The ITU’s Study Group 15 has given first stage approval to a new Gigabit broadband standard called G.fast, which delivers up to 1 Gbps fibre performance over existing copper cables at lower costs by using vectoring technology. G.fast is designed to deliver superfast broadband downloads up to a distance of 250 meters, thereby eliminating the expense of installing fibre between the distribution point and people’s homes. The new G.fast standard is being coordinated with the Broadband Forum’s system architecture project, Fibre to the Distribution Point (FTTdp).
The study group’s decision covered the ITU-T G.9700 recommendation, which specifies methods to minimise the risk of G.fast equipment interfering with FM radio and other broadcast services, paving the way for G.fast to be approved in early 2014. The ITU expects G.fast to be deployed by service providers wanting to provide ‘FttH-like’ services and bandwidth-intensive applications such as streaming Ultra-HDTV movies, communicating via HD video and uploading high-resolution video and photo libraries to cloud-based storage.
High speeds are achieved through a modern encoding and a higher frequency use. VDSL uses frequencies of 17-30MHz, while G.Fast can use 100 MHz or even 200 MHz. Higher frequencies suffer more from attenuation, which limits the length of the cable that can be used. Crosstalk is also an issue, therefore vectoring is applied.
Vectoring is an upgrade to increase the capacity of the copper access network, making higher download speeds over the last mile possible. Connections to multiple homes are increasingly grouped in thicker cables, for example with 24 copper pairs. The cables experience 'crosstalk', as the signals from adjacent cables interfere with each other. This can reduce the effective bandwidth, and the impact increases on longer copper lines, weakening the signal further.
Vectoring is a way to measure, predict and compensate for the cross talk. This requires computing power, which has become increasingly affordable in recent years. Under the right conditions, vectoring can result in a near doubling of the VDSL line's capacity.
