solution is to improve the work procedures by standardizing the methods, which could be done by cooperating more with PEMA and using the pickers’ knowledge. Some suggestions and adjacent activities must be investigated further to find the best solutions.

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  • 971.
    Larsson, Karl
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Digitization in ArcGIS, QGIS and MapInfo. A systematic survey and recommendation of program.2018Independent thesis Basic level (university diploma), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Idag är det mycket vanligt att använda och förlita sig på GIS-programvaror inom byggsektorn. Det finns flera alternativ att välja mellan som QGIS, ArcGIS, MapInfo, GRASS GIS, Surfer och Maptitude men om man inte redan är välbekant med området eller programmen är det svårt att veta hur dom skiljer sig åt och vad man kan förvänta sig. Därmed är syftet med arbetet att utföra en systematisk undersökning av GIS-programvaror utifrån en generell digitaliseringsarbetsgång för att kunna identifiera fördelar och nackdelar samt lämna en slutgiltig rekommendation. För att besvara syftet har följande frågeställningar tagits fram: • Vilket program är lämpligast för georeferering? • Vilket program är lämpligast för att rita kartor digitalt, dvs. att skapa vektorskikt och ”rita av” information från grundkartan? • Vilket program är lämpligast för att skapa en karta och diverse tillhörande detaljer? • Vilket program rekommenderas utav de tre möjliga med tanke på bedömningsmallen, tidsinsats för arbetet och kostnad? För att besvara frågeställningarna har tre programvaror valts ut (QGIS, ArcGIS och MapInfo) som jämförs utifrån en digitaliseringsarbetsgång och utvärderas efter samma utvärderingsmall som tagits fram efter hur ett idealt GIS-program tänks prestera inom arbetsgången. För att hjälpa slutgiltig rekommendationen har även tidsinsatsen för hela arbetsgången mätts och kostnaden för dom olika programmen har tagits fram. Inom georeferering fick QGIS och ArcGIS mest poäng men eftersom QGIS har flera alternativ inom transformation- och omsamplingsmetoder bedöms det vara ett bättre alternativ än ArcGIS. Inom rita kartan digitalt presterade QGIS och ArcGIS bäst enligt utvärderingsmallen men eftersom QGIS har bättre funktioner för att sätta ID-nummer och attributdata anses det vara bättre alternativ. Inom att skapa en karta presterade ArcGIS och MapInfo bäst men eftersom ArcGIS har bättre möjligheter för att anpassa elementen i kartan bedöms det som ett bättre alternativ än MapInfo. Den slutgiltiga rekommendationen gick till QGIS eftersom det prestare bäst genom hela utvärderingsmallen, hade kortast tidsinsats för att genomföra arbetsgången och har lägst kostnad.

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    Digitization in ArcGIS, QGIS and MapInfo. A systematic survey and recommendation of program
  • 972.
    Larsson, Per
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Mahmoud, Bawan
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Work environment and safety on the construction site - a matter of mindset2017Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Olyckor och tillbud hör till vardagen inom byggbranschen och är något som sker dagligen. I Sverige rapporteras det tusentals olyckor varje år, varav ett tiotal är dödsolyckor. Strängare krav på arbetsmiljö och säkerhet ute på byggarbetsplatserna är utmaningar som branschen ställs inför, samtidigt som behovet av en snabbare produktionstakt ökat under de senaste åren.

    Studien belyser vikten av förhållningssättet till den egna säkerheten samt hur detta kan påverkas för att bidra till ett förhöjt säkerhetstänk och i förlängningen en säkrare byggarbetsplats. Som grund till detta har säkerhetsklimat och några av de vanligaste arbetsmetoderna som rör arbetsmiljö- och säkerhet undersökts.

    För att söka svar på studiens frågeställningar har en litteraturstudie i kombination med fallstudier gjorts. I den inledande litteraturstudien studerades tidigare studier och artiklar på området samt information om gällande lagar och regler. Fallstudien bygger främst på intervjuer och enkäter utförda med personer som på olika sätt berörs av ämnet, samt dokumentstudie där arbetssätt och rutiner undersökts. Fallstudien genomfördes i samarbete med NCC Building Östergötland.

    Studiens resultat visar att en av de största utmaningarna i arbetsmiljöarbetet är att säkerställa kommunikationen av arbetsmiljö- och säkerhetsrelaterade frågor. Inte minst med tanke på den ökande internationalisering som pågår i byggbranschen. Att synliggöra och utbilda om arbetsmiljöfrågor beskrivs som centrala för att påverka inställningen och säkerhetsklimatet. Även känslan av delaktighet och att tillåtas vara med och påverka spelar en stor roll för att kunna utveckla arbetsmiljöarbetet.

    Åtgärdsförslag som studien kommit fram till berör till stor del redan existerande rutiner och hur dessa kan utvecklas. På ett mer visionärt plan diskuteras möjligheten till en branschgemensam standard när det gäller arbetsmiljö- och säkerhetsfrågor.

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    Work environment and safety on the construction site - a matter of mindset
  • 973.
    Larsson, Robert
    et al.
    Lund University, Sweden.
    Rudberg, Martin
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    A simulation-based approach for systematic analysis of workflow during the construction of in-situ concrete frames2020Report (Other academic)
    Abstract [en]

    The construction workflow of in-situ concrete frames in multi-storey residential buildings is highly complex and dynamic. Discrete-event simulation (DES) offers capabilities to model and analyse such complexity. Although DES has successfully been used by researchers in a wide range of construction-related applications there are not many examples demonstrating how different simulation outputs (time, cost, queue waiting time, resource usage) could be used in an integrated and systematic way to facilitate in-depth analysis of construction workflow. This report presents a simulation model of concrete framework construction and demonstrates how it can be used for systematic analysis of a production setup using multiple performance indicators such as construction time, cost, resource utilization, and workflow waiting times. It was found that the proposed model can describe the complexity in construction workflow and support systematic analyses. Multiple simulation measures were also found valuable, e.g. in order to identify and remove bottlenecks. This research has been financially supported by the Swedish National Board of Housing, Building and Planning (Boverket), the Swedish construction industry's organization for research and development (SBUF), and Cementa AB. Several concrete manufacturers and contractor companies are also kindly acknowledged for their involvement and collaboration during this research project. The authors would also thank Jonas Enhörning at Duke Systems AB for technical support related to ExtendSim.

