The linear zero-forcing crosstalk canceler is near-optimal in DSL channels

Abstract

Crosstalk is a serious problem in next-generation DSL systems, such as VDSL. Several non-linear crosstalk cancelers and pre-compensators have been proposed to address this. Unfortunately, they all suffer from high complexity, DFE error propagation and/or require modification of CPE. We propose the use of a simple linear zero-forcing crosstalk canceler in upstream transmission and a simple linear diagonalizing crosstalk precoder in downstream transmission. Certain properties of DSL channels ensure that these simple linear designs lead to near-optimal performance. We formulate a bound on the performance of these schemes and show that in 99% of upstream DSL channels, the linear zero-forcing canceler achieves 97% of the theoretical channel capacity. Similarly, in 99% of downstream DSL channels, the linear diagonalizing precoder achieves 91% of the theoretical channel capacity.