High-speed Power Line Communication System based on Wavelet OFDM

Recently, the demand of high-speed network in home is increasing. PLC (Power Line Communication) is expected as one method of realizing it. OFDM is one of the methods, which realizes high-speed PLC. But the minimum stopband attenuation of OFDM modulation is only -13dB. It indicates that OFDM subchannels are not spectrally isolated, therefore OFDM is sensitive to the locations of narrow band interferences. In order to hardly give interference to other systems, OFDM scheme needs skipping many subchannels or using a notch filter in the frequency bands used by the other systems. The former method degrades the efficiency of frequency use and the latter method increases circuit scale. The system we propose is not Fast Fourier Transform (FFT) based OFDM but wavelet based OFDM. Wavelet OFDM (WOFDM) provides subchannel isolation that is superior to FFT based OFDM. In WOFDM, the stopband attenuation and the transition width from stopband to passband can be selected. Thus WOFDM can be designed for a given level of interference rejection by skipping a few subchannels in the frequency bands. And narrowband interference affects only a few subchannels which correspond to these interferences due to a limited spectral overlap between its subchannels. In this paper, we show the WOFDM system suitable for PLC and its Bit Error Rate (BER) characteristic in Additive White Gaussian Noise (AWGN) and its Carrier to Noise Ratio (CNR) property with an imitated transmission channel.