Residential Automation
According to Andrade & Souza (2004), to allow the transmission of data in broad band, is necessary the use of higher frequencies, in the band between 1MHz and 30MHz. As the electric energy passes through in the band of Hz and the waves of the transmission signals are in the order of MHz, the transmission of signals PLC is made through wires of copper (or aluminum) of the nets of distribution of low and average tension. In accordance with Bolzani (2004), as the electric nets had not been idealized for the transmission of data yes optimized for this use, the nets of energy distribution are half more problematic physicists for the ticket of signals of high frequency and, amongst them, we can consider: Noise: in an electric net, without shield, the sources of noises are innumerable. Distance enters the access points: the more far the points, greater the attenuation of signal and the incidence of noises. Discontinuity and impedance: throughout the net, depending if the taking they are being used or not, points of reflection of signal are created.
Load: all the household-electric ones plugados in the taking, that exactly off, they constitute a resistiva and reactive load wasting the energy transmitted in high frequency. High frequency: generally, how much bigger the frequency, greater the attenuation of the signal. Figure 1: Noises in nets PLC Source: Bolzani, C. (2004). Intelligent residences: Domestic Domtica, Nets, Residential Automation However, exist the modulation technique that it must allow to minimize these restrictions, such as: the technique of modulation of spectral scattering, technique OFMD, and technique GSMK. The technique of spectral scattering consists of distributing the power of the signal throughout a band of very ample frequency, guaranteeing that the spectral density of power is sufficiently ample.