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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 line's 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 line's need and capability. The algorithm can achieve significant rate and reach gains in real VDSL deployments.
Date of Conference: 5-9 Dec. 2011