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  • 301.
    Bildtmark, Kim
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Jädersand, Robin
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Security Awareness for Mobility: En studie om företagsmobilitet och de säkerhetsrisker som följer2015Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
  • 302.
    Bilien, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Key Agreement for Secure Voice over IP2003Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This thesis reviews the usual properties and requirements for key agreement protocols. It then focuses on MIKEY, a work-in-progress protocol designed to conduct key agreements for secure multimedia exchanges. The protocol was implemented and incorporated in a SIP user agent - minisip. This implementation was used to measure the additional delay required for key exchange during call establishment. Finally, some schemes are proposed regarding the use of MIKEY in advanced VoIP scenarios, such as conferences and terminal mobility.

  • 303.
    Billman, Johan
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system.
    Hellström, Victor
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system.
    Abusing Keep-Alive Forwarding to flood a VANET: When safety messages become a safety risk2016Independent thesis Basic level (university diploma), 10,5 poäng / 16 hpOppgave
    Abstract [en]

    Cooperative Intelligent Transport Systems (C-ITS) enable vehicles to cooperate with each other and can be used to increase traffic safety and traffic flow. There are several standard initiatives for C-ITS, such as WAVE in the US, ARIB in Japan and ETSI ITS G5 in Europe.

    Decentralized Environment Notification Message (DENM) is a kind of message within ETSI TC ITS. DENMs are event-triggered, multi-hop notification messages that can be for- warded using Keep-Alive Forwarding (KAF).

    In this thesis, KAF is used to flood the network with DENMs sent from a single attack- ing vehicle. Using the simulation tools SUMO, OmNet++ and Veins, a highway scenario is studied. In the scenario, a vehicle sends out a DENM into a network that is being attacked by one other vehicle. Due to how KAF allows messages to be forwarded the other vehicles help flood the network. The results clearly indicate that KAF can be abused to create a Denial of Service (DoS) attack. After just a few seconds, the attack has introduced large de- lays and very high packet loss. The delay to receive a DENM is increased by several orders of magnitude and the packet loss reach unacceptable levels. By getting DENMs several seconds after they are needed, or by not getting them at all, could lead to traffic hazards. 

  • 304.
    Bilstrup, Urban
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Centrum för forskning om inbyggda system (CERES).
    Parsapoor, Mahboobeh
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Centrum för forskning om inbyggda system (CERES).
    A Framework and Architecture for a Cognitive Manager Based on a Computational Model of Human Emotional Learning2013Inngår i: Proceedings of SDR-WInnComm-Europe 2013: Wireless Innovation European Conference on Wireless Communications Technologies and Software Defined Radio / [ed] Lee Pucker, Kuan Collins & Stephanie Hamill, 2013, s. 64-72Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we propose an architecture for a cognitive engine that is based on the emotional learning cycle instead of the traditional cognitive cycle. The cognitive cycle that traditionally has been used as reference for cognitive radio is on the basis of the Unified Theories of Cognition (UTC) to model rational decision making in humans. UTC represents a rational goal-oriented decision-action made by an intelligent agent. However, the emotional cycle represents an emotional reaction-oriented cycle instead. These two models differ in function and structure of learning, decision making and optimization. In this work the structure of these two learning cycles are compared and a computational model for artificial emotional learning based engine is suggested.

  • 305.
    Bilstrup, Urban
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE).
    Sjöberg, Katrin
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE).
    Svensson, Bertil
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE).
    Wiberg, Per-Arne
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE).
    Capacity limitations in wireless sensor networks2003Inngår i: ETFA 2003: 2003 IEEE Conference on Emerging Technologies and Factory Automation, September 16-19, 2003, Lisbon, Portugal : proceedings, Piscataway, N.J.: IEEE , 2003, s. 529-536, artikkel-id 1247752Konferansepaper (Fagfellevurdert)
    Abstract [en]

    It is expected that wireless sensor network will be used in home automation and industrial manufacturing in the future. The main driving forces for wireless sensor networks are fault tolerance, energy gain and spatial capacity gain. Unfortunately, an often forgotten issue is the capacity limits that the network topology of a wireless sensor network represents. In this paper we identify gains, losses and limitations in a wireless sensor network, using a simplified theoretical network model. Especially, we want to point out the stringent capacity limitations that this simplified network model provide. Where a comparison between the locality of the performed information exchange and the average capacity available for each node is the main contribution.

  • 306.
    Bilstrup, Urban
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE).
    Sjöberg, Katrin
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE).
    Wiberg, Per-Arne
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE).
    A comparison of spatial energy consumption distribution for single- and mulihop wireless network architectures2004Konferansepaper (Fagfellevurdert)
  • 307.
    Bilstrup, Urban
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE).
    Svensson, Bertil
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE).
    Wiberg, Per-Arne
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE).
    Knowledge Horizon - Dynamic limitations in a wireless ad hoc network2003Inngår i: SNCNW 2003 Swedish National Computer Networking Workshop 2003 on-line proceedings, 2003, s. 1-3Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we investigate the impact of node mobility in a wireless ad hoc network (WAHN). Especially we investigate the possibility to provide guaranteed services in a WAHN, i.e., the network topology predictability. We combine link expiration time (LET) estimation with information propagation speed (IPS) in a time-space diagram and as result an operation area is revealed. The result gives that a WAHN, where the nodes are mobile, has a knowledge horizon (KH), the distance of which is dependent on the mobility of the nodes. Beyond the KH, knowledge about the network state is impossible to achieve. Thus, we can not predict long distance network topology state when the node mobility is high.

  • 308.
    Bilstrup, Urban
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Wiberg, Per-Arne
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Routing protocol for wireless real-time multihop networks1999Konferansepaper (Fagfellevurdert)
  • 309.
    Bin, Yang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Using Six Sigma Methodology to improve the performance of the Shipment Test2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Competition and lead-time pressure motivates us to find new and better ways of continuously improving the output of our work. The emphasis on improvement in both efficiency and quality has become more and more significant in daily activities. The performance of Ericsson’s AXE/APZ products during shipment test phase is one such activity and is the focus of this thesis project. One of the essential principles of shipment testing is to ensure that the test campaigns finish on time. Over the last several decades companies have spent large amounts of time and money on improving test quality and efficiency. Unfortunately, the results have not always been as good as expected. It seems that it is very difficult to improve shipment testing performance using traditional test management methods.

    Motorola introduced Six Sigma in 1986 and achieved 5.4 Sigma level which help them saved 2.2 Billion dollars during the first six years. From Statistic aspect, it means only 3.4 defects per million opportunities. The Six Sigma methodology has been applied as a management philosophy focused on improving efficiency and performance during the shipment test period.

    This thesis gives an introduction to the Six Sigma approach, including the concepts of Six Sigma, its history, development, and methodology. More specifically the author uses the Define, Measure, Analyze, Improve, and Control (DMAIC) approach to evaluate the performance of Ericsson’s AXE/APZ Shipment Testing. This project goal was defined: Compare with the performance of 08AXE shipment test which 87% of test campaigns (2.68 sigma level) were finished on time, 3 sigma level in 09AXE shipment test which means 93%of the test campaigns will be finished on time has to be achieved.  The thesis measured the 08AXE shipment test performance and analyzed the lead time of test campaigns, found the root causes such as poor documents quality from the legacy project, lack of test resources, no system impact analysis. The thesis also provided a set of proposals for improvements and control of the improved process in order to ensure sustainable improved performance results. Finally 93% test campaigns were finished on time in 09AXE and project goal was fulfilled.

