Thiago R. Oliveira

A sounding method based on OFDM modulation for PLC channel measurement

The measurement and characterization of electric power grid as medium to provide data communication is a task of practical importance for understanding signal propagation and impairment as well as pursuing new generation of power line communication (PLC) technologies. With this regards, this contribution aims at discussing a channel estimation methodology that is constituted by a sounding technique for channel estimation, a time synchronization technique, and a measurement setup. This methodology allow to measure linear time invariant, time variant, and periodically time variant PLC channels if the clock offset between the transmitter and receiver devices of the measurement setup is irrelevant. Measurement results reveal the effectiveness of this methodology for estimating PLC channels.

Cooperative power line communication: Analysis of Brazilian In-Home channels

This contribution aims at analyzing the suitability of cooperation concepts for improving the performance of power line communication (PLC) systems, more specifically in Brazilian In-Home (IH) electric power grids. For this purpose, the performance of the amplify-and-forward (AF) and decode-and-forward (DF) protocols, together with the equal gain (EGC), selection (SC), and maximal-ratio (MRC) combining techniques were analyzed. The analysis is carried out on measured data covering a frequency band from 1.705 up to 100 MHz. The measured data addresses four scenarios for possible locations of the relay node. The attained results show that the AF is of limited applicability in the PLC context and the opposite is valid to the DF protocol, mainly if the error probability of detecting symbols at the relay is zero. Additionally, it is shown that the EGC can in some cases reduce the system performance.

Measurement setup for characterizing low-voltage and outdoor electric distribution grids for PLC systems

This paper describes a measurement setup that characterizes low-voltage electric distribution grids as a medium for data communication when the frequency band is between 1.7 and 50 MHz. This setup is constituted by several equipment and algorithms that allow to extract the following information from the measured data: i) channel frequency response, ii) additive noise, iii) access impedance, and iv) radio signals. A brief report about the use of this setup in a measurement campaign carried out at Juiz de Fora city is presented. This report reveals the usefulness and applicability of this measurement setup to characterize electric distribution grids for data communication (power line communication - PLC).

The characterization of hybrid PLC-wireless channels: A preliminary analysis

This work aims at measuring, characterizing, and analyzing hybrid channels for mobile data communication with power line communication (PLC) technologies. These channels denote the concatenation of power line and wireless as only one channel. A measurement setup and OFDM-based technique for channel estimation were applied to carry out a measurement campaign of hybrid channels in the PLC → wireless and wireless → PLC directions. Preliminary results as well as analysis when estimates of the hybrid channels cover the frequency band between 1.7 up to 100 MHz are presented. The attained results reveals that these hybrid channels are very challenging ones. Also, they could be useful for data communication if more investigation concerning the PLC coupling device, the antenna geometry, and theoretical formulation for the signal propagation through the hybrid channel is deeply investigated.

Statistical analysis of Brazilian in-home PLC channels: First results

This contribution outlines a statistical characterization of Brazilian in-home and low-voltage electric energy distribution networks as a data communication medium. The discussions are based on estimated channels obtained in a measurement campaign carried out in several apartments whose size ranges from 50 up to 90 square meters. The parameters considered for this analysis is the root-mean square delay spread (RMS-DS), the average channel gain, and the channel capacity. For the sake of comparison with electric networks in US, the frequency band ranging from 1.705 up to 30 MHz was set. The reported analysis shows that the RMS-DS can be modeled as a log-normal variable in only 33.33% of the cases and the average channel gain does not follow a log-normal distribution, the average channel gain is lower in Brazil than in US and the inter-symbol interference is quite similar in both US and Brazil.

PLC Channel Estimation Based on Pilots Signal for OFDM Modulation: A Review

This contribution aims at discussing channel esti- mation techniques for power line communication systems, which makes use of multicarrier modulation based on orthogonally frequency division multiplexing and pilots signals. In this regards, channel models for linear and time varying and linear and periodically time varying channels are described as well as models to impulsive noises. Then, a comprehensive analysis of channel estimation techniques for OFDM-based power line communication systems is addressed. Basically, Adaptive or non- adaptive and supervised or non-supervised estimation techniques are addressed because the power line channels can be modeled, due to the load characteristic, as linear and time invariant, linear and time varying, and linear and periodically time varying. Several simulation results considering power line channel and noise models emphasize the effectiveness of several estimation techniques.

Analysis of a hybrid OFDM synchronization algorithm for power line communication

This paper outlines a hybrid OFDM synchronization technique for powerline communication. Initially, the timing and frequency offset are estimated by searching for the peak of an evaluated metric provided by a reference block transmitted at the beginning of each OFDM frame, and subsequently, autocorrelation properties induced at cyclic prefix on the time domain are exploited to maintain estimates of the timing and frequency offset without the use of a new reference block for synchronization purpose. This strategy is interesting because once a first synchronization of the first OFDM block (the start point of the frame) is accomplished, any loss in spectral efficiency will occur subsequently. Additionally, we propose an interesting strategy with low computational complexity to improve the timing and frequency estimates after synchronization is carried out at the beginning of the frame. Basically, this strategy consists of averaging the peaks spacing between successive peaks of the evaluated autocorrelation metric. Simulation results reveal good performance in PLC scenarios, specially in the cases of occurrences of impulsive noise.

HOS-based impulsive noise detection technique for power line communication systems

This paper discusses a detection technique for impulsive noise in power line cables. Essentially, a reduced set of features (signature vector), which is selectively extracted from the power line signal feeds a detection technique. The features are higher-order statistics and the Fishers discriminant ratio is the selection technique. The designed detectors are a multilayer perceptron neural network and a Bayes implemented according the maximum likelihood criterium. Simulation results indicate that improved performance can be attained if multilayer perceptron neural network is considered as a nonlinear detector. Also, the results reveal that higher-order statistics is a very interesting technique to extract a reduced and representative signature vector of impulsive noise.

Statistical modeling of the average channel gain and delay spread in in-home PLC channels

This work describes a complete statistical modeling of the average channel gain in dB (ACGdB) and the root mean squared delay spread (RMS-DS) for power line communication (PLC) systems. The PLC channel features are estimated from 148,037 channel frequency responses measured in 7 typical different places in an urban area in Brazil. Two frequency bands are considered: from 1.7 up to 30 MHz and from 1.7 up to 100 MHz. The resulting datasets for ACGdB and RMS-DS were fitted to well known continuous distributions, including symmetric (Logistic and Normal) and asymmetric (Exponential, Gamma, Inverse Gaussian, Loglogistic, Lognormal, Nakagami, Rayleigh, Rician, Skew-normal, t-Student and Weibull) cases. The best distribution fitted to the considered dataset is indicated by the log-likelihood value and three distinct information criteria. The achieved results revealed that the ACGdB is better modeled by the Skew-normal and the Nakagami distributions for the frequency bands from 1.7 up to 30 MHz and 100 MHz, respectively, whereas the RMS-DS is little bit better modeled by the Gamma distribution, then by the Lognormal distribution, in both frequency bands considered.

Preliminary analysis of additive noise on outdoor and low voltage electric power grid in Brazil

This work aim at presenting a preliminary analysis of additive noises on outdoor and low voltage electric power grid when the frequency band between 1.7 and 100 MHz is considered. These noises were obtained during a measurement campaign carried out in a Brazilian suburban area comprising a low-income community. The statistical analysis in the time and frequency domains reveal the hardness of such environment for data communication as well as the white holes that can be opportunistic used by PLC systems to operate in the same frequency band of primary users.