Channel Characterization for Indoor Power-Line Networks

Power-line networks are promising mediums by which broadband services can be offered, such as Internet services, voice over Internet protocol, digital entertainment, etc. In this paper, an analysis of delay spread, coherence bandwidth, channel capacity, and averaged delay in the frequency bands up to 100 MHz for typical indoor power-line networks are studied. Earlier studies for indoor power-line networks considered frequencies up to 30 MHz only and earlier works have shown that at these frequency bands, the data rates are generally low and are inefficient for digital entertainment in comparison with wireless local-area networks standards, such as IEEE 802.11 n. In this paper, it is shown that at 100 MHz, the average channel capacity for typical indoor power-line networks can be up to 2 Gb/s and it is found that by increasing the number of branches in the link between transmitting and receiving ends, the average channel capacity decreases from 2 Gb/s to 1 Gb/s (when the number of branches was increased by four times for a power spectral density of -60 dBm/Hz). At the same time, the coherence bandwidth decreased from 209.45 kHz to 137.41 kHz, which is much better than the coherence bandwidths corresponding to 30-MHz systems. It is therefore recommended to operate the indoor power-line networks at 100-MHz bandwidths for a wide variety of broadband services.     

A Medium-Voltage Cables Model for Power-Line Communication

The aim of this paper is the development of a theoretical model of medium-voltage (MV) cables in the frequency range of 25–200 kHz, which can be easily implemented in the Simulink enviroment. Two transmission-line configurations: 1) line-ground and 2) line-line were considered. The model requires the knowledge of the transmission channel parameters in the frequency domain. Thus, a characterization of MV cables in the two transmission-line configurations by means of experimental measurements was performed on commonly used MV cables, RG7H1R, of different sections, 95 mm$^{2}$ and 185 mm$^{2}$ with an aluminum core and copper shielded. To validate the model, a comparison between the attenuation constant $alpha$ measured and the one simulated for both configurations under study was carried out.      

Broadband Power-Line Communications: The Channel Capacity Analysis

The power line has been proposed as a solution to deliver broadband services to end users. Various studies in the recent past have reported a decrease in channel capacity with an increase in the number of branches for a given channel type whether it is an indoor or low-voltage (LV) or medium-voltage (MV) channel. Those studies, however, did not provide a clear insight as to how the channel capacity is related to the number of distributed branches along the line. This paper attempts to quantify and characterize the effects of channel capacity in relation to the number of branches and with different terminal loads for a given type of channel. It is shown that for a power spectral density (PSD) between 90 dBm/Hz to 30 dBm/Hz, the channel capacity decreases by a 20-30 Mb/s/branch, 14-24 Mb/s/branch, and a 20-25 Mb/s/branch for an MV channel, LV channel, and indoor channel, respectively. It is also shown that the channel capacity is minimum when the load impedance is terminated in characteristic impedances for any type of channel treated here. It is shown that there could be a significant loss in channel capacity if a ground return was used instead of a conventional adjacent conductor return. The analysis presented in this paper would help in designing appropriate power-line communication equipment for better and efficient data transfer.     

A Novel Approach to Power-Line Channel Modeling

In this paper, a novel approach to statistical modeling of power-line channels is illustrated and its application to low-voltage indoor power networks is analyzed in the bandwidth 1-30 MHz. The proposed approach is based on the well-known bifilar model and on a generalization of the so-called N-branch network topology. It is shown that our model can be exploited to devise an efficient channel simulator predicting the mean impedance matrix and transfer function between an arbitrary couple of plugs in a class of indoor networks sharing multiple parameters (e.g., number of branches, minimum and maximum cable lengths, power-loading conditions). Finally, it is shown that Monte Carlo results generated by our simulator are in good agreement with a set of experimental data acquired in a measurement campaign.     

