Figure 3: Example of Distribution of 3 subcarriers in technique OFDM. Source: GTA/UFR, the GSMK is a special type of modulation of narrow band that transmits the data in the phase of the carrier, resulting a signal of constant envelope. This allows the use of less complex amplifiers, without producing riots harmonic. Figure 4: Spectro of the wave Spread Spectrum, OFDM and GSMK Source: School of Engineering Electric and Computation, 2.3. Topology and Equipment of Interconnection of Net PLC As cited previously, to the transmission of data are made in sequence of different signals, MHz or Hz.
The equipment must be projected so that it has this union of electric net and transmission of data. In accordance with Teixeira (2005) a typical topology of net PLC can be visualized of the following form, considering itself 4 levels of net. Figure 5: Typical topology of net PLC Source: TELECO. (s.d.). teleco.com.br Figure 5 illustrates the four levels of net, which is, internal net, net of access, net of distribution and net of transport (interconnection with the Internet).
2.3.1.Rede Internal In accordance with Teixeira (2005) the internal net of the final user is constituted by the net of electric distribution in the existing installations already and by modems for connection of the equipment that will be linked to the service. Diverse modems can be linked in the available taking in the residence. Figure 6: Computer using modem PLC. Source: 2.3.2.Rede of Access As Teixeira (2005) the net of access PLC if initiates next to the measurer of electric energy of the user with introduction of an equipment, called repeating ' ' BT' ' or Intermediate equipment ' ' IE' '. This equipment has as main function, to receive signals PLC generated in the modem (s), to effect bypass (shunting line) of the measurer and to reinjetar them in the net of low tension.