AN ALTERNATIVE APPROACH IN POWER LINE COMMUNICATION CHANNEL MODELLING

Abstract

In this paper, we present the measurement methodology and results for a low voltage Power line Communications (PLC) network under difierent conflgurations. Based on the measurements, a correlation of the channel transfer characteristics to the network topology is established and a deterministic model based on two-wire transmission line theory for transverse electromagnetic (TEM) wave propagation is proposed. The channel frequency response in frequency range of 1{30MHz is determined, where the model results agree well with the measurements. The development of accurate power line communication (PLC) channel transfer characteristics models is important as it forms the basis for computer simulations which are useful in appropriate system design, and further enable the analysis of the performance of difierent network conflgurations and loads (1). There is therefore continued research in the characterization of the power line as a communication medium. Difierent techniques which are based on either measurements or theoretical derivations from physical parameters, denoted as top-down or empirical models (2,3), and bottom-up or deterministic models (4{6), respectively, are employed. The empirical model is easy to use as it calls for little computation and is easy to implement. It is however susceptible to measurement errors and cannot be used to reproduce the channel characteristics of a difierent PLC network. The deterministic model difiers from the latter in that it necessitates detailed knowledge of all components and their respective characteristics. Therefore the network behaviour in relation to the model parameters is clearly deflned, and is considered in this work. True to its original purpose, the low voltage power line network within a typical in-building structure is optimized for the transmission of high voltages at low frequencies contrary to data transmission which necessitates the transmission of low voltage at high frequencies. The communication signals therefore sufier some hostile channel parameters. The three most important parameters are noise, impedance mismatch, and attenuation which are frequency, time and location variant (7). Subsequently, accurate approximation of the line parameters, the characteristic impedance Z0, and propagation constant ∞, which in turn are used to determine the PLC channel constants, is essential in the channel transfer function calculations. Meticulous measurements are required in the investigation of the channel parameters and consequent modelling of the same. The behaviour of the channel is better understood by varying difierent components, which in the case of PLC, are: the topology; the cable types; the cable length and number of branches; as well as the loads terminating at each end of the network. Once relations of the variations of these are obtained, any given network can then be su-ciently modelled.