  • 974.
    Larsson, Robert
    et al.
    Lund Univ, Sweden.
    Rudberg, Martin
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Effects of weather conditions on concrete work task productivity - a questionnaire survey2023In: Construction Innovation, ISSN 1471-4175, E-ISSN 1477-0857, Vol. 23, no 2, p. 306-321Article in journal (Refereed)
    Abstract [en]

    Purpose This paper aims to study the effects of different weather conditions on typical concrete work tasks productivity. Weather is one important factor that has a negative impact on construction productivity. Knowledge about how weather affects construction works is therefore important for the construction industry, e.g. during planning and execution of construction projects. Design/methodology/approach A questionnaire survey method is used involving means to perform pairwise comparisons of different weather factors according to the analytical hierarchical process (AHP). The survey also contains means to enable assessment of the loss in productivity for typical work tasks exposed to different weather types. The survey targets practitioners involved in Swedish concrete construction projects, and the results are compared with previous research findings. Findings The survey covers responses from 232 practitioners with long experience of concrete construction. The pairwise comparisons reveal that practitioners rank precipitation as the most important followed by wind and temperature. The loss in productivity varies significantly (from 0 to 100%) depending on the type of work and the type of weather factor considered. The results partly confirm findings reported in previous research but also reveal a more complex relationship between weather and productivity indicating several underlying influencing factors such as type of work, type of weather (e.g. rain or snow) and the intensity of each weather factor. Originality/value This paper presents new data about how 232 practitioners assess the effects of weather on construction productivity involving novel means to perform objective rankings such as the AHP methodology.

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  • 975.
    Larsson, Robert
    et al.
    Lund Univ, Sweden.
    Rudberg, Martin
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Impact of Weather Conditions on In Situ Concrete Wall Operations Using a Simulation-Based Approach2019In: Journal of construction engineering and management, ISSN 0733-9364, E-ISSN 1943-7862, Vol. 145, no 7, article id 05019009Article in journal (Refereed)
    Abstract [en]

    The purpose of this research is to study the impact of temperature, precipitation, and wind speed on in situ concrete wall operations, and its combined resulting effect on project duration. The research presented is anchored in the learnings gained through a literature review on weather effects on construction operations, an analysis of weather data with high resolution, and two field studies of in situ concrete wall operations. These learnings are implemented in a discrete event simulation (DES) model for the analysis of weather impact on project duration. The simulation results show that (1) weather greatly impacts project duration and has to be accounted for when planning operations; (2) there are huge differences between weather seasons that could affect the timing of project start-up; and (3) the height of buildings and threshold values for different types of cranes have to be accounted for when planning lifting operations. The main contribution of this paper lies both in the methods, in which high-resolution weather data can be incorporated in DES models to analyze project duration, and in the actual results of the simulation runs, showing to what level weather variables have to be incorporated in the planning of concrete wall construction.

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  • 976.
    Larsson, Torbjörn
    et al.
    Linköping University, Department of Mathematics, Optimization . Linköping University, The Institute of Technology.
    Lundgren, Jan
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Communications and Transport Systems.
    Peterson, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Communications and Transport Systems.
    Allocation of Link Flow Detectors for Origin-Destination Matrix Estimation-A Comparative Study2010In: COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, ISSN 1093-9687, Vol. 25, no 2, p. 116-131Article in journal (Refereed)
    Abstract [en]

    Origin-destination (OD) matrices are essential for various analyses in the field of traffic planning, and they are often estimated from link flow observations. We compare methods for allocating link flow detectors to a traffic network with respect to the quality of the estimated OD-matrix. First, an overview of allocation methods proposed in the literature is presented. Second, we construct a controlled experimental environment where any allocation method can be evaluated, and compared to others, in terms of the quality of the estimated OD-matrix. Third, this environment is used to evaluate and compare three fundamental allocation methods. Studies are made on the Sioux Falls network and on a network modeling the city of Linkoping. Our conclusion is, that the most commonly studied approach for detector allocation, maximizing the coverage of OD-pairs, seems to be unfavorable for the quality of the estimated OD-matrix.

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  • 977.
    Leblet, Jimmy
    et al.
    Telecom Bretagne.
    Li, Zhe
    Telecom Bretagne.
    Simon, Gwendal
    Telecom Bretagne.
    Yuan, Di
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Communications and Transport Systems.
    Optimal network locality in distributed virtualized data-centers2011In: Computer Communications, ISSN 0140-3664, E-ISSN 1873-703X, Vol. 34, no 16, p. 1968-1979Article in journal (Refereed)
    Abstract [en]

    Cost efficiency is a key aspect in deploying distributed service in networks within decentralized service delivery architectures. In this paper, we address this aspect from an optimization and algorithmic standpoint. The research deals with the placement of service components to network sites, where the performance metric is the cost for acquiring components between the sites. The resulting optimization problem, which we refer to as the k-Component Multi-site Placement Problem, is applicable to service distribution in a wide range of communication networking scenarios. We provide a theoretical analysis of the problems computational complexity, and develop an integer programming model for providing reference results for performance benchmarking. On the algorithmic side, we present four approaches: an algorithm with approximation guarantee and three heuristics algorithms. The first heuristic is derived from graph theory on domatic partition. The second heuristic, built on intuition, admits distributed computation. The third heuristic emphasizes on fairness in cost distribution among the sites. We report simulation results for sets of networks where cost is represented by round-trip time (RTT) originating from real measurements. For small networks, the integer model is used to study algorithm performance in terms of optimality. Large networks are used to compare the algorithms relatively to each other. Among the algorithms, the heuristic based on intuition has close-to-optimal performance, and the fairness heuristic achieves a good balance between single-site cost and the overall one. In addition, the experiments demonstrate the significance of optimization for cost reduction in comparison to a the random allocation strategy.

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  • 978. Order onlineBuy this publication >>
    Lei, Lei
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    From Orthogonal to Non-orthogonal Multiple Access: Energy- and Spectrum-Efficient Resource Allocation2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The rapid pace of innovations in information and communication technology (ICT) industry over the past decade has greatly improved people’s mobile communication experience. This, in turn, has escalated exponential growth in the number of connected mobile devices and data traffic volume in wireless networks. Researchers and network service providers have faced many challenges in providing seamless, ubiquitous, reliable, and high-speed data service to mobile users. Mathematical optimization, as a powerful tool, plays an important role in addressing such challenging issues.

    This dissertation addresses several radio resource allocation problems in 4G and 5G mobile communication systems, in order to improve network performance in terms of throughput, energy, or fairness. Mathematical optimization is applied as the main approach to analyze and solve the problems. Theoretical analysis and algorithmic solutions are derived. Numerical results are obtained to validate our theoretical findings and demonstrate the algorithms’ ability of attaining optimal or near-optimal solutions.

    Five research papers are included in the dissertation. In Paper I, we study a set of optimization problems of consecutive-channel allocation in single carrier-frequency division multiple access (SCFDMA) systems. We provide a unified algorithmic framework to optimize the channel allocation and improve system performance. The next three papers are devoted to studying energy-saving problems in orthogonal frequency division multiple access (OFDMA) systems. In Paper II, we investigate a problem of jointly minimizing energy consumption at both transmitter and receiver sides. An energy-efficient scheduling algorithm is developed to provide optimality bounds and near-optimal solutions. Next in Paper III, we derive fundamental properties for energy minimization in loadcoupled OFDMA networks. Our analytical results suggest that the maximal use of time-frequency resources can lead to the lowest network energy consumption. An iterative power adjustment algorithm is developed to obtain the optimal power solution with guaranteed convergence. In Paper IV, we study an energy minimization problem from the perspective of scheduling activation and deactivation of base station transmissions. We provide mathematical formulations and theoretical insights. For problem solution, a column generation approach, as well as a bounding scheme are developed. Finally, towards to 5G communication systems, joint power and channel allocation in non-orthogonal multiple access (NOMA) is investigated in Paper V in which an algorithmic solution is proposed to improve system throughput and fairness.