Performance of Underground Cables That Use OFDM Systems for Broadband Power-Line Communications

Power-line networks are proposed for broadband data transmission. The presence of multipaths within the broadband power-line communication (BPLC) system, due to stochastic changes in the network load impedances, branches, etc. pose a real challenge as it affects network performance. This paper attempts to investigate the performance of an orthogonal frequency-division multiplexing (OFDM)-based BPLC system that uses underground cables. It is found that when a branch is added in the link between the sending and receiving end, there is an average of 4-dB power loss. In addition, when the terminal impedances of the branches that are connected to the link between the transmitting and receiving end vary from line characteristic impedance to low-impedance values, the power loss (signal-to-noise ratio) is about 0.35 dB/ Omega. On the contrary, for an increase in the terminal impedances by 100 Omega above line characteristic impedance, the power loss is 0.23 dB//Omega. When the branch terminal impedances are close to short or open circuits, OFDM techniques show degraded performance. This situation is also observed when the number of branches increases. It is shown that to overcome degraded network performance, the concatenated Reed-Solomon codes/interleaved Viterbi methods can be used, which could be used for an efficient design of the BPLC system that uses OFDM techniques.     

Indoor Power-Line Communications Channel Characterization up to 100 MHz—Part II: Time-Frequency Analysis

Estimations of coherence bandwidth and time-delay parameters from wideband channel sounding measurements made in the 30 kHz-100 MHz band in several indoor environments are described in and taken back in this paper. Powerline communications (PLC) modems rather see a channel which starts almost from 2 MHz . A comparison between coherence bandwidth and time-delay parameters estimated in both frequency bands 30 kHz-100 MHz and 2 MHz-100 MHz is elaborated in this paper. Results are intended for applications in high-capacity indoor power-line networks. The investigation is aimed to show that the PLC channel studies in a band starting from a frequency lower than 2 MHz distorts the real values that an implementer should take, as the PLC modem see only the frequencies from 2 MHz. The coherence bandwidth and the time delay parameters are estimated from measurements of the complex transfer functions of the PLC channels. For the 30 kHz-100 MHz frequency band, the 90 th percentile of the estimated coherence bandwidth at 0.9 correlation level stay above 65.5 kHz and below 691.5 kHz. It was observed to have a minimum value of 32.5 kHz. The maximum excess delay spread results show that 80% of the channels exhibit values between 0.6 s and 6.45 s. And a mean rms delay spread of 0.413 s is obtained. The passage to the 2 MHz-100 MHz frequency band induced an increase of the coherence bandwidth, whose min value is brought back to 43.5 kHz, and an important reduction of the time delay parameters: The min, max, mean, and standard deviation values of the maximum excess delay are almost divided by 2. For the twice frequency bands, this paper studies, also, the variability of the coherence bandwidth and time-delay spread parameters with the channel class , and thus with the location of the receiver with respect to the transmitter, and finally relates the rms delay spread to the coherence bandwidth.     

Indoor Power-Line Communications Channel Characterization Up to 100 MHz—Part I: One-Parameter Deterministic Model

Advanced communication technologies have allowed the power-line-communication (PLC) channel to be a transmission medium that enables the transfer of high-speed digital data over the classical indoor electrical wires. The development of PLC systems for Internet, voice, and data services requires measurement-based models of the transfer characteristics of the mains network suitable for performance analysis by simulation. This paper presents a deterministic model describing the magnitude and phase of complex transfer functions of power-line networks using only one parameter. First, a PLC channel classification is realized, and an average magnitude and phase channel model by class is proposed. Second, the multipath characteristic of PLC channels is introduced. A statistical-based channel magnitude generator is built, and a group delay-based phase model is suggested.     

A Distributed Circuit Model for Power-Line Communications

This paper presents a computational efficient distributed circuit model for broadband power-line communications (PLC) in the frequency range of 1 to 30 MHz. The model is derived based on the full wave approach and it takes into account the mutual coupling between the power lines, the effect of the ground plane and the discontinuity along the lines (e.g., PLC line bent with an arbitrary angle and the terminations). To derive the distributed circuit model, the PLC lines were divided into many small elements with each element treated as a dipole antenna. The electromagnetic fields along the power lines were considered as the summation of the field of these elements solved by the boundary conditions at the air-conductor and the air-ground interfaces from which the explicit expressions of the per-unit-length circuit parameters were obtained. To check the accuracy of our proposed model, the current distributions along PLC lines excited by an external source were determined using the chain matrix approach. Common-mode current is calculated with the transmission line equations. The agreement between our theoretical calculations with the experimental data as well as with full wave approach shows the validity and applicability of our proposed model for such PLC applications.     

