Energy Management of DSL Systems: Experimental Findings

A considerable amount of theoretical work has been reported on power optimization in digital subscriber line (DSL) ethnology. It involves in general extensive simulations of optimal and near optimal spectral optimization applied to different topologies. There could be a large gap between theory and practice due to limitations such as the hardware used and the technology itself that does not allow direct application of the theory. In this paper we focus on the realistic energy efficiency of DSL technology that can be achieved when optimizing the power within the technology constraints. More specifically, in lab experiments, we have measured the energy savings of a line card and by extrapolation the DSL access multiplexer by enforcing certain rate/power profiles. In a crosstalk-free environment, experiments revealed that basic power spectral density shapes using breakpoints are sufficient to achieve better power/rate tradeoffs when they can sufficiently enforce the target noise margin per tone. As an example, for a 500m VDSL2 loop, going from 1 Mb/s up to 100 Mb/s data rate, the resulting power increase is less than 9% (through better use of water-filling) in contrast to 24% with the default power spectral density (PSD) template. We also benchmark with the theoretical optimal power profile resulting from water-filling which yields performance very close to the flat PSD template.