ADSL transcievers applying DSM and their non-atationary noise robustness

Dynamic spectrum management (DSM) comprises a new set of techniques for multi-user power allocation and/or detection in digital subscriber line (DSL) networks. At the Alcatel Research and Innovation Labs we have recently developed a DSM test bed, which allows the performance of DSM algorithms to be evaluated in practice. With this test bed we have evaluated the performance of a DSM level 1 algorithm known as iterative water-filling in an ADSL scenario. This paper describes the results of, on the one hand, the performance gains achieved with iterative water-filling, and, on the other hand, the non-stationary noise robustness of DSM-enabled ADSL modems. It will be shown that DSM trades off non-stationary noise robustness for performance improvements. A new bit swap procedure is then introduced to increase the noise robustness when applying DSM

Near-Capacity Coding for Discrete Multitone Systems with Impulse Noise

<p/> <p>We consider the design of near-capacity-achieving error-correcting codes for a discrete multitone (DMT) system in the presence of both additive white Gaussian noise and impulse noise. Impulse noise is one of the main channel impairments for digital subscriber lines (DSL). One way to combat impulse noise is to detect the presence of the impulses and to declare an erasure when an impulse occurs. In this paper, we propose a coding system based on low-density parity-check (LDPC) codes and bit-interleaved coded modulation that is capable of taking advantage of the knowledge of erasures. We show that by carefully choosing the degree distribution of an irregular LDPC code, both the additive noise and the erasures can be handled by a single code, thus eliminating the need for an outer code. Such a system can perform close to the capacity of the channel and for the same redundancy is significantly more immune to the impulse noise than existing methods based on an outer Reed-Solomon (RS) code. The proposed method has a lower implementation complexity than the concatenated coding approach.</p