Channel Model for Broadband Power-Line Communication

This paper presents a novel approach to model the transfer function of a power-line network. The channel frequency responses of a single-phase power-line channel with interconnections are derived considering different loading at different branches. The model is verified using Alternative Transients Program-Electromagnetic Transients Program (ATP-EMTP). The model simulation results are comparable to ATP-EMTP results. Therefore, the modeling can be considered as a procedure to characterize the power-line channel     

Adaptive Robust Turbo Equalization for Power-Line Communications

Data communication over power lines requires advanced signal-processing techniques to cope with time-varying intersymbol interference and severe impulsive noise. A further challenge comes from strict regulatory constraints that stipulate low transmission power. In this paper, we propose an adaptive robust turbo equalizer for single-carrier coded systems. The turbo equalizer has a component equalizer to deal with the deep frequency notches present in power-line channels. The component equalizer exchanges extrinsic information with a component decoder to perform iterative detection. To facilitate adaptive equalization in time-varying power-line channels, a simple system identification-based channel estimator is incorporated. Most important, a nonlinear-matched myriad filter (MMyF) is used for efficient baseband filtering in impulsive channels. The results show that the MMyF is indispensable for the turbo equalizer to achieve reliable channel estimation and data detection in impulsive power lines. Substantial performance improvements over the conventional scheme designed for Gaussian channels are observed.     

Link-Adaptive Physical Layer for Indoor Broadband Power-Line Communications

Increasing interest in smart home automation systems or home networks has driven the use of low-voltage power lines as a high-speed data channel. Since this type of power line is not designed for communication purposes, the channel exhibits unfavorable transmission properties. In this paper, a novel orthogonal frequency-division multiplexing-based physical-layer architecture for indoor broadband power-line communications is proposed. For the design of the layer, a new constellation for bit-mapping (or modulation) is introduced to increase the transmission rate over a sudden phase-shift-prone channel. In addition, a simple bit-loading scheme is adopted and a new preamble for a packet-based power-line communication system is proposed. The proposed layer is implemented as a type of testbed, and is field-tested in labs and in residential homes. The test results demonstrate that the proposed system has good channel adaptivity and achieves high transmission rates.      

Resource Allocation Management for Indoor Power-Line Communications Systems

Power-line communications (PLC) is recognized as an alternative technology for delivering broadband services in home and small-office environments. Multicarrier modulation is one of the most effective solutions for combating the imperfections of the power-line channel. One of the technical challenges in increasing the potentiality of PLC technology is the utilization of the available spectrum when different users compete for the available resources. Due to the frequency and time-varying characteristics of the power-line network, the various users experience different channel conditions, thus the application of efficient resource allocation will increase the overall network performance. This paper addresses the problem of subchannel and power allocation for indoor PLC networks with multiple links employing power spectral density limitations, and presents an efficient multiuser loading algorithm. The proposed solution encounters both uplink and downlink traffic, guarantees a set of minimum data rates to all users, and allocates the available resources with fairness according to the channel quality of each link. We demonstrate the performance of the proposed algorithm using an illustrative example of a typical indoor network and we examine its effectiveness under various channel conditions     

Coupler Winding Ratio Selection for Effective Narrowband Power-Line Communications

Coupling losses caused by impedance mismatches are often underestimated and neglected by power-line communications researchers and manufacturers. Further, the variations in network topology combined with unknown cable and load impedances obscure the requirements for impedance adaptation, causing researchers and manufacturers to default to a guessed impedance level and a fixed winding ratio. Attempting to clarify said requirements, this paper approaches the transmitter-to-receiver chain using a simplified lumped-parameter model, which distinguishes between the influences of series (cable) and parallel (load) power-line impedances. Using apparent power transfer to the receiver as criterion, the influence of both the transmitter and receiver coupler winding ratios are investigated for 50- modems at frequencies below 1 MHz. Live measurements indicate that the results are useful regardless of power-line topology, yielding gains up to 10 dB.     

