Equalization and echo cancellation for DMT-based DSL modems

Broadband communications over the local telephone loop has become feasible nowadays by means of Digital Subscriber Line (DSL) technologies. Asymmetric DSL and one proposal for Very high bit rate DSL adopt Discrete Multitone (DMT) as modulation scheme. In this thesis we develop new equalization and echo cancellation structures for DMT-based receivers. Our main motivation is the application to DMT-based DSL-modems. In literature, a DMT-based receiver containing a multitap time domain equalizer (TEQ) and a 1-taps frequency domain equalizer per tone, has been presented. The TEQ is usually initialized by means of the so-called channel shortening algorithm. This does however not correspond to bit rate optimization, which is a major disadvantage. In part I, we aim at improving upon the channel shortening algorithm. In a first attempt, we maintain the receiver structure and only change the TEQ-initialization algorithm. In a second attempt, we change the receiver structure such that each tone has its own multitap equalizer (per tone equalization). The latter structure is shown to enable bit rate optimization. In part II, we study echo cancellation. With (partly) overlapping up and downstream bands, echo cancellation may allow to achieve a higher overall bit rate. Echo cancellation may also be employed in a frequency division duplexing set-up as an alternative to highly selective filters. We investigate the combination of an echo canceller presented in literature, with TEQ and per tone equalization. We further propose a new echo cancellation structure based on an echo filter for each tone separately (per tone echo cancellation).