Roll-out of Giga-bit Copper: Impact-analysis of deploying G.fast in FTTC Access Networks

G.fast is the latest digital subscriber line (DSL) technology that provides Giga-bit access from the distribution point (DP). Although it promises to satisfy the short and mid-term requirements of internet-based services, providers are not upgrading instantaneously all legacy systems to G.fast. Instead, the consolidation process is progressive and therefore must minimize the impacts on legacy systems such VDSL2, providing seamless migration and friendly coexistence experience. To achieve this goal, service providers are considering to avoid mutual interference using non-overlapping band-plans. This strategy reduces G.fast data rates and coverage, though. A less harmful approach is to allow partial overlapping, but the benefits and spectrum that must be removed to reduce the impact are unknown. In this work, we analyze the performance impact that G.fast roll-out conveys when VDSL2 systems served from a cabinet are gradually upgraded to G.fast deployed at the DP. We carry out a simulation study to evaluate the mutual performance losses when G.fast is first introduced with a low user share in different fiber-to-the-cabinet (FTTC) scenarios. Based on the obtained results, we select representative access network topologies to determine the expected minimum and maximum losses as the user share progressively increases. In order to establish the benefits and drawbacks of implementing G.fast band-plans that partially overlap with VDSL2, we evaluate G.fast and VDSL2 performance when the operative start frequency of G.fast is set along VDSL2 spectrum. We consider in our study both the current version of G.fast and its recently proposed long reach (LR) extension that aims to achieve longer coverage range by enabling larger bit-constellation size (Bmax = 12bits) and higher maximum aggregate transmit power (MAXATP = 8dBm). The obtained numerical results are intended to help service providers estimate the impact of G.fast on existing VDSL2 systems, as well as its under-performance when they jointly operate in different network topologies. So they can evaluate: 1) which FTTC scenarios are eligible for deploying G.fast and how much it impacts non-upgraded users; 2) how much performance degradation to expect during the progressive deployment of G.fast; and 3) the expected data rate loss for G.fast when its spectrum is partially limited, and how much this strategy reduces the impact on VDSL2.