Introduction to PLC

"Power Line Communications" basically means any technology that enables data transfer at narrow or broad band speeds through power lines by using advanced modulation technology.

Depending on the country, the institution and the company, power line communications are grouped under several different key words:

• PLC (Power Line Communications)
• PLC (Power Line Communications)
• PLT (Power Line Telecommunications)
• PPC (Power Plus Communications)

Brief history of PLC

Power line communication has been around for quite some time, but has only been used for narrow band tele-remote relay applications, public lighting and home automation.

Broadband over PLC only began at the end of the 1990s:

• 1950: at a frequency of 10Hz, 10kW of power, one-way: town lighting, relay remote control.
• Mid 1980s: beginning of research into the use of the electrical grid to support data transmission, on bands between 5 - 500Khz, always in a one-way direction,
• 1997: first tests for bidirectional data signal transmission over the electrical supply network and the beginning of research by Ascom (Switzerland) and Norweb (U.K.)
• 2000: first tests carried out in France by EDF R&D and Ascom.

Operating principles

PLC Broadband technology is capable of transmitting data via the electrical supply network, and therefore can extend an existing local area network or share an existing Internet connection through electric plugs with the installation of specific units.

The principle of PLC consists in superimposing a high frequency signal (1.6 to 30 Mhz) at low energy levels over the 50 Hz electrical signal. This second signal is transmitted via the power infrastructure and can be received and decoded remotely. Thus the PLC signal is received by any PLC receiver located on the same electrical network.

An integrated coupler at the PLC receiver entry points eliminates low frequency components before the signal is treated.

Legal framework and regulation

All technology running on a defined frequency band must be part of a legal framework. PLC networks are at the same time both electrical supply networks and telecommunications networks, with the result that the authorities have encounter difficulties defining their legal framework. Futhermore, no precise regulation exists for PLC equipment and networks. There are currently works in place with the PLC Forum and the ETSI, but results have not been published to date.

Therefore the installation of PLC networks is currently unregulated as regards the installations located behind a private meter (called "Indoor" or "InHome"), they are however subject to the condition that they do not cause negative side-effects, in which case the equipment must be removed. Regarding external installations (called "Outdoor") where the signal is transmitted at the HVA/LV transformer level to create local electrical loops, testing permits are required from the Telecommunications Regulatory Authority so long as the technology is still in development and standards have not been published.

Standardisation

Only one such standard currently exists, the American: Homeplug V1.0.1 standard. This standard is only applicable for "indoor" installations and is not interoperable with current "outdoor" applications. Other standards will emerge over the coming months or years.

NB: All equipment available to the public to date conforms to the "Homeplug" standard.

Written by Françoise Cacciaguerra – November 2003

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