    List of papers
    1. A Unified Graph Labeling Algorithm for Consecutive-Block Channel Allocation in SC-FDMA
    Open this publication in new window or tab >>A Unified Graph Labeling Algorithm for Consecutive-Block Channel Allocation in SC-FDMA
    2013 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 12, no 11, p. 5767-5779Article in journal (Refereed) Published
    Abstract [en]

    Optimal channel allocation is a key performance engineering aspect in single-carrier frequency-division multiple access (SC-FDMA). In SC-FDMA with localized channel assignment, the channels of each user must form a consecutive block. Subject to this constraint, various performance objectives, such as maximum utility, minimum power, and minimum number of channels, have been studied. We present a unified graph labeling algorithm for these problems, based on the structural insight that SC-FDMA channel allocation can be modeled as finding an optimal path in an acyclic graph. By this insight, our algorithm applies the concept of labeling and label domination that represent non-trivial extensions of finding a shortest or longest path. The key parameter in trading performance versus computation is the number of labels kept per node. Increasing the number ultimately enables global optimality. The algorithms approach is further justified by its global optimality guarantee with strong polynomial-time complexity for two specific scenarios, where the input is user-invariant and channel-invariant, respectively. For the general case, we provide numerical results demonstrating the algorithms ability of attaining near-optimal solutions.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2013
    Keywords
    Algorithm, channel allocation, optimization, single carrier frequency division multiple access
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-102855 (URN)10.1109/TWC.2013.092313.130092 (DOI)000328058400034 ()
    Note

    R)||A*STAR, Singapore||Linkoping-Lund Excellence Center in Information Technology (ELLIIT), Sweden||

    Available from: 2014-01-07 Created: 2014-01-02 Last updated: 2017-12-06
    2. Resource Scheduling to Jointly Minimize Receiving and Transmitting Energy in OFDMA Systems
    Open this publication in new window or tab >>Resource Scheduling to Jointly Minimize Receiving and Transmitting Energy in OFDMA Systems
    2014 (English)In: 2014 11TH INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATIONS SYSTEMS (ISWCS), IEEE , 2014, p. 187-191Conference paper, Published paper (Refereed)
    Abstract [en]

    Resource scheduling in orthogonal frequency division multiple access (OFDMA) for energy saving has attracted extensive attention. Most current research considers the reduction of energy at the transmitter or the receiver separately. In this paper, we focus on minimizing the energy consumption in both sides concurrently by formulating the problem of joint receiving and transmitting energy-efficient scheduling (RTEES) in OFDMA downlink. We show that this problem can be cast as a binary integer programme. We solve the RTEES problem by a computationally efficient algorithm. We proposed a specialized solution approach, named time-slot-oriented column generation (TSOCG) algorithm, for approaching and bounding the global optimality. Numerical studies show that the proposed algorithm solution is competitive and time-efficient to provide a close-to-optimum solution and a tight bound.

    Place, publisher, year, edition, pages
    IEEE, 2014
    Keywords
    Energy saving; column generation; resource allocation; resource scheduling; OFDMA
    National Category
    Civil Engineering
    Identifiers
    urn:nbn:se:liu:diva-123094 (URN)000363906500036 ()978-1-4799-5863-4 (ISBN)
    Conference
    11th International Symposium on Wireless Communications Systems (ISWCS)
    Available from: 2015-12-03 Created: 2015-12-03 Last updated: 2016-04-08
    3. Power and Load Coupling in Cellular Networks for Energy Optimization
    Open this publication in new window or tab >>Power and Load Coupling in Cellular Networks for Energy Optimization
    2015 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 1, p. 509-519Article in journal (Refereed) Published
    Abstract [en]

    We consider the problem of minimization of sum transmission energy in cellular networks where coupling occurs between cells due to mutual interference. The coupling relation is characterized by the signal-to-interference-and-noise-ratio (SINR) coupling model. Both cell load and transmission power, where cell load measures the average level of resource usage in the cell, interact via the coupling model. The coupling is implicitly characterized with load and power as the variables of interest using two equivalent equations, namely, non-linear load coupling equation (NLCE) and non-linear power coupling equation (NPCE), respectively. By analyzing the NLCE and NPCE, we prove that operating at full load is optimal in minimizing sum energy, and provide an iterative power adjustment algorithm to obtain the corresponding optimal power solution with guaranteed convergence, where in each iteration a standard bisection search is employed. To obtain the algorithmic result, we use the properties of the so-called standard interference function; the proof is nonstandard because the NPCE cannot even be expressed as a closed-form expression with power as the implicit variable of interest. We present numerical results illustrating the theoretical findings for a real-life and large-scale cellular network, showing the advantage of our solution compared to the conventional solution of deploying uniform power for base stations.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2015
    Keywords
    Cellular networks; energy minimization; load coupling; power coupling; power adjustment allocation; standard interference function
    National Category
    Civil Engineering
    Identifiers
    urn:nbn:se:liu:diva-115830 (URN)10.1109/TWC.2014.2353043 (DOI)000349675400041 ()
    Note

    Funding Agencies|Linkoping-Lund Excellence Center in Information Technology (ELLIIT), Sweden; Chinese Scholarship Council (CSC); Institute for Infocomm Research (I2R), A*STAR, Singapore

    Available from: 2015-03-20 Created: 2015-03-20 Last updated: 2017-12-04
    4. Optimal Cell Clustering and Activation for Energy Saving in Load-Coupled Wireless Networks
    Open this publication in new window or tab >>Optimal Cell Clustering and Activation for Energy Saving in Load-Coupled Wireless Networks
    2015 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 11, p. 6150-6163Article in journal (Refereed) Published
    Abstract [en]

    Optimizing activation and deactivation of base station transmissions provides an instrument for improving energy efficiency in cellular networks. In this paper, we study the problem of performing cell clustering and setting the activation time of each cluster, with the objective of minimizing the sum energy, subject to a time constraint of serving the users traffic demand. Our optimization framework accounts for inter-cell interference, and, thus, the users achievable rates depend on cluster formation. We provide mathematical formulations and analysis, and prove the problems NP hardness. For problem solution, we first apply an optimization method that successively augments the set of variables under consideration, with the capability of approaching global optimum. Then, we derive a second solution algorithm to deal with the trade-off between optimality and the combinatorial nature of cluster formation. Numerical results demonstrate that our solutions achieve more than 40% energy saving over existing schemes, and that the solutions we obtain are within a few percent of deviation from global optimum.

