Research And Application Of COFDM Technology In High Voltage Power Line Carrier Communication

Once the high voltage power line carrier (PLC) is the basic power communication network of our country, playing an important role in the power system dispatching and security operation steadily. With the rapid development of power system and the gradual improvement of automatization, it calls for high requirement of the power communication network. In contrast to the new fiber communication, the traditional PLC has some limitations including low transmission speed and poor communication performance and cannot meet the demand of power system communication today.Many manufacturers and R&D institutions have developed the research and application of new technology on high voltage PLC, and produce some advanced Digital PLC machines, which make great progress in the data speed and anti-interference ability. These new type Digital PLC use SSB, QAM or TCM modulation technology and occupy the bandwidth between several kHz to dozens of kHz with the transmission speed less than 100kbps. OFDM modulation technology has got good application in the middle voltage power line and low voltage power line. Compared with them, high voltage power line has some excellences such as slow variety load, simple route and low noise level. So it is possible to introduce the OFDM technology into the high voltage PLC so as to acquire higher transmission speed. Integrated with the effective channel coding scheme the COFDM technology shows many favorable properties such as high spectral efficiency, robustness to channel fading and interference, and capability of handling multipath fading. At the same time, the realization of COFDM communication system is simple because the IDFT/DFT operation can accomplish the modulation and demodulation process. From the info source coding to the frequency conversion, it is finished that every step is the digitization. Therefore the whole system works more stably.This thesis presents the idea of application of COFDM technology on high voltage PLC in order to acquire more than IMbps in transmission speed. Firstly the, thesis introduces the development course of high voltage PLC and the basic theory, and analyses the channel characteristic. Then the principle of OFDM technology is explained and the baseband signal process and the frequency conversion are discussed primarily with some detail problems explained. In the same time it shows the selective channel coding scheme, a kind of concatenated code with digital interleaving, and provides the coding method and realization. The BER performance is discussed in the AWGN channel. Furthermore some solutions to the key problems such as synchronization, PAPR and frequency offset, whichaffect the performance of COFDM communication system badly, are talked about. Finally the paper presents the particular parameters of high voltage COFDM communication system and the realization method.Proved by the theoretic deriving and simulation result, the COFDM modulation technology is well suitable for high voltage PLC with a high transmission speed, low BER and high reliability. The thesis points out a new direction for the development of new-style digital carrier machine.