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Edited by Lars T. Berger Andreas Schwager Pascal Pagani Daniel M. Schneider MIMO Power Line Communications Narrow and Broadband Standards, EMC, and Advanced Processing

MIMO Power Line Communications - Narrow and Broadband Standards, EMC, And Advanced Processing

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  • Electr ical Engineering

    K15474

    One of the first publications of its kind in the exciting field of multiple input multiple output (MIMO) power line communications (PLC), MIMO Power Line Communications: Narrow and Broadband Standards, EMC, and Advanced Processing contains contributions from experts in industry and academia, making it practical enough to provide a solid understanding of how PLC technologies work, yet scientific enough to form a base for ongoing R&D activities.

    This book is subdivided into five thematic parts. Part I looks at narrow- and broadband channel characterization based on measurements from around the globe. Taking into account current regulations and electro-magnetic compatibility, part II describes MIMO signal processing strategies and related capacity and throughput estimates. Current narrow- and broadband PLC standards and specifications are described in the various chapters of part III. Advanced PLC processing options are treated in part IV, drawing from a wide variety of research areas such as beamforming/precoding, time reversal, multi-user processing, and relaying. Lastly, part V contains case studies and field trials, where the advanced technologies of tomorrow are put into practice today.

    Suitable as a reference or a handbook, MIMO Power Line Communi-cations: Narrow and Broadband Standards, EMC, and Advanced Processing features self-contained chapters with extensive cross-referencing to allow for a flexible reading path.

    MIMO Power Line Communications Narrow and Broadband Standards, EMC, and Advanced Processing

    E d i t e d b y

    Lars T. Berger Andreas SchwagerPascal Pagani Daniel M. Schneider

    MIMO Power LineCommunications

    Narrow and Broadband Standards, EMC, and Advanced Processing

    B e r g e rS c h w a g e r

    P a g a n iS c h n e i d e r

    MIMO Power Line Communications

  • MIMO Power LineCommunications

    Narrow and Broadband Standards, EMC, and Advanced Processing

  • Devices, Circuits, and Systems

    Series Editor Krzysztof Iniewski

    CMOS Emerging Technologies Research Inc., Vancouver, British Columbia, Canada

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    MIMO Power Line Communications: Narrow and Broadband Standards, EMC, and Advanced Processing

    Lars Torsten Berger, Andreas Schwager, Pascal Pagani, and Daniel Schneider

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  • CRC Press is an imprint of theTaylor & Francis Group, an informa business

    Boca Raton London New York

    E d i t e d b y

    Lars T. Berger Andreas SchwagerPascal Pagani Daniel M. Schneider

    MIMO Power LineCommunications

    Narrow and Broadband Standards, EMC, and Advanced Processing

  • MATLAB is a trademark of The MathWorks, Inc. and is used with permission. The MathWorks does not warrant the accuracy of the text or exercises in this book. This books use or discussion of MATLAB software or related products does not constitute endorsement or sponsorship by The MathWorks of a particular pedagogical approach or particular use of the MATLAB software.

    CRC PressTaylor & Francis Group6000 Broken Sound Parkway NW, Suite 300Boca Raton, FL 33487-2742

    2014 by Taylor & Francis Group, LLCCRC Press is an imprint of Taylor & Francis Group, an Informa business

    No claim to original U.S. Government worksVersion Date: 20131227

    International Standard Book Number-13: 978-1-4665-5753-6 (eBook - PDF)

    This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the valid-ity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint.

    Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or uti-lized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopy-ing, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers.

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    Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe.Visit the Taylor & Francis Web site athttp://www.taylorandfrancis.comand the CRC Press Web site athttp://www.crcpress.com

  • ix 2008 Taylor & Francis Group, LLC

    Contents

    Preface ........................................................................................................................................... xiiiEditors .............................................................................................................................................xvContributors ................................................................................................................................ xvii

    Part I Power Line Channel and Noise: Characteristics andModelling

    1. Introduction to Power Line Communication Channel and Noise Characterisation ................................................................................................................... 3Lars T. Berger, Pascal Pagani, Andreas Schwager and Piet Janse van Rensburg

    2. Narrowband Characterisation inan Office Environment ........................................... 39Klaus Dostert, Martin Sigle and Wenqing Liu

    3. Narrowband Measurements inDomestic Access Networks ....................................... 69Weilin Liu, Guangbin Chu and Jianqi Li

    4. Broadband In-Home Characterisation and Correlation-Based Modelling .............. 89Kaywan Afkhamie, Paola Bisaglia, Arun Nayagam, FabioOsnato, Deniz Rende, Raffaele Riva and Larry Yonge

    5. Broadband In-Home Statistics and Stochastic Modelling ......................................... 123Andreas Schwager, Pascal Pagani, Daniel M. Schneider, Rehan Hashmat andThierryChonavel

    Part II Regulations, Electromagnetic Compatibility andMIMO Capacity

    6. Power Line Communication Electromagnetic Compatibility Regulations ............ 169Andreas Schwager and Lars T. Berger

    7. MIMO PLC Electromagnetic Compatibility Statistical Analysis ............................ 187Andreas Schwager

    8. MIMO PLC Signal Processing Theory .......................................................................... 199Daniel M. Schneider and Andreas Schwager

    9. MIMO PLC Capacity andThroughput Analysis ........................................................ 231Daniel M. Schneider, Pascal Pagani and Andreas Schwager

  • x Contents

    2008 Taylor & Francis Group, LLC

    Part III Current PLC Systems and Their Evolution

    10. Current Power Line Communication Systems: A Survey .......................................... 253Lars T. Berger, Andreas Schwager, Stefano Galli, PascalPagani, DanielM.Schneider and Hidayat Lioe

    11. Narrowband Power Line Standards ............................................................................... 271Stefano Galli and James Le Clare

    12. ITU G.hn: Broadband Home Networking .................................................................... 301Erez Ben-Tovim

    13. IEEE 1901: Broadband over Power Line Networks ...................................................... 357Arun Nayagam, Purva R. Rajkotia, Manjunath Krishnam, MarkusRindchen, MatthiasStephan and Deniz Rende

    14. HomePlug AV2: Next-Generation Broadband over Power Line ............................... 391Larry Yonge, Jose Abad, Kaywan Afkhamie, Lorenzo Guerrieri, SrinivasKatar, HidayatLioe, Pascal Pagani, Raffaele Riva, Daniel M. Schneider andAndreasSchwager

    15. IEEE 1905.1: Convergent Digital Home Networking ..................................................427Etan G. Cohen, Duncan Ho, Bibhu P. Mohanty and Purva R. Rajkotia

    Part IV Advanced PHY and MAC Layer Processing

    16. Smart Beamforming: Improving PLC Electromagnetic Interference ..................... 457Daniel M. Schneider and Andreas Schwager

    17. Radiation Mitigation for Power Line Communications Using Time Reversal ..... 473Pascal Pagani, Amilcar Mescco, Michel Ney and Ahmed Zeddam

    18. Linear Precoding for Multicarrier and Multicast PLC ............................................... 493Jean-Yves Baudais and Matthieu Crussire

    19. Multi-user MIMO for Power Line Communications ................................................. 531Yago Snchez Quintas, Daniel M. Schneider and Andreas Schwager

    20. Relaying Protocols for In-Home PLC ............................................................................. 553Salvatore DAlessandro and Andrea M. Tonello

  • xiContents

    2008 Taylor & Francis Group, LLC

    Part V Implementations, Case Studies and Field Trials

    21. Narrowband PLC Channel and Noise Emulation ....................................................... 575Klaus Dostert, Martin Sigle and Wenqing Liu

    22. Cognitive Frequency Exclusion in EN 50561-1:2012 ....................................................601Andreas Schwager

    23. Mitigating PLC Interference to Broadcast Radio ......................................................... 625Yang Lu and Weilin Liu

    24. MIMO PLC Hardware Feasibility Study .......................................................................645Daniel M. Schneider and Andreas Schwager

  • xiii 2008 Taylor & Francis Group, LLC

    Preface

    Multiple-input multiple-output (MIMO) systems have been heavily investigated since the mid 1990s, targeting wireless communications. Nowadays, different MIMO processing options, with the aim of increasing data rates and communication reliability, are in operation in major wireless cellular systems such as WCDMA, LTE and WiMAX, as well as wireless local area networks (WLANs) based on IEEE 802.11n. Also, in the wireline world, digital sub-scriber line (DSL) systems have to deal with near-end and far-end crosstalk between individual modems. Recent developments treat DSL cable binders as MIMO communication channels, with the aim of applying multi-user coordination and interference mitigation techniques.

