STUDY OF TOMLINSON-HARASHIMA AND TRELLIS PRECODING

Abstract

The transmission of progressively higher rates of digital data over bandwidth limited channels has been the focus of attention of communication techniques over the last few decades. Signal design using partial response system and efficient equalizers are two solutions that efficiently combat the ISI environment in such channels. Higher order spectrally efficient modulation schemes permit higher bit rates. Coding modulation systems offer coding gain allowing operation at lower transmitted powers. Precoding enhances the performance of the system further. Efforts are being made to understand the theoretical basis and practically implement the improved performance precoded modulation systems. ~. This dissertation attempts to present a review of development in precoding techniques. Tomlinson-Harashima (T-H) precoding is explained in detail with examples for uncoded and coded modulation systems. T-H precoding combined with the coded modulation performs better than the uncoded system. Trellis precoding, a generalisation of T-a precoding with coded modulation is discussed and some practical applications like High Speed Digital Subscriber Loop (HDSL), High Definition Television (HDTV) and Telephone Line Modems are explained in detail. Experimental results for some of the applications are reviewed and compared. With trellis precoding channel behaves like an ideal one and the capacity can be approached to a value very close to that of an ideal channel.