Blind Equalization Techniques for xDSL using Channel Coding and Precoding

A new concept for digital communication over severe intersymbol interference producing channels, e.g., high–rate digital transmission over twisted pair lines (xDSL techniques) is proposed including channel coding, precoding, equalization, and synchronization. Channel coding improves data reliability or tolerable signal attenuation, e.g., field length, whereas a nonlinear predistortion method, a modification of the well–known Tomlinson–Harashima precoding (THP) including signal shaping and dynamics limitation at the receiver side, is used in order to cope with intersymbol interference. In contrast to prior approaches, a fixed compromise precoder together with a linear blind adaptive fine tuning equalizer at the receiver side is proposed in order to avoid any retransmission of channel measurement data to the receiver. By this, neither a blocking of bidirectional communication can happen nor sophisticated start–up protocols are necessary. For this purpose new algorithms for blind adaptive equalization are introduced which are able to operate at very low signal–to–noise ratios due to channel coding and for highly correlated data sequences, typically for the application of precoding techniques. Additionally, methods for symbol timing synchronization are proposed.