    For a long time, the power line channel has been regarded as a single-input single-output (SISO) channel based on two conductors. In reality, many in-home installations make use of three wires, and medium- and high-voltage installations often have four or more conduc-tors. Although the theoretical foundation of multi-conductor transmission line theory was extensively laid out in the last century, large-scale measurement results on MIMO power line channel and noise characteristics became available only in recent years, and only in 2011 did the International Telecommunications Union (ITU) publish a MIMO transceiver extension (G.9963) to their G.hn standard family. Simultaneously, the industry alliance, HomePlug, introduced MIMO signal processing within the HomePlug AV2 specification.

    Demand for higher data rates and multi-user support is driven by increasing home entertainment and communication needs. For example, one can imagine a household whose inhabitants consume several high-definition television streams, while simultane-ously browsing the Internet and making voice over IP (VoIP) calls. In this scenario, the focus is on high data rate applications with advanced quality of service differentiation. On the other hand, demand is also driven by the increasing number of intelligent devices that form part of the emerging Smart Grid. In such cases, coverage, reliability, and scalability are important attributes. Last but not least, the ever growing Internet of things (IoT) requires a huge amount of low data rate devices to communicate simultaneously, with stringent demands on power consumption and re-configurability.

    All these aspects are reflected in this book, which gives a profound introduction to pres-ent day power line communications (PLC), as follows:

    Part I: Power Line Channel and Noise: Characteristics and ModellingPart II: Regulations, Electromagnetic Compatibility and MIMO CapacityPart III: Current PLC Systems and Their EvolutionPart IV: Advanced PHY and MAC Layer ProcessingPart V: Implementations, Case Studies and Field Trials

    The individual chapters of Part I focus on narrow- and broadband channel characteri-sation, presenting measurement and modelling results from the United States, Europe and China. Building on this foundation, and taking into account current regulations and aspects of electromagnetic compatibility (EMC), Part II describes MIMO signal process-ing strategies and related MIMO capacity and throughput estimates. Current narrow- and broadband PLCstandards and specifications are described in detail in the various chap-ters of Part III. Especially, the narrowband power line standards ITU-T G.9902, G.9903,

  • xiv Preface

    2008 Taylor & Francis Group, LLC

    G.9904 and IEEE 1901.2 are discussed, followed by individual broadband PLC chapters on ITU G.hn, IEEE 1901 and HomePlug AV2. Part III is rounded off by an introduction to hybrid systems based on IEEE 1905.1, combining PLC with other wireless and wireline technologies. AdvancedPLC processing options are treated in Part IV, drawing from a wide variety of research areas such as beamforming/precoding, time reversal, multi-user pro-cessing and relaying. The book is concluded by Part V, which contains case studies and field trials where advanced technologies are explained with practical examples. Topics are as diverse as channel and noise emulation, cognitive notching, interference mitigation and MIMO PLC hardware feasibility.

    All chapters are written as much as possible in a self-contained manner. Additionally, the chapters have been extensively cross-referenced, allowing each reader to pursue a per-sonal reading path. We hope you enjoy the diverse contents contributed by experts from industry and academia, making this book one of the first of its kind in the exciting world of MIMO PLC.

    Lars T. BergerAndreas Schwager

    Pascal PaganiDaniel M. Schneider

    Significant portions of this book, particularly Chapters 13 and 15, were excerpted from IEEE 1901-2010, IEEE Standard for Broadband over Power Line Networks: Medium Access Control and Physical Layer Specifications, and from IEEE 1905.1-2013, IEEE Standard for a Convergent Digital Home Network for Heterogeneous Technologies, copyright IEEE, and reproduced with permission by limited license from IEEE. Permission for further use of this material must be obtained from IEEE. Requests may be sent to [email protected]/sg. For a full copy of the standards, please visit IEEEs online store at standards.ieee.org/store.

    MATLAB is a registered trademark of The MathWorks, Inc. For product information, please contact:

    The MathWorks, Inc.3 Apple Hill DriveNatick, MA 01760-2098 USATel: 508-647-7000Fax: 508-647-7001E-mail: [email protected]: www.mathworks.com

  • xv 2008 Taylor & Francis Group, LLC

    Editors

    Dr. Lars Torsten Berger is director of the R&D department of Kenus Informtica, Paterna, Spain, and founder of BreezeSolve, a Valencia-based company offering engineering and consultancy services in telecommunications, signal processing and Smart Grid.

    Dr. Berger received his Dipl-Ing in electrical engineering, MSc in communication sys-tems and signal processing and PhD in wireless communications from the Ravensburg University of Cooperative Education, Germany; the University of Bristol, United Kingdom; and Aalborg University, Denmark, in 1999, 2001 and 2005, respectively.

    While working for Nortel Networks, United Kingdom, and during his four years stay at Aalborg University financed by Nokia Networks, he focused extensively on MIMO channel modelling, MIMO signal processing and MIMO scheduling algorithms for 3G cellular systems. During a visiting professor term at the University Carlos III of Madrid, Spain, he extended his work to 4G cellular, as well as wireless LAN systems and sensor networks. From 2006 to 2010, he became senior engineer at Design of Systems on Silicon (DS2, Spain, in 2010 acquired by Marvell Semiconductors), forming part of the key system architecture team responsible for MIMO and multi-user-enabled power line silicon solutions. More recently, he has extended his area of interest to Smart Grid technologies.

    Dr. Berger has published numerous MIMO, scheduling and PLC-related articles in con-ference proceedings and in international journals. He is the inventor of an international patent related to MIMO PLC signal transmission, has several patent applications pending and is editor of the book entitled Smart Grid Applications, Communications and Security.

    Dr. Andreas Schwager has had interest in PLC for over 15 years. Currently, he works as a principal engineer in Sonys European Technology Center in Stuttgart, Germany. Sonys R&D in Stuttgart includes the areas of digital radio and video broadcasting, as well as home networking.

    Dr. Schwager earned a diploma in telecommunication engineering from the University of Cooperative Education, Stuttgart, in 1993. In May 2010, the University of Duisburg-Essen awarded him a PhD (doctor of science [engineering]) following the publication of his thesis Powerline Communications: Significant Technologies to Become Ready for Integration, which discussed the utilisation of MIMO PLC and the concept of dynamic notching to solve the vast EMC discussion on PLC.

    Dr. Schwagers career began at the advanced development labs at ANT Bosch Telecom, Backnang, Germany, and Grundig, Nrnberg, Germany, where he developed narrowband PLC functions for satellite headends. He joined Sony in 1997, where the development of both software and hardware components for home-networking applications ignited his enthusiasm for PLC. Today, Dr. Schwager represents Sony at various standardisation com-mittees at IEEE, ITU, CISPR, CENELEC, Homeplug and ETSI. He is the rapporteur of more than ten work items where technical standards and reports are published, the most recent being the three-part ETSI TR specifying MIMO PLC field measurements and presenting results of MIMO PLC properties. He also led several task forces at international standardi-sation bodies.

    Dr. Schwager is the author of numerous papers presented at research conferences and the inventor of tens of granted IPR in the area of PLC and communications.

  • xvi Editors

    2008 Taylor & Francis Group, LLC

    Dr. Pascal Pagani is an associate professor at the graduate engineering school Telecom Bretagne in Brest, France, and is a member of the Lab-STICC laboratory (UMR CNRS 6285) dedicated to information and communication science.

    He received his MSc in communication systems and signal processing from the University of Bristol, United Kingdom, in 2002, and his PhD in electronics from INSA Rennes, France, in 2005.

    Prior to joining Telecom Bretagne in 2012, he worked with France Telecom Orange Labs, where he was active in various projects, including UWB propagation channel characterisation and modelling, short range wireless system design and development of in-home wireline communications. He led France Telecom standardisation activities in the IEEE 802.15.3c, ITU SG15 G.hn and HomePlug TWG groups and participated in the ETSI Specialist Task Force 410 for the experimental assessment of the PLC MIMO transmission channel.

    Dr. Pagani is a member of the Technical Committee on PLC within the IEEE Communications Society. He is the author of more than 50 publications, including books, book chapters and journal and conference papers in the fields of wireless and wired com-munication and has filed several pending patents. His current research interests are in the field of radio and wireline transmission, particularly long-haul radio wave propagation and advanced PLC.

    Dr. Daniel Schneider currently works as a senior engineer in the European Technology Center of Sony in Stuttgart, Germany, where his work is concerned with communications systems and PLC in particular. He contributed to the work of the PLC HomePlug AV2 specification and was involved in the ETSI MIMO PLC field measurement campaign.