Electrical Parameters of Low-Voltage Power Distribution Cables Used for Power-Line Communications

Many models proposed in the literature to describe low-voltage power distribution networks in consumer premises as communication media require knowledge of the electrical parameters of the cables comprising these networks. These parameters are nevertheless affected by a large number of factors which may vary greatly from case to case, making it thus very difficult to achieve an exact estimation about them. In this work, a study of the electrical parameters of two cable types widely used in residential low-voltage power distribution networks is presented. Moreover, a finite-element approach is used for the verification of the results of the theoretical model concerning the series impedance per unit length of the cable type under study with respect to its normal operational conditions     

The Influence of Load Impedance, Line Length, and Branches on Underground Cable Power-Line Communications (PLC) Systems

An underground cable power transmission system is widely used in urban low-voltage power distribution systems. In order to assess the performance of such distribution systems as a low-voltage broadband power-line communication (BPLC) channel, this paper investigates the effects of load impedance, line length, and branches on such systems, with special emphasis on power-line networks found in Tanzania. From the frequency response of the transfer function (ratio of the received and transmitted signals), it is seen that the position of notches and peaks in the magnitude are largely affected (observed in time-domain responses too) by the aforementioned network configuration and parameters. Additionally, channel capacity for such PLC channels for various conditions is investigated. The observations presented in this paper could be helpful as a suitable design of the PLC systems for better data transfer and system performance.     

Channel Model and Measurement Methods for 10-kV Medium-Voltage Power Lines

Based on the typical topology and physical properties of a 10-kV power network, this paper first proposes a linear time-variant filter with additive noise to be the general channel model which takes into account the main problems that interfere with communications. Then it discusses the corresponding measurement methods. Next, for the first time in the related research area, the electrical loop wire was applied for the measurement of amplitude and phase responses of the transfer function H(f), which provides a better way to solve the problem of obtaining the phase response if the power line is relatively long. Also, the multitones method for the narrow-band fading measurement is put forward. Finally, it is concluded that moving the calibration reference plane of the network analyzer to a proper position improves the measurements efficiency and accuracy and these methods can be referred to in the 10-kV power-line channel study     

On Reed–Solomon Coding for Data Communications Over Power-Line Channels

The problem of data communications through impulsive power-line channels using Reed–Solomon (RS) codes combined with $M$-ary modulation is treated. It is shown that under the influence of impulsive interference, the seemingly robust algebraic RS decoder can suffer drastic performance degradation even with the aid of an interleaver. We attempt to elucidate the mechanism that leads to the breakdown of such coding schemes. It is found that in impulse channels, excessive random and burst errors can occur prior to RS decoding mainly due to the deficiency of the Gaussian-based demodulator. An impulse mitigation strategy derived from the myriad filtering framework is incorporated into the demodulator for efficient baseband filtering and RS decoding. Even without an interleaver, the proposed solution leads to substantial performance improvements over the conventional interleaved scheme in impulsive channels. Consequently, the delay caused by interleaving can be avoided, which has significant benefits for future broadband power-line communication systems supporting interactive applications.      

Power-Line Communication Channel Model for Interconnected Networks—Part I: Two-Conductor System

This paper presents a generalized transmission-line approach to determine the transfer function of a power-line network of a two-conductor system (two parallel conductors) with distributed branches. The channel frequency responses are derived considering different terminal loads and branches. The model's time-domain behavior is validated using commercial power system simulation software called Alternative Transients Program–Electromagnetic Transients Program (ATP–EMTP). The simulation results from the model for three different topologies considered have excellent agreement with corresponding ATP–EMTP results. Hence, the model can be considered as a tool to characterize any given power-line channel topology that involves the two-conductor system. In the companion paper (Part II), the proposed method is extended for a multiconductor power-line system.      

Power-Line Communication Channel Model for Interconnected Networks—Part II: Multiconductor System

In this paper, we present an approach to determine the transfer function for multiconductor power-line networks with distributed branches and load terminations for broadband power-line communication (BPLC) applications. The applicability of the proposed channel model is verified numerically in time domain using the finite-difference-time domain (FDTD) method for the solution of transmission lines. The channel model simulation results are in excellent agreement with the corresponding FDTD results. The model therefore could be useful in the analysis and design of BPLC systems involving multiconductor power-line topology.      

Modeling and Analysis of Common-Mode Current Propagation in Broadband Power-Line Communication Networks

This paper proposes a new approach to modeling the common-mode (CM) current propagation path of electrical power-line cables for broadband power-line communications (PLC). In this approach, a CM current propagation model for a three-wire power-line cable is developed using the multiconductor transmission-line theory. The model is used to study the electromagnetic-interference radiation mechanism from the PLC network in the frequency range of 1 to 30 MHz. The accuracy of the model is verified through numerical simulations and practical measurements conducted on the actual power-line network. The developed model allows us to predict the CM current in the power-line cable with reasonable accuracy.