Emulation of Narrowband Powerline Data Transmission Channels and Evaluation of PLC Systems

This work proposes advanced emulation of the physical layer behavior of NB-PLC channels and the application of a channel emulator for the evaluation of NB-PLC systems. In addition, test procedures and reference channels are proposed to improve efficiency and accuracy in the system evaluation and classification. This work shows that the channel emulator-based solution opens new ways toward flexible, reliable and technology-independent performance assessment of PLC modems

Virtual PLC Lab Enabled Physical Layer Improvement Proposals for PRIME and G3-PLC Standards

Narrowband (NB) powerline communication (PLC) is extensively adopted by utilities for the communication in advanced metering infrastructure (AMI) systems. PLC technology needs to overcome channel disturbances present in certain grid segments. This study analyzes improvement proposals of the physical layer of the main narrowband PLC technologies approved by international communication organizations that are currently deployed in Europe: Powerline Intelligent Metering Evolution (PRIME) 1.3.6, PRIME 1.4, and G3-PLC, in order to improve PLC performance under channel disturbances. This thorough study is based on simulations carried out by an innovative ad hoc Virtual PLC Lab, developed by the authors, applied in replicable, fully-automated, and cost reduced test scenarios. The analysis is performed by applying standardized test methods and metrics, and by evaluating the influence of a set of representative channel disturbances defined by the European Telecommunications Standards Institute (ETSI) and selected noises generated by distributed energy resources (DER) in normal operation. PLC performance improvements in terms of equalizer curve fitting, error correction codes, and noisy subcarrier suppression mechanisms are presented. The performance gain due to each physical improvement proposal is accurately measured and compared under the same conditions in a replicable and automated test environment in order to evaluate the use of the proposals in the evolution of future PLC technologies.This work was financially supported in part by the Basque Government under the grant numbers Elkartek KK-2018/00037 and IT1234-19, and by the Spanish Government under the grant RTI2018-099162-B-I00 (MCIU/AEI/FEDER, UE)

Characterization and Emulation of Low-Voltage Power Line Channels for Narrowband and Broadband Communication

The demand for smart grid and smart home applications has raised the recent interest in power line communication (PLC) technologies, and has driven a broad set of deep surveys in low-voltage (LV) power line channels. This book proposes a set of novel approaches, to characterize and to emulate LV power line channels in the frequency range from0.15to 10 MHz, which closes gaps between the traditional narrowband (up to 500 kHz) and broadband (above1.8 MHz) ranges

Characterization and Emulation of Low-Voltage Power Line Channels for Narrowband and Broadband Communication

The demand for smart grid and smart home applications has raised the recent interest in power line communication (PLC) technologies, and has driven a broad set of deep surveys in low-voltage (LV) power line channels. This book proposes a set of novel approaches, to characterize and to emulate LV power line channels in the frequency range from0.15to 10 MHz, which closes gaps between the traditional narrowband (up to 500 kHz) and broadband (above1.8 MHz) ranges