    He received his Dipl-Ing in electrical engineering, with a focus on signal processing and communications, and his Dr-Ing for his thesis In-Home Power Line Communications Using Multiple Input Multiple Output Principles from the University of Stuttgart in 2006 and 2012, respectively.

    Dr. Schneider has published multiple papers related to PLC and MIMO and is inventor of several international patents.

  • xvii 2008 Taylor & Francis Group, LLC

    Jose AbadBroadcom CorporationMalaga, Spain

    Kaywan AfkhamieSystems Group Qualcomm AtherosOcala, Florida

    Jean-Yves BaudaisCentre National de la Recherche

    ScientifiqueInstitut dElectronique et de

    Tlcommunications de RennesRennes, France

    Erez Ben-TovimSigma Designs Israel S.D.I Ltd.Tel-Aviv, Israel

    Lars T. BergerKenus InformaticaPaterna, Spain

    and

    BreezeSolveValencia, Spain

    Paola BisagliaDORA S.p.A., STMicroelectronics GroupAosta, Italy

    Thierry ChonavelTelecom BretagneBrest, France

    Guangbin ChuDepartment of Information and

    CommunicationChina Electrical Power Research InstituteFangshan, Beijing, Peoples Republic

    ofChina

    Etan G. CohenQualcomm AtherosSan Jose, California

    Matthieu CrussireInstitut National des Sciences AppliquesInstitut dElectronique et de

    Tlcommunications de RennesRennes, France

    Salvatore DAlessandroWiTiKee S.r.l.Udine, Italy

    Klaus DostertKarlsruhe Institute of TechnologyInstitute of Industrial Information

    TechnologyKarlsruhe, Germany

    Stefano GalliASSIA, Inc.CTO OfficeNew York City, New York

    Lorenzo GuerrieriDORA S.p.A., STMicroelectronics GroupAosta, Italy

    Rehan HashmatEurecomValbonne, France

    Duncan HoQualcomm Inc.San Diego, California

    Srinivas KatarSystems Group Qualcomm AtherosOcala, Florida

    Contributors

  • xviii Contributors

    2008 Taylor & Francis Group, LLC

    Manjunath KrishnamQualcomm AtherosOcala, Florida

    James Le ClareMaxim Integrated ProductsSan Jose, California

    Jianqi LiDepartment of Information and

    CommunicationChina Electrical Power Research InstituteFangshan, Beijing, People Republic

    ofChina

    Hidayat LioeMarvell Semiconductor Inc.Santa Clara, California

    Weilin LiuDepartment of Information and

    CommunicationChina Electrical Power Research InstituteFangshan, Beijing, Peoples Republic

    ofChina

    Wenqing LiuKarlsruhe Institute of TechnologyInstitute of Industrial Information

    TechnologyKarlsruhe, Germany

    Yang LuDepartment of Information and

    CommunicationChina Electric Power Research InstituteFangshan, Beijing, Peoples Republic

    ofChina

    Amilcar MesccoTelecom BretagneBrest, France

    Bibhu P. MohantyQualcomm Inc.San Diego, California

    Arun NayagamQualcomm AtherosOcala, Florida

    Michel NeyTelecom BretagneBrest, France

    Fabio OsnatoSTMicroelectronics SrlAdvanced System TechnologyAgrate Brianza, Italy

    Pascal PaganiTelecom BretagneBrest, France

    Purva R. RajkotiaQualcomm AtherosOcala, Florida

    Deniz RendeSystems Group Qualcomm AtherosOcala, Florida

    Markus RindchenPower Plus Communications AGMannheim, Germany

    Raffaele RivaSTMicroelectronics SrlAdvanced System TechnologyAgrate Brianza, Italy

    Yago Snchez QuintasSony Deutschland GmbHStuttgart, Germany

    Daniel M. SchneiderSony Deutschland GmbHStuttgart, Germany

    Andreas SchwagerSony Deutschland GmbHStuttgart, Germany

  • xixContributors

    2008 Taylor & Francis Group, LLC

    Martin SigleKarlsruhe Institute of TechnologyInstitute of Industrial Information

    TechnologyKarlsruhe, Germany

    Matthias StephanPower Plus Communications AGMannheim, Germany

    Andrea M. TonelloWiPLi LabDipartimento di Ingegneria Elettrica,

    Gestionale e MeccanicaUniversit degli Studi di UdineUdine, Italy

    Piet Janse van RensburgWalter Sisulu UniversityEast London, South Africa

    Larry YongeSystems Group Qualcomm AtherosOcala, Florida

    Ahmed ZeddamFrance Telecom OrangeLannion, France

  • 2008 Taylor & Francis Group, LLC

    Part I

    Power Line Channel and Noise: Characteristics and Modelling

  • 3 2008 Taylor & Francis Group, LLC

    1Introduction to Power Line Communication Channel and Noise Characterisation

    Lars T. Berger, Pascal Pagani, Andreas Schwager and Piet Janse van Rensburg

    1.1 Introduction*

    Since the late 1990s, an increased effort has been put into the characterisation of power line communication (PLC) channels with the aim of designing communication systems that use the electrical power distribution grid as data transmission medium.

    Reliable PLC systems, for home networking, Internet protocol television (IPTV), Smart Grid and smart building applications are now a reality. However, power lines have not been designed for communication purposes and constitute a difficult environment to convey information via early analogue signalling or nowadays widespread advanced digital PLC systems. The PLC channel exhibits frequency-selective multi-path fading, a low-pass behaviour,

    * Chapter in parts based on material from [14].

    CONTENTS

    1.1 Introduction ............................................................................................................................31.2 PLC Frequency Bands and Topologies ...............................................................................41.3 Coupling Methods .................................................................................................................61.4 Channel and Noise Measurement Set-Up ........................................................................ 11

    1.4.1 Transfer Function Measurements .......................................................................... 111.4.2 Reflection Measurements and Input Impedance Calculation ........................... 131.4.3 Noise Measurements ............................................................................................... 14

    1.5 Channel Characterisation and Modelling Approaches ................................................. 151.5.1 Channel Characteristics .......................................................................................... 151.5.2 Channel Modelling Overview ............................................................................... 151.5.3 MIMO Channel Models .......................................................................................... 19

    1.6 Noise Characterisation and Modelling Approaches ......................................................221.6.1 Noise Characteristics ...............................................................................................221.6.2 Noise Modelling for MIMO PLC ...........................................................................23

    1.7 Conclusion ............................................................................................................................ 24Appendix 1.A: Introduction to Transmission Line Theory .....................................................25Acknowledgements ...................................................................................................................... 31References ....................................................................................................................................... 31

  • 4 MIMO Power Line Communications

    2008 Taylor & Francis Group, LLC

    cyclic short-term variations and abrupt long-term variations that are introduced in Section 1.5. Further, power line noise can be grouped based on temporal as well as spectral characteris-tics. Following, for example [5,6], one can distinguish coloured background noise, narrowband (NB) noise, periodic impulsive noise (asynchronous or synchronous to the alternating current [AC] frequency), as well as aperiodic impulsive noise (see Section 1.6). These impairments are leading some researchers to speak of a horrible channel [7].

    Apart from these, the very principle of PLC implies that small-signal, high-frequency technologies are being deployed over power-carrying cables and networks that were designed for electricity transmission at low frequencies. In terms of voltage, the equip-ments communication ports would fail if they were connected directly to the power grid. This is similarly true when looking at PLC testing and measurement equipment, such as a spectrum analyser, which is why PLC couplers are needed to couple the com-munication signal into and out of the power line while at the same time protecting the communication equipment. Couplers may be of either inductive or capacitive nature with detailed coupling schemes introduced in Section 1.3. Before that, however, this chapter looks at PLC frequency bands and common topologies in Section 1.2 as these are possibly the most profound stage setters when characterising PLC channel and noise scenarios. In the sequel, the aim of Section 1.4 is to provide information on measurement equipment and procedures that have been used to generate a plurality of results for various chapters throughout this book. Further, Sections 1.5 and 1.6 introduce the underlying concepts of PLC channel and noise modelling, respectively, and guide the reader to the more detailed chapters on each topic. This chapter is rounded off by an appendix that explains the basics of dual conductor transmission line theory, considered interesting background reading for those new to PLC signal propagation.