    Place, publisher, year, edition, pages
    IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2015
    Keywords
    Cell activation; cell clustering; energy minimization; load coupling; column generation
    National Category
    Civil Engineering
    Identifiers
    urn:nbn:se:liu:diva-123331 (URN)10.1109/TWC.2015.2449295 (DOI)000365046100020 ()
    Note

    Funding Agencies|European Union FP7 Marie Curie Project MESH-WISE [434515]; European Union FP7 Marie Curie Project WiNDOW [318992]; Chinese Scholarship Council; Institute for Infocomm Research (I2R); A*STAR, Singapore, through overseas Ph.D. research internship scheme; Swedish Research Council; European Union FP7 Marie Curie IOF [329313]

    Available from: 2015-12-14 Created: 2015-12-11 Last updated: 2017-12-01
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  • 979.
    Lei, Lei
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Radio Resource Optimization for OFDM-based Broadband Cellular Systems2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The rapid growth of users’ traffic demand in broadband wireless communication systems requires high-speed data transmission and intelligent resource allocation approaches. The Third Generation Partnership Project-Long Term Evolution (3GPPLTE) has standardized multiple access (MA) schemes for 4G cellular networks. Two advanced schemes, orthogonal frequency division multiple access (OFDMA) and single carrier frequency division multiple access (SC-FDMA), have been adopted for downlink and uplink, respectively.

    Optimization-based approaches play a crucial role in network operation and resource management. The optimization problems considered in this thesis are addressed in four research papers. For the single cell scenario, the optimization problems of joint power and channel allocation in OFDMA and consecutive-channel assignment in SCFDMA are investigated in Papers I, II, and III. For the OFDM-based multi-cell scenario, an energy minimization problem is addressed in Paper IV.

    In the thesis, theoretical analysis, algorithm development, and numerical studies are carried out. Mathematical optimization is applied as the main approach to facilitate the problem solving. In Paper I, we evaluate the performance gain and loss for various  allocation policies in the OFDMA system. In Papers II and III, resource allocation algorithms are proposed to obtain competitive and high-quality solutions for consecutive-channel allocation problems in the SC-FDMA system. The theoretical analysis and the proposed algorithm in Paper IV provide optimal solution for energy minimization.

    List of papers
    1. Performance analysis of chunk-based resource allocation in wireless OFDMA systems
    Open this publication in new window or tab >>Performance analysis of chunk-based resource allocation in wireless OFDMA systems
    2012 (English)In: Proceedings from the 17th IEEE International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD), September 17-19, 2012, Barcelona, Spain, IEEE , 2012, p. 90-94Conference paper, Published paper (Refereed)
    Abstract [en]

    In typical resource allocation for Orthogonal Frequency Division Multiple Access (OFDMA), assigning subcarriers to the more favorable users provides beneficial diversity and increased system performance. It is however relevant to consider OFDMA resource allocation with a subcarrier adjacency restriction, grouping a number of adjacent subcarriers into a chunk, both for physical design simplicity and for complexity mitigation. In this paper, we classify different resource allocation policies for chunk-based allocation. We investigate how to optimally allocate resources by using discrete rates and discrete power levels. This is enabled by developing binary integer optimization models to obtain the optimal solution for this comparative study. We present numerical results to evaluate the performance of different resource allocation policies under different parameters and scenarios.

    Place, publisher, year, edition, pages
    IEEE, 2012
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-105496 (URN)10.1109/CAMAD.2012.6335386 (DOI)978-1-4673-3123-4 (ISBN)978-1-4673-3124-1 (ISBN)
    Conference
    17th IEEE International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD), September 17-19, 2012, Barcelona, Spain
    Available from: 2014-03-25 Created: 2014-03-25 Last updated: 2014-03-25Bibliographically approved
    2. Improved Resource Allocation Algorithm Based on Partial Solution Estimation for SC-FDMA Systems
    Open this publication in new window or tab >>Improved Resource Allocation Algorithm Based on Partial Solution Estimation for SC-FDMA Systems
    2013 (English)In: Proceedings from the 78th IEEE Vehicular Technology Conference (VTC Fall), September 2-5, Las Vegas, USA, IEEE , 2013, p. 1-5Conference paper, Published paper (Refereed)
    Abstract [en]

    Single carrier frequency division multiple access (SC-FDMA) has been adopted as the standard multiple access scheme for 3GPP LTE uplink. In comparison to orthogonal frequency division multiple access (OFDMA), the subcarriers assigned to each user are required to be consecutive in SC-FDMA localized scheme, which imposes more difficulties on resource allocation problem. Subject to this constraint, various optimization objectives, such as utility maximization and power minimization, have been studied for SC-FDMA resource allocation. In this paper, we focus on developing a general algorithm framework with near-optimal performance and polynomial-time complexity to maximize the total utility for SC-FDMA systems. The proposed algorithm is based on low-complexity estimation for the partial solution space. Compared with existing algorithms, simulation results show that our algorithm improves the system utility significantly and has less deviation to global optimum. In addition, the proposed algorithm framework allows a flexible trade-off between computational effort and solution performance by varying the complexity of estimation approaches.

    Place, publisher, year, edition, pages
    IEEE, 2013
    Series
    Vehicular Technology Conference, ISSN 1090-3038 ; 78
    Keywords
    SC-FDMA; Algorithm; Resource Allocation; Binary Integer Programming; Partial Solution; Estimation
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-105049 (URN)10.1109/VTCFall.2013.6692229 (DOI)000330585400207 ()978-1-4673-6187-3 (Article) (ISBN)978-1-4673-6185-9 (ISBN)
    Conference
    78th IEEE Vehicular Technology Conference (VTC Fall), September 2-5, Las Vegas, USA
    Available from: 2014-03-06 Created: 2014-03-06 Last updated: 2015-03-18Bibliographically approved
    3. A Unified Graph Labeling Algorithm for Consecutive-Block Channel Allocation in SC-FDMA
    Open this publication in new window or tab >>A Unified Graph Labeling Algorithm for Consecutive-Block Channel Allocation in SC-FDMA
    2013 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 12, no 11, p. 5767-5779Article in journal (Refereed) Published
    Abstract [en]

    Optimal channel allocation is a key performance engineering aspect in single-carrier frequency-division multiple access (SC-FDMA). In SC-FDMA with localized channel assignment, the channels of each user must form a consecutive block. Subject to this constraint, various performance objectives, such as maximum utility, minimum power, and minimum number of channels, have been studied. We present a unified graph labeling algorithm for these problems, based on the structural insight that SC-FDMA channel allocation can be modeled as finding an optimal path in an acyclic graph. By this insight, our algorithm applies the concept of labeling and label domination that represent non-trivial extensions of finding a shortest or longest path. The key parameter in trading performance versus computation is the number of labels kept per node. Increasing the number ultimately enables global optimality. The algorithms approach is further justified by its global optimality guarantee with strong polynomial-time complexity for two specific scenarios, where the input is user-invariant and channel-invariant, respectively. For the general case, we provide numerical results demonstrating the algorithms ability of attaining near-optimal solutions.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2013
    Keywords
    Algorithm, channel allocation, optimization, single carrier frequency division multiple access
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-102855 (URN)10.1109/TWC.2013.092313.130092 (DOI)000328058400034 ()
    Note