  • 310.
    Bjorklund, Svante
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för matematik och naturvetenskap.
    Johansson, Tommy
    Swedish Def Res Agcy FOI, SE-58111 Linkoping, Sweden..
    Petersson, Henrik
    Swedish Def Res Agcy FOI, SE-58111 Linkoping, Sweden..
    Target Classification in Perimeter Protection with a Micro-Doppler Radar2016Inngår i: 2016 17TH INTERNATIONAL RADAR SYMPOSIUM (IRS), 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In security surveillance at the perimeter of critical infrastructure, such as airports and power plants, approaching objects have to be detected and classified. Especially important is to distinguish between humans, animals and vehicles. In this paper, micro-Doppler data (from movement of internal parts of the target) have been collected with a small radar of a low complexity and cost-effective type. From time-velocity diagrams of the data, some physical features have been extracted and used in a support vector machine classifier to distinguish between the classes "human", "animal" and "man-made object". Both the type of radar and the classes are suitable for perimeter protection. The classification result are rather good, 77% correct classification. Particularly interesting is the surprisingly good ability to distinguish between humans and animals. This also indicates that we can choose to have limitations in the radar and still solve the classification task.

  • 311.
    Bjorklund, Svante
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för matematik och naturvetenskap.
    Petersson, Henrik
    Swedish Def Res Agcy FOI, SE-58111 Linkoping, Sweden..
    Hendeby, Gustaf
    Swedish Def Res Agcy FOI, SE-58111 Linkoping, Sweden.;Linkoping Univ, SE-58183 Linkoping, Sweden..
    Features for micro-Doppler based activity classification2015Inngår i: IET radar, sonar & navigation, ISSN 1751-8784, E-ISSN 1751-8792, Vol. 9, nr 9, s. 1181-1187Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Safety and security applications benefit from better situational awareness. Radar micro-Doppler signatures from an observed target carry information about the target's activity, and have potential to improve situational awareness. This article describes, compares, and discusses two methods to classify human activity based on radar micro-Doppler data. The first method extracts physically interpretable features from the time-velocity domain such as the main cycle time and properties of the envelope of the micro-Doppler spectra and use these in the classification. The second method derives its features based on the components with the most energy in the cadence-velocity domain (obtained as the Fourier transform of the time-velocity domain). Measurements from a field trial show that the two methods have similar activity classification performance. It is suggested that target base velocity and main limb cadence frequency are indirect features of both methods, and that they do often alone suffice to discriminate between the studied activities. This is corroborated by experiments with a reduced feature set. This opens up for designing new more compact feature sets. Moreover, weaknesses of the methods and the impact of non-radial motion are discussed.

  • 312.
    Bjurefors, Fredrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för datorteknik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Datorteknik.
    Measurements in opportunistic networks2012Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Opportunistic networks are a subset of delay tolerant networks where the contacts are unscheduled. Such networks can be formed ad hoc by wireless devices, such as mobile phones and laptops. In this work we use a data-centric architecture for opportunistic networks to evaluate data dissemination overhead, congestion in nodes' buffer, and the impact of transfer ordering. Dissemination brings an overhead since data is replicated to be spread in the network and overhead leads to congestion, i.e., overloaded buffers.

    We develop and implement an emulation testbed to experimentally evaluate properties of opportunistic networks. We evaluate the repeatability of experiments in the emulated testbed that is based on virtual computers. We show that the timing variations are on the order of milliseconds.

    The testbed was used to investigate overhead in data dissemination, congestion avoidance, and transfer ordering in opportunistic networks. We show that the overhead can be reduced by informing other nodes in the network about what data a node is carrying. Congestion avoidance was evaluated in terms of buffer management, since that is the available tool in an opportunistic network, to handle congestion. It was shown that replication information of data objects in the buffer yields the best results. We show that in a data-centric architecture were each data item is valued differently, transfer ordering is important to achieve delivery of the most valued data.

  • 313.
    Bjurefors, Fredrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för datorteknik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Datorteknik.
    Opportunistic Networking: Congestion, Transfer Ordering and Resilience2014Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Opportunistic networks are constructed by devices carried by people and vehicles. The devices use short range radio to communicate. Since the network is mobile and often sparse in terms of node contacts, nodes store messages in their buffers, carrying them, and forwarding them upon node encounters. This form of communication leads to a set of challenging issues that we investigate: congestion, transfer ordering, and resilience.

    Congestion occurs in opportunistic networks when a node's buffers becomes full. To be able to receive new messages, old messages have to be evicted. We show that buffer eviction strategies based on replication statistics perform better than strategies that evict messages based on the content of the message.

    We show that transfer ordering has a significant impact on the dissemination of messages during time limited contacts. We find that transfer strategies satisfying global requests yield a higher delivery ratio but a longer delay for the most requested data compared to satisfying the neighboring node's requests.

    Finally, we assess the resilience of opportunistic networks by simulating different types of attacks. Instead of enumerating all possible attack combinations, which would lead to exhaustive evaluations, we introduce a method that use heuristics to approximate the extreme outcomes an attack can have. The method yields a lower and upper bound for the evaluated metric over the different realizations of the attack. We show that some types of attacks are harder to predict the outcome of and other attacks may vary in the impact of the attack due to the properties of the attack, the forwarding protocol, and the mobility pattern.

  • 314.
    Bjurefors, Fredrik
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Datorteknik.
    Karaliopoulos, Markourios
    Rohner, Christian
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Datorteknik.
    Smith, Paul
    Theodoropoulos, George
    Gunningberg, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Datorteknik.
    Resilience and Opportunistic Forwarding: Beyond Average Value Analysis2014Inngår i: Computer Communications, ISSN 0140-3664, E-ISSN 1873-703X, Vol. 48, nr SI, s. 111-120Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Opportunistic networks are systems with highly distributed operation, relying on the altruistic cooperation of highly heterogeneous, and not always software and hardware-compatible, user nodes. Moreover, the absence of central coordination and control makes them vulnerable to malicious attacks. In this paper, we study the resilience of popular forwarding protocols to a representative set of challenges to their normal operation. These include jamming locally disturbing message transfer between nodes, hardware/software failures and incompatibility among nodes rendering contact opportunities useless, and free-riding phenomena. We first formulate and promote the metric envelope concept as a tool for assessing the resilience of opportunistic forwarding schemes. Metric envelopes depart from the standard practice of average value analysis and explicitly account for the differentiated challenge impact due to node heterogeneity (device capabilities, mobility) and attackers’ intelligence. We then propose heuristics to generate worst- and best-case challenge realization scenarios and approximate the lower and upper bounds of the metric envelopes. Finally, we demonstrate the methodology in assessing the resilience of three popular forwarding protocols in the presence of the three challenges, and under a comprehensive range of mobility patterns. The metric envelope approach provides better insights into the level of protection path diversity and message replication provide against different challenges, and enables more informed choices in opportunistic forwarding when network resilience becomes important.

