Abstract
Low-power modes (LPM) are a standardized means in asymmetric digital subscriber lines (ADSL) 2 for reducing the power consumption at the central office. However, the activation of LPMs is hampered by the operators’ concern for instability introduced by frequent transmit power changes. The injection of artificial noise (AN) has been proposed as a standard-compliant stabilization technique. We develop an analytical solution for setting the AN power spectrum. Based on this solution we jointly optimize the AN power spectrum and the signal-to-noise ratio (SNR) margin. Simulation results show the performance gain in terms of rate and energy compared to heuristic rules for setting the AN power spectrum. We propose and demonstrate three approaches for evaluating the performance of AN-enabled DSL systems, including (a) joint spectrum balancing, AN, and margin optimization, (b) single-user worst-case-stable optimization, and (c) worst-case-stable optimization based on sequential initialization. Simulation results confirm a strong dependency of the performance under AN on the selected SNR margins, and highlight the total AN power consumption as well as the residual energy savings under low-power modes stabilized by AN.
Highlights
The activation of low-power modes (LPM) [14] in the digital subscriber line (DSL) access network implies frequent transmit power changes, resulting in signal-to-noise ratio (SNR) variations with which current DSL systems can hardly cope [22]
We proposed three deterministic approaches for the performance evaluation in artificial noise (AN) enabled asymmetric digital subscriber line (ADSL) networks
In all three cases the simulation results confirm the gain by performing the standard-compliant joint optimization of the artificial noise” (AN) power spectrum and the SNR margin, e.g., by over 7 % in terms of bit-rate and beyond 32 % in terms of reach up to 1 km looplength
Summary
The activation of low-power modes (LPM) [14] in the digital subscriber line (DSL) access network implies frequent transmit power changes, resulting in signal-to-noise ratio (SNR) variations with which current DSL systems can hardly cope [22]. The only theoretical disadvantage of AN is that it leads to higher transmit power, background noise, and crosstalk noise levels This may reduce the achievable bit-rate and conflict with the initial intention behind the usage of AN: namely to enable LPMs and thereby to reduce the energy consumption in DSL. In order to facilitate a deterministic performance evaluation of AN-enabled networks we study three approaches: (a) the joint optimization of AN with the transmit power spectra, bit-allocations, and SNR margins, (b) the single-user bit-loading problem stabilizing the line for the worst-case crosstalk noise, and (c) the multi-user sequential initialization of the lines assuming the same worst-case noise as in (b) but considering the actual crosstalk noise levels at initialization.
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