Miguel Peeters

Synchronization with DMT modulation

In a digital transmission system, synchronization is an essential receiver function. Accurate timing information must be known to the demodulator in order to produce reliable estimates of the transmitted data sequence. In this article, synchronization for discrete multitone transmission (DMT) is examined. The effect of imperfect timing on the receiver performance is investigated. An overview of timing estimation and correction circuits based on data-aided and non-data-aided algorithms derived from maximum-likelihood estimation theory is given.

The ITU-T's new g.vector standard proliferates 100 mb/s dsl

This article explores the recently issued ITUT G.vector (G.993.5) that allows expanded use of 100 Mb/s DSL. A tutorial description on G.vectors crosstalk noise reduction methods leads to specific projections and measurements of expanded DSL 100 Mb/s reach. A discussion on dynamic maintenance to enhance G.vectors practical application then concludes this article.

A new digital timing correction scheme for DMT systems combining temporal and frequential signal properties

In discrete multi-tone (DMT) systems, demodulation of the QAM modulated sinusoids is achieved by a fast Fourier transform (FFT) on blocks of samples generated from the received continuous-time signal. A clock difference between transmitter and receiver, annihilates the orthogonality of the carriers. Therefore, a receiver using asynchronous sampling must perform timing correction in the discrete-time domain. A new digital timing synchronization method is presented which is based on temporal and frequency domain digital signal processing. Correction of the sample clock offset is done in the time domain whereas DMT symbol timing alignment is done in the frequency domain. The method alleviates the need for accurate free running Xtals generating the sample clocks and can be used for high rate DMT systems like for instance the emerging very high rate digital subscriber loop (VDSL) transceivers.