José Antonio Cortés

A channel model proposal for indoor power line communications

In this article, a channel model for broadband indoor Power Line Communications (PLC) is presented and discussed. The modeling approach is based on the physical structure of the electrical networks inside homes and small offices. The structure has been simplified to derive a parametric model that still preserves the essential behavior of these channels in the HF band (up to 30 MHz). The model provides realistic channels by setting values to a reduced number of physical parameters. In addition, statistical distributions for such parameters that allow generating ensembles of random channels are suggested. The validity of the generated channels is assessed by comparing their behavior to the one of channels measured at several indoor power networks. Hence, this model can be employed to estimate the performance of transmission techniques on PLC channels, to aid in the design of PLC systems or to make prototype conformance tests.

Broadband modelling of indoor power-line channels

The main purpose of this paper is to describe and model the characteristics of low voltage distribution lines inside consumer premises, when used as a broadband communication channel. Results from measurements performed both in the laboratory and in residential buildings, are presented and discussed. Also a channel model to simulate the behaviour of these lines for high bit-rate digital communications is proposed. The model contemplates the topology of the power grid and the characteristics of the wires and loads connected to them; it incorporates as well statistical time variation of the loads, so that the dynamic evolution of the channel performance can be evaluated.

Analysis of the Indoor Broadband Power-Line Noise Scenario

Indoor broadband power-line noise is composed of three main terms: impulsive components, narrowband interferences, and background noise. Most impulsive components have a cyclostationary behavior. However, while some of them consist of impulses of considerable amplitude, width, and repetition rates of 50/100 Hz (in Europe), others have lower amplitude and shorter width but repetition rates of up to hundreds of kilohertz. Classical studies compute statistics of the impulse characteristics without taking into account these significant differences. This paper presents a detailed analysis of these noise terms with a clear distinction between their constituent terms. A classification of the narrowband interferences according to their power spectral density and their statistical behavior is also given. Finally, the instantaneous power spectral density of the background noise and its probability distribution are investigated. Some of the results presented in this paper are available for download from the web site http://www.plc.uma.es/index_eng.htm.

Modeling and evaluation of the indoor power line transmission medium

The aim of this article is to outline the possibilities of indoor power lines when used to support local area networks in homes or small offices. For this purpose, the channel characteristics are described and a channel model is presented. This model is related to the physical nature of common indoor power lines, so its parameters can be defined in a straightforward way. Based on it, the performance of communication systems that use discrete multitone modulation, which appears to be the most suitable technique for these channels, is evaluated. Finally, a discussion about medium access control strategies is included.

Fundamentals of the cyclic short-time variation of indoor power-line channels

In this paper, indoor power-line channels properties are analyzed. The focus is put on the short-term variation that channel exhibits due to the behavior of electrical devices, which is influenced by the presence of mains voltage. Devices high-frequency parameters are time-varying and this makes the channel varies as well. To characterize this behavior it is proposed a model with an LPTV system and cyclostationary noise. In addition, examples of measurements corresponding to actual channels that illustrate these features are shown. More quantitative measurements results performed according to this channel model are presented in JA Cortes, et al. (2005).

Characterization of the cyclic short-time variation of indoor power-line channels response

Indoor power-line channels response exhibits a time-varying behaviour with a twofold nature. The first one is the well-known long-term variation caused by the connection and disconnection of electrical devices. The second one is a short-time variation, synchronous to the mains, whose origin is the dependence of the impedance presented by electrical devices on the mains voltage (Canete, FJ et al., 2005). The purpose of this paper is to assess the importance of this latter aspect in actual channels. To this end, a measurement procedure able to extract these short-time variations is described at first. Afterwards, a statistical analysis of the results obtained from a measurement campaign performed at different scenarios is given. Specifically, the delay spread, the peak excursion and the rate of change of the frequency response in the band from 1 MHz to 20 MHz are presented and discussed.

Characterization and Evaluation of In-Vehicle Power Line Channels

This paper presents a statistical characterization of in-vehicle power lines, based on channel measurements carried out in a automobile. In particular, the impact of the engine speed on the characteristics of the channels is analyzed. Performance of an Orthogonal Frequency-Division Multiplexing (OFDM) system is assessed using the channel measurements.

On the statistical properties of indoor power line channels: Measurements and models

In the last years, numerous works have analyzed the statistical distribution of indoor power line channels response. A set of models based on two main approaches, bottom-up and top-down, have been proposed. This work analyzes the statistical distribution of the attenuation and the delay spread of indoor power line channels. First, results obtained from a set of more than 200 channel responses measured in 25 different premises are presented. Then, the suitability of various channel models proposed in the literature is evaluated by comparing their statistical distributions with the one of the measured channels.

Analysis of the periodic impulsive noise asynchronous with the mains in indoor PLC channels

Indoor broadband power-line noise is composed of three main terms: impulsive components, narrowband interferences and background noise. Impulsive components can be classified into three groups according to their behavior with respect to the mains cycle: periodic synchronous with the mains, periodic asynchronous with the mains and aperiodic. Periodic asynchronous terms are the most interesting ones because they have significant spectral components in the band used by broadband power-line communication systems. This paper presents a detailed analysis of this noise component in the frequency band up to 25MHz. By means of a methodology that combines both frequency and time domain techniques, repetition rates and pulse waveforms are obtained even in scenarios in which the remaining noise terms have significant level.

Comparative Analysis of Pilot-based Channel Estimators for DMT Systems Over Indoor Power-line Channels

This work addresses the problem of pilot-based channel estimation in DMT systems for broadband indoor power-line communications. The study is carried out over a set of measured channels. Three estimation schemes are compared: the least-squares (LS), the linear minimum mean-squared error (LMMSE) estimator and the least-mean-square (LMS) with cubic interpolation between pilot carriers. The use of a generic LMMSE design based on channel statistics derived from measurements is proposed. Performance as a function of the pilot spacing is analyzed in terms of the mean-squared error (MSE), the error probability and the attained bit-rate.