According to the twenty-first issue of "Silicon Valley" magazine in 2012, PowerLineCommunication utilizes the existing low-voltage network as a carrier for information transmission. In recent years, with the development of power system, the existing power line network system can provide low cost and high efficiency network service. However, China's power line network complexity, strong interference, load conditions are complex, signal attenuation and other factors, seriously affecting the quality of communications. Therefore, it is necessary to further analyze the low-voltage power line carrier.

1 Development history and current situation at home and abroad

Foreign research on power line carrier has more than a hundred years. At present, several international research institutes have carried out research and development on high-speed power line carrier technology and achieved excellent results. The transmission rate of products has also risen from the initial 1 Mbps to 24 Mbps, 48 ​​Mbps and even 85 Mbps. Compared with other countries, the domestic research on power line carrier started later, but the rapid development. Domestic research is being carried out by early use of foreign power-line modulation techniques and chips for research and development, and for the development of modulation techniques and carrier-based chips suitable for the complicated channel characteristics of China's power grid. Some major advances have been made.

2 low-voltage power line carrier communication technology research

2.1 low-voltage power network characteristics

Low-voltage power line communication technology has many advantages, as long as there are power lines in the region there, so as a carrier of data transmission, compared with other modes of communication has the following advantages: 1) the price advantage. Power line carrier communication carrier power line, no longer need to lay the broadband and optical cable lines, it does not require high sending and receiving equipment. 2) the use of advantages. When the equipment input and output terminals connected to the power, that access to the power line. 3) High power network coverage and broad application prospect. The popularity of power line network is far better than other communication networks, laying a solid foundation for the realization of the Internet of Things.

At present, the power network channel in China is particularly complicated and the communication environment is very poor. In actual use, the load on the power grid is large, the types are complex, randomness and other factors have a greater impact on the input impedance, noise interference, signal attenuation and so on [2].

2.2 key technical analysis

In order to overcome various noise and interference existing in low voltage power line and reduce the signal attenuation, the research shows that the modulation technology can be used to improve the anti-interference and anti-noise ability of the system [3]. The following is a simple analysis of the current popular modulation techniques:

1) Two-phase frequency shift keying technology BFSK. Binary frequency shift keying modulation is characterized by fast conversion, anti-interference ability, high stability and easy to implement, but its transmission efficiency is relatively low. At present, Qingdao Neusoft PLCi36G-III-E chip and tripod TCC081C chip is the BFSK technology. Its communication rate up to 9600bps, with communication relay capabilities, can automatically detect the carrier node, take the initiative to report and other functions.

2) Code Division Multiple Access CDMA, CDMA assign a specific address code for each user, the quasi-orthogonality between address codes, the use of pseudo-random code modulation, the original bandwidth expansion, the receiving end of the reverse process of despreading Get the final signal. CDMA with anti-interference ability, confidentiality, easy to implement code division multiple access, with anti-fading, anti-multipath interference ability. CDMA also has the disadvantage that if the spreading codes for different users are not perfectly orthogonal, the CDMA system performance will be reduced. Beijing Fuxing Xiao Cheng PL3201 chip is the use of CDMA technology, its single-phase multi-function digital energy meter chip products have excellent performance.

3) Orthogonal Frequency Division Multiplexing OFDM is the channel is divided into a number of orthogonal sub-channel, the high-speed data signals into parallel low-speed sub-data stream, modulated onto each sub-channel for transmission. OFDM has a strong ability to resist inter-wave interference and inter-symbol interference. But also susceptible to carrier frequency offset, the average peak power ratio is too large, the bandwidth utilization is not high shortcomings. OFDM technology uses a force fit Shenzhen micro electronic LME2980 chip. LME2980 instantaneous rate of up to 36kbps, zero-crossing the average speed over 10kbps.

4) Multi-carrier code division multiplexing technology MC-CDMA. MC-CDMA is a combination of OFDM and CDMA technology. The information is first spread by a spreading code, and then the spread data is separately modulated onto the subcarriers for transmission. Finally, the receiver demodulates and despreads the data and restores original signal. MC-CDMA has the characteristics of the two, can effectively avoid the impact of delay spread, with anti-multipath, intersymbol and inter-wave interference ability, large capacity, effectively overcome the sub-carrier affected by the deep fading and Very high bandwidth utilization, very suitable for high-speed PLC data transmission.

2.3 power line carrier communication chip and module development

At present, chips that can be used domestically are general-purpose power carrier chips imported from abroad such as PL3170 series chips of Echelon echelon Corporation of the United States and power carrier chips independently developed in China such as XZ386 chip of Changsha Hsinchu Co., Ltd., Electronics company's LME2980 chip, etc.). The following table for the domestic market, a variety of chip modules introduced.

Table 1 on the domestic market power carrier chip and module introduction

Chip Features Applications represent the chip model or module

BFSK technology is used late in our country, and the application effect is good. RISE3301, PL3170, PL350, PL3120, ST7538, Mi200E, PLCi36G-III-

CDMA technology used in our country later, the effect is good PL2101;

OFDM technology in recent years began to apply and respond well MAX2992, MX2991, INT5500;

MC-CDMA technology emerged in the past two years, the application less LME2980;

3 low-voltage power line carrier technology

Low-voltage power line carrier communications without re-wiring, do not take up radio channel resources, low cost, easy maintenance, etc., in our application is also more and more widely. At present, typical applications include the following three aspects.

3.1 smart home

People-oriented science and technology, with the development of science and technology, people

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