3 High-speed subscriber lines according to G.fast standard
3.1 Standard G.fast – basic features

We can found in literature that the standard G.fast is called as the 4th generation xDSL system. The beginnings of the development of this standard are dated back to the beginning of February 2012. The standardization took place in 2014. The objectives of the new standard of xDSL are several:

All the above mentioned objectives are closely related into two key areas. The first area is the question how to increase throughput, the second is an area of increasing reliability. Throughput of connections can be increased in two ways:

Increasing the reliability of the entire system provides by the following two mechanisms:

In contrast to ADSL and VDSL, which use FDD, the connections with the extreme bandwidth uses TDD. This allows for much more efficient and flexible allocation of bandwidth and eliminates the dilemma of allocating bands for each direction of transmission. Time synchronization is not a problem, because they must be dealt already with regard to the modulation VDMT.

Introduction of TDD also provides simple support for saving modes. In the context of TDD duplex mode timing are introduced mandatory divider ratios of 90/10 and 50/50, an optional divider ratios are then from 50/50 to 10/90.

Among the last-mentioned, but key features of a standard G.fast include the implementation of adaptive modulation DMT with required support VDMT.