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  • 1.
    Björnson, Emil
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Marzetta, Thomas L.
    Nokia, France.
    Massive MIMO: Ten Myths and One Critical Question2016In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 54, no 2, p. 114-123Article in journal (Refereed)
    Abstract [en]

    Wireless communications is one of the most successful technologies in modern years, given that an exponential growth rate in wireless traffic has been sustained for over a century (known as Coopers law). This trend will certainly continue, driven by new innovative applications; for example, augmented reality and the Internet of Things. Massive MIMO has been identified as a key technology to handle orders of magnitude more data traffic. Despite the attention it is receiving from the communication community, we have personally witnessed that Massive MIMO is subject to several widespread misunderstandings, as epitomized by following (fictional) abstract: "The Massive MIMO technology uses a nearly infinite number of high-quality antennas at the base stations. By having at least an order of magnitude more antennas than active terminals, one can exploit asymptotic behaviors that some special kinds of wireless channels have. This technology looks great at first sight, but unfortunately the signal processing complexity is off the charts and the antenna arrays would be so huge that it can only be implemented in millimeter-wave bands." These statements are, in fact, completely false. In this overview article, we identify 10 myths and explain why they are not true. We also ask a question that is critical for the practical adoption of the technology and which will require intense future research activities to answer properly. We provide references to key technical papers that support our claims, while a further list of related overview and technical papers can be found at the Massive MIMO Info Point: http://massivemimo.eu

  • 2.
    de Carvalho, Elisabeth
    et al.
    Aalborg University, Denmark.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Sorensen, Jesper H.
    Aalborg University, Denmark.
    Popovski, Petar
    Aalborg University, Denmark.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Random Access Protocols for Massive MIMO2017In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 55, no 5, p. 216-222Article in journal (Refereed)
    Abstract [en]

    5G wireless networks are expected to support new services with stringent requirements on data rates, latency and reliability. One novel feature is the ability to serve a dense crowd of devices, calling for radically new ways of accessing the network. This is the case in machine-type communications, but also in urban environments and hotspots. In those use cases, the high number of devices and the relatively short channel coherence interval do not allow per-device allocation of orthogonal pilot sequences. This article addresses the need for random access by the devices to pilot sequences used for channel estimation, and shows that Massive MIMO is a main enabler to achieve fast access with high data rates, and delay-tolerant access with different data rate levels. Three pilot access protocols along with data transmission protocols are described, fulfilling different requirements of 5G services.

  • 3.
    Falconer, David
    Department of Systems and Computer Engineering, Carleton University, Ottawa, Canada .
    History of equalization 1860-19802011In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 49, no 10, p. 42-50Article in journal (Refereed)
    Abstract [en]

    Operators of the first transatlantic telegraph cable in 1858, and subsequent cables from the mid-1860s, noticed that they had to transmit Morse code dots and dashes very slowly to be understood at the other end.1 This phenomenon, due to smearing out of pulses by the capacitive effects of very long cables, had been predicted by William Thomson (more about him below), and was one of the first instances of the need for equalization of digital signals.

  • 4.
    Hoymann, Christian
    et al.
    Ericsson Research, Sweden; Ericssons 3GPP RAN Delegat, Sweden.
    Astely, David
    Nokia Networks, Sweden; Ericsson, Sweden.
    Stattin, Magnus
    Ericsson Research, Sweden.
    Wikstrom, Gustav
    Ericsson Research, Sweden.
    (Thomas) Cheng, Jung-Fu
    Ericsson Silicon Valley, Sweden.
    Hoglund, Andreas
    Ericsson Research, Sweden.
    Frenne, Mattias
    Ericsson, Sweden.
    Blasco, Ricardo
    Ericsson Research, Sweden.
    Huschke, Joerg
    Ericsson GmbH, Germany.
    Gunnarsson, Fredrik
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering. Ericsson Research, Sweden.
    LTE Release 14 Outlook2016In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 54, no 6, p. 44-49Article in journal (Refereed)
    Abstract [en]

    Todays 4G LTE systems bring unprecedented mobile broadband performance to over a billion of users across the globe. Recently, work on a 5G mobile communication system has begun, and next to a new 5G air interface, LTE will be an essential component. The evolution of LTE will therefore strive to meet 5G requirements and to address 5G use cases. In this article, we provide an overview of foreseen key technology areas and components for LTE Release 14, including latency reductions, enhancements for machine-type communication, operation in unlicensed spectrum, massive multi-antenna systems, broadcasting, positioning, and support for intelligent transportation systems.