Electromagnetic compatibility of power line communication systems

The power system has been used for communication purposes for many decades, although it was mainly the power utility companies that used low bit rates for control and monitoring purposes. In the last ten years, however, the deregulation of the power and telecommunication markets has spurred the idea of using and commercializing the power networks for a range of new communication applications and services. The idea has been developed and implemented into both, narrowband and broadband systems, which are defined in terms of the operation frequency band. Depending on the frequency band, the systems over powerlines can be: Narrow-band. They use frequencies ranging from 3-148.5 kHz in Europe, with the upper frequency extending up to 500 kHz in the United States and Japan. In Europe, this frequency range is standardized by CENELEC Standard EN 50065. Broadband. The used frequency range is 1-30MHz; 1-15MHz for outdoor systems and 15-30MHz for indoor systems. In this frequency range, the standardization situation is still unclear and there exist no regulations. The developed applications and systems use different parts of the power network: medium voltage (MV) and low voltage (LV) cabling for outdoor applications and building cabling for indoor applications. These cables are designed and optimized for power transmission at frequencies of 50/60Hz and represent a hostile medium for transmissions at higher frequencies. This thesis concentrates on electromagnetic compatibility (EMC) aspects and some optimization issues of the broadband systems, currently known as Powerline Communications (PLC) or Broadband Power Line (BPL). The work presented here was preformed in the framework of the European project OPERA (http://www.ist-opera.org/). A short description of the project is given in Chapter 1. The second chapter presents the basis, introduction, description and state of the art of the topics of interest for this thesis. That chapter is divided into three parts. Each of these parts starts with a short introduction to the topic to be addressed. The introductions are intended for those not familiar with the topic at hand and they can be skipped by those already knowledgeable of it. The first part of Chapter 2 gives an overview and introduction to telecommunication issues relevant to the thesis, as well as the general technical specifications of the OPERA system. The second part deals with the transmission medium which, for the case of PLC, is the power system. The fundamentals and the different components of the PLC system are given there and the state of the art regarding the transmission channel is presented. The third part deals with the EMC and standardization issues related to the technology. The main contributions of the thesis are presented in chapters 3 to 7. The PLC technology distinguishes itself from other technologies in that it uses already existing, ubiquitous wiring, so that no new infrastructure is needed. On the other hand, using a channel designed originally for other purposes means that it is not optimized for the frequencies and applications of interest for broadband transmission. If PLC is to compete with other technologies, these problems have to be well understood and solved, so that the system can be optimized by taking into account the parameters and constrains of the already existing medium. Although the PLC system is being improved continuously, there are still concerns about emissions, immunity and standardization. These issues are important since PLC operates in an environment already populated by other services at the same frequencies, so that fair co-existence is needed. Moreover, the PLC modem has a combined mains and telecom port and, as a consequence, the standards for conducted emissions from those two types of ports are not directly applicable. In addition, the symmetry of the cables used is low and, therefore, emissions are higher than, for example, emissions from twisted pair cables used in xDSL. A good understanding of emissions and immunity in PLC systems is therefore of great importance for the optimization of the system and for EMC standardization to be based on objective technical criteria. Even if the basic phenomena are essentially the same as for any other wire transmission system, the complexity and variability of the topologies of existing structures is so large that simple, straightforward solutions are often not applicable. Emissions from the cabling are primarily due to the common mode signals. Part of the energy in this mode is injected by the imperfectly balanced output stages of the PLC modems themselves. In addition, the common mode appears at punctual imbalanced discontinuities and distributed asymmetry along the PLC signal path in the power cables. Chapter 3 presents the work performed to improve our understanding of the sources of the common-mode current and the parameters that influence its behavior, including related measurements and simulations. For the purpose of this study, a model house was built at the EPFL's test site. Different cablings were used to study the influence of different parameters on the behavior of the common-mode current since it is the main source for both types of emissions, conducted and radiated ones. The influence of different parameters such as the cable terminations, the symmetry of the termination, the height of the conductors above the ground, the presence of power outlets, switches, empty and occupied sockets and the topology, are analyzed. The data are also used to test two methods used to simulate the differential-to-common-mode conversion and the conducted emissions, namely the transmission line model and the full wave approach provided by the Method of Moments through the Numerical Electromagnetic Code (NEC). In Chapter 4, problems related to PLC immunity testing