ZyXEL Communications PLA-470 V2 - V3.0.5 Przewodnik Instalacji Pobierz pdf (Strona 176)

In addition, and unlike Wi-Fi, the network configuration does not require you

to make choices according to the other assigned channels. All the channels of the

permitted bands, called “sub-bands” are used. Therefore, the network can be con-

gested by the various technologies coexisting on the same electrical network. In this

case, free or infrequently used sub-bands are used by PLC technology. In Chapter

13, we’ll examine the coexistence of PLC technologies and the work in progress on

an interoperability standard.

Figure 8.5 illustrates the frequency domain of the various PLC modulation

OFDM sub-bands and the associated binary data in the case of a HomePlug 1.0

PLC network.

Electromagnetic Compatibility and Frequency Bands

The various electrical and electronic devices that we use within a domestic, profes-

sional, or industrial background produce radio electromagnetic emissions in the

environment close to where they operate.

The frequencies of these radio electromagnetic devices may interfere with the

operation of the network’s PLC devices and prevent data communications in fre-

quency sub-bands. Some devices produce more disturbances than other devices on

PLC networks. For example, the CE marking in force in the European Community

stipulates the limits for the radioelectromagnetic emissions of electrical and elec-

tronic devices sold in stores.

Chapter 7 (see Table 7.7) gives a list of PLC network disturbing devices. We’ll

examine this a bit further in this chapter about interference.

Reciprocally, PLC devices emit electromagnetic waves that may interfere with

the operation of the surrounding telecommunications devices around the electrical

wirings. The CISPR (international special committee on radio interference) of the

IEC (International Electrotechnical Commission) indicates wave emission limits for

PLC devices.

Current PLC technologies, such as HomePlug AV, implement a notching tech-

nique in order to comply with these emission constraints.

Frequency Bands 157

Figure 8.5 HomePlug 1.0 PLC modulation OFDM sub-bands

1 2 ... 171 172 173 174 175 176 177 178 179 180 181 ... 348 349

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