Near End Crosstalk (NEXT) Canceller and Modulation Clustering for Asymmetric Digital Subscriber Line (ADSL) systems.

Summary The work of this thesis aims at improving the range and throughput offered on the downstream channel of an ADSL transmission. The first part of the thesis details the ADSL transmission chain, its propagation channel and the crosstalk noise. The second part focuses on a solution to reduce the impact of NEXT noise at the subscriber. To this end, a second "noise-only reference" sensor is introduced at the receiver and a subcarrier algorithm maximizes the SNR. A statistical study confirms that this system significantly increases the performance. The third part introduces the "clustering" modulation which allows to improve the performances on long lines whatever the noise environment is. This modulation groups the tones, which do not have a sufficient SNR to accommodate a "minimal" constellation, into "clusters" carrying the same information. By this means, the unused capacity of a DMT symbol is reduced by nearly 75%.