    R)||A*STAR, Singapore||Linkoping-Lund Excellence Center in Information Technology (ELLIIT), Sweden||

    Available from: 2014-01-07 Created: 2014-01-02 Last updated: 2017-12-06
    4. Optimal Energy Minimization inLoad-Coupled Wireless Networks: Computation and Properties
    Open this publication in new window or tab >>Optimal Energy Minimization inLoad-Coupled Wireless Networks: Computation and Properties
    2014 (English)Conference paper, Published paper (Other academic)
    Abstract [en]

    We consider the problem of sum transmission energy minimization in a cellular network where base stations interfere with one another. Each base station has to serve a target amount of data to its set of users, by varying its power and load, where the latter refers to the average level of channel resource usage in the cell. We employ the signal-tointerference-and-noise-ratio (SINR) load-coupled model that takes into account the load of each cell. We show analytically that operating at full load is optimal to minimize sum energy. Moreover, we provide an iterative power adjustment algorithm for all base stations to achieve full load. Numerical results are obtained that corroborate the analysis and illustrate the advantage of our solution compared to the conventional solution where uniform power is used for all base stations.

    Keywords
    Energy minimization, load balancing, load coupling, Perron-Frobenius theorem.
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-105497 (URN)
    Conference
    The 2014 IEEE International Conference on Communications (ICC), June 10-14, Sydney, Australia
    Available from: 2014-03-25 Created: 2014-03-25 Last updated: 2014-03-25Bibliographically approved
    Download (pdf)
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  • 980.
    Lei, Lei
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Angelakis, Vangelis
    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.
    Performance analysis of chunk-based resource allocation in wireless OFDMA systems2012In: Proceedings from the 17th IEEE International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD), September 17-19, 2012, Barcelona, Spain, IEEE , 2012, p. 90-94Conference paper (Refereed)
    Abstract [en]

    In typical resource allocation for Orthogonal Frequency Division Multiple Access (OFDMA), assigning subcarriers to the more favorable users provides beneficial diversity and increased system performance. It is however relevant to consider OFDMA resource allocation with a subcarrier adjacency restriction, grouping a number of adjacent subcarriers into a chunk, both for physical design simplicity and for complexity mitigation. In this paper, we classify different resource allocation policies for chunk-based allocation. We investigate how to optimally allocate resources by using discrete rates and discrete power levels. This is enabled by developing binary integer optimization models to obtain the optimal solution for this comparative study. We present numerical results to evaluate the performance of different resource allocation policies under different parameters and scenarios.

  • 981.
    Lei, Lei
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Fowler, Scott
    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.
    Improved Resource Allocation Algorithm Based on Partial Solution Estimation for SC-FDMA Systems2013In: Proceedings from the 78th IEEE Vehicular Technology Conference (VTC Fall), September 2-5, Las Vegas, USA, IEEE , 2013, p. 1-5Conference paper (Refereed)
    Abstract [en]

    Single carrier frequency division multiple access (SC-FDMA) has been adopted as the standard multiple access scheme for 3GPP LTE uplink. In comparison to orthogonal frequency division multiple access (OFDMA), the subcarriers assigned to each user are required to be consecutive in SC-FDMA localized scheme, which imposes more difficulties on resource allocation problem. Subject to this constraint, various optimization objectives, such as utility maximization and power minimization, have been studied for SC-FDMA resource allocation. In this paper, we focus on developing a general algorithm framework with near-optimal performance and polynomial-time complexity to maximize the total utility for SC-FDMA systems. The proposed algorithm is based on low-complexity estimation for the partial solution space. Compared with existing algorithms, simulation results show that our algorithm improves the system utility significantly and has less deviation to global optimum. In addition, the proposed algorithm framework allows a flexible trade-off between computational effort and solution performance by varying the complexity of estimation approaches.

  • 982.
    Lei, Lei
    et al.
    University of Luxembourg, Luxembourg.
    Vu, Thang X
    University of Luxembourg, Luxembourg.
    You, Lei
    Uppsala University, Sweden.
    Fowler, Scott
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Yuan, Di
    Uppsala University, Sweden.
    Efficient Minimum-Energy Scheduling with Machine-Learning Based Predictions for Multiuser MISO Systems2018In: 2018 IEEE International Conference on Communications (ICC), IEEE, 2018, p. 1-6Conference paper (Refereed)
    Abstract [en]

    We address an energy-efficient scheduling problem for practical multiple-input single-output (MISO) systems with stringent execution-time requirements. Optimal user-group scheduling is adopted to enable timely and energy-efficient data transmission, such that all the users' demand can be delivered within a limited time. The high computational complexity in optimal iterative algorithms limits their applications in real-time network operations. In this paper, we rethink the conventional optimization algorithms, and embed machine-learning based predictions in the optimization process, aiming at improving the computational efficiency and meeting the stringent execution-time limits in practice, while retaining competitive energy-saving performance for the MISO system. Numerical results demonstrate that the proposed method, i.e., optimization with machine- learning predictions (OMLP), is able to provide a time-efficient and high-quality solution for the considered scheduling problem. Towards online scheduling in real-time communications, OMLP is of high computational efficiency compared to conventional optimal iterative algorithms. OMLP guarantees the optimality as long as the machine- learning based predictions are accurate.

  • 983.
    Lei, 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.
    Keong Ho, Chin
    ASTAR, Singapore .
    Sun, Sumei
    ASTAR, Singapore .
    A Unified Graph Labeling Algorithm for Consecutive-Block Channel Allocation in SC-FDMA2013In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 12, no 11, p. 5767-5779Article in journal (Refereed)
    Abstract [en]

    Optimal channel allocation is a key performance engineering aspect in single-carrier frequency-division multiple access (SC-FDMA). In SC-FDMA with localized channel assignment, the channels of each user must form a consecutive block. Subject to this constraint, various performance objectives, such as maximum utility, minimum power, and minimum number of channels, have been studied. We present a unified graph labeling algorithm for these problems, based on the structural insight that SC-FDMA channel allocation can be modeled as finding an optimal path in an acyclic graph. By this insight, our algorithm applies the concept of labeling and label domination that represent non-trivial extensions of finding a shortest or longest path. The key parameter in trading performance versus computation is the number of labels kept per node. Increasing the number ultimately enables global optimality. The algorithms approach is further justified by its global optimality guarantee with strong polynomial-time complexity for two specific scenarios, where the input is user-invariant and channel-invariant, respectively. For the general case, we provide numerical results demonstrating the algorithms ability of attaining near-optimal solutions.

