Power Line Carrier
Definition
Power line communication or power line carrier (PLC), also known as Power line Digital Subscriber Line (PDSL), mains communication, power line telecom (PLT), or power line networking (PLN), is a system for carrying data on a conductor also used for electric power transmission. Broadband over Power Lines (BPL) uses PLC by sending and receiving radio signals over power lines to provide access to the internet.
Electrical power is transmitted over high voltage transmission lines, distributed over medium voltage, and used inside buildings at lower voltages. Powerline communications can be applied at each stage. Most PLC technologies limit themselves to one set of wires (for example, premises wiring), but some can cross between two levels (for example, both the distribution network and premises wiring).
All power line communication systems operate by impressing a modulated carrier signal on the wiring system. Different types of powerline communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used. Since the power wiring system was originally intended for transmission of AC power, the power wire circuits have only a limited ability to carry higher frequencies. The propagation problem is a limiting factor for each type of power line communications.
Data rates over a power line communication system vary widely. Low-frequency (about 100-200 kHz) carriers impressed on high-voltage transmission lines may carry one or two analog voice circuits, or telemetry and control circuits with an equivalent data rate of a few hundred bits per second; however, these circuits may be many miles (kilometres) long. Higher data rates generally imply shorter ranges; a local area network operating at millions of bits per second may only cover one floor of an office building, but eliminates installation of dedicated network cabling.
Overview
There are defined standards for narrow band PLC systems as laid out by CENELEC, the European Committee for Electro Technical Standardisation. CENELEC standard EN 50065 defines the signalling on low voltage electrical installations in the frequency range 3 kHz to 148.5 kHz, whereby the use of frequencies within the band 3 kHz to 95 kHz is restricted for use by electricity suppliers and their licensees and more commonly referred to as CENELEC A.
Furthermore there are a number of modulation schemes which can be used in PLC such as FSK, SFSK, DCSK, OFDM etc. and as with all technology, advancements are continuous. The selection of the right PLC technology will play an important part in ensuring reliable and cost effective network operation. Whilst Differential Code Shift Keying (DCSK) technology is considered the most robust PLC technology and has been deployed in many AMM installations already, there is increasing interest around Orthogonal Frequency Division Multiplexing (OFDM) as a preferred modulation for PLC.
