Luis Díez

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.

System for automated diagnosis in cellular networks based on performance indicators

This paper presents a system for automated diagnosis of problems in a cellular network, which comprises a method and a model. The reasoning method, based on a naive Bayesian classifier, can be applied to the identification of the fault cause in GSM/GPRS, 3G or multi-systems networks. A diagnosis model for GSM/GPRS radio access networks is also described, whose elements are available in the network management systems (NMSs) of most networks. It is shown that the statistical relations among the elements, that is the quantitative part of the model, under certain assumptions, can be completely specified by means of the parameters of beta density functions. In order to support the theoretical concepts, a model has been built based on data from a real network and the automated diagnosis system has been used to classify problems in a cellular network, showing that the solution is easily implemented and that the diagnosis accuracy is very high, therefore leading to a reduction in the operational costs of running the network. Copyright

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).

A Channel Simulator for Indoor Power-line Communications

In this paper, a simulator for indoor power-line channels is presented. Its behavioral model includes both the long-and short-time variation of the channel. The long-time variation is due to the electrical appliances switching and is modeled in a statistical way. The cyclic short-time variation is related to the presence of the mains voltage and is characterized modeling the channel response as a linear periodically time-variant (LPTV) system and including an additive cyclostationary noise term. The cyclic model is simplified by using a slow variation approach, so that the channel can be modeled by means of a cyclic sequence of LTI systems with stationary noise terms. Channels according to the behavioral model are generated based on the physical structure of the network. The model for this physical structure comprises: the wiring, characterized as a set of terminated transmission lines connected in a tree-like fashion; and the electrical appliances, which are modeled as electric bipoles acting as impedances and noise sources. The simulator can perform the calculation of the channel frequency response and noise power spectral density at the receiver given a network topology. Afterwards, a channel simulation can be carried out using two banks of filters, one for the LPTV channel response and the other to obtain cyclostationary noise by filtering AWGN. Some test results for the channel generation and simulation are presented, and practical applications of this simulator are discussed.

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.

Learning of model parameters for fault diagnosis in wireless networks

Self-management is essential for Beyond 3G (B3G) systems, where the existence of multiple access technologies (GSM, GPRS, UMTS, WLAN, etc.) will complicate network operation. Diagnosis, that is, fault identification, is the most difficult task in automatic fault management. This paper presents a probabilistic system for auto-diagnosis in the radio access part of wireless networks, which comprises a model and a method. The parameters of the model are thresholds for the discretization of Key Performance Indicators (KPIs) and probabilities. In this paper, some techniques are proposed for the automatic learning of those model parameters. In order to support the theoretical concepts, experimental results are examined, based on data from a live network. It has been proven that calculating parameters from network statistics, instead of being defined by diagnosis experts, highly increases the performance of the diagnosis system. In addition, the proposed techniques enhance the results obtained with continuous diagnosis models previously exposed in the literature.

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.