    1.2 PLC Frequency Bands and Topologies

    The frequency bands as agreed upon by the International Telecommunications Union [8] are shown in Figure 1.1. The band name abbreviations stand for super low, ultra low, very low, low, medium, high, ultra high, very high, super high, extremely high and tremendously high frequency, respectively. As indicated in Figure 1.1, currently only the VLF up to the UHF bands are interesting for PLC systems. These systems are usually subdivided into narrowband (NB) and broadband (BB) PLC; the former operating below 1.8 MHz, the latter operating above [9]. Details on the regulations corresponding to these frequency bands can be found in Chapter6. An overview on systems that belong to either the class of NB-PLC or the class of BB-PLC can be found in Chapter 10.

    Besides the distinction into NB-PLC and BB-PLC, it has been common practice to dis-tinguish power line topologies according to operation voltages of the power lines [2,9,10].

    SLF ULF VLF LF MF HF UHF VHF SHF EHF THF30 Hz 300 Hz 3 kHz 30 kHz 300 kHz 3 MHz 30 MHz 300 MHz 3 GHz 30 GHz 300 GHz 3 THz

    3 kHz 1.8 MHz 100 MHz

    Ultra-narrowband PLC Narrowband PLC Broadband PLC

    FIGURE 1.1ITU frequency bands and their usage in power line communications.

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    High-voltage (HV) lines, with voltages in the range from 110 to 380 kV, are used for nation-wide or even international power transfer and consist of long overhead lines with little or no branches. This makes them acceptable wave guides with less attenuation per line length as for their medium-voltage (MV) and low-voltage (LV) counterparts. However, their potential for BB communication services has up to the present day been limited. Time-varying HV arcing and corona noise with noise power fluctuations in the order of several tens of dBs as well as the practicalities and costs of coupling communication signals in and out of these lines have been an issue. Further, there is a fierce competition of fibre optical links. In some cases, these links might even be spliced together with the ground conductor of the HV system [11,12]. Nevertheless, several successful trials using HV lines have been reported in [1316].

    MV lines, with voltages in the range from 10 to 30 kV, are connected to the HV lines via primary transformer substations. The MV lines are used for power distribution between cities, towns and larger industrial customers. They can be realised as overhead or underground lines. Further, they exhibit a low level of branches and directly connect to intelligent electronic devices (IED) such as reclosers, sectionalisers, capacitor banks and pha-sor measurement units. IED monitoring and control requires only relatively low data rates and NB-PLC can provide economically competitive communication solutions for these tasks. MV-related studies and trials can be found in [1720].

    LV lines, with voltages in the range from 110 to 400 V, are connected to the MV lines via secondary transformer substations. A communication signal on an MV line can pass through the secondary transformer onto the LV line, however, with a heavy attenuation in the order of 5575 dB [21]. Hence, a special coupling device (inductive, capacitive) or a PLC repeater is frequently required if one wants to establish a high data rate communications path. The LV lines lead directly or over street cabinets to the end customers premises. Note that considerable regional topology difference exits. For example, in the United States, a smaller secondary transformer on a utility pole might service a single house or a small number of houses. In Europe, however, it is more common that up to 100 households get served from a single secondary transformer substation. Further, as pointed out in [22], significant differences exist between building types. They may be categorised as multi-flat buildings with riser, multi-flat buildings with common meter room, single family houses and high-rise buildings. Their different electrical wiring topologies influence signal attenuation as well as interference between neighbouring PLC networks [23]. In most cases, the electrical grid enters the customers premises over a house access point (HAP) followed by an electric-ity meter (M) and a distribution board (fuse box). From there, the LV lines run in a tree or star topology up to the different power sockets in every room. One frequently refers to PLC systems operating from outside to inside a customers premises as access systems while systems operating within the premises are referred to as in-home. It can be summarised that the access scenario establishes data connections to a group of customers through the overhead and/or underground electrical power distribution grid [7,2426]. The in-home scenario enables the communication of different devices within a users premises [7,2732].

    Besides these operation voltage-oriented distinctions, one may distinguish in-vehicle PLC and MIMO PLC.

    In-vehicle PLC has been considered to provide data access to moving vehicles like trains [33], as well as within the vehicles themselves, for example, in cars [34], aerospace and outer space applications [35,36], ships [37] and submarines [38]. Among others, advantages of PLC over other wireline communication techniques are weight reduction, reduced pin numbers for device internal connections and, in general, wiring complexity reductions. Especially, communicating with parked plug-in electrical vehicles has been at the focus

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    of attention with respect to integrating electrical vehicle fleets into the Smart Grid that is currently built up all around the world [39]. Besides, in-cars PLC is starting to revitalise the after-sales market business for consumer electronics.

    MIMO PLC Building on the success of multiple-input multiple-output (MIMO) signal processing within wireless communications [40,41], it is worth noting that MV and HV installations often make use of four or more conductors. In this respect, a theoretical frame-work of multi-conductor transmission line (MTL) theory is extensively treated in [42]. Further, in many in-home installations three wires, namely live (L) (also called phase), neutral (N) and protective earth (PE), are common. Exactly how common on a worldwide scale was investi-gated by the European Telecommunications Standards Institute (ETSI).* The investigation of Specialist Task Force (STF) 410 [43] was based on

    A study of individual grounding systems and investigations into which ground-ing systems are used in which countries; such information could be derived from, for example, education material for electricians.

    The creation of a list of AC wall socket types and their respective usage area. For example, universal travel adapters indicate how many different power outlets exist in the world. Plugs and sockets could easily be checked for the presence of a PE pin. However, the existence of the pin does not guarantee the existence of a PE wire leading up to the socket. When renewing older buildings frequently, the protective earth of the socket is shortcut with the neutral wire behind the outlet or simply not connected at all.

    Research on the dates when the PE installation became mandatory in a country and an estimate of how many electrical installations have taken place since then.

    A survey of sales information, for example, worldwide sales numbers of residual-current devices (RCDs) or power cables including ground which in the sequel allows estimates on the PE availability level in a country.

    A worldwide survey of data from electrical standardisation committees and engi-neering clubs for each country.

    Reference [43] lists detailed information and statistical evaluations on each of these points. It is almost impossible to summarise all this information into a single sentence, but when trying to do so, the result would be something like

    The third wire is present at all outlets in China and the Commonwealth of Nations, at most outlets in the western countries and only at very few outlets in JP and Russia.

    1.3 Coupling Methods

    When turning to coupling methods, one may generally distinguish between inductive and capacitive couplers. It should be noted that inductive couplers guarantee a balance between the lines whereas capacitive couplers often introduce asymmetries due to component

    * ETSI is an independent, non-profit, standardisation organisation formed by equipment makers, network oper-ators and other stakeholders from telecommunications industry.

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    manufacturing tolerances. Besides symmetry, signal bandwidth and the dimensioning to protect the communications equipment, for example, against lightning strikes or other HV spikes on the grid side are decisive coupler properties. Moreover, the observed channel characteristics are not independent from the coupling devices used to inject and receive the power line signal. Inductive as well as capacitive couplers especially tailored to MV, HV and even up to extra HV lines can be found in ([44, Section 5.5.1]). Further, details on LV inductive single-input single-output (SISO) couplers may, for example, be found in [45,46]. The following will focus on LV inductive MIMO coupling options that play an important role throughout various chapters of this book.

    Figure 1.2 presents three inductive MIMO coupler options, that is, a delta-style (D) coupler [47], a T-style (T) coupler [48] and a star-style (S) coupler [47]. Coupler designs are tightly related to radiated emission treated in more detail in Chapters 6 and 7. According to the BiotSavart law, the main source of radiated emission is the common-mode (CM) current denoted ICM. To avoid radiated emission, traditionally PLC modem manufactur-ers aim at injecting the signal as symmetrically as possible. This way, 180 out of phase electric fields are generated that neutralise each other resulting in little radiated emis-sion. This desired symmetrical way of propagation is also known as differential-mode (DM) with its associated signal voltage UDM. In a symmetrical network, the differential current IDM flows from its feeding point via the network back to its source as indicated in Figure1.3. In case of asymmetries, for example, caused by parasitic capacitances (inside the refrigerator in Figure 1.3), a small part of the differentially injected radio frequency (RF) current IDM turns into CM current ICM. It flows to ground or to any other consumer device and returns to its source via a series of asymmetries in the network. Normally, there are many asymmetries inside a PLC topology. For example, an open light switch causes an asymmetric circuit and, hence, even if only DM is injected by a PLC coupler, DM to CM conversion occurs [49].

