Review of the main techniques to improve the energy efficiency of broadband copper access networks and their practical performance

Abstract--- We review in this paper the main techniques that can be applied to improve the energy efficiency of broadband copper access networks. Starting from a holistic view of the end-to-end copper access networks, we identify green opportunities in the different building blocks and for different deployment practices. We shift the focus to the access telecommunication equipment and its supporting functions needed to operate the equipment in different environments depending on the access architecture. This system level approach, guided by the power breakdown of the access nodes, reveals that some optimizations can result in significant energy savings as opposed to others. In the second part of this paper we narrow the scope and focus on the realistic energy saving in the telecommunication equipment when optimizing rate-power-stability tradeoffs at the physical layer through spectral optimization. For this purpose we first review the main state of the art DSL spectral optimization techniques. Then we conduct (system level) power measurements of an operator-side DSL line board under various conditions of data rate, power spectral density and stability. The experiments highlight practical opportunities and challenges for optimizing rate-power-stability tradeoffs in broadband copper access systems with comparison to available simulation-based studies focused on energy reduction through spectral optimization. We validate models for line board consumption based on the aggregate transmit power, and study some rate-power-stability tradeoff scenarios obtained through external line management of data rate, Signal-to-Noise-Ratio margin and power spectral density parameters.