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Part I
Power Line Channel and Noise: Characteristics and Modelling
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1
Introduction to Power Line Communication Channel and Noise Characterisation
Lars T. Berger, Pascal Pagani, Andreas Schwager and Piet Janse van Rensburg
CONTENTS
1.1 Introduction
1.2 PLC Frequency Bands and Topologies
1.3 Coupling Methods
1.4 Channel and Noise Measurement Set-Up
1.4.1 Transfer Function Measurements
1.4.2 Reflection Measurements and Input Impedance Calculation
1.4.3 Noise Measurements
1.5 Channel Characterisation and Modelling Approaches
1.5.1 Channel Characteristics
1.5.2 Channel Modelling Overview
1.5.3 MIMO Channel Models
1.6 Noise Characterisation and Modelling Approaches
1.6.1 Noise Characteristics
1.6.2 Noise Modelling for MIMO PLC
1.7 Conclusion
Appendix 1 A: Introduction to Transmission Line Theory
Acknowledgements
References
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, 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 characteristics. 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 equipments’ 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 communication 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 Chapter 6. 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 distinguish power line topologies according to operation voltages of...
