The Normalized-Rate Iterative Algorithm: A Practical Dynamic Spectrum Management Method for DSL
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The Normalized-Rate Iterative Algorithm: A Practical Dynamic Spectrum Management Method for DSL ¨ and Rickard Nilsson Driton Statovci, Tomas Nordstrom, Telecommunications Research Center Vienna (ftw.), Donau-City-Straße 1, A-1220 Vienna, Austria Received 17 December 2004; Revised 1 June 2005; Accepted 2 June 2005 We present a practical solution for dynamic spectrum management (DSM) in digital subscriber line systems: the normalized-rate iterative algorithm (NRIA). Supported by a novel optimization problem formulation, the NRIA is the only DSM algorithm that jointly addresses spectrum balancing for frequency division duplexing systems and power allocation for the users sharing a common cable bundle. With a focus on being implementable rather than obtaining the highest possible theoretical performance, the NRIA is designed to efficiently solve the DSM optimization problem with the operators’ business models in mind. This is achieved with the help of two types of parameters: the desired network asymmetry and the desired user priorities. The NRIA is a centralized DSM algorithm based on the iterative water-filling algorithm (IWFA) for finding efficient power allocations, but extends the IWFA by finding the achievable bitrates and by optimizing the bandplan. It is compared with three other DSM proposals: the IWFA, the optimal spectrum balancing algorithm (OSBA), and the bidirectional IWFA (bi-IWFA). We show that the NRIA achieves better bitrate performance than the IWFA and the bi-IWFA. It can even achieve performance almost as good as the OSBA, but with dramatically lower requirements on complexity. Additionally, the NRIA can achieve bitrate combinations that cannot be supported by any other DSM algorithm. Copyright © 2006 Driton Statovci 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
In the development of currently deployed digital subscriber line (DSL) systems, a single user scenario was assumed with worst case crosstalk models. This passive strategy was motivated by the goal of maximizing the robustness of DSL systems. In practice, however, it often leads to overly conservative performance figures and sometimes even to failures to deliver a specific DSL service. This is often due to a poorly optimized resource allocation among different loops in a cable bundle, combined with unmotivated high noise margins, which result in too pessimistic bitrates. Furthermore, if the system environment changes in a practical scenario, for example, where unmodelled noise sources appear, the initial robustness of a static deployed DSL system easily breaks down. With an active approach to copper bundle resource management, the cable resources can be more efficiently shared among the users. Combined with more accurate crosstalk figures obtained from accurate online cable measurements, higher and more balanced bitrates can be achieved on most loops. In the
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