  • 315.
    Bjurefors, Fredrik
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Datorteknik.
    Karaliopoulos, Merkourios
    Rohner, Christian
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Datorteknik.
    Smith, Paul
    Theodoropoulos, George
    Gunningberg, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Datorteknik.
    Resilience and Opportunistic Forwarding: Beyond Average Value Analysis2013Inngår i: CHANTS '13 Proceedings of the 8th ACM MobiCom workshop on Challenged networks, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Opportunistic networks are systems with highly distributed operation, relying on the altruistic cooperation of heterogeneous, and not always software- and hardware-compatible user nodes. Moreover, the absence of central control makes them vulnerable to malicious attacks. In this paper, we take a fresh look at the resilience of opportunistic forwarding to these challenges. In particular, we introduce and promote the use of metric envelopes as a resilience assessment tool. Metric envelopes depart from the standard practice of average value analysis and explicitly account for the differentiated impact that a challenge may have on the forwarding performance due to node heterogeneity (device capabilities, mobility) and attackers’ intelligence. The use of metric envelopes is demonstrated in the case of three challenges: jamming, hardware/software failures and incompatibilities, and free-riding phenomena. For each challenge, we first devise heuristics to generate worst- and best-case realization scenarios that can approximate the metric envelopes. Then we derive the envelopes of common performance metrics for three popular forwarding protocols under a comprehensive range of mobility patterns. The metric envelope approach enables more informed choices in opportunistic forwarding whenever network resilience considerations become important. 

  • 316.
    Bjurén, Johan
    Högskolan i Skövde, Institutionen för informationsteknologi.
    USING CASE-BASED REASONING FOR PREDICTING ENERGY USAGE2013Independent thesis Advanced level (degree of Master (Two Years)), 30 poäng / 45 hpOppgave
    Abstract [en]

    In this study, the inability to in a future meet the electricity demand and the urge to change the consumption behavior considered. In a smart grid context there are several possible ways to do this. Means include ways to increase the consumer’s awareness, add energy storages or build smarter homes which can control the appliances. To be able to implement these, indications on how the future consumption will be could be useful. Therefore we look further into how a framework for short-term consumption predictions can be created using electricity consumption data in relation to external factors. To do this a literature study is made to see what kind of methods that are relevant and which qualities is interesting to look at in order to choose a good prediction method. Case Based Reasoning seemed to be able to be suitable method. This method was examined further and built using relational databases. After this the method was tested and evaluated using datasets and evaluation methods CV, MBE and MAPE, which have previously been used in the domain of consumption prediction. The result was compared to the results of the winning methods in the ASHRAE competition. The CBR method was expected to perform better than what it did, and still not as good as the winning methods from the ASHRAE competition. The result showed that the CBR method can be used as a predictor and has potential to make good energy consumption predictions. and there is room for improvement in future studies.

  • 317.
    Björklund, Daniel
    Linköpings universitet, Institutionen för systemteknik, Elektroniksystem. Linköpings universitet, Tekniska högskolan.
    Implementation of a Software-Defined Radio Transceiver on High-Speed Digitizer/Generator SDR142012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This thesis describes the specification, design and implementation of a software-defined radio system on a two-channel 14-bit digitizer/generator. The multi-stage interpolations and decimations which are required to operate two analog-to-digital converters at 800 megasamples per second (MSps) and two digital-to-analog converters at 1600 MSps from a 25 MSps software-side interface, were designed and implemented. Quadrature processing was used throughout the system, and a combination of fine-tunable low-rate mixers and coarse high-rate mixers were implemented to allow frequency translation across the entire first Nyquist band of the converters. Various reconstruction filter designs for the transmitter side were investigated and a cheap implementation was done through the use of programmable base-band filters and polynomial approximation.

  • 318.
    Björklund, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Fordonssystem.
    Karlström, Elin
    Linköpings universitet, Institutionen för systemteknik, Fordonssystem.
    Enabling Testing of Lateral Active Safety Functions in a Multi-rate Hardware in the Loop Environment2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    As the development of vehicles moves towards shorter development time, new ways of verifying the vehicle performance is needed in order to begin the verification process at an earlier stage. A great extent of this development regards active safety, which is a collection name for systems that help both avoid accidents and minimize the effects of a collision, e.g brake assist and steering control systems. Development of these active safety functions requires extensive testing and verification in order to guarantee the performance of the functions in different situations. One way of testing these functions is to include them in a Hardware in the Loop simulation, where the involved hardware from the real vehicle are included in the simulation loop.

    This master thesis investigates the possibility to test lateral active safety functions in a hardware in the loop simulation environment consisting of multiple subsystems working on different frequencies. The subsystems are all dependent of the output from other subsystems, forming an algebraic loop between them. Simulation using multiple hardware and subsystems working on different frequencies introduces latency in the simulation. The effect of the latency is investigated and proposed solutions are presented. In order to enable testing of lateral active safety functions, a steering model which enables the servo motor to steer the vehicle is integrated in the simulation environment and validated.

  • 319.
    Björklund, Svante
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för matematik och naturvetenskap.
    Grahn, Per
    Nelander, Anders
    Pettersson, Mats
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för matematik och naturvetenskap.
    Measurement of Rank and Other Properties of Direct and Scattered Signals2016Inngår i: International Journal of Antennas and Propagation, ISSN 1687-5869, E-ISSN 1687-5877, Vol. 2016, artikkel-id 5483547Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have designed an experiment for low-cost indoor measurements of rank and other properties of direct and scattered signals with radar interference suppression in mind. The signal rank is important also in many other applications, for example, DOA (Direction of Arrival) estimation, estimation of the number of and location of transmitters in electronic warfare, and increasing the capacity in wireless communications. In real radar applications, such measurements can be very expensive, for example, involving airborne radars with array antennas. We have performed the measurements in an anechoic chamber with several transmitters, a receiving array antenna, and a moving reflector. Our experiment takes several aspects into account: transmitted signals with different correlation, decorrelation of the signals during the acquisition interval, covariance matrix estimation, noise eigenvalue spread, calibration, near-field compensation, scattering in a rough surface, and good control of the influencing factors. With our measurements we have observed rank, DOA spectrum, and eigenpatterns of direct and scattered signals. The agreement of our measured properties with theoretic and simulated results in the literature shows that our experiment is realistic and sound. The detailed description of our experiment could serve as help for conducting other well-controlled experiments. © Copyright 2016 Svante Björklund et al.

  • 320.
    Björklund, Ulf
    KTH, Tidigare Institutioner, Teleinformatik.
    Understanding the Performance of the Linux IPv6 Implementation1998Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The new version of the Internet protocol, IP version 6, will eventually replace the current version IP version 4. Before that change can take place the different implementations of IPv6 must be able to perform at least as well as their predecessors, The implementation that is considered here is that of the Linux operating system. All measurements considers native IPv6, e.g. no tunneling in IPv4 packets.

    A small network of two computers was set up on which the performance tests were performed. Throughput and response times were measured on both Ethernet and Fast Ethernet. The conclusions are that IPv6 performs almost as well as IPv4 in both cases. IPv4's slight advantage is due to the fact that it has less overhead on the network since the header is smaller.

    Later a connection to the 6bone is setup. It is run on an ATM network. The performance across that network is also tested.

