Towards a range-enhanced and spectrum-friendly G.fast

The first standardized version of G.fast has been conceived to provide gigabit internet access from the distribution point (DP). Low transmit levels along its operational frequency range and low maximum aggregate transmit power (MAXATP) have been specified to restrict its electromagnetic emissions and enable the use of power available at customer premises to feed its access systems. Power constraints and a maximum bit-constellation size (Bmax=12 bits) limit its coverage and data rates, which could discourage service providers to deploy G.fast. This work analyzes different strategies that could be potentially pursued to enhance its coverage and improve its spectral compatibility with VDSL2 systems. We carry out an extensive simulation study to evaluate a) capacity boundaries of current G.fast systems; b) benefits of increasing MAXATP, Bmax and power spectrum density (PSD) mask levels; and c) spectral shaping as means to improve G.fast compatibility. Our simulation results show that increasing MAXATP and Bmax boosts data rates and coverage in short loop scenarios, whereas improvements in long loops performance are only determined by MAXATP. Since such modifications generally increase the interference on legacy systems, we propose to perform power back-off (PBO) in order to improve G.fast spectrum-compatibility. As a proof of concept we adopt the PBO from VDSL2 with a fixed parameter set. Although clearly not optimized for the combination of TDD G.fast and FDD legacy systems and despite the simplicity of the adopted approach, our results indicate that spectral shaping can be an effective means to turn G.fast into a more spectrum-friendly system.