An overview of discrete multitone modulation/demodulation systems in xDSL applications

This paper presents an overview of discrete multitone (DMT) modulation/demodulation systems with particular emphasis on channel equalization techniques. Three popular time-domain equalization techniques are discussed, including the minimum mean-squared error, the shortening signal-to-noise ratio (SNR) and the geometric SNR method. As an example of the frequency-domain equalization technique, the per tone equalization technique, commonly used in the conventional DMT systems, is discussed. This technique equalizes each tone separately such that a higher channel capacity is reached. These equalization techniques are subsequently compared in terms of their computational complexity and capability for bit-rate maximization through the channel. This is followed by a discussion of other multitone modulation/demodulation systems, such as discrete wavelet multitone and filtered multitone. The latter systems may be designed to give rise to better subchannel isolation and robustness in noisy environments.