  • 5.
    Jorswieck, Eduard A.
    et al.
    Dresden Univeristy of Technology.
    Badia, Leonardo
    Università degli Studi di Padova.
    Fahldieck, Torsten
    Bell Labs, Alcatel-Lucent.
    Karipidis, Eleftherios
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Luo, Jian
    Fraunhofer Heinrich Hertz Institute.
    Spectrum sharing improves the network efficiency for cellular operators2014In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 52, no 3, p. 129-136Article in journal (Refereed)
    Abstract [en]

    The paper describes the potential gain by spectrum sharing between cellular operators in terms of network efficiency. The focus of the study is on a specific resource sharing scenario: spectrum sharing between two operators in cellular downlink transmission. If frequency bands are allocated dynamically and exclusively to one operator – a case called orthogonal spectrum sharing – significant gains in terms of achievable throughput (spectrum sharing gains between 50% and 100%) and user satisfaction are reported for asymmetric scenarios at link and system level as well as from two hardware demonstrators. Additionally, if frequency bands are allocated simultaneously to two operators – a case called non-orthogonal spectrum sharing – further gains are reported. In order to achieve these, different enablers from hardware technologies and base station capabilities are required. However, we argue that all requirements are fulfilled in 3GPP and newer mobile standards. Therefore, the results and conclusions of this overview paper encourage to seriously consider the inter-operator spectrum sharing technologies.

  • 6.
    Larsson, Erik G
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Edfors, Ove
    Lund University, Sweden .
    Tufvesson, Fredrik
    Lund University, Sweden .
    Marzetta, Thomas L.
    Bell Labs, Alcatel-Lucent, NJ, USA .
    Massive MIMO for Next Generation Wireless Systems2014In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 52, no 2, p. 186-195Article in journal (Refereed)
    Abstract [en]

    Multi-user MIMO offers big advantages over conventional point-to-point MIMO: it works with cheap single-antenna terminals, a rich scattering environment is not required, and resource allocation is simplified because every active terminal utilizes all of the time-frequency bins. However, multi-user MIMO, as originally envisioned, with roughly equal numbers of service antennas and terminals and frequency-division duplex operation, is not a scalable technology. Massive MIMO (also known as large-scale antenna systems, very large MIMO, hyper MIMO, full-dimension MIMO, and ARGOS) makes a clean break with current practice through the use of a large excess of service antennas over active terminals and time-division duplex operation. Extra antennas help by focusing energy into ever smaller regions of space to bring huge improvements in throughput and radiated energy efficiency. Other benefits of massive MIMO include extensive use of inexpensive low-power components, reduced latency, simplification of the MAC layer, and robustness against intentional jamming. The anticipated throughput depends on the propagation environment providing asymptotically orthogonal channels to the terminals, but so far experiments have not disclosed any limitations in this regard. While massive MIMO renders many traditional research problems irrelevant, it uncovers entirely new problems that urgently need attention: the challenge of making many low-cost low-precision components that work effectively together, acquisition and synchronization for newly joined terminals, the exploitation of extra degrees of freedom provided by the excess of service antennas, reducing internal power consumption to achieve total energy efficiency reductions, and finding new deployment scenarios. This article presents an overview of the massive MIMO concept and contemporary research on the topic.

  • 7.
    Matijasevic, M.
    et al.
    Department of Telecommunications, Faculty of Elec. Eng. and Computing, University of Zagreb, Zagreb, Croatia, Virtual Reality and Multimedia Lab., A-CIM Center, University of Louisiana at Lafayette, Lafayette, LA, United States, Technical University of Graz, Graz, Austria.
    Pandzic, I.S.
    Department of Telecommunications, Faculty of Elec. Eng. and Computing, University of Zagreb, Zagreb, Croatia, MIRALab, University of Geneva, Geneva, Switzerland, Image Coding Group, University of Linkoping, Linkoping, Sweden.
    Pakstas, A.
    London Metropolitan University, Department of CCTM, London, United Kingdom.
    Guest editorial: Networked virtual environments2004In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 42, no 4, p. 26-27Article in journal (Other academic)
  • 8.
    Mollén, Christopher
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Gustavsson, Ulf
    Ericson Res, Sweden.
    Eriksson, Thomas
    Chalmers Univ Technol, Sweden.
    Heath, Robert W. Jr.
    Univ Texas Austin, TX 78712 USA.
    Out-of-Band Radiation from Large Antenna Arrays2018In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 56, no 4, p. 196-203Article in journal (Refereed)
    Abstract [en]

    The OOB radiation from large arrays with nonlinear hardware has a different radiation pattern than the beamformed in-band signal. This is the main difference between the OOB radiation from large arrays and from well-studied legacy systems. Beamforming might focus the OOB radiation in certain directions but also significantly reduce the total power that has to be transmitted. For cost and power-consumption reasons, large arrays might have to be built from low-complexity hardware without advanced pre-compensation for linearization, which increases the relative amount of OOB radiation. Given that large arrays will be used in future base stations, a correct understanding of the OOB radiation is crucial to specify appropriate linearity requirements for the hardware. We show that the OOB radiation from large arrays varies little between coherence times; it is isotropic in many cases; and when it is beamformed, it is directed toward the served user in a very narrow beam with an array gain equal to or less than that of the in-band signal. We draw the conclusion that, compared to legacy systems, less stringent linearity requirements can be used in many systems with large arrays by virtue of the lower transmit power needed to upkeep the same received signal-to-noise ratio.

