Wonjong Rhee

Distributed Crosstalk Management for Upstream VDSL Using Dynamic Power Control

The severe interference from neighbor copper lines, commonly known as crosstalk, is a well-known limitation that can reduce the upstream rate of a victim user by 50% or more in dense VDSL (Very high bit-rate Digital Subscriber Lines) deployment. This problem has been partially addressed by the use of UPBO (Upstream Power BackOff). UPBO blindly controls transmit PSD (Power Spectral Densities) based on the pre-defined parameters and channel measurements without considering each users target data rate. Although UPBO can provide fair protection against crosstalk, it still leaves room for practical improvement. This paper proposes a distributed algorithm that dynamically controls transmit power according to each lines need and capacity. The algorithm effectively improves data rates and line reaches in real VDSL deployment.

On the Ergodic Capacity-Achieving Covariance Matrix of Certain Classes of MIMO Channels

Multiple-input multiple-output (MIMO) flat fading channels with channel state information available at the receiver and channel state distribution available at the transmitter are considered. The ergodic capacity-achieving covariance matrix (ECACM) under an average input power constraint is shown to be not unique in general, and three sufficient conditions for the uniqueness are derived. Then, the ECACM structure is characterized for certain classes of MIMO channels including the following classes of MIMO channels: i) right-permutationally-invariant channels including i.i.d. channels; ii) right-symmetrically-distributed channels; and iii) right-permutationally-invariant and right-symmetrically-distributed channels

Greener Copper with Dynamic Spectrum Management

Power-saving benefits of Dynamic Spectrum Management (DSM) result from its increased robustness to channel and noise changes, as in this paper. A proposed intermittent noise model enables evaluation of the performance of DSM algorithms. Polite Level-1 DSM algorithm consumes much less power than non-polite DSL management algorithms in the presence of intermittent noise. Secondly, a proposed robust level- 2 DSM algorithm compares favorably with methods that change the PSDMASK only upon modem initialization or retraining. The proposed robust level-2 DSM algorithm significantly reduces power consumption. This DSM reduction of DSL transmit power can be even more significant when considering the additional loss of robustness and stability of non-DSM methods.

Practical Crosstalk Management for Upstream VDSL Using Dynamic Power Control

The severe interference from neighbor copper lines, commonly known as crosstalk, is a well-known limitation that can cause 50% or larger reduction in the upstream rates of dense VDSL (Very high bit-rate Digital Subscriber Lines) deployments. To handle this problem, UPBO (Upstream Power BackOff) has been studied in literature, and subsequently standardized. UPBO blindly selects transmit PSD (Power Spectral Densities) based on the pre-defined parameters and channel measurement without considering each lines target data rate. Although UPBO can provide significant protection against crosstalk, it still leaves room for practical improvement. This paper proposes a distributed algorithm that dynamically controls transmit power based on each lines need and capability. The algorithm can achieve significant rate and reach gains in real VDSL deployments.