  • 321.
    Björkman, Anders
    KTH, Tidigare Institutioner, Teleinformatik.
    Configuration of IPv4 Hosts in Zero-Configuration Networks2000Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Zero-configuration networks are networks that require no/zero manual configuration or administration to operate. The essence of a zero-configuration network is that it can be used without having to think about the network at all. The most basic zero-configuration network just provides network communication but more advanced services can be provided as long as no configuration is needed. An important area of use is networks for homes and small businesses. Many of the devices that we have in our homes are or will in a near future be ‘networked’ i.e. capable of network communication. Examples are computers and computer equipment such as printers and scanners, the next generation home-appliances such as the refrigerator and the washing machine, the TV, the stereo, climate sensors etc. etc. The main driving forces for this development are the need for resource sharing e.g. of printers or Internet access, home automation and devices, applications or services that use network communication. Networks for the home must be ‘automatic’ because the average person today has problems programming his VCR and cannot be expected to configure or administrate his/her home-network. Today’s solutions are insufficient because they require manual configuration and some technical knowledge. The market potential is enormous. Almost all homes and most small businesses lack a network infrastructure and many will in a near future acquire it.

    In this thesis I discuss the need and areas of use for zero-configuration networks and I look at how to configure IP hosts in general. Solutions on configuration of hosts in zero-configuration networks are discussed and I propose a solution for IPv4 hosts that enables link-local communication, the most basic type of network communication using IP.

    This master’s thesis was carried out at Ericsson Research in Kista during the fall of 1999 and spring of 2000.

  • 322.
    Björkman Höglund, Matilda
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska högskolan.
    Olsson, Maria
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska högskolan.
    The future of e-commerce2017Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    E-handeln växer eftersom allt fler personer handlar via internet. Konsumtionsmönstret ändras och allt fler söker sig till företags hemsidor för att köpa varor online. Även tjänster som exempelvis musik och film blir mer internetbaserat och köps och beställs ofta via internet. Nu kan nästan vad som helst köpas online, allt från mat till kläder och elektronik. E-handeln är ett smidigare och ibland billigare komplement till den traditionella handeln. Detta underlättar för kunderna och kan frigöra mer tid till de personer som e-handlar. Med den ökade e-handeln uppstår det också problem. Det behövs bra distributionsupplägg som kan ta hand om alla varor som ska transporteras. Den ökade e-handeln innebär fler transporter i städerna. Om e-handeln fortsätter att öka och det blir ännu fler transporter, vilka konsekvenser får det? Vilka olika distributionsupplägg kommer det att finnas i framtiden för att kunna leverera varor till kunderna på ett effektivt sätt? I det här examensarbetet har klädbranschen och dess e-handel undersökts. Det som har studerats, är hur branschen påverkar transporterna kopplat till e-handeln. Intervjuer med olika företag har genomförts i examensarbetet för att få en överblick över hur deras e-handel har utvecklats över tid samt hur de tror att e-handeln kommer att se ut i framtiden. Intervjuer med teoretiker som arbetar med citylogistik har även gjorts, för att få information hur de tror e-handeln kommer påverka transporterna kopplat till e-handeln. I framtiden kommer det troligtvis inte användas några nya distributionsupplägg, utan de som redan finns kommer bli mer utvecklade. De distributionsupplägg som finns idag är att kunderna hämtar sina varor via ett ombud, i en butik/lagerlokal, paketombud eller att varorna skickas hem till kunden. I framtiden kan det bli allt vanligare med hemleverans och att kunderna eventuellt kommer att få styra sina leveranser mer än vad som är möjligt idag. För att se konsekvenserna av transporterna kopplat till e-handeln presenteras två olika fall. Dessa två fall delas upp i åtta olika scenarier. Dessa scenarier är uppbyggda efter olika antaganden om vilka transportmedel som används och i vilken utsträckning. Det scenario som gav lägst koldioxidutsläpp och lägst fordonskilometer var det scenario där 100 % av godset levereras till ett utlämningsställe via en samlastningscentral utan att kunderna använder sin personbil mer. En förändrad volym av e-handel ger olika konsekvenser på transporterna, beroende på vilken typ av distributionsupplägg som används och vilket transportmedel som utnyttjas, samt vilken systemavgränsning som görs. Generellt sett tyder det på att antalet transportkilometer kopplat till e-handeln kommer att öka i framtiden. Vad gäller koldioxidutsläppen är det svårare att göra en bedömning, beroende på vilka transportmedel som kommer att användas i framtiden men också på den tekniska utvecklingen av dessa. Även om antalet fordonskilometer ökar kan effektivare transporter leda till minskade koldioxidutsläpp.

  • 323.
    Björnson, Emil
    KTH Royal Institute Technology, Sweden; Supelec, France.
    Kountouris, Marios
    CentraleSupelec, France.
    Debbah, Merouane
    CentraleSupelec, France.
    Massive MIMO Systems with Non-Ideal Hardware: Energy Efficiency, Estimation, and Capacity Limits2014Inngår i: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 60, nr 11, s. 7112-7139Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The use of large-scale antenna arrays can bring substantial improvements in energy and/or spectral efficiency to wireless systems due to the greatly improved spatial resolution and array gain. Recent works in the field of massive multiple-input multiple-output (MIMO) show that the user channels decorrelate when the number of antennas at the base stations (BSs) increases, thus strong signal gains are achievable with little interuser interference. Since these results rely on asymptotics, it is important to investigate whether the conventional system models are reasonable in this asymptotic regime. This paper considers a new system model that incorporates general transceiver hardwareimpairments at both the BSs (equipped with large antenna arrays) and the single-antenna user equipments (UEs). As opposed to the conventional case of ideal hardware, we show that hardwareimpairments create finite ceilings on the channel estimation accuracy and on the downlink/uplink capacity of each UE. Surprisingly, the capacity is mainly limited by the hardware at the UE, while the impact of impairments in the large-scale arrays vanishes asymptotically and interuser interference (in particular, pilot contamination) becomes negligible. Furthermore, we prove that the huge degrees of freedom offered by massive MIMO can be used to reduce the transmit power and/or to tolerate larger hardware impairments, which allows for the use of inexpensive and energy-efficient antenna elements.

  • 324.
    Björnson, Emil
    KTH Royal Institute Technology, Sweden; Supelec, France.
    Debbah, Merouane
    CentraleSupelec, France.
    Ottersten, Björn
    KTH Royal Institute of Technology.
    Multi-Objective Signal Processing Optimization: The Way to Balance Conflicting Metrics in 5G Systems2014Inngår i: IEEE signal processing magazine (Print), ISSN 1053-5888, E-ISSN 1558-0792, Vol. 31, nr 6, s. 14-23Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The evolution of cellular networks is driven by the dream of ubiquitous wireless connectivity: any data service is instantly accessible everywhere. With each generation of cellular networks, we have moved closer to this wireless dream; first by delivering wireless access to voice communications, then by providing wireless data services, and recently by delivering a Wi-Fi-like experience with wide-area coverage and user mobility management. The support for high data rates has been the main objective in recent years [1], as seen from the academic focus on sum-rate optimization and the efforts from standardization bodies to meet the peak rate requirements specified in IMT-Advanced. In contrast, a variety of metrics/objectives are put forward in the technological preparations for fifth-generation (5G) networks: higher peak rates, improved coverage with uniform user experience, higher reliability and lower latency, better energy efficiency (EE), lower-cost user devices and services, better scalability with number of devices, etc. These multiple objectives are coupled, often in a conflicting manner such that improvements in one objective lead to degradation in the other objectives. Hence, the design of future networks calls for new optimization tools that properly handle the existence of multiple objectives and tradeoffs between them.