    Download full text (pdf)
    fulltext
  • 984.
    Lei, Lei
    et al.
    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. University of Maryland, MD 20742 USA.
    Keong Ho, Chin
    ASTAR, Singapore.
    Sun, Sumei
    ASTAR, Singapore.
    Joint Optimization of Power and Channel Allocation with Non-orthogonal Multiple Access for 5G Cellular Systems2015In: 2015 IEEE GLOBAL COMMUNICATIONS CONFERENCE (GLOBECOM), IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    Non-orthogonal multiple access (NOMA) with successive interference cancellation (SIC), is considered as a candidate multi-user access scheme for 5G cellular systems. In this paper, we provide theoretical insights and solution algorithm for optimizing multi-user power and channel allocation in NOMA systems. We mathematically formulate the NOMA resource allocation problem and prove its NP-hardness. For solving the problem, we propose an algorithm combining Lagrangian duality and dynamic programming to deliver a competitive suboptimal solution. Numerical results demonstrate that the proposed algorithmic solution can significantly improve the system performance over orthogonal frequency division multiple access (OFDMA) as well as over other existing NOMA resource allocation scheme.

  • 985.
    Lei, Lei
    et al.
    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. University of Maryland, MD 20740 USA.
    Keong Ho, Chin
    ASTAR, Singapore.
    Sun, Sumei
    ASTAR, Singapore.
    Optimal Cell Clustering and Activation for Energy Saving in Load-Coupled Wireless Networks2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 11, p. 6150-6163Article in journal (Refereed)
    Abstract [en]

    Optimizing activation and deactivation of base station transmissions provides an instrument for improving energy efficiency in cellular networks. In this paper, we study the problem of performing cell clustering and setting the activation time of each cluster, with the objective of minimizing the sum energy, subject to a time constraint of serving the users traffic demand. Our optimization framework accounts for inter-cell interference, and, thus, the users achievable rates depend on cluster formation. We provide mathematical formulations and analysis, and prove the problems NP hardness. For problem solution, we first apply an optimization method that successively augments the set of variables under consideration, with the capability of approaching global optimum. Then, we derive a second solution algorithm to deal with the trade-off between optimality and the combinatorial nature of cluster formation. Numerical results demonstrate that our solutions achieve more than 40% energy saving over existing schemes, and that the solutions we obtain are within a few percent of deviation from global optimum.

    Download full text (pdf)
    fulltext
  • 986.
    Lei, Lei
    et al.
    Linköping University, Department of Science and Technology. 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.
    Keong Ho, Chin
    Agency Science Technology and Research, Singapore.
    Sun, Sumei
    Agency Science Technology and Research, Singapore.
    Power and Channel Allocation for Non-Orthogonal Multiple Access in 5G Systems: Tractability and Computation2016In: IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, ISSN 1536-1276, Vol. 15, no 12, p. 8580-8594Article in journal (Refereed)
    Abstract [en]

    A promising multi-user access scheme, nonorthogonal multiple access (NOMA) with successive interference cancellation (SIC), is currently under consideration for 5G systems. NOMA allows more than one user to simultaneously access the same frequency-time resource and separates multi-user signals by SIC. These render resource optimization in NOMA different from orthogonal multiple access. We provide theoretical insights and algorithmic solutions to jointly optimize power and channel allocation in NOMA. We mathematically formulate NOMA resource allocation problems, and characterize and analyze the problems tractability under a range of constraints and utility functions. For tractable cases, we provide polynomial-time solutions for global optimality. For intractable cases, we prove the NP-hardness and propose an algorithmic framework combining Lagrangian duality and dynamic programming to deliver nearoptimal solutions. To gauge the performance of the solutions, we also provide optimality bounds on the global optimum. Numerical results demonstrate that the proposed algorithmic solution can significantly improve the system performance in both throughput and fairness over orthogonal multiple access as well as over a previous NOMA resource allocation scheme.

    Download full text (pdf)
    fulltext
  • 987.
    Lei, Lei
    et al.
    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.
    Keong Ho, Chin
    ASTAR, Singapore.
    Sun, Sumei
    ASTAR, Singapore.
    Resource Scheduling to Jointly Minimize Receiving and Transmitting Energy in OFDMA Systems2014In: 2014 11TH INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATIONS SYSTEMS (ISWCS), IEEE , 2014, p. 187-191Conference paper (Refereed)
    Abstract [en]

    Resource scheduling in orthogonal frequency division multiple access (OFDMA) for energy saving has attracted extensive attention. Most current research considers the reduction of energy at the transmitter or the receiver separately. In this paper, we focus on minimizing the energy consumption in both sides concurrently by formulating the problem of joint receiving and transmitting energy-efficient scheduling (RTEES) in OFDMA downlink. We show that this problem can be cast as a binary integer programme. We solve the RTEES problem by a computationally efficient algorithm. We proposed a specialized solution approach, named time-slot-oriented column generation (TSOCG) algorithm, for approaching and bounding the global optimality. Numerical studies show that the proposed algorithm solution is competitive and time-efficient to provide a close-to-optimum solution and a tight bound.

  • 988.
    Lei, Lei
    et al.
    Linköping University, Department of Science and Technology. 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.
    Värbrand, Peter
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    On Power Minimization for Non-orthogonal Multiple Access (NOMA)2016In: IEEE COMMUNICATIONS LETTERS, ISSN 1089-7798, Vol. 20, no 12, p. 2458-2461Article in journal (Refereed)
    Abstract [en]

    We formulate a power optimization problem for non-orthogonal multiple access systems mathematically, and prove its NP-hardness. For tackling the problem, we first identify a convex problem by relaxation. Based on this convexity, we then propose an efficient "relax-then-adjust" algorithm and provide results of performance evaluation.

    Download full text (pdf)
    fulltext
  • 989.
    Lei, M.
    et al.
    School of Computer Science, Shaanxi Normal University, Xi’an, Shaanxi, 710119, China..
    Yu, B.
    School of Computer Science and Technology, Xidian University, Xi’an, Shaanxi, 710071, China..
    Fowler, Scott
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Zhang, X.
    School of Computer Science, Xi’an Jiaotong University, Xi’an, Shaanxi, 710049, China..
    Lu, C.
    College of Electrical Engineering, Nantong University, Nantong, Jiangsu, 226019, China..
    Throughput Maximization in Backbone-Assisted Wireless Powered Communication Networks With Successive Interference Cancellation2021In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, IEEE Communications Letters, Vol. 25, no 8, p. 2688-2692Article in journal (Refereed)
    Abstract [en]

    In this mymargin letter, we investigate a backbone-assisted wireless powered communication network (WPCN) under the protocol of "harvest-then-transmit" protocol, where user nodes (UNs) harvest energy from the sinks in the downlink (DL), then they use the energy to transmit signals to the sinks by a non-orthogonal multiple access in the uplink (UL). We consider joint successive interference cancellation and backbone-assisted sink cooperation to reduce the impact of co-channel interference on the throughput performance. We maximize the system throughput by jointly optimizing user scheduling and the time allocation for DL energy harvesting and UL transmission. For solving the maximum throughput problem efficiently, we propose a column generation method based on a greedy algorithm. Numerical results show that our proposed energy and information transfer design is superior to other reference methods in WPCNs.