    Specifically, to avoid additional CM currents, feeding MIMO PLC signals can be done using the delta or T-style couplers from Figure 1.2 while it is not recommended using the star-style coupler known also as longitudinal coupler due to the risk of CM signal injec-tion. As shown in Figure 1.2, the delta-style coupler, also called transversal probe, consists of three baluns arranged in a triangle between L, N and PE. The sum of the three voltages injected has to be zero (following Kirchhoffs law). Hence, only two of the three signals are independent. Turning to the T-style coupler, it feeds a DM signal between L and N plus a second signal between the middle point of L-N to PE. Further details on the pros and cons of each coupler type are discussed in [43].

    All three coupler types are well suited for reception. However, especially the star-style coupler, where three wires are connected in a star topology to the centre point, is

    N

    L

    PE

    S1

    S2S3

    S4

    D1

    D2

    D3L

    N PE

    T1

    T2

    N

    L

    PE

    (a) (b) (c)

    FIGURE 1.2Inductive MIMO PLC couplers. (a) Delta-style (D), (b) T-style (T) and (c) star-style (S).

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    interesting. Kirchhoffs law forces the sum of all currents arriving at the centre point to be zero. Thus, only two of the three receive (Rx) signals are independent. Nevertheless, due to parasitic components the signals at the third port may additionally improve the capacity of MIMO PLC system (see Chapter 5 for details). However, a more significant benefit is the possibility to receive CM signals, that is, a fourth reception path. The CM transformer is magnetically coupled (Faraday type). On average, CM signals are less attenuated than DM signals which makes their reception interesting, especially for highly attenuated channels [47] (see also Chapter 5).

    In general, looking at the experienced input impedance of a mains network, there might be an impedance unbalanced between L-N and L-PE. This is especially true for lower frequencies where 50 Hz loads play an important role [27]. Further, the effective CM impedance is also very different from DM impedances (see Chapter 5 for details). Table 1.1 shows a summary of approximate expected power line input impedances as obtained from the open literature and other chapters in this book. Table 1.1 shows that, for example, impedances in Europe and the United States are very similar. Comparing L-N with L-PE impedances, a marked difference can be observed. For example, for fre-quencies below 500 kHz this difference can be more than three times and for frequencies between 1and 30 MHz the L-PE impedance may be around two times larger than in the L-N impedance. However, when looking at the average statistics up to 100 MHz, imped-ance levels converge, yielding a more balanced MIMO system, the reason possibly also

    Local ground plane

    Parasiticcapacitance

    Parasiticcapacitance

    Switch

    Feeds DM signals

    PLCmodem

    PLCmodem

    UCM

    ICM

    ICM

    IDMR

    FIGURE 1.3Generation of CM signals in a building.

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    being that MIMO couplers used in the related measurement campaign terminated all three ports at signal injection. More details are found in Chapter 5.

    Statistical knowledge of the input impedances may be taken into account in the MIMO coupler design. That is, isolation transformers/baluns are required for most MIMO cou-pling strategies to allow the multiple signals to float independently. In this respect, to obtain BB channel and noise characterisation and EMC results in Chapters 5 and 7, a single coupling circuit capable of implementing the T-style, delta-style and star-style coupler as introduced in Figure 1.2, has been designed with its schematic shown in Figure 1.4.

    The physical connection to the power grid via a Schuko-type plug is shown on the left. Selection between the coupling types is performed via the switches labelled Sw1 and Sw2, shown in the centre. On the right-hand side, there are the terminals T1 to T2, D1 to D3 and S1 to S4 for connecting the coupler to measurement equipment such as a network analyser (NWA) or a digital sampling oscilloscope (DSO). The delta-style and T-style terminals are connected through current baluns to facilitate floating signals, and further minimise CM injection as well as any subsequent increase in radiation. The baluns in the delta-style cou-pler are 1:4 Guanella transformers with very low loss. They perform a 50200 impedance conversion. Considering a DM impedance of any pair of the three wires of 102 where in the MIMO case this impedance exists twice in series plus once in parallel (resulting in 68 ), the 200 output of the Guanella transformer appears to be the optimal matching compromise. Sw3 allows toggling between MIMO and SISO terminations of the feeding ports. The star-style terminals use coupled current transformers (CM chokes). Their function is to measure the CM current flowing through the three wires (L || PE || N). Theinductance of each winding is selected small enough not to filter the PLC frequen-cies of interest (1100 MHz). An additional switch (not shown in Figure 1.4) might short circuit the secondary (and thus magnetising inductance) of these CM chokes, thus making them transparent to the overall circuit when not in use.

    Looking at the other electronic components in Figure 1.4, one can see that in series with each line, there is a 4.7 nF coupling capacitor, fulfilling the main coupling function protection by means of filtering, while the capacitor to the Earth wire is implemented to maintain symmetry. Furthermore, it lowers the leakage current that could otherwise cause

    TABLE 1.1

    Power Line Impedances

    Frequencies Country L-N in L-PE in N-PE in Source

    50500 kHz JP 0.520 (6.5) na na [50,51]Germany 160 (10) na na Chapter 2Europe na 1200 (30) na [52]China 19 (5) na na Chapter 3United States na 1150 (18) na [52,53]

    130 MHz JP 31 k (83) na na [54]Germany 10300 (30) 20400 (60) na [27]Europe (102) 9400 (90) na [47,52]United States na 6400 (95) na [52,53]

    1100 MHz Europe 10190 (86) 10190 (89) 10190 (87) Chapter 5

    Note: Value in brackets indicates median. If there is more than one reference, the range was taken over the minima/maxima from the references and the arithmetic mean was calculated to obtain a single median value.

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    a residual current device (RCD) to fail. The breakdown voltage of these capacitors are rated roughly twice the expected root mean square (rms) value, that is, 1.5 times the expected peak value of the power waveform to be blocked. The mains connection can be unplugged at any time. Hence, the capacitors may be charged to dangerous voltages, and they are in this case discharged by a parallel resistor, large enough not to short circuit significant current past the blocking capacitor thereby impacting on the filtering action of this capacitor. The RC time constant is adjusted so that the blocking capacitor discharge within 15 ms to protect against accidentally touching the prongs of the attached Schuko when unplug-gingit. Apart from the protection offered by the coupling capacitor, supplementary protec-tive devices are deployed to absorb voltage transients. Surge protection diodes can be seen in parallel with the three lines. The input impedance of these and other protective devices

    DE37-501M

    ERZ-V07D471

    LNPE

    3*GBLC08C-LF Delta/

    star T-style Star/T-style

    BNC to50 Ohn

    3* 4.7 nF2* 820 k

    Sw 3 200

    200

    GuanellaD1

    D2

    D3

    S1

    S2

    S3

    S4

    T1

    T2

    CM choke

    BAL 2

    200

    Sw 3

    Sw 3

    Sw1 Sw2

    BAL 1

    FIGURE 1.4A 2-Tx 4-Rx MIMO PLC coupler with added protective circuitry. (Based on European Telecommunication Standards Institute (ETSI), Powerline Telecommunications (PLT); MIMO PLT Universal Coupler, Operating Instructions Description, May 2011. Available online at: http://www.etsi.org/deliver/etsi_tr/101500_101599/101562/01.01.01_60/tr_101562v010101p.pdf.)

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    are sufficiently high not to drain or filter the PLC signal. On the mains side of the coupling capacitors (across L-N), gas-discharge devices and metal-oxide varistors (MOVs) are used. They serve as over-voltage protection and are deployed in parallel as they possess dif-ferent speed versus power characteristics and are, hence, complementary. Supplementary information on surge protection in general may be found in [5558]. The specific safety components of the coupler as shown in Figure 1.4 are given in [45] alongside the couplers calibration data.

    1.4 Channel and Noise Measurement Set-Up

    This section describes the measurement set-up and the equipment used to record channel, reflection and noise properties of the MIMO PLC channel on a LV grid. It therewith forms the basis for the results in Chapters 5, 7 through 9, 16, 17 and 22. The following measure-ment campaign objectives are defined:

    Frequency range from 1 to 100 MHz. Channel transfer function (CTF) measurements. Noise-level measurements. Input impedance measurements. Coupling factor measurements (i.e. the coupling factor or k-factor is the ratio

    between the electric field caused by signal radiation and the signal power fed into the main grid [59] [see also Chapter 7]).

    All measurements are to be performed with the same coupler design to allow for straightforward comparability of results.

    1.4.1 Transfer Function Measurements

    The CTF can be measured in the frequency domain by recording the scattering param-eter S21 using a conventional NWA (for an introduction to scattering parameters see, for example, [60]). Figure 1.5 depicts the set-up for channel measurements in a private home.

