| As new forms of power distribution like feeder automation and intelligent community are developing rapidly, a great demand for reforming old power distribution networks and construction of modern power communication systems appeared. The PLC (Power Line Communication) technic, which implements communication via the existing electric power supply system, advanced enormously in lower expense cost by the infrastructure and in much convenience of networking.The paper includes several topics about PLC:the composition of a typical PLC system, analyzes on the amplitude-frequency characteristic of the 10kV electric power line, the method of picking an appropriate operating frequency, the solutions of reducing the channel interferences and raising the SNR, analyzes on digital carrier communication implemented with DMT (Discrete Multi-Tone) modulation technic.The DMT technic divides the band of 10kV electric power line (40 kHz-500 kHz) into 106 subcarrier channels, with interval of 4.3125 kHz. Signals in the channel are modulated and demodulated in QAM (Quadrature Amplitude Modulation) and OFDM (Orthogonal Frequency Division Multiplexing). The channels also adapt the emission power for each subcarrier channel due to number of bytes they carry. Against the waveform distortion come from the lines, this paper bring out a method of frequency domain equalization, with which we can revise the waveform received, then the SNR of the signal would meet the demand of demodulation.In order to gain the best transmission quality of the channels, the paper introduced a way of optimizing the transmitting condition of the lines and raising the channel transmission rate by including adaptive filter to raise the SNR. |