  • 990.
    Lei, Ming
    et al.
    School of Computer Science, Shaanxi Normal University, Xi'an, China.
    Fowler, Scott
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Wang, Juzhen
    Electronic Information School, Wuhan University, Wuhan, China.
    Zhang, Xingjun
    Xi'an Jiaotong University, Xi'an, China.
    Yu, Bocheng
    Xi'an Jiaotong University, Xi'an, China.
    Yu, Bin
    School of Computer Science and Technology, Xidian University, Xi'an, China.
    Double deep Q-learning network-based path planning in UAV-assisted wireless powered NOMA communication networks2021In: 2021 IEEE 94TH VEHICULAR TECHNOLOGY CONFERENCE (VTC2021-FALL), Institute of Electrical and Electronics Engineers (IEEE), 2021, p. 1-5Conference paper (Refereed)
    Abstract [en]

    This paper studies an unmanned aerial vehicle (UAV)-enabled wireless power communication networks (WPCN-s), where the UAV provides energy for mobile user nodes (M-UNs) and receives information from M-UNs. The movement of M-UN complies with a Gauss-Markov random model. To ensure acceptable quality-of-service (QoS), we consider dynamically planning the flight path of the UAV according to the movements of M-UNs. Since the flight time of UAV is restricted by limited energy, nonorthogonal multiple access (NOMA) is adopted to access a large number of M-UNs for simultaneous information transmission. Based on the above considerations, we aim to maximize the throughput via path planning of the UAV, subject to the QoS requirements of M-UNs and the UAV's energy constraint. To handle the challenges brought by dynamically changing channels to solving the problem, we propose a QoS-based double deep Q-learning network (DDQN). Numerical simulation results show that, compared with the conventional algorithms, the proposed framework achieves higher throughput.

  • 991.
    Lei, Ming
    et al.
    Shaanxi Normal Univ, Peoples R China.
    Yu, Bin
    Xidian Univ, Peoples R China.
    Zhang, Xingjun
    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.
    Yu, Bocheng
    Xi An Jiao Tong Univ, Peoples R China.
    Wang, Peng
    Shaanxi Normal Univ, Peoples R China.
    Joint power control and user scheduling for backbone-assisted industrial wireless networks with successive interference cancellation2022In: Telecommunications Systems, ISSN 1018-4864, E-ISSN 1572-9451, Vol. 81, no 1, p. 41-52Article in journal (Refereed)
    Abstract [en]

    In a backbone-assisted industrial wireless network (BAIWN), the technology of successive interference cancellation (SIC) based non-orthogonal multiple access (NOMA) provides potential solutions for improving the delay performance. Previous work emphasizes minimizing the transmission delay by user scheduling without considering power control. However, power control is beneficial for SIC-based NOMA to exploit the power domain and manage co-channel interference to simultaneously serve multiple user nodes with the high spectral and time resource utilization characteristics. In this paper, we consider joint power control and user scheduling to study the scheduling time minimization problem (STMP) with given traffic demands in BAIWNs. Specifically, STMP is formulated as an integer programming problem, which is NP-hard. To tackle the NP-hard problem, we propose a conflict graph-based greedy algorithm, to obtain a sub-optimal solution with low complexity. As a good feature, the decisions of power control and user scheduling can be made by the proposed algorithm only according to the channel state information and traffic demands. The experimental results show that compared with the other methods, the proposed method effectively improves the delay performance regardless of the channel states or the network scales.

  • 992.
    Lei, Ming
    et al.
    Shaanxi Normal Univ, Peoples R China.
    Zhang, Xingjun
    Xi An Jiao Tong Univ, Peoples R China.
    Yu, Bocheng
    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.
    Yu, Bin
    Xidian Univ, Peoples R China.
    Throughput maximization for UAV-assisted wireless powered D2D communication networks with a hybrid time division duplex/frequency division duplex scheme2021In: Wireless networks, ISSN 1022-0038, E-ISSN 1572-8196, Vol. 25, p. 2147-2157Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate a low-altitude unmanned aerial vehicle (UAV)-assisted wireless power- ed device-to-device (D2D) network with the "harvest-transmit-store" model, where a UAV broadcasts energy to all D2D transmitters and the transmitters then store or use the energy for transmission information. In the proposed model, the UAV does not transmit energy in the transmission information time, resulting in a limited charging time. In addition, the interference may be caused by communicating information of an arbitrary number of D2D pairs simultaneously. In this paper, we propose a hybrid time division duplex/frequency division duplex communication scheme, which performs the power transfer and information transmission simultaneously in the transmission information time. The scheme cancels the cochannel interference by using the time division duplex scheme and guarantees the charging time by using the frequency division duplex. We consider optimizing the throughput based on the scheme via joint power control, spectrum allocation, and scheduling time. We propose a two-step algorithm to solve the formulated nonconvex problem. The simulation results show that the proposed algorithm improves the average throughput compared to the other schemes.

  • 993.
    Lei, Ming
    et al.
    Xi An Jiao Tong University, Peoples R China.
    Zhang, Xingjun
    Xi An Jiao Tong University, Peoples R China.
    Zhang, Tong
    Xi An Jiao Tong University, Peoples R China.
    Lei, Lei
    Linköping University, Department of Science and Technology. Linköping University, Faculty of Science & Engineering.
    He, Qing
    Linköping University, Department of Science and Technology. 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.
    Successive Interference Cancellation for Throughput Maximization in Wireless Powered Communication Networks2016In: 2016 IEEE 84TH VEHICULAR TECHNOLOGY CONFERENCE (VTC FALL), IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    In wireless powered communication networks (WPCNs), each user node, e.g., wireless powered sensor, is capable of either harvesting energy from a power station or transmitting data to a sink node. In the previous works, time division multiple access (TDMA) is typically used for transmission scheduling in WPCNs, that is, only one node can transmit data in one time slot. The spectrum efficiency is therefore limited by this orthogonality in time-domain scheduling. In this paper, to maximize the throughput in WPCNs, we present a new scheduling approach for energy harvesting and data transmission. Unlike TDMA, we consider that multiple nodes can simultaneously transmit their data in the same time slot, and the signals are separated at the sink node by performing successive interference cancellation (SIC). We formulate the throughput maximization problem as a linear programming problem. For solving the large scale instances, we design an algorithmic framework based on column generation. Numerical results demonstrate that compared to the TDMA based scheduling approach, substantial throughput improvement is achieved by the proposed algorithm.

