introduction
Power line carrier communication is a technology in which the power line is used as a transmission medium to transmit analog or digital signals through carrier waves, and there is no external communication line. Introduce the basic principles of orthogonal frequency division multiplexing. According to the characteristics of using orthogonal frequency division multiplexing OFDM (Orthogal Frequency Division MulTIplexing) technology to better modulate and demodulate the signal, a design scheme of power line carrier communication system based on OFDM is proposed Carrier communication is realized using power lines.
2 Power line carrier communication
Power line carrier communication is a communication method unique to the power system. It can be used to transmit signals such as telephones, telecontrol data, and remote protection. It is an important communication method for ensuring the safety, high quality, and economic operation of the power grid, and realizing dispatch automation and management modernization. It uses the power line as a transmission channel, which has the advantages of high channel reliability, less investment and quick results, and synchronization with power grid construction.
Figure 1 is a composition diagram of the power line carrier communication system. The basic principle is to apply information-carrying high-frequency signals to the power line for data transmission, and then separate the high-frequency signals of the power line channel through power line modulation and demodulation, and then transmit them to the terminal equipment.
Various mature modulation and demodulation technologies have been applied to power line carrier communication systems. For adapting to high-rate transmission, orthogonal frequency division multiplexing modulation and demodulation technology is an effective method to solve the transmission band utilization rate. Power line carrier communication technology has different application technologies, line conditions and application requirements in the three voltage levels of high, medium and low voltage. High-voltage power line carrier refers to carrier communication equipment applied to voltage levels of 35 kV and above. The carrier line is in good condition, mainly transmitting information about dispatching telephones, telecontrol, high-frequency protection and other monitoring systems.
3 OFDM modulation and demodulation technology
OFDM is a method of combining several independent signals into a composite signal that can be transmitted on the same channel. The basic principle of data transmission is to convert the serial data stream into N parallel data streams with a lower rate, and use them to modulate N subcarriers and transmit them in parallel. The subcarriers are orthogonal to each other, and their spectrums overlap with each other, which has a strong Resistant to channel fading capability and higher spectrum utilization, and can well suppress inter-symbol interference.
The frequency of the nth subcarrier is selected as:
In the formula, X (k) is the output signal of the k-th subcarrier at the receiving end.
It can be seen from equation (4) that it is equal to the k-th subcarrier signal at the sending end, so that the original signals X0, X1, ... XN-1 of the carrier can be demodulated correctly.
The triode, the full name should be a semiconductor triode, also known as a bipolar transistor, a crystal triode, is a semiconductor device that controls current. Its function is to amplify the weak signal into an electrical signal with a large amplitude value, and also as a non-contact switch.
Transistor is one of the basic components of semiconductors, with current amplification, is the core component of electronic circuits. The triode is made up of two closely spaced PN junctions on a semiconductor substrate. The two PN junctions divide the monolithic semiconductor into three parts, the middle part is the base area, and the two sides are the emitter area and the collector area, and the arrangement is PNP. And NPN two.
Small Signal Transistor,Digital Transistor,Darlington Transistor,Power Transistor
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