are treated. We show that the conversion of the differential mode to the common mode is coupled with the reverse conversion by reciprocity. Due to the low symmetry of PLC cabling, part of the injected common mode test signal is converted into a differential mode signal that interferes with the wanted signal at the input of the modem being tested. Depending on the actual symmetry of the Coupling-Decoupling Network (CDN), not specified in the standards, the immunity test may yield erroneous results due to the effect of this differential mode component. Working under the assumption that the CDN is built to exhibit a symmetry similar to that of PLC networks as inferred from its longitudinal conversion loss, we estimate the differential mode disturbance level that the modems should withstand from a narrowband interferer. The bit error rate induced by the presence of the disturbing differential mode current from the CDN is also estimated, for a total physical channel transmission rate of 200 Mbps, to be of the order of 1×10-5 to 5×10-5. Since these rates can be handled by error correcting coding and MAC ARQ procedures, it is concluded that the modems are not likely to suffer any severe performance degradation due to immunity testing if the CDN exhibits a symmetry similar to that of PLC networks. Simulating the complete PLC network or any significant part of it using numerical techniques such as the method of moments proves to be of limited practical use due to the fact that PLC networks extend over many wavelengths. The transmission line approximation, on the other hand, although more efficient and sufficiently accurate for differential mode calculations, is not directly applicable to simulate the EMC behavior since it neglects the antenna-mode currents that are significant contributors to the radiated emissions. Chapter 5 presents a novel approach to evaluate the antenna-mode currents using a modified transmission line theory, thus making this numerically efficient technique applicable to the estimation of emissions in PLC. An integral equation describing the antenna-mode currents along a two-wire transmission line is derived. It is further shown that, when the line cross-sectional dimensions are electrically small, the integral equation reduces to a pair of transmission line-like equations with equivalent line parameters (per-unit-length inductance and capacitance). The derived equations make it possible to compute the antenna mode currents using a traditional transmission line code with appropriate parameters. The derived equations are tested versus numerical results obtained using NEC and reasonably good agreement is found. Another important EMC issue related to PLC is the mitigation of emissions. Chapter 6 describes a technique that has been proposed to achieve a reduction of emissions associated with indoor PLC networks through the introduction of a 180° out-of-phase replica of the PLC signal into the unused neutral-ground circuit. A modification to this technique is proposed based on the selection of the appropriate amplitude and phase of the auxiliary signal, allowing a higher degree of field attenuation. A way of implementing this technique is proposed and studied, namely the integration of a required antenna into the PLC modems themselves. The measured fields very close to the modem allow the determination of the magnitude and phase of the compensation voltage. The proposed implementation should be used only to handle customer complaints, when emissions should be lowered at locations where PLC signals might cause unwanted interference or when additional capacity is required and it can be obtained through the gained signal to noise margin. Although, in principle, due to nonalignment of the wanted and the compensation field directions, minimizing one component of the field may result in an increase of the other components, we show that the application of the technique results in an overall average reduction of 10-20 dB of all the field components in the region of interest. In the same Chapter 6, we address the more general issue of the application of mitigation techniques' gained emissions margin to increase the overall throughput of PLC systems. We show that an increase in the signal power (made possible by the inclusion of mitigation techniques) leads to a considerable increase in the PLC channel capacity. Using a number of simplifications, we show that the capacity of the channel can indeed be increased by up to 66 Mbps for mitigation efficiencies of only 10 dB. We also present the results of laboratory measurements aimed at studying, under controlled conditions, different characteristics of notching in OPERA PLC modems, such as total and effective notch width, notch depth, maximum notch depth, etc. These measurements show that it is possible to obtain attenuations of up to about 45 dB for notches in all frequency bands, 10MHz, 20MHz and 30MHz. What differs for these three bands is the minimum number of carriers that need to be notched to obtain that maximum attenuation. This is an important point, since, to implement notches that have the required depth and width, one must know how many subcarriers to suppress and how deep these need to be reduced. High density PLC deployment requires the increase of overall system data rate. To achieve the higher data rates, frequency reuse in these systems is needed. In Chapter 7, we present the idea for using so-called blocking filters as a possible solution for a frequency reuse. Experimental data obtained on a real distribution network show that the use of blocking filters can, in certain cases, ensure high enough RF separation of the LV feeders belonging to the same substation. In some cases, even with the possibility to design and integrate effective blocking filters, the system needs to provide additional synchronization mechanisms for frequency reuse