  • 325.
    Björnson, Emil
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. Dept. of Electrical Engineering, Linkoping University, Sweden.
    Bengtsson, Mats
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Ottersten, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Optimal Multiuser Transmit Beamforming: A Difficult Problem with a Simple Solution Structure2014Inngår i: IEEE signal processing magazine (Print), ISSN 1053-5888, E-ISSN 1558-0792, Vol. 31, nr 4, s. 142-148Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Transmit beamforming is a versatile technique for signal transmission from an array of antennas to one or multiple users [1]. In wireless communications, the goal is to increase the signal power at the intended user and reduce interference to nonintended users. A high signal power is achieved by transmitting the same data signal from all antennas but with different amplitudes and phases, such that the signal components add coherently at the user. Low interference is accomplished by making the signal components add destructively at nonintended users. This corresponds mathematically to designing beamforming vectors (that describe the amplitudes and phases) to have large inner products with the vectors describing the intended channels and small inner products with nonintended user channels.

  • 326.
    Björnson, Emil
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    de Carvalho, Elisabeth
    Aalborg University, Denmark.
    Larsson, Erik G
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Popovski, Petar
    Aalborg University, Denmark.
    Random Access Protocol for Massive MIMO: Strongest-User Collision Resolution (SUCR)2016Inngår i: 2016 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC), IEEE , 2016, s. 820-825Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Wireless networks with many antennas at the base stations and multiplexing of many users, known as Massive MIMO systems, are key to handle the rapid growth of data traffic. As the number of users increases, the random access in contemporary networks will be flooded by user collisions. In this paper, we propose a reengineered random access protocol, coined strongest-user collision resolution (SUCR). It exploits the channel hardening feature of Massive MIMO channels to enable each user to detect collisions, determine how strong the contenders channels are, and only keep transmitting if it has the strongest channel gain. The proposed SUCR protocol can quickly and distributively resolve the vast majority of all pilot collisions.

  • 327.
    Björnson, Emil
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    de Carvalho, Elisabeth
    Aalborg University, Denmark.
    Sorensen, Jesper H.
    Aalborg University, Denmark.
    Larsson, Erik G
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Popovski, Petar
    Aalborg University, Denmark.
    A Random Access Protocol for Pilot Allocation in Crowded Massive MIMO Systems2017Inngår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, nr 4, s. 2220-2234Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The massive multiple-input multiple-output (MIMO) technology has great potential to manage the rapid growth of wireless data traffic. Massive MIMO achieves tremendous spectral efficiency by spatial multiplexing many tens of user equipments (UEs). These gains are only achieved in practice if many more UEs can connect efficiently to the network than today. As the number of UEs increases, while each UE intermittently accesses the network, the random access functionality becomes essential to share the limited number of pilots among the UEs. In this paper, we revisit the random access problem in the Massive MIMO context and develop a reengineered protocol, termed strongest-user collision resolution (SUCRe). An accessing UE asks for a dedicated pilot by sending an uncoordinated random access pilot, with a risk that other UEs send the same pilot. The favorable propagation of massive MIMO channels is utilized to enable distributed collision detection at each UE, thereby determining the strength of the contenders signals and deciding to repeat the pilot if the UE judges that its signal at the receiver is the strongest. The SUCRe protocol resolves the vast majority of all pilot collisions in crowded urban scenarios and continues to admit UEs efficiently in overloaded networks.

  • 328.
    Björnson, Emil
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Jorswieck, Eduard
    Dresden University of Technology, Communications Theory, Communications Laboratory, Dresden, Germany.
    Optimal Resource Allocation in Coordinated Multi-Cell Systems2013Bok (Fagfellevurdert)
    Abstract [en]

    The use of multiple antennas at base stations is a key component in the design of cellular communication systems that can meet high-capacity demands in the downlink. Under ideal conditions, the gain of employing multiple antennas is well-recognized: the data throughput increases linearly with the number of transmit antennas if the spatial dimension is utilized to serve many users in parallel. The practical performance of multi-cell systems is, however, limited by a variety of nonidealities, such as insufficient channel knowledge, high computational complexity, heterogeneous user conditions, limited backhaul capacity, transceiver impairments, and the constrained level of coordination between base stations.

    This tutorial presents a general framework for modeling different multi-cell scenarios, including clustered joint transmission, coordinated beamforming, interference channels, cognitive radio, and spectrum sharing between operators. The framework enables joint analysis and insights that are both scenario independent and dependent.

    The performance of multi-cell systems depends on the resource allocation; that is, how the time, power, frequency, and spatial resources are divided among users. A comprehensive characterization of resource allocation problem categories is provided, along with the signal processing algorithms that solve them. The inherent difficulties are revealed: (a) the overwhelming spatial degrees-of-freedom created by the multitude of transmit antennas; and (b) the fundamental tradeoff between maximizing aggregate system throughput and maintaining user fairness. The tutorial provides a pragmatic foundation for resource allocation where the system utility metric can be selected to achieve practical feasibility. The structure of optimal resource allocation is also derived, in terms of beamforming parameterizations and optimal operating points.

    This tutorial provides a solid ground and understanding for optimization of practical multi-cell systems, including the impact of the nonidealities mentioned above. The Matlab code is available online for some of the examples and algorithms in this tutorial.

    Note: The supplementary Matlab Code is available at http://dx.doi.org/10.1561/0100000069_supp

  • 329.
    Björnson, Emil
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. Alcatel-Lucent Chair on Flexible Radio, Supélec, France.
    Jorswieck, Eduard
    Dresden University of Technology, Communications Theory, Communications Laboratory, Dresden, Germany.
    Optimal Resource Allocation in Coordinated Multi-Cell Systems: Matlab Code2013Rapport (Annet vitenskapelig)
    Abstract [en]

    This is the documentation of the Matlab code supplement to the monograph "Optimal Resource Allocation in Coordinated Multi-Cell Systems" by Emil Björnson and Eduard Jorswieck; see [1] for the full publication details.

    This documentation is distributed along with the code package mentioned above. The package contains Matlab implementations of many of the algorithms described in [1]. The use of these algorithms is exemplified by Matlab scripts (m-files) that generate some of the figures shown in the monograph. The algorithms are briefly described in Section 5 and the selected example figures are described and shown in Section 6. Please note that the all channel vectors are generated randomly as Rayleigh fading in these examples, thus this code package is not able to reproduce exactly the same curves as was shown in the monograph.

  • 330.
    Björnson, Emil
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Larsson, Erik G
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Three Practical Aspects of Massive MIMO: Intermittent User Activity, Pilot Synchronism, and Asymmetric Deployment2015Inngår i: 2015 IEEE Globecom Workshops (GC Wkshps), Institute of Electrical and Electronics Engineers (IEEE), 2015, s. 1-6Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper considers three aspects of Massive MIMO (multiple- input multiple-output) communication networks that have received little attention in previous works, but are important to understand when designing and implementing this promising wireless technology. First, we analyze how bursty data traffic behaviors affect the system. Using a probabilistic model for intermittent user activity, we show that the spectral efficiency (SE) scales gracefully with reduced user activity. Then, we make an analytic comparison between synchronous and asynchronous pilot signaling, and prove that the choice between these has no impact on the SE. Finally, we provide an analytical and numerical study of the SE achieved with random network deployment.