    A NWA is connected to two PLC couplers via its transmit (Tx) and receive (Rx) ports. The couplers follow the schema as introduced in Figure 1.4. All terminals T1 to T2, D1 to D3 and S1 to S4 are terminated by 50 each. Terminating the ports avoids additional signal reflections caused by connecting measurement equipment. When terminating the three-wire system, the impedance of each wire pair is present three times in parallel. Afinal PLC modem implementation might terminate two or three of the three wires with, for example, a low impedance when transmitting and a high impedance when receiving.

    Further, a ground plane as shown in Figure 1.6 is connected tight to the receiving cou-pler. To achieve a low impedance or high capacity connection to ground, a huge ground plane is necessary, especially also for reproducibility of the received CM signal. The size of the ground plane is sufficiently large when human contact no longer influences mea-surement results. From a physical point of view, human contact results in a capacitance increase towards ground, which will not influence the result when the ground planes stand-alone capacity is already sufficiently large. In this respect also, the reception of lower

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    Local counterpoise

    Asymmetries in themains grid cause

    CM currents

    Ferrite beads

    Tx

    RxNWA Mains filterCM + DM

    To neighbour

    ICM

    FIGURE 1.5Private home with channel measurement equipment.

    FIGURE 1.6Ground plane with connected PLC coupler.

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    frequencies requires a larger ground plane than the reception of higher frequencies. In a practical setting, the backplane, for example, of a high-definition television (HDTV) could serve as a ground plane for an incorporated PLC modem. Coming back to the NWA, it provides a dynamic range of 120 dB for through, that is, S21, measurements. Considering that the dynamic range of many commercial PLC modems lies in the order of 90 dB, 120 dB seems sufficient. However, to obtain meaningful results, the coaxial cables especially the one connecting the Rx coupler with the Rx port of the NWA have to support such a dynamic range, which means double-shielded cables are required. Moreover, due to long distances inside the buildings, low attenuation cables are preferred. RG214 or Ecoflex 10 cables fulfil these requirements. Further, to avoid signal ingress to the cable going back from the Rx coupler to the NWA, the cable is surrounded by suppression axial ferrite bead with a 15 cm inter-bead spacing as indicated in Figure 1.5.

    If the test instruments (namely the NWA) are connected to the mains section for electromagnetic interference (EMI), impedance and CTF measurements, the instruments rep-resent an additional load and may cause measurement errors. Hence, whenever possible the power for the measurement equipment is drawn from a neighbouring flat via an exten-sion cable. Further, on the right hand side of Figure 1.5, one can see a mains filter CM+CD. This filter is used to isolate the PE wire and consists of an isolation transformer and a line impedance stabilisation network (LISN). Additionally, a MIMO mains filter is used on each of the three wires eliminating DM signals, plus a CM choke to get rid of potential longitu-dinal signals. Such MIMO mains filter is not commercially available and was specifically manufactured for this measurement campaign. S21 measurement results using this set-up may be found in Chapter 5.

    1.4.2 Reflection Measurements and Input Impedance Calculation

    The LV distribution network (LVDN) is a network with undefined complex characteristic impedance. The often measured absolute value of the input impedance has little practi-cal significance. Adding a short piece of mains cable may change the results considerably. Thus, ETSI STF 410 measured the reflection loss expressed through the scattering param-eter S11 [60] at the delta terminals of the couplers instead.

    Generally, reflection measurement signals are fed and received at one and the same NWA port and require only the Tx coupler. The set-up is as shown in Figure 1.5 but with-out connecting the Rx coupler. The NWA is calibrated with a short, open and a 50 termination connected at the end of the coaxial cable. The MIMO PLC coupler is consid-ered to be part of the PLC channel.

    S11 is a complex value which is a function of the load impedance and of the characteristic impedance of the measurement system (see Equation 1.14 for a general definition). Here, the measurement system consists of the NWA, which has a characteristic impedance of 50 and the balun inside the MIMO coupler, which transforms the 50200 , that is, Zcoup = 200. Theoretically, S11 on the 50 side is identical to S11 if measured on the 200 side, except for a phase shift due to the length of the transmission lines inside the balun. The real and the imaginary parts of S11 are recorded. For engineering purposes, the absolute value |S11| is often sufficient. It allows calculating the maximum line input impedance ZDM max, that is,

    Z Z

    SSDM coupmax

    .= +( )-( )

    11

    11

    11

    (1.1)

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    However, the phase is also required to calculate ZDM as a function of frequency and line length of the balun (0.3 m1) denoted x, that is,

    Z ZS eS e

    j x

    j xDM coup=+( )-( )

    ,11

    11

    11

    b

    b

    (1.2)

    where the phase constant may be obtained as outlined in Appendix 1.A, Equation 1.12, assuming a wave speed v in the balun to be 200,000,000 m/s.

    1.4.3 Noise Measurements

    The noise measurement set-up is depicted in Figure 1.7. The MIMO coupler from Figure1.4 is used in the star configuration (ports S1, S2, S3 and S4). Thus, the noise volt-age present at the L, N and PE wires as well as the CM voltage can be directly sampled in the time domain by connecting a DSO (with digital signal processing [DSP] probe P1toP4). The sampling rate is 500 Msamples/s. Further, care is taken that the DSP memory can store the four signals over 20 ms, corresponding to a single period of the AC line cycle at 50 Hz.

    One drawback of the time domain measurement is that out-of-band noise can eas-ily influence the result. Hence, DSO probes are using band-pass filters in order to reduce out-of-band noise. In each configuration, four different bands were tested, with

    P1 DSOP2P3P4

    Mains filterCM + DM

    Coupler

    Filters

    Local counterpoise

    To neighbour

    Amplifiers

    FIGURE 1.7Private home with noise measurement equipment.

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    the respective frequency ranges 2100 MHz, 288 MHz, 30100 MHz and 3088 MHz. Further, in environments with low noise levels, low noise amplifiers are used to boost the input signal before recording. Each amplifier presented a flat frequency response up to 100 MHz and a gain of 28 dB.

    1.5 Channel Characterisation and Modelling Approaches

    The power line channel and noise situations heavily depend on the scenario as outlined in Section 1.2 and, hence, span a very large range. Generally, frequency-selective multi-path fading, a low-pass behaviour, AC-related cyclic short-term variations and abrupt long-term variations can be observed (see, for example, Chapters 2 through 5).

    1.5.1 Channel Characteristics

    Multi-path fading is caused by inhomogeneities of the power line segments where cabling and connected loads with different impedances give rise to signal reflections and in the sequel in-phase and anti-phase combinations of the arriving signal components. The corresponding transfer function can readily be derived in close form as infinite impulse response (IIR) filter [1] and underlying basics are outlined in Appendix 1.A. One impor-tant parameter capturing the frequency-selective characteristics is the rms delay spread (DS). For example, designing orthogonal frequency-division multiplexing (OFDM) systems, the guard interval might be chosen as 23 times the rms DS to deliver good system per-formance [61]. To provide an orientation, the mean of the observed rms DS for a band from 1 MHz up to 30 MHz in the MV, LV-access and LV-in-home situations in [21,61] was reported to be 1.9, 1.2 and 0.73 s, respectively. Similarly, in Chapter 4, rms DS in the range 0.22.5 s are reported from LV-in-home measurements performed within the 1.888 MHz frequency band.

    Besides multi-path fading, the PLC channel exhibits time variation due to loads and/or line segments being connected or disconnected [62]. Further, through synchronising chan-nel measurements with the electrical grid AC mains cycle, Caete et al. were able to show that the in-home channel changes in a cyclostationary manner [47,63] (see also especially Chapters 2 and 21).

    Until now, the low-pass behaviour of PLC channels has not been considered. It results from dielectric losses in the insulation between the conductors and is more pronounced in long cable segments such as outdoor underground cabling. Transfer function measure-ments on different cable types and for different length can be found in [6,25].

    1.5.2 Channel Modelling Overview

    Channel characterisation and modelling are tightly intervened. Channel characterisation in terms of channel measurements is indispensable to derive, validate and fine-tune chan-nel models, while the channel models themselves often provide valuable understanding and insight that might stimulate more advanced channel characterisation.

    In general, PLC channel models can be grouped into physical and parametric models (or into bottom-up and top-down models as in [7]). While physical models describe the

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    electrical properties of a transmission line, for example, through the specification of cable type (line parameters), the cable length and the position of branches [48,6467] (see also Appendix 1.A), parametric models use a much higher level of abstraction from the physi-cal reality and describe the channel, for example, through its impulse response or transfer function [25,68,69] (see also especially Chapters 4 and 5).