An experimental investigation into the electromagnetic compatibility aspects of high frequency power line communications

Power line communications technology, long established for low data rate applications, is now charting new territory with respect to data rates and provided services. This can only be achieved by increasing PLC operating frequencies from the low frequency band (below 148.5 kHz) to the high frequency band (1 MHz and upwards). There is now only one technical barrier to widespread deployment - Electromagnetic Compatibility. Existing low voltage power networks are optimised for the safe supply of electrical energy. Low voltage cables are often pseudo co-axial in their cross section, but when high frequency signals are coupled onto the network, part of the signal will be radiated. There is therefore a potential for interference to be caused to legitimate users of the radio spectrum. This thesis, and the experimental program underlying it, seeks to quantify potential problems and to propose mechanisms by which they could be mitigated to the extent that wide scale deployment of PLC networks becomes possible. The first part of the thesis offers a detailed introduction to the topics of electricity supply networks, power line communications, modulation techniques and electromagnetic compatibility. Existing EMC standards are examined and although some do not directly cover power line communications networks, key principals are drawn for later use in standards development. The thesis then seeks to examine the mechanisms by which high frequency interference might be caused. Radio propagation modes are discussed and a clear technical distinction is drawn between localised interference from a single PLC network to an individual radio user, and cumulative interference from wide spread deployment of PLC systems. Both such scenarios are examined in detail. The experimental program IS described quantifying radiated signal strength regression from a number of power networks and at a number of operating frequencies within the high frequency band. In this context, signal strength regression is the rate at which electrical field strength reduces with increasing measurement distance. The experimental setup uses a conventional signal generator to supply single test frequencies of known power spectral density, which are coupled onto a power network. The subsequent radiated signal is received via a conventional antenna and radio receiver at a number of locations surrounding the power network at known distances, and signal regression is derived. The experiment was repeated for a number of different frequencies and at representative urban, suburban and rural locations. Indeed, the experimental technique was evolved over a number of months to allow increased portability of the signal receiving equipment, and hence the number of measurements that could be taken. From the experimental results, presented both In tabular and graphical format, a number of conclusions can be drawn. Firstly, based on these results, antenna factors in the order of 85 dB/m can be expected of power line communication networks. It can be concluded that the field strength regression to be anticipated from PLC networks is likely to be significantly below the -20 dB per decade 'free space' regression figure that has often been used in interference models. In fact a regression figure of -35 dB/decade IS more representative of ground wave propagated interference from PLC networks. It is also possible to conclude that the adoption of orthogonal frequency division multiplexing as a multi-carrier spectral technique offers specific advantages in EMC terms. Due to its nature, it is possible to apply a frequency 'mask' to an OFDM based PLC system. Such a mask might be static, applied on a national or regional basis in order to guarantee non-interference with specific frequencies, for example those used for emergency radio channels. It would also be possible to add a dynamic frequency mask, controllable on each PLC system, to mitigate interference with radio services operating within the PLC operating band

Noise Sources, Effects and Countermeasures in Narrowband Power-Line Communications Networks: A Practical Approach

The integration of Distributed Generation, Electric Vehicles, and storage without compromising the quality of the power delivery requires the deployment of a communications overlay that allows monitoring and controlling low voltage networks in almost real time. Power Line Communications are gaining momentum for this purpose since they present a great trade-off between economic and technical features. However, the power lines also represent a harsh communications medium which presents different problems such as noise, which is indeed affected by Distributed Generation, Electric Vehicles, and storage. This paper provides a comprehensive overview of the types of noise that affects Narrowband Power Line Communications, including normative noises, noises coming from common electronic devices measured in actual operational power distribution networks, and noises coming from photovoltaic inverters and electric vehicle charging spots measured in a controlled environment. The paper also reviews several techniques to mitigate the effects of noise, paying special attention to passive filtering, as for being one of the most widely used solution to avoid this kind of problems in the field. In addition, the paper presents a set of tests carried out to evaluate the impact of some representative noises on Narrowband Power Line Communications network performance, as well as the effectiveness of different passive filter configurations to mitigate such an impact. In addition, the considered sources of noise can also bring value to further improve PLC communications in the new scenarios of the Smart Grid as an input to theoretical models or simulations.This work has been partly funded by the Spanish Ministry of Economy and Competitiveness through the National Program for Research Aimed at the Challenges of Society under the project OSIRIS (RTC-2014-1556-3) and through the network of excellence REDYD2050 (ENE2015-70032-REDT)

Power line communication (PLC) channel measurements and characterization.