  • 331.
    Björnson, Emil
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Larsson, Erik G
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Debbah, Merouane
    CentraleSupelec, France.
    Optimizing Multi-Cell Massive MIMO for Spectral Efficiency: How Many Users Should Be Scheduled?2014Inngår i: 2014 IEEE Global Conference on Signal and Information Processing, GlobalSIP 2014, Institute of Electrical and Electronics Engineers (IEEE), 2014, s. 612-616Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Massive MIMO is a promising technique to increase the spectral efficiency of cellular networks, by deploying antenna arrays with hundreds or thousands of active elements at the base stations and performing coherent beamforming. A common rule-of-thumb is that these systems should have an order of magnitude more antennas, N, than scheduled users, K, because the users' channels are then likely to be quasi-orthogonal. However, it has not been proved that this rule-of-thumb actually maximizes the spectral efficiency. In this paper, we analyze how the optimal number of scheduled users, K*, depends on N and other system parameters. The value of K* in the large-N regime is derived in closed form, while simulations are used to show what happens at finite N, in different interference scenarios, and for different beamforming.

  • 332.
    Björnson, Emil
    et al.
    KTH Royal Institute Technology, Sweden; Supelec, France.
    Matthaiou, Michail
    Chalmers, Sweden; Queens University of Belfast, North Ireland.
    Debbah, Merouane
    CentraleSupelec, France.
    Massive MIMO with Non-Ideal Arbitrary Arrays: Hardware Scaling Laws and Circuit-Aware Design2015Inngår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, nr 8, s. 4353-4368Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Massive multiple-input multiple-output (MIMO) systems are cellular networks where the base stations (BSs) are equipped with unconventionally many antennas, deployed on co-located or distributed arrays. Huge spatial degrees-of-freedom are achieved by coherent processing over these massive arrays, which provide strong signal gains, resilience to imperfect channel knowledge, and low interference. This comes at the price of more infrastructure; the hardware cost and circuit power consumption scale linearly/affinely with the number of BS antennas N  . Hence, the key to cost-efficient deployment of large arrays is low-cost antenna branches with low circuit power, in contrast to today's conventional expensive and power-hungry BS antenna branches. Such low-cost transceivers are prone to hardware imperfections, but it has been conjectured that the huge degrees-of-freedom would bring robustness to such imperfections. We prove this claim for a generalized uplink system with multiplicative phase-drifts, additive distortion noise, and noise amplification. Specifically, we derive closed-form expressions for the user rates and a scaling law that shows how fast the hardware imperfections can increase with N  while maintaining high rates. The connection between this scaling law and the power consumption of different transceiver circuits is rigorously exemplified. This reveals that one can make the circuit power increase as N − −  √   , instead of linearly, by careful circuit-aware system design

  • 333.
    Björnson, Emil
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Matthaiou, Michail
    Chalmers, Sweden; Queens University of Belfast, North Ireland.
    Pitarokoilis, Antonios
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Larsson, Erik G
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Distributed Massive MIMO in Cellular Networks: Impact of Imperfect Hardware and Number of Oscillators2015Inngår i: 23rd European Signal Processing Conference, EUSIPCO 2015, Institute of Electrical and Electronics Engineers (IEEE), 2015, s. 2436-2440Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Distributed massive multiple-input multiple-output (MIMO) combines the array gain of coherent MIMO processing with the proximity gains of distributed antenna setups. In this paper, we analyze how transceiver hardware impairments affect the downlink with maximum ratio transmission. We derive closed-form spectral efficiencies expressions and study their asymptotic behavior as the number of the antennas increases. We prove a scaling law on the hardware quality, which reveals that massive MIMO is resilient to additive distortions, while multiplicative phase noise is a limiting factor. It is also better to have separate oscillators at each antenna than one per BS

  • 334.
    Björnson, Emil
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten. KTH Royal Institute Technology, Sweden; Supelec, France.
    Sanguinetti, Luca
    University of Pisa, Italy; CentraleSupelec, France.
    Hoydis, Jakob
    Bell Labs, Germany.
    Debbah, Merouane
    CentraleSupelec, France.
    Optimal Design of Energy-Efficient Multi-User MIMO Systems: Is Massive MIMO the Answer?2015Inngår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, nr 6, s. 3059-3075Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Assume that a multi-user multiple-input multiple-output (MIMO) system is designed from scratch to uniformly cover a given area with maximal energy efficiency (EE). What are the optimal number of antennas, active users, and transmit power? The aim of this paper is to answer this fundamental question. We consider jointly the uplink and downlink with different processing schemes at the base station and propose a new realistic power consumption model that reveals how the above parameters affect the EE. Closed-form expressions for the EE-optimal value of each parameter, when the other two are fixed, are provided for zero-forcing (ZF) processing in single-cell scenarios. These expressions prove how the parameters interact. For example, in sharp contrast to common belief, the transmit power is found to increase (not to decrease) with the number of antennas. This implies that energy-efficient systems can operate in high signal-to-noise ratio regimes in which interference-suppressing signal processing is mandatory. Numerical and analytical results show that the maximal EE is achieved by a massive MIMO setup wherein hundreds of antennas are deployed to serve a relatively large number of users using ZF processing. The numerical results show the same behavior under imperfect channel state information and in symmetric multi-cell scenarios.

  • 335.
    Björnson, Emil
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Sanguinetti, Luca
    University of Pisa, Italy; University of Paris Saclay, France.
    Kountouris, Marios
    Huawei Technology Co Ltd, France.
    Deploying Dense Networks for Maximal Energy Efficiency: Small Cells Meet Massive MIMO2016Inngår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 34, nr 4, s. 832-847Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    What would a cellular network designed for maximal energy efficiency look like? To answer this fundamental question, tools from stochastic geometry are used in this paper to model future cellular networks and obtain a new lower bound on the average uplink spectral efficiency. This enables us to formulate a tractable uplink energy efficiency (EE) maximization problem and solve it analytically with respect to the density of base stations (BSs), the transmit power levels, the number of BS antennas and users per cell, and the pilot reuse factor. The closed-form expressions obtained from this general EE maximization framework provide valuable insights on the interplay between the optimization variables, hardware characteristics, and propagation environment. Small cells are proved to give high EE, but the EE improvement saturates quickly with the BS density. Interestingly, the maximal EE is achieved by also equipping the BSs with multiple antennas and operate in a "massive MIMO" fashion, where the array gain from coherent detection mitigates interference and the multiplexing of many users reduces the energy cost per user.

  • 336.
    Björnson, Emil
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Sanguinetti, Luca
    University of Pisa, Italy; CentraleSupelec, France.
    Kountouris, Marios
    CentraleSupelec, France.
    Designing Wireless Broadband Access for Energy Efficiency: Are Small Cells the Only Answer?2015Inngår i: 2015 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATION WORKSHOP, Institute of Electrical and Electronics Engineers (IEEE), 2015, s. 136-141Konferansepaper (Fagfellevurdert)
  • 337.
    Björnson, Emil
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
    Sanguinetti, Luca
    University of Pisa, Italy; Central Supelec, France.
    Kountouris, Marios
    Huawei Technology Co Ltd, Peoples R China.
    Energy-Efficient Future Wireless Networks: A Marriage between Massive MIMO and Small Cells2015Inngår i: 2015 IEEE 16th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), IEEE , 2015, s. 211-215Konferansepaper (Fagfellevurdert)
    Abstract [en]

    How would a cellular network designed for high energy efficiency look like? To answer this fundamental question, we model cellular networks using stochastic geometry and optimize the energy efficiency with respect to the density of base stations, the number of antennas and users per cell, the transmit power levels, and the pilot reuse. The highest efficiency is neither achieved by a pure small-cell approach, nor by a pure massive MIMO solution. Interestingly, it is the combination of these approaches that provides the highest energy efficiency; small cells contributes by reducing the propagation losses while massive MIMO enables multiplexing of users with controlled interference.

