Introduction to the basic principles of power line communication

Power Line Communication (PLC) technology refers to a communication method that uses power lines to transmit data and media signals. This technology loads the high frequency that carries information onto the current and then transmits it through the wire. The adapter that receives the information then separates the high frequency from the current and transmits it to the computer or phone to achieve information transmission. The biggest advantage of this technology is that it does not require rewiring to carry multiple services such as data, voice, and video on the existing wires, achieving the integration of four networks. Terminal users only need to plug in the power plug to access the Internet, receive TV channels, make phone calls, or make video calls.

Rationale

When sending, the user data is modulated by modulation technology, and the high frequency carrying information is loaded onto the current, and then transmitted on the power line; at the receiving end, the modulated signal is first taken out through a filter, and then demodulated to obtain the original communication signal, which is then transmitted to the computer or telephone to realize information transmission. The PLC equipment is divided into a central office and a modem. The central office is responsible for communicating with the internal PLC modem and connecting to the external network. During communication, the data from the user enters the modem for modulation, and is transmitted to the central office equipment through the user's power distribution line. The central office demodulates the signal and then transfers it to the external Internet. The specific design concept of the power line carrier bidirectional transmission module: a transmission module composed of a modulator, an oscillator, a power amplifier, a T/R steering switch, a coupling circuit and a demodulator, wherein the oscillator provides a carrier signal for the modulator. When transmitting data, the signal to be sent is sent from the TXD end, modulated by the modulator, and then the modulated signal is sent to the power amplifier stage for amplification, and then the modulated signal is loaded onto the power line through the T/R steering switch and the coupling circuit. When receiving data, the modulated signal sent by the transmitting module enters the demodulator through the coupling circuit and the T/R steering switch. After demodulation by the demodulator, the original signal is extracted and sent from the RXD end to the next-level digital device.

Modulation method of power line communication

The debugging method commonly used in power line communication is OFDM, that is, OFDM is a technical measure to ensure stable and complete data transmission in severe communication environments. The HpmePLUG 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 divided by 90 degrees of phase. As a result, when the waveform of a certain channel passes through the zero point, the waveform of the adjacent channel is exactly the maximum amplitude, which ensures that the waveforms between channels will not overlap or crosstalk due to external interference.

Network interface for power line communication

Common interfaces for power line communication equipment are as follows:

RJ-45 connector

The RJ-45 interface is the most commonly used interface for Ethernet. RJ-45 is a common name that refers to an 8-position (8-pin) modular jack or plug standardized by IEC (60) 603-7 and defined by international connector standards.

USB interface

USB (Universal Serial Bus) is a new peripheral interface standard initiated by several major manufacturers such as Intel, Microsoft, Compaq, IBM, and NEC. The transmission speed of USB1.1 is 12Mbps, and USB2.0 can reach 480Mbps; the maximum cable length is 5 meters. The USB cable has 4 wires, including 2 signal wires and 2 power wires, which can provide 5 volt power. USB cables are also divided into shielded and unshielded types. The shielded cable has a transmission speed of up to 12Mbps and is more expensive, while the unshielded cable has a speed of 1.5Mbps, but is cheaper; USB can connect up to 127 devices in series; it supports plug-and-play and hot-swap.