M. Sc. Eng. University of KwaZulu-Natal, Durban 2014.The potential of the power line to transport both power and communication signals simultaneously has been realized and practiced for over a century, dating back to the 1900’s. Since the key aspect of power line communications being its expansivity, its implementations were largely as a retrofit technology. This motivation of power line communication is typical for low-, medium-, and high voltage distribution networks. Beyond the “last mile” part, there’s an uprising appeal for intra-building networks currently targeted for home automation (smart homes/buildings) and in-building networking. The optimum use of the existing power line channels has been a focus area for researchers and designers, with the inherent channel hostility proving a serious drawback for high speed data communications. The low-voltage electrical network has unpredictable noise sources, moreover it has two other main disadvantages as a communication channel. The first short coming has to do with the unknown characteristics of the power cable and topology of the network, the second arises from the time-dependent fluctuation of the impedance level of the power line as the loads are switched into and out of the power line network in an unpredictable manner. These factors determine the behaviour of the power line channel when a high frequency signal is impressed on it. This study has shown that the behaviour of indoor power line channels can be captured using a multipath based model even with limited qualitative and/or quantitative knowledge of the network topology. This model is suitable for typical indoor power line channels where knowledge of the topology is near impossible. Some of the feed parameters are obtained through measurements. With sufficient adjustment of control parameters, this model was successfully validated using sample measured channels from the numerous measurements. Through noise measurements, this study has established that impulsive noise is the rifest in the frequency band of interest. The impulsive energy rises well above background noise, which translates to possible data “black outs”. The statistics of the components of this noise are presented. A model of sufficient simplicity is used to facilitate the qualitative description of the background noise through its power spectral density. Two descriptions are provided in terms of the worst and best case scenarios of the background noise occurrences. The model has a good macroscopic capture of the noise power spectral density, with narrow-band interference visible for the worst case noise. Due to the multipath nature of the power line channel, this study also presents the dispersive characteristics of the power line as a communication channel. The power delay profile is used to determine parameters such as first arrival delay, mean excess delay, root mean square delay spread and maximum delay spread. The statistics of these parameters are presented. Also, the coherence bandwidth of power line channels is studied and its relationship with the rms delay spread is developed. It is in view of this work that further research in power line communication and related topics shall be inspired

Noise Sources, Effects and Countermeasures in Narrowband Power-Line Communications Networks: A Practical Approach

The integration of Distributed Generation, Electric Vehicles, and storage without compromising the quality of the power delivery requires the deployment of a communications overlay that allows monitoring and controlling low voltage networks in almost real time. Power Line Communications are gaining momentum for this purpose since they present a great trade-off between economic and technical features. However, the power lines also represent a harsh communications medium which presents different problems such as noise, which is indeed affected by Distributed Generation, Electric Vehicles, and storage. This paper provides a comprehensive overview of the types of noise that affects Narrowband Power Line Communications, including normative noises, noises coming from common electronic devices measured in actual operational power distribution networks, and noises coming from photovoltaic inverters and electric vehicle charging spots measured in a controlled environment. The paper also reviews several techniques to mitigate the effects of noise, paying special attention to passive filtering, as for being one of the most widely used solution to avoid this kind of problems in the field. In addition, the paper presents a set of tests carried out to evaluate the impact of some representative noises on Narrowband Power Line Communications network performance, as well as the effectiveness of different passive filter configurations to mitigate such an impact. In addition, the considered sources of noise can also bring value to further improve PLC communications in the new scenarios of the Smart Grid as an input to theoretical models or simulations.This work has been partly funded by the Spanish Ministry of Economy and Competitiveness through the National Program for Research Aimed at the Challenges of Society under the project OSIRIS (RTC-2014-1556-3) and through the network of excellence REDYD2050 (ENE2015-70032-REDT)

Characterization and modeling of the channel and noise for broadband indoor Power Line Communication (PLC) networks.