  • 338.
    Blad, Anton
    et al.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Axell, Erik
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Larsson, Erik G.
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Spectrum Sensing of OFDM Signals in the Presence of CFO: New Algorithms and Empirical Evaluation Using USRP2012Inngår i: Proceedings of the 13th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), IEEE , 2012, s. 159-163Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this work, we consider spectrum sensing of OFDM signals. We deal withthe inevitable problem of a carrier frequency offset, and propose modificationsto some state-of-the-art detectors to cope with that. Moreover, the (modified)detectors are implemented using GNU radio and USRP, and evaluated over aphysical radio channel. Measurements show that all of the evaluated detectorsperform quite well, and the preferred choice of detector depends on thedetection requirements and the radio environment.

  • 339.
    Blank, Bruno
    et al.
    KTH, Tidigare Institutioner, Teleinformatik.
    Häggström, Mattias
    KTH, Tidigare Institutioner, Teleinformatik.
    Mobile Communication In a Multiple Device Environment1998Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    It is nowadays common that users have more than one computer. At the office, a stationary computer or possibly a laptop is used. When travelling, a Personal Digital Assistant is better suited for e-mail, address book, and scheduling. Probably the user also has an advanced mobile phone. A problem for many users is it has traditionally been quite complex to handle having multiple computers, since the support for mobile use has been insufficient.

    We have looked into common scenarios for mobile users and given and overview of related products and technologies. Some of the traditional protocols for e-mail have been reviewed. We have listed problems with those and suggested improvements. Sendit has a proprietary protocol, which we have compared to traditional protocols.

    This report gives an overview from the user’s point of view. From what we have seen, there are lots of upcoming technologies and solutions to assist mobile users. However, many problems still remain and need to be solved to facilitate the mobile user’s situation.

  • 340.
    Blom, Rolf
    Linköpings universitet, Institutionen för systemteknik. Linköpings universitet, Tekniska högskolan.
    An Upper Bound on the Key Equivocation for Pure Ciphers1979Rapport (Annet vitenskapelig)
    Abstract [en]

    An upper bound on key equivocation for a pure cipher applied on a memoryless message source is derived.

  • 341.
    Blom, Rolf
    et al.
    Linköpings universitet, Institutionen för systemteknik. Linköpings universitet, Tekniska högskolan.
    Fåk, Viiveke
    Linköpings universitet, Institutionen för systemteknik. Linköpings universitet, Tekniska högskolan.
    Ingemarsson, Ingemar
    Linköpings universitet, Institutionen för systemteknik. Linköpings universitet, Tekniska högskolan.
    Data Network Security: Part I Problem Survey and Model1977Rapport (Annet vitenskapelig)
    Abstract [en]

    Data encryption and related methods may be used to preserve information security i n a data network. Here information security is defined as the degree to which the destruction, change or loss of information is presented. Information is defined as the content of the message represented by the data. The information in a block of data is unchanged if the intended result of the transmission of the block is obtained. This means for example that the original message reaches the correct destination where it is interpreted as intended. Undisturbed information does not, in general, require un disturbed data.

    The network is supposed to be a public network, accessed by many different users. We are interested in a well defined group of users who are communicating mainly among themselves. Different groups, however, are also allowed to communicate in a well defined manner. The logical structure of the communication within a group is star-shaped. The information communicated within the groups hall be protected against threats from other users of the network, from illegitimate users (wiretappers etc) and from members in the group. The structure of the threats is described in section 3 of this paper.

    The network itself and the requirement it imposes are supposed to be unchanged. Encryption and decryption are taking place outside the network. The encrypted data shall comply with the requirements of the network. The communication process in the group consists of time-limited messages which are essentially transmitted from one point to another in the network. This is the basis for the model of the communication which is described in section 4. The model, although simple, enables us to structure the problems in connection with encryption/decryption. This is done in section 5 and 6. The purpose of the paper is to form a basis for synthesis of security measures by means on cryptological methods. The analysis is general enough to be applied to any data network and any type of user group.

  • 342.
    Blomberg, Patrik
    KTH, Tidigare Institutioner, Teleinformatik.
    Construction and Implementation of a Walkstation Mobile-distributed File System Testbed1995Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In this Master's Thesis an investigation, design and implementation of an object-oriented prototype of a new kind of client-agent-server based distributed file system, suited for wireless mobile computing, are presented. An overview is given of the characteristics and the inherent problems of mobile-wireless computing. Some solutions and techniques to reduce the effects of these problems are described. A presentation of a project (the Walkstation project) that tries to solve these problems is also given. Software to support a mobile-distributed file system is designed and implemented. Various software development techniques and mobile file system design solutions are proposed, and used in the implementation. An integrated caching and prefetching scheme with dynamically loadable cache and prefetch manager objects is designed and implemented. It is proposed that different cache and prefetch algorithms should be used for different kinds of network links. A cache/prefetch-manager object architecture with automatically location-dependant dynamical swapping of network specific manager objects at run-time is therefore proposed and implemented. A mechanism is designed with which an application optionally can be mobility-aware by subscribing for network-change events. Finally, an expedient example of a methodology to achieve easy-understandable and well-designed code, and good extensibility possibilities is explained and used in the development. This is done by utilizing an object-oriented software development methodology in the entire software development cycle.

  • 343. Boano, Carlo Alberto
    et al.
    Voigt, Thiemo
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Datorteknik.
    Noda, Claro
    Römer, Kay
    Zuniga, Marco
    JamLab: Augmenting sensornet testbeds with realistic and controlled interference generation2011Inngår i: IPSN, 2011, s. 175-186Konferansepaper (Fagfellevurdert)
  • 344.
    Boano, Carlo Alberto
    et al.
    University of Lübeck.
    Wennerström, Hjalmar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Datorteknik.
    Zúñiga, Marco Antonio
    TU Delft.
    Brown, James
    Lancaster University.
    Keppitiyagama, Chamath
    Swedish Institute of Computer Science.
    Oppermann, Felix Jonathan
    University of Lübeck.
    Roedig, Utz
    Lancaster University.
    Nordén, Lars-Åke
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Datorteknik.
    Voigt, Thiemo
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Datorteknik.
    Römer, Kay
    University of Lübeck.
    Hot Packets: A systematic evaluation of the effect of temperature on low power wireless transceivers2013Inngår i: Proc. 5th Extreme Conference on Communication, New York: ACM Press, 2013, s. 7-12Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Temperature is known to have a significant effect on the performance of radio transceivers: the higher the temperature, the lower the quality of links. Analysing this effect is particularly important in sensor networks because several applications are exposed to harsh environmental conditions. Daily or hourly changes in temperature can dramatically reduce the throughput, increase the delay, or even lead to network partitions. A few studies have quantified the impact of temperature on low-power wireless links, but only for a limited temperature range and on a single radio transceiver. Building on top of these preliminary observations, we design a low-cost experimental infrastructure to vary the onboard temperature of sensor nodes in a repeatable fashion, and we study systematically the impact of temperature on various sensornet platforms. We show that temperature affects transmitting and receiving nodes differently, and that all platforms follow a similar trend that can be captured in a simple first-order model. This work represents an initial stepping stone aimed at predicting the performance of a network considering the particular temperature profile of a given environment.

