ZyXEL Communications PLA-470 V2 - V3.0.5 Przewodnik Instalacji Pobierz pdf (Strona 171)

nologies are installed and implemented under the responsibility of MV electrical net-

work operators.

The 3- to 148-kHz and 1-to 30-MHz bands are called license-free bands, mean-

ing that there is neither a need to ask for authorization nor a need to pay for a sub-

scription in order to use them. However, they are subject to regulation by the ETSI

(in Europe) and the FCC (in the USA) which lay down certain restrictions of their use

in terms of transmission power.

These bands are divided into sub-bands over which transmissions take place.

Insofar as all technologies use these frequency bands, standardization work is in

progress so that various PLC systems can coexist on the same electrical network. In

Chapter 14, we will once more discuss the coexistence and interoperability of PLC

technologies.

Regulation of Radio Frequencies

The issue when deploying telecommunications networks is the achievement of the

best possible performance in terms of bit rate, latency, jitter, EMC (electromagnetic

compatibility), and coexistence of technologies while complying with the limits laid

down by the regulations in force.

Limits on the transmission power and authorized frequency bands are set by

these regulations. Rules are also promulgated concerning the acceptable level of dis-

turbances created according to the various radio technologies (amateur radio, ana-

log shortwave, digital radio waves, and so forth).

Due to their technology and medium, PLC devices emit radio waves induced in

the electrical wirings conveying the signals.

Unlike Wi-Fi wireless radio networks, PLC devices sold in stores in Europe try to

remain within the limits set by Cenélec (European committee for electrotechnical

standardization) and ETSI (European Telecommunications Standards Institute).

These devices are de facto designed to comply with these limits, and no hardware or

software modification is authorized to override them.

The software element of HomePlug devices does not give access to any hardware

parameters (carrier frequency, frequency sub-bands, or transmission power). This

means that the Ethernet frames sent by the configuration tools of PLC devices (see

Chapter 10) cannot be used to modify the frequencies and power used by the

devices. Therefore, for the PLC network user, the configuration does not give access

to the physical layer’s parameters, unlike Wi-Fi, with its 11 channels and its

parameterization of the interface transmission power.

Figure 8.1 illustrates the sending of a frame by the configuration tool to the PLC

device to be configured. This frame is a conventional Ethernet frame recognizable

on a network with its ETHERTYPE field, which, in its data, contains the parameters

to be configured so that the PLC network can operate in the best way possible.

The frequency utilization spectrum defined by the ETSI is globally broken down

as illustrated in Figure 8.2. Referring to the rules promulgated by the regulatory

authorities, it gives an idea on the distribution of general public radio frequencies

close to those used by the various PLC technologies.

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