LDPC Coding for Non-Uniform Power-Line Channels

Irregular low-density parity-check coding is studied for frequency selective channels and discreet multi-tone (DMT) systems that are used for power-line channels. To let a long block-length code with a practical buffer delay, we protect all the symbols that are transmitted in a DMT symbol with one code. The main challenge, therefore, is the varying signal to noise ratio in different frequency tones, which normally necessitates using different codes for different frequency tones (according to their signal to noise ratios). We show that if this non-uniformity is considered in the code design process, low-density parity-check codes that approach the capacity of such frequency selective channels can he found. Compared to codes that are designed for uniform channels, our codes have a significantly smaller gap from the capacity. As an extreme case, we focus on systems that - for reducing signalling and detection complexity - use only one non-binary modulation in all frequency tones. Therefore, the soft information at the receiver experiences a dramatic non-uniform quality from bit to bit. Surprisingly, even in this case, very close-to-capacity performance can be obtained