What Is a Power Line Communication?

Power Line Communication (PLC for short) technology refers to a communication method that uses power lines to transmit data and media signals ^[1] . The technology is to load the high frequency carrying information to the current, and then use the wire to transmit the adapter to receive the information. Then the high frequency is separated from the current and transmitted to the computer or telephone to realize the information transmission.

Common interfaces for power line communication equipment are as follows:

The debugging method usually used in power line communication is OFDM, which is orthogonal frequency division multiplexing. OFDM is a technical measure to ensure the stable and complete transmission of data in a severe electromagnetic interference communication environment. The HomePLUG 1.0 specification covers the 4-21MHz communication frequency band, and 84 OFDM communication channels are divided in this frequency band. The principle of OFDM is that several communication channels are frequency-divided according to a 90-degree phase. The result is that when the waveform of a certain channel crosses zero, the waveform of the adjacent channel is exactly the maximum amplitude. This ensures that the waveform between channels is not Overlap and crosstalk due to external interference.

From the perspective of occupied frequency bandwidth, it can be divided into narrow-band PLC and wide-band PLC. ^[5]

There are various forms of PLC applications. For example, when a commercial appears on a digital TV, the product information can be downloaded to the computer through the power line. After that, the computer can also send order information to the supplier or browse the product web page for more detailed information. You can also record music or video programs through the power line. When playing music on TV or on a music channel, you can record music directly to the power line

Traditional power line carrier communication (PLC) mainly uses high-voltage power transmission lines as transmission channels for high-frequency signals. It is limited to transmitting voice and telecontrol signals, and has a narrow application range and low transmission rate, which cannot meet the requirements of broadband development. PLC is developing towards high-capacity and high-speed. At the same time, it is shifting to carrier communication using low-voltage power distribution networks, enabling home users to use power lines to make phone calls and access the Internet. ^[6]

Foreign countries such as the United States, Japan, Israel and other countries are conducting research and experiments on low-voltage distribution network communications. Thirteen companies including 3COM, Intel, Cisco, and Matsushita of Japan jointly established a home network promotion group, "Homeplug Powerline Alliance", which uses power lines as a transmission medium, and has proposed a Home Plug plan to promote power line transmission Digital Home of the Media (DigitalHome).

The following issues remain to be further studied:

Hardware platform: It mainly includes reasonable selection of communication methods and optimization of communication network structure. Spread spectrum method, OFDM technology and multi-dimensional trellis coding method have their own advantages. Which one is suitable for low-voltage networks remains to be studied, or the idea of software radio can also be used to provide a unified platform for these three methods. The power network structure is very complex and the network topology is ever-changing. How to optimize the structure of the communication network is also a question worthy of study.