  • 9.
    Ouvrier, Gustaf
    et al.
    Linköping University, Faculty of Science & Engineering.
    Laterman, Michel
    SAP, Germany.
    Arlitt, Martin
    University of Calgary, Canada.
    Carlsson, Niklas
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Characterizing the HTTPS Trust Landscape: A Passive View from the Edge2017In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 55, no 7, p. 36-42Article in journal (Refereed)
    Abstract [en]

    Our society increasingly relies on web-based services like online banking, shopping, and socializing. Many of these services heavily depend on secure end-to-end transactions to transfer personal, financial, and other sensitive information. At the core of ensuring secure transactions are the HTTPS protocol and the trust relationships between many involved parties, including users, browsers, servers, domain owners, and the third-party CAs that issue certificates binding ownership of public keys with servers and domains. This article presents an overview of the current trust landscape and provides statistics to illustrate and quantify some of the risks facing typical users. Using measurement results obtained through passive monitoring of the HTTPS traffic between a campus network and the Internet, we provide concrete examples and characterize the certificate usage and trust relationships in this complex landscape. By comparing our observations against known vulnerabilities and problems, we highlight and discuss the actual security that typical Internet users (e.g., the people on campus) experience. Our measurements cover both mobile and stationary users, consider the involved trust relationships, and provide insights into how the HTTPS protocol is used and the weaknesses observed in practice. While the security properties vary significantly between sessions, out of the 232 million HTTPS sessions we observed, more than 25 percent had weak security properties.

  • 10.
    Stenumgaard, Peter
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. Swedish Defence Research Agency (FOI).
    Chilo, José
    Högskolan i Gävle, Sweden.
    Ferrer-Coll, Javier
    Högskolan i Gävle, Sweden.
    Ängskog, Per
    Högskolan i Gävle, Sweden.
    Challenges and Conditions for Wireless Machine-to-Machine Communications in Industrial Environments2013In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 51, no 6, p. 187-192Article in journal (Refereed)
    Abstract [en]

    Wireless solutions are rapidly growing in machine-to-machine communications in industrial environments. These environments provide challenging conditions in terms of radio wave propagation as well as electromagnetic interference. In this article, results from the characterization of radio channel properties are summarized in order to provide some guidelines for the choice of wireless solutions in industrial environments. In conclusion, it is essential to know the sensitivity of industrial processes to time delay in data transfer. Furthermore, it is important to be aware of the radio interference environment and the manner in which different wireless technologies react upon interference. These steps will minimize the risk of unforeseen expensive disturbances in industrial processes.

  • 11.
    Stenumgaard, Peter
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Persson, Daniel
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Wiklundh, Kia
    FOI.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    An Early-Warning Service for Emerging Communication Problems in Security and Safety Applications2013In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 51, no 5, p. 186-192Article in journal (Refereed)
    Abstract [en]

    Experience has shown that unpredictable disruption of communications during emergency operations can have severe consequences both for personal safety and for the ability to conduct a successful operation. An early-warning service for emerging communication disruption due to both unintentional interference and jamming, would therefore be a significant contribution for increased safety and security in such operations. We propose a solution for such an early-warning service both on the terminal and on higher system level. The solution is based on historical recorded data of both local and global information such as signal-to-interference ratio, interference classification, and position. We show by an example that with this service implemented, the operator will have increased time to take actions before a disruption occurs on a specific terminal.

  • 12.
    Stenumgaard, Peter
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Wiklundh, Kia
    FOI, Swedish Defense Research Agency, Linköping.
    Fors, Karina
    FOI, Swedish Defense Research Agency, Linköping.
    Linder, Sara
    FOI, Swedish Defense Research Agency, Linköping.
    Electromagnetic Interference on Tactical Radio Systems from Collocated Medical Equipment on Military Camps2012In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 50, no 10, p. 64-69Article in journal (Refereed)
    Abstract [en]

    On military camps for joint international operations, the intersystem interference can be highly unpredictable, and situation changes can occur very fast. For such situations it is highly important to perform intersystem interference analyses not only for intentional transmitters but also for electromagnetic interference from other electric equipment. One example of such an interference source to consider is medical equipment in field hospitals since the hospitals can contain a large amount of interfering equipment.  In this article, we show examples of necessary safety distances between medical equipment and tactical radio systems at military camps for international missions. We give an example of how wideband electromagnetic interference can degrade the performance even for a wideband frequency hopping army combat radio.

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