    Further, within each group, it can be distinguished between deterministic and stochastic models. While deterministic models aim at the description of one or a small set of specific reproducible PLC channels realisations, stochastic models aim at reflecting a wide range of channel realisations according to their probability of occurrence. This categorisation of channel modelling options is reflected in Figure 1.8 with a short description of each in the following.

    Physical-deterministic modelling describes the electrical properties of a transmission line, for example, through the specification of cable parameters, cable length, the position of branches, etc. [6467,70]. Most physical models are based on representing power line elements and connected loads in the form of their ABCD or S-parameters [60], which are subsequently interconnected to produce the channels frequency response [6467,7073]. Alternatively, [1,74] introduced power line elements as well as connected loads as IIR fil-ters, which is a novel and still intuitive approach if one considers that a communication signal travels in the form of an electromagnetic wave over the PLC channel and may bounce an infinite amount of times between neighbouring line discontinuities. Physical-deterministic models are especially well suited to represent and test deterministic power line situations. An introduction on to the underlying transmission line theory is provided in more detail in Appendix 1.A. MTL theory [42] is particularly well suited in the case of PLC propagation, since it allows describing the signal transmission along any arbitrary topology of interconnected wires and any set of connected loads. Physical-deterministic techniques are sometimes referred to as bottom up, as they start from a precise descrip-tion of the electrical network under consideration in order to derive a global behaviour of the propagation channel. For a given electrical network, the physical-deterministic method can provide a CTF model very close to actual measurement. The drawback is that it requires a significant amount of input data and computational resources, espe-cially if one wishes to derive channel statistics from a large number of different network topologies.

    Deterministic

    PLC channel models

    Stochastic Deterministic Stochastic

    Physical(bottom-up)

    Parametric(top-down)

    FIGURE 1.8PLC channel modelling options.

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    Physical-stochastic models combine the aforementioned deterministic approach with stochastic elements. In [75,76] a so-called statistical bottom-up approach is presented, where the CTF is computed from the exact network topology using a deterministic algorithm. The stochastic nature of the model arises from the random generation of real-istic electrical network topologies, based on a number of rules derived from observed cabling practices, an approach that has also been proposed in [1]. Physical stochastic models include the advantages of the deterministic approach in terms of accuracy with respect to physical transmission phenomena, while allowing for the random generation of statistically representative channel realisations. System engineers generally run digi-tal simulations of the full system, which allow evaluating the behaviour and efficiency of different signal processing algorithms. A stochastic channel model is thus expected to reproduce the main effects of the propagation channel by generating a large num-ber of random channel realisations, which are statistically representative of real-world observations.

    Parametric-deterministic models are possibly one of the categories most used but not usually labelled as parametric-deterministic. Here, this label is referring to a database of measured parameters, such as the CTF, where simple playback of the measurement results can be used in PLC system simulations and performance studies. The advantage is that the exact parameters as observed in real situations are used without the risk to generate unrealistic channels due to modelling inaccuracies. On the other hand, a large and diverse database is needed to obtain meaningful results on a more general level. An example of such a huge database sourced from six European countries is documented in Chapter 5.

    Parametric-stochastic models use a high level of abstraction and describe the channel, for example, through its impulse response characteristics [6,68,77]. The analysis of collected measurement data allows defining a model in the form of a mathematical expression. The mathematical form of the model is not necessarily linked to the physical phenomena taking place in the transmission of electromagnetic signals, but is designed to faithfully reproduce the main characteristics of the channel under study. The model parameters are defined in a statistical way, which allows generating different random realisations of the CTF (or the channels impulse response) exhibiting similar statistics as the experimental data. This modelling strategy is sometimes referred to as a top-down approach, in the sense that it first considers global statistics of the propagation channel in order to define deeper details of the channel structure. This approach generally provides realistic results, with the drawback of requiring a large amount of experimental data to produce the model. The model in [25] is an early example of such statistical channel model, where a general CTF model has been defined based on physical considerations of the signal propagation through simple electrical network topologies. The model parameters were then obtained by fitting the mathematical model to a number of experimental measurements taken in the 020 MHz range. A more recent example of this modelling strategy is given in [78,79], where a channel model is defined on the basis of 144 measurements taken in different dwelling units in the 0100 MHz range. The measurements are subdivided into nine dif-ferent classes according to the observed channel capacity, and a statistical channel model is provided for each class.

    Table 1.2 provides a comparison between the different PLC channel modelling options. Each of the four exists in its own right and bears advantages and disadvantages when it comes to specific applications. Thus, before deciding the type of channel model, the question

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    What is the channel model supposed to do? is key. Some desirable properties of a channel model could, for example, be to

    1. Describe the influence of the time-variant channel on the received signal quality in link and system simulations and algorithm testing, for example, on impulsive noise avoidance, signal-to-noise ratio estimation, channel filter tracking, MIMO schemes.

    2. Model the correlation between temporal and spatial channel and noise variations. 3. Support the investigation of multi-point (multi-user) PLC systems. 4. Allow extension to various propagation scenarios based only on a small set of

    additional scenario measurements. 5. Describe modal coupling to be used in the design of MIMO couplers. 6. Assist in the development of the modems analogue front-end.

    The objectives (1) to (3) and (5) can with more or less effort be realised with either a physical (bottom-up) or a parametric (top-down) model implementation. However, the objectives (4) and (6) are hard to realise with a parametric model. In general, parametric models require a larger range of measurement results to adjust the model parameters. On the contrary, physical models allow deploying knowledge, for example, on the physical dimensions of a new scenario, to adjust physical model parameters. Afterwards, only a smaller set of measurements is needed for rough verification purposes. Looking at signal processingrelated issues with respect to MIMO PLC systems, a parametric model has certain advantages. Itmight be more easily deployed and parameters such as spatial cor-relation are well understood due to related studies in the wireless world [80]. However, looking at the practical implementation of, for example, MIMO couplers or the adjusting of

    TABLE 1.2

    Comparison of PLC Channel Modelling Options

    FeaturePhysical

    DeterministicPhysical

    StochasticParametric

    DeterministicParametric Stochastic

    Modelling principle Electromagnetic transmission theory

    Electromagnetic theory and topology generator

    Playback of experimental measurement parameters

    Statistical fit to experimental measurement parameters

    Measurement requirements

    None None Large data base Large data base

    Topology knowledge

    Detailed Detailed stochastic models

    None None

    Complexity of model design

    Medium High Low Medium

    Complexity of channel generation

    High High Very low Low

    Correlated multi-user studies

    Straightforward Straightforward Straightforward Difficult

    Closeness to experimental data

    Accurate for considered topology

    On a statistical basis

    Exact On a statistical basis

    Ability to extrapolate

    Yes Yes No No

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    analogue front-ends, a physical model, being significantly closer to the reality of electronic components, might be more useful. After these examples, it becomes clear that channel model selection has to be carried out on a case-by-case basis.

    1.5.3 MIMO Channel Models

    Turning specifically to MIMO channels, besides in the early patents [8184], one of the first public investigations of the MIMO access case appears in [85] with perfectly isolated multiple phase wires. Sparked also through the success of MIMO signal processing in the wireless world [41], larger public parametric-deterministic investigations of MIMO signal processing for BB in-home PLC appears in [86]. Similar evaluations, based on a limited set of measurements, are conducted in [87,88]. Following this trend, experimental channel and noise characterisation for MIMO PLC systems have been conducted in [47,8992]. For example, [87,88] conclude that the application of 2 2 MIMO signal processing to in-home PLC provides a capacity gain in the order of 1.9. Further, [86] showed that this capacity gain even increased with the number of Rx ports. In a 2 3 MIMO configuration, the average capacity gain ranged between 1.8 and 2.2 depending on the Tx power level. When adding CM reception, average gains between 2.1 and 2.6 were observed. Along these lines, addi-tional MIMO capacity and throughput results can be found in Chapter 9.

