Design of a Gigabit DSL modem using super orthogonal complete complementary codes

This paper describes the preliminary design and simulation towards a gigabit digital subscriber line modem that provides multi-user interference-free communication in a far-end crosstalk dominated environment by incorporating super orthogonal complete complementary spreading into the existing xDSL modem architecture. This is in contrast to existing vectoring and dynamic spectral management techniques that use joint processing and pre-processing of each user's signal to mitigate far-end crosstalk. A novel code allocation algorithm is introduced to provide all users with equal data rate ratios, even with bad line profiles and high-required data rates. Preliminary simulation results show that 1 Gbps aggregate throughput can be obtained for the system over a single pair of 0.5 mm copper wire over a distance from 180 to 150 m, depending on whether ADSL2+ or VDSL2 Profile 30a service bands are avoided, if present.The National Research Foundation of South Africa (Grant reference TP1207183332), Telkom and Bytes Universal Systems.http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)2161-39152017-11-30Electrical, Electronic and Computer Engineerin

A Near-Optimal Linear Crosstalk Canceler for VDSL

Crosstalk is the major source of performance degradation in VDSL. Several crosstalk cancelers have been proposed to address this. Unfortunately they suffer from error propagation, high complexity and long latency. In this paper we present a simple, linear zero forcing (ZF) crosstalk canceler. This design has a low complexity, no latency and does not suffer from error propagation. Furthermore, due to the well conditioned structure of the VDSL channel matrix, the ZF design causes negligible noise enhancement. A lower bound on the performance of the linear ZF canceler is derived. This allows performance to be predicted without explicit knowledge of the crosstalk channels, which simplies service provisioning considerably. This bound shows that the linear ZF canceler operates close to the single user bound. So the linear ZF canceler is a low complexity, low latency design with predictable, near-optimal performance. The combination of spectral optimization and crosstalk cancellation is also considered. Spectra optimization in a multi-access channel generally involves a highly complex optimization problem. Since the linear ZF canceler decouples transmission on each line, the spectrum on each modem can be optimized independently, leading to a signicant reduction in complexity.