Selective Iterative Waterfilling for Digital Subscriber Lines
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Research Article Selective Iterative Waterfilling for Digital Subscriber Lines Yang Xu, Tho Le-Ngoc, and Saswat Panigrahi Department of Electrical and Computer Engineering, McGill University, 3480 University Street, Montr´eal, Qu´ebec, Canada H3A 2A7 Received 7 August 2006; Revised 15 December 2006; Accepted 5 March 2007 Recommended by H. Vincent Poor This paper presents a high-performance, low-complexity, quasi-distributed dynamic spectrum management (DSM) algorithm suitable for DSL systems. We analytically demonstrate that the rate degradation of the distributed iterative waterfilling (IW) algorithm in near-far scenarios is caused by the insufficient utilization of all available frequency and power resources due to its nature of noncooperative game theoretic formulation. Inspired by this observation, we propose the selective IW (SIW) algorithm that can considerably alleviate the performance degradation of IW by applying IW selectively to different groups of users over different frequency bands so that all the available resources can be fully utilized. For N users, the proposed SIW algorithm needs at most N times the complexity of the IW algorithm, and is much simpler than the centralized optimal spectrum balancing (OSB), while it can offer a rate performance much better than that of the IW and close to the maximum possible rate region computed by the OSB in realistic near-far DSL scenarios. Furthermore, its predominantly distributed structure makes it suitable for DSL implementation. Copyright © 2007 Yang Xu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
Crosstalk is the dominant source of performance degradation in digital subscriber lines (DSLs) systems where multiple users coexist in a binder and cause crosstalk interference into each other due to close physical proximity of twisted pairs within the same binder. Crosstalk is typically 10–20 dB larger than the background noise, and can severely limit system performance if left unmitigated. Crosstalk cancellation can be performed by exploiting the crosstalk structure through signal level coordination [1] and leads to spectacular performance gain. However, crosstalk cancellation techniques generally require tremendous computation complexity, and thus render them unsuitable for deployment in many scenarios. In this case, the effects of crosstalk must be mitigated through spectrum management in interference-limited DSL systems. The detrimental effects of crosstalk can be mitigated through spectrum management in interference-limited DSL systems. Traditional static spectrum management (SSM) techniques employ identical spectral masks based on the worstcase scenarios [2] for all modems. Consequently, these spectral masks are unduly restrictive and lead to conservative performance. Recently, dynamic spectrum management (DSM) [3, 4] is gaining popularity as a new paradigm, which jointly
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