    Only a few proposals for physical-deterministic MIMO channel modelling have been made so far. The most straightforward bottom-up approach of modelling a channel composed of several wires is to apply MTL theory [42,60]. As shown in Figure 1.9, MTL theory can be applied to compute the currents i1(x,t), i2(x,t) and i3(x,t) flowing in a three-wire transmission line as well as the corresponding differential voltages v1(x,t), v2(x,t) and v3(x,t) for a given line position x and a given time t. To do so, a long list of per unit length line parameters needs to be known, that is, the inductances L11, L22 and L33 and the resistances R11, R22 and R33 of wires 1, 2 and 3, respectively, the mutual inductance between any pair of wires

    L22dx R22dx

    L33dx R33dx

    x x+dx

    v2(x+dx,t)

    v3(x+dx,t)

    i2(x+dx,t)

    i3(x+dx,t)

    L23dx

    L11dx R11dxi1(x+dx,t)

    L12dxv1(x+dx,t)

    L13dx

    v2(x,t)

    v3(x,t)

    i2(x,t)

    i3(x,t)

    i1(x,t)

    v1(x,t)

    Line

    Neutral

    Protectiveearth

    Ground

    G 12dx

    C 12dx

    C 13dx

    G 13dx

    C 23dx

    G 23dx

    C 22dx

    G 22dx

    C 11dx

    G 11dx

    C 33dx

    G 33dx

    i1(x,t)+i2(x,t)+i3(x,t)

    i1(x+dx,t)+ i 2(x+dx,t)+ i 3(x+dx,t)

    FIGURE 1.9MTL theory: equivalent circuit of a per unit length section of a three-wire transmission line.

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    (L12, L13 and L23), the capacitances (C11, C22 and C33) and conductances (G11, G22 and G33) of each wire with respect to the ground, the mutual capacitances (C12, C13 and C23) and finally the conductances (G12, G13 and G23) between any pair of wires. Note that some authors con-sider a simplified model with three conductors only, where the PE wire is assumed to be equivalent to the ground [93]. At high frequencies this assumption is not valid, especially when the reception of CM signals is expected as introduced in Figure 1.3. In such cases, a more complete model such as the one presented in Figure 1.9 is necessary to provide accu-rate results. The MTL modelling approach has been used in the work of Banwell and Galli for in-home LV electrical networks [48,66,94], and by Anatory et al. [73] for overhead MV or HV networks. However, these studies do not consider the use of three electrical wires for the purpose of MIMO communication.

    The first use of MTL theory to explicitly model a MIMO PLC channel in a physical- stochastic approach appears in [93,95]. The work therein extends the physical-stochastic SISO channel model presented in [76] by recomputing the MTL equations in the case of three conductors. Using the stochastic topology generator from [76], it is then possible to produce the CTF matrix for a large set of random electrical networks.

    On the other hand, a parametric-stochastic approach has been applied by several research teams to devise models of the MIMO PLC channel. The first attempt is described in [96]. This study considers a 2 4 MIMO channel, where two differential input ports can be addressed simultaneously, and up to four Rx ports are considered, including the CM path. The model first considers a SISO PLC channel impulse response (CIR) composed of 520 taps according to the model defined within the European project OPERA [21]. It then builds the 2 4 MIMO channel matrix by producing eight variants of this CIR. Each of the variants has the same tap structure, but the amplitudes of some of these taps are multiplied using differ-ent random phases uniformly drawn from the interval [0,2). The more taps are modified using a random phase shift, the more uncorrelated the channel becomes. The model pro-duces MIMO channels that exhibit similar correlation values as observed in the measure-ments of [87]. The same approach is further developed in [97], where a 3 3 MIMO channel model has been designed to fit observations from a measurement campaign in France. In total, 42 3 3 MIMO channels were measured in five different houses using a vector NWA. The proposed MIMO channel model builds on the SISO channel model first defined by Zimmermann and Dostert [25], and later extended by Tonello by providing complementary channel statistics [98]. In the following, the notation adopted during the OMEGA project [99] will be used, where the CTF H(f) is given as a function of the frequency f by

    H f A g e epp

    Nj d v f a a f d

    pp

    Kp( )=

    =

    - - + 1

    ( ) ( )/ ,2 0 1p

    (1.3)

    wherev represents the speed of the electromagnetic wave in the copper wire (which may be

    approximated as two-thirds the speed of light*), that is, 200,000,000 m/sdp and gp represent the length and gain of the propagation pathNp represents the number of propagation pathsParameters a0, a1, K and A are attenuation factors

    * Speed of light in vacuum 299,792,458 m/s.

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    An example of channel realisation is given in Figure 1.10 and the approach will be revisited in Chapter 5 to devise a novel channel model on the basis of European field measurements.

    An alternative parametric-stochastic approach is presented in [100]. This study character-ised the MIMO channel covariance matrix Rh, by analysing 96 MIMO channel measure-ments recorded in five houses in North America. Following a similar approach as in [80], the MIMO channel matrix H( f ) is then modelled for each frequency f as

    H f K f R f H f R fr t( )= ( ) ( ) ( ) ( ) ,/ /1 2 1 2 (1.4)

    whereK( f ) is a normalising constantH( f ) is a channel matrix composed of independent and identically distributed complex

    Gaussian variablesRr( f ) and Rt( f ) represent the Rx and Tx correlation matrices, respectively

    Each channel correlation matrix is modelled by its decomposition in eigenvectors and eigenvalues. Details on this alternative model that allows very straightforward reproduc-tion of the MIMO channels correlation properties can be found in Chapter 4.

    5

    10

    15

    20

    25

    30

    35

    40

    45

    50

    55

    Atte

    nuat

    ion

    [dB]

    0 10 20 30 40 50 60 70 80 90 100

    Rx port: D1Rx port: D2Rx port: D3

    Frequency [MHz]

    FIGURE 1.10Example of CTF simulated using the MIMO PLC channel model of Hashmat et al. [97]. Tx port D1 only.

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    1.6 Noise Characterisation and Modelling Approaches

    Turning from the channel to the noise situation, one should note that in contrast to many other communication channels the noise in a power line channel cannot be described as additive white Gaussian noise (AWGN).

    1.6.1 Noise Characteristics

    The noise observed on indoor power line networks has been traditionally categorised into several classes, depending on its origin, its level and its time domain signature [101]. Power line noise can be grouped based on temporal as well as on spectral char-acteristics. Following, for example [5,6], one can distinguish coloured background noise, narrowband (NB) noise, periodic impulsive noise asynchronous to the mains frequency, peri-odic impulsive noise synchronous to the mains frequency and aperiodic impulsive noise as indicated in Figure 1.11.

    A first class consists of the impulsive noise generated by electronic devices connected to the mains grid, such as switched mode power supplies, light dimmers or compact fluorescent lamps. This type of noise is of short duration (a few s) but of relatively high level in the order of tens of mV. Due to the periodic nature of the mains, noisy devices can generate impulses in a synchronous way with the mains period. In this case, the impulsive noise is said to be periodic and synchronous to the mains frequency and presents a repetition rate at multiples of 50 or 60 Hz dependent on the mains frequency. Other noise sources generate impulses at a higher periodical rate up to several kHz, which are classi-fied as periodic and asynchronous to the mains frequency. Finally, strong impulses can also be observed more sporadically, without any periodicity with the mains or with itself. This type of noise is sometimes referred to as aperiodic impulsive noise. Examples of such noise types recorded during field measurements are given in Chapter 5. The different charac-teristics of the impulsive noise have been statistically analysed through the observation of experimental data in[102]. A comprehensive model of the PLC impulsive noise has been proposed in [101]. The pulses are first statistically characterised in terms of amplitude, duration and repetition rate, and the global noise scenario is then modelled in the form of a Markov chain of noise states.

    A second class of noise consists of narrowband (NB) noise. This type generally corresponds to ingress noise from broadcasting radio sources, in particular from the short-wave (SW)

    Periodicsynchronous

    Periodicasynchronous Aperiodic

    PLC noise

    Narrowbandnoise

    Impulsivenoise

    Backgroundnoise

    FIGURE 1.11Classification of PLC noise.

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    and frequency-modulation (FM) bands. Other ingress noise corresponds to leakages from nearby electrical or industrial equipment. This type of noise usually generates strong inter-ference over long durations in a narrow frequency bandwidth in the order of tens of kHz.

    Finally, the remaining noise sources, presenting a lower level of interference, form a third class of noise called background noise. The background noise is generally coloured, in the sense that its power spectral density (PSD) is usually stronger at lower frequencies. In [30], the background noise PSD is modelled with decreasing power as a function of frequency. A similar approach has been adopted in the OMEGA Project [99], where the decaying function of frequency is complemented with a NB model representing the broad-cast interference. Specifically, a statistical approach to average coloured background noise modelling is presented in [21] based on a large amount of noise measurements in MV as well as LV-access and LV-in-home situations. One general finding is that the mean noise power falls off exponentially with frequency. Alternatively, an interesting, quite different approach to model SISO PLC background noise is taken in [103], where a neural network technique is deployed for model generation.

    An important feature relevant to all types of noise is their time dependency. Due to the uncontrolled nature of the noise source, the characteristics of the noise perceived at a given outlet can drastically change over time. For instance, the increase of human activity