Doctor of Philosophy in Electronic Engineering. University of KwaZulu-Natal, Durban 2016Power Line Communication (PLC) is an interesting approach in establishing last mile broadband access especially in rural areas. PLC provides an already existing medium for broadband internet connectivity as well as monitoring and control functions for both industrial and indoor usage. PLC network is the most ubiquitous network in the world reaching every home. However, it presents a channel that is inherently hostile in nature when used for communication purposes. This hostility is due to the many problematic characteristics of the PLC from a data communications’ perspective. They include multipath propagation due to multiple reflections resulting from impedance mismatches and cable joints, as well as the various types of noise inherent in the channel. Apart from wireless technologies, current high data rate services such as high speed internet are provided through optical fibre links, Ethernet, and VDSL (very-high-bit-rate digital subscriber line) technology. The deployment of a wired network is costly and demands physical effort. The transmission of high frequency signals over power lines, known as power line communications (PLC), plays an important role in contributing towards global goals for broadband services inside the home and office. In this thesis we aim to contribute to this ideal by presenting a powerline channel modeling approach which describes a powerline network as a lattice structure. In a lattice structure, a signal propagates from one end into a network of boundaries (branches) through numerous paths characterized by different reflection/transmission properties. Due to theoretically infinite number of reflections likely to be experienced by a propagating wave, we determine the optimum number of paths required for meaningful contribution towards the overall signal level at the receiver. The propagation parameters are obtained through measurements and other model parameters are derived from deterministic power system. It is observed that the notch positions in the transfer characteristics are associated with the branch lengths in the network. Short branches will result in fewer notches in a fixed bandwidth as compared to longer branches. Generally, the channel attenuation increase with network size in terms of number of branches. The proposed model compares well with experimental data. This work presents another alternative approach to model the transfer characteristics of power lines for broadband power line communication. The model is developed by considering the power line to be a two-wire transmission line and the theory of transverse electromagnetic (TEM) wave propagation. The characteristic impedance and attenuation constant of the power line are determined through measurements. These parameters are used in model simplification and determination of other model parameters for typical indoor multi-tapped transmission line system. The transfer function of the PLC channel is determined by considering the branching sections as parallel resonant circuits (PRC) attached to the main line. The model is evaluated through comparison with measured transfer characteristics of known topologies and it is in good agreement with measurements. Apart from the harsh topology of power line networks, the presence of electrical appliances further aggravates the channel conditions by injecting various types of noises into the system. This thesis also discusses the process of estimating powerline communication (PLC) asynchronous impulsive noise volatility by studying the conditional variance of the noise time series residuals. In our approach, we use the Generalized Autoregressive Conditional Heteroskedastic (GARCH) models on the basis that in our observations, the noise time series residuals indicate heteroskedasticity. By performing an ordinary least squares (OLS) regression of the noise data, the empirical results show that the conditional variance process is highly persistent in the residuals. The variance of the error terms are not uniform, in fact, the error terms are larger at some portions of the data than at other time instances. Thus, PLC impulsive noise often exhibit volatility clustering where the noise time series is comprised of periods of high volatility followed by periods of high volatility and periods of low volatility followed by periods of low volatility. The burstiness of PLC impulsive noise is therefore not spread randomly across the time period, but instead has a degree of autocorrelation. This provides evidence of time-varying conditional second order moment of the noise time series. Based on these properties, the noise time series data is said to suffer from heteroskedasticity. GARCH models addresses the deficiencies of common regression models such as Autoregressive Moving Average (ARMA) which models the conditional expectation of a process given the past, but regards the past conditional variances to be constant. In our approach, we predict the time-varying volatility by using past time-varying variances in the error terms of the noise data series. Subsequent variances are predicted as a weighted average of past squared residuals with declining weights that never completely diminish. The parameter estimates of the model indicates a high degree of persistence in conditional volatility of impulsive noise which is a strong evidence of explosive volatility. Parameter estimation of linear regression models usually employs least squares (LS) and maximum likelihood (ML) estimators. While maximum likelihood remains one of the best estimators within the classical statistics paradigm to date, it is highly reliant on the assumption about the joint probability distribution of the data for optimal results. In our work, we use the Generalized Method of Moments (GMM) to address the deficiencies of LS/ML in order to estimate the underlying data generating process (DGP). We use GMM as a statistical technique that incorporate observed noise data with the information in population moment conditions to determine estimates of unknown parameters of the underlying model. Periodic impulsive noise (short-term) has been measured, deseasonalized and modeled using GMM. The numerical results show that the model captures the noise process accurately. Usually, the impulsive signals originates from connected loads in an electrical power network can often be characterized as cyclostationary processes. A cyclostationary process is described as a non-stationary process whose statistics exhibit periodic time variation, and therefore can be described by virtue of its periodic order. The focus of this chapter centres on the utilization of cyclic spectral analysis technique for identification and analysis of the second-order periodicity (SOP) of time sequences like those which are generated by electrical loads connected in the vicinity of a power line communications receiver. Analysis of cyclic spectrum generally incorporates determining the random features besides the periodicity of impulsive noise, through the determination of the spectral correlation density (SCD). Its effectiveness on identifying and analysing cyclostationary noise is substantiated in this work by processing data collected at indoor low voltage sites