  • 994.
    Leinonen, Markus
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering. Univ Oulu, Finland.
    Codreanu, Marian
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering. Univ Oulu, Finland.
    Low-Complexity Vector Quantized Compressed Sensing via Deep Neural Networks2020In: IEEE Open Journal of the Communications Society, E-ISSN 2644-125X, Vol. 1, p. 1278-1294Article in journal (Refereed)
    Abstract [en]

    Sparse signals, encountered in many wireless and signal acquisition applications, can be acquired via compressed sensing (CS) to reduce computations and transmissions, crucial for resource-limited devices, e.g., wireless sensors. Since the information signals are often continuous-valued, digital communication of compressive measurements requires quantization. In such a quantized compressed sensing (QCS) context, we address remote acquisition of a sparse source through vector quantized noisy compressive measurements. We propose a deep encoder-decoder architecture, consisting of an encoder deep neural network (DNN), a quantizer, and a decoder DNN, that realizes low-complexity vector quantization aiming at minimizing the mean-square error of the signal reconstruction for a given quantization rate. We devise a supervised learning method using stochastic gradient descent and backpropagation to train the system blocks. Strategies to overcome the vanishing gradient problem are proposed. Simulation results show that the proposed non-iterative DNN-based QCS method achieves higher rate-distortion performance with lower algorithm complexity as compared to standard QCS methods, conducive to delay-sensitive applications with large-scale signals.

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  • 995.
    Leinonen, Markus
    et al.
    Univ Oulu, Finland.
    Codreanu, Marian
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Quantized Compressed Sensing via Deep Neural Networks2020In: 2020 2ND 6G WIRELESS SUMMIT (6G SUMMIT), IEEE , 2020Conference paper (Refereed)
    Abstract [en]

    Compressed sensing (CS) is an efficient technique to acquire sparse signals in many wireless applications to, e.g., reduce the amount of data and save low-power sensors batteries. This paper addresses efficient acquisition of sparse sources through quantized noisy compressive measurements where the encoder and decoder are realized by deep neural networks (DNNs). We devise a DNN based quantized compressed sensing (QCS) method aiming at minimizing the mean-square error of the signal reconstruction. Once trained offline, the proposed method enjoys extremely fast and low complexity decoding in the online communication phase. Simulation results demonstrate the superior rate-distortion performance of the proposed method compared to a polynomial-complexity QCS reconstruction scheme.

  • 996.
    Leinonen, Markus
    et al.
    Univ Oulu, Finland.
    Codreanu, Marian
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Giannakis, Georgios
    Univ Minnesota, USA.
    Compressed Sensing with Applications in Wireless Networks2019In: FOUNDATIONS AND TRENDS IN SIGNAL PROCESSING, ISSN 1932-8346, Vol. 13, no 1-2Article in journal (Refereed)
    Abstract [en]

    Sparsity is an attribute present in a myriad of natural signals and systems, occurring either inherently or after a suitable projection. Such signals with lots of zeros possess minimal degrees of freedom and are thus attractive from an implementation perspective in wireless networks. While sparsity has appeared for decades in various mathematical fields, the emergence of compressed sensing (CS) - the joint sampling and compression paradigm - in 2006 gave rise to plethora of novel communication designs that can efficiently exploit sparsity. In this monograph, we review several CS frameworks where sparsity is exploited to improve the quality of signal reconstruction/detection while reducing the use of radio and energy resources by decreasing, e.g., the sampling rate, transmission rate, and number of computations. The first part focuses on several advanced CS signal reconstruction techniques along with wireless applications. The second part deals with efficient data gathering and lossy compression techniques in wireless sensor networks. Finally, the third part addresses CS-driven designs for spectrum sensing and multi-user detection for cognitive and wireless communications.

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  • 997.
    Leinonen, Markus
    et al.
    Univ Oulu, Finland.
    Codreanu, Marian
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Juntti, Markku
    Univ Oulu, Finland.
    Practical Compression Methods for Quantized Compressed Sensing2019In: IEEE CONFERENCE ON COMPUTER COMMUNICATIONS WORKSHOPS (IEEE INFOCOM 2019 WKSHPS), IEEE , 2019, p. 756-761Conference paper (Refereed)
    Abstract [en]

    In order to save energy of low-power sensors in Internet of Things applications, minimizing the number of bits to compress and communicate real-valued sources with a pre-defined distortion becomes crucial. In such a lossy source coding context, we study rate-distortion (RD) performance of various single-sensor quantized compressed sensing (QCS) schemes for compressing sparse signals via quantized/encoded noisy linear measurements. The paper combines and refines the recent advances of QCS algorithm designs and theoretical analysis. In particular, several practical symbol-by-symbol quantizer based QCS methods of different complexities relying on 1) compress-and-estimate, 2) estimate-and-compress, and 3) support-estimation-and-compress strategies are proposed. Simulation results demonstrate the RD performances of different schemes and compare them to the information-theoretic limits.

  • 998.
    Leinonen, Markus
    et al.
    Univ Oulu, Finland.
    Codreanu, Marian
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Juntti, Markku
    Univ Oulu, Finland.
    Signal Reconstruction Performance under Quantized Noisy Compressed Sensing2019In: 2019 DATA COMPRESSION CONFERENCE (DCC), IEEE , 2019, p. 586-586Conference paper (Refereed)
    Abstract [en]

    We study rate-distortion (RD) performance of various single-sensor compressed sensing (CS) schemes for acquiring sparse signals via quantized/encoded noisy linear measurements, motivated by low-power sensor applications. For such a quantized CS (QCS) context, the paper combines and refines our recent advances in algorithm designs and theoretical analysis. Practical symbol-by-symbol quantizer based QCS methods of different compression strategies are proposed. The compression limit of QCS - the remote RDF - is assessed through an analytical lower bound and a numerical approximation method. Simulation results compare the RD performances of different schemes.

  • 999.
    Lekander, Kalle
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Sandberg, Johan
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Process improvements using lean - A case study at the Port of Norrköping2021Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    En fallstudie som med hjälp av lean identifierat slöseri och gett för slag på processförbättringar hos Norrköpings Hamn

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  • 1000.
    Leknes, Hakon
    et al.
    Norwegian University of Science and Technology, Norway.
    Skorge Aartun, Eirik
    Norwegian University of Science and Technology, Norway.
    Andersson, Henrik
    Norwegian University of Science and Technology, Norway.
    Christiansen, Marielle
    Norwegian University of Science and Technology, Norway.
    Andersson Granberg, Tobias
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Strategic ambulance location for heterogeneous regions2017In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 260, no 1, p. 122-133Article in journal (Refereed)
    Abstract [en]

    Providing Emergency Medical Services (EMS) is a key function of society. To achieve high quality EMS, planning is of vital importance. An important strategic and tactical problem is the location of ambulance stations and the allocation of ambulances to these stations. This paper presents a new mixed integer model for this problem especially suitable for regions with heterogeneous demand and multiple performance measures. The model decides on the location/allocation of stations/ambulances, calculates the service and arrival rates for each station and the probabilities that a call is served by a particular station. The model is tested on a combined urban and rural area in Norway with multiple performance measures. Compared with the current solution for the area, the best solution from the model has a higher expected performance on each of the performance measures used. (C) 2016 Elsevier B.V. All rights reserved.

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