  • 345. Boccardi, Federico
    et al.
    Andrews, Jeffrey
    Elshaer, Hisham
    Dohler, Mischa
    Parkvall, Stefan
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. Univ Calif San Diego, San Diego.
    Popovski, Petar
    Singh, Sarabjot
    Why to Decouple the Uplink and Downlink in Cellular Networks and How To Do It2016Inngår i: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 54, nr 3, s. 110-117Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ever since the inception of mobile telephony, the downlink and uplink of cellular networks have been coupled, that is, mobile terminals have been constrained to associate with the same base station in both the downlink and uplink directions. New trends in network densification and mobile data usage increase the drawbacks of this constraint, and suggest that it should be revisited. In this article we identify and explain five key arguments in favor of downlink/uplink decoupling based on a blend of theoretical, experimental, and architectural insights. We then overview the changes needed in current LTE-A mobile systems to enable this decoupling, and then look ahead to fifth generation cellular standards. We demonstrate that decoupling can lead to significant gains in network throughput, outage, and power consumption at a much lower cost compared to other solutions that provide comparable or lower gains.

  • 346.
    Bodinger, Ronnie
    KTH, Tidigare Institutioner, Teleinformatik.
    An MPLS Connection Manager for an Edge Router1998Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The Internet has been growing rapidly over the last couple of years. The increasing demand for network bandwidth is becoming a huge problem. To solve this problem, new methods must be developed. Ericsson’s solution is the use of MultiProtocol Label Switching (MPLS). MPLS has the potential to have a major impact on IP networking. It has the simplicity and dynamic nature of an IP network, but retains the performance of an ATM network. Furthermore, from an administrator’s point of view, MPLS will drastically simplify network management.

    The key principle behind MPLS is to be able to forward by switching packets through a network instead of routing packets. In order to do this, paths are established at the data link layer throughout the MPLS network. A fixed length identifier known as “label” identifies each path. Then the packets are simply forwarded on the path using layer two switching, instead of performing layer three routing.

    By using MPLS, performance is increased and it provides a good basis for traffic engineering, Quality of Service (QoS) guarantees, and Virtual Private Networks (VPN).

    I have implemented an MPLS ATM driver for an Ericsson AXI 510 Edge Router. The driver is responsible for converting generic MPLS labels into standard ATM labels (VPI/VCI). The driver also modifies the forwarding process in the router so that ATM paths are used to forward the packets, instead of the conventional forwarding methods. This implementation has been partly tested and it complies with MPLS current Internet drafts so far.

  • 347.
    Boeira, Felipe
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS). Federal University of Rio Grande do Sul, Porto Alegre, Brazil & Linköping University, Linköping, Sweden.
    Barcellos, Marinho P.
    Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
    Pignaton de Freitas, Edison
    Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
    Vinel, Alexey
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Centrum för forskning om inbyggda system (CERES).
    Asplund, Mikael
    Linköping University, Linköping, Sweden.
    Effects of Colluding Sybil Nodes in Message Falsification Attacks for Vehicular Platooning2017Inngår i: 2017 IEEE Vehicular Networking Conference (VNC) / [ed] Onur Altintas, Claudio Casetti, Nicholas Kirsch, Renato Lo Cigno & Rui Meireles, 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper studies the impact of vulnerabilities associated with the Sybil attack (through falsification of multiple identities) and message falsification in vehicular platooning. Platooning employs Inter-Vehicular Communication (IVC) to control a group of vehicles. It uses broadcast information such as acceleration, position, and velocity to operate a longitudinal control law. Cooperation among vehicles allows platoons to reduce fuel consumption and risks associated with driver mistakes. In spite of these benefits, the use of network communication to control vehicles exposes a relevant attack surface that can be exploited by malicious actors. To carry out this study, we evaluate five scenarios to quantify the potential impact of such attacks, identifying how platoons behave under varying Sybil attack conditions and what are the associated safety risks. This research also presents the use of location hijacking attack. In this attack, innocent vehicles that are not part of a platoon are used as a way to create trust bond between the false identities and the physical vehicles. We demonstrate that the ability to create false identities increases the effectiveness of message falsification attacks by making them easier to deploy and harder to detect in time.

  • 348.
    Boeira, Felipe
    et al.
    Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
    Barcellos, Marinho
    Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
    Pignaton de Freitas, Edison
    Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
    Vinel, Alexey
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Centrum för forskning om inbyggda system (CERES).
    Asplund, Mikael
    Linköping University, Linköping, Sweden.
    On the impact of sybil attacks in cooperative driving scenarios2017Inngår i: 2017 IFIP Networking Conference (IFIP Networking) and Workshops, IEEE, 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Platooning employs a set of technologies to manage how a group of vehicles operates, including radar, GPS and Inter-Vehicular Communication (IVC). It uses broadcasted information such as acceleration, position and velocity to operate vehicle members of the platoon. Cooperation among vehicles allows platoons to reduce fuel consumption and risks associated with driver mistakes. In spite of these benefits, the use of IVC to control vehicles exposes a relevant attack surface that can be exploited by malicious actors. In this paper we study the impact of vulnerabilities associated with the Sybil attack (through falsification of multiple identities) and message falsification in vehicular platooning. Simulation results show that this attack may impact the longitudinal control and compromise the entire platoon control. © Copyright 2018 IEEE

  • 349.
    Bogdanov, Kirill
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab).
    Latency Dataset for the paper "The Nearest Replica Can Be Farther Than You Think"2015Dataset
  • 350.
    Bogdanov, Kirill
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS, Network Systems Laboratory (NS Lab).
    Reducing Long Tail Latencies in Geo-Distributed Systems2016Licentiatavhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    Computing services are highly integrated into modern society. Millions of people rely on these services daily for communication, coordination, trading, and accessing to information. To meet high demands, many popular services are implemented and deployed as geo-distributed applications on top of third party virtualized cloud providers. However, the nature of such deployment provides variable performance characteristics. To deliver high quality of service, such systems strive to adapt to ever-changing conditions by monitoring changes in state and making run-time decisions, such as choosing server peering, replica placement, and quorum selection.

    In this thesis, we seek to improve the quality of run-time decisions made by geo-distributed systems. We attempt to achieve this through: (1) a better understanding of the underlying deployment conditions, (2) systematic and thorough testing of the decision logic implemented in these systems, and (3) by providing a clear view into the network and system states which allows these services to perform better-informed decisions.

    We performed a long-term cross datacenter latency measurement of the Amazon EC2 cloud provider. We used this data to quantify the variability of network conditions and demonstrated its impact on the performance of the systems deployed on top of this cloud provider.

    Next, we validate an application’s decision logic used in popular storage systems by examining replica selection algorithms. We introduce GeoPerf, a tool that uses symbolic execution and lightweight modeling to perform systematic testing of replica selection algorithms. We applied GeoPerf to test two popular storage systems and we found one bug in each.

    Then, using traceroute and one-way delay measurements across EC2, we demonstrated persistent correlation between network paths and network latency. We introduce EdgeVar, a tool that decouples routing and congestion based changes in network latency. By providing this additional information, we improved the quality of latency estimation, as well as increased the stability of network path selection.

    Finally, we introduce Tectonic, a tool that tracks an application’s requests and responses both at the user and kernel levels. In combination with EdgeVar, it provides a complete view of the delays associated with each processing stage of a request and response. Using Tectonic, we analyzed the impact of sharing CPUs in a virtualized environment and can infer the hypervisor’s scheduling policies. We argue for the importance of knowing these policies and propose to use them in applications’ decision making process.

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