Hernan X. Cordova, Leo Van Biesen, Rob F.M. van den Brink
A SIMPLE POLYNOMIAL METHOD FOR OPTIMIZING UPSTREAM PERFORMANCE IN MULTIUSER VDSL2 LINES
In telecommunications, much efforts are spent nowadays to make ICT more Green. Rising energy costs, an economic slowdown and environmental awareness have introduced serious strategic challenges to enterprises worldwide. There are a variety of new and existing technologies available that aid in green IT, such as more efficient hardware that demand less power. In access networks, often the copper telephony network ensuring POTS is used to offer Digital Subscriber Line services to industry and private customers; e.g. to offer high bandwidth Internet access. The reduction of the electrical power in the modems (both in the Central Office and at the premises of the customers) for the transmission of the digital data is a key issue in making xDSL a more green ICT service. In this paper attention is paid to optimize Power Back off methods in upstream VDSL2. We study the excess of power that is required and the performance degradation that occurs when no power control measures are taken at the upstream of a Very high-speed Digital Subscriber Line (VDSL2). We propose a two-step approach: first, to perform an off-line exhaustive search algorithm that can find the optimal upstream power back-off (UPBO) parameters for almost every constraint within a cable bundle, following the current spectrum management specifications and regulations. As any exhaustive search approach, finding the parameters becomes typically very time-consuming, thus, secondly, we propose a simplified polynomial method based on the initial results such that the time to find the optimal parameters is significantly reduced. The algorithm turns out to be a pragmatic approach for current operators and performs well in practice though it does not exploit dynamic spectrum management (DSM) capabilities (being considered a Level-1 DSM-sort of algorithm) and relies on accurate insertion loss calculations for the different users distributed along the cable. However, in practice, given specific conditions per country, higher levels of DSM coordination might not be feasible; thus the motivation of our proposal. Simulation results show very similar results between these steps but at a reduced complexity for the polynomial approach, making the second method attractive for practical VDSL2 lines. We do not maximize the minimum capacity of the system; as it is common practice for operators to try to maximize the performance up to certain distance, we pursue this approach, instead. Finally, we show how our proposed method could be adopted in a specific region/country via a spectrum management policy such that it can be enforced by the regulatory local entities ensuring that all operators properly follow it. We also demonstrate the severe impact when the policy is not properly applied by all DSL operators.
