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AlcaLu sends 1.1Gbps over copper cabling
23-07-2013

Vectoring 2.0 uses advanced maths to compensate for high crosstalk


Telcos still use tons of copper cabling in their local plant, which offer a big cost advantage over new optical fiber. Some 2/3rd of the world's broadband subscribers are connected through DSL. So telcos were all agog when Alcatel Lucent recently demoed a technology called G.fast, transmitting 1.1 Gbps over 70 m of outside plant copper cabling, and upto 800Mbps over 100 meters. The variant of G.fast used was developed in its Alcalu's Bell Labs.

G.fast is an ITU standardization initiative, seen as a natural evolution of VDSL2, which is used today for fixed broadband. Used in conjunction with vectoring VDSL2 reaches speeds of 100 Mbps and beyond.

VDSL2 Vectoring is noise-canceling technology, reducing so-called 'cross-talk' between the copper lines that serve neighboring homes. It works a lot like noise-canceling headphones. It cuts out all of the noise, or interference, among the VDSL2 lines in a bundle. With no interference, every VDSL2 line can operate at peak speeds, as if it were the only line in the bundle.

While G.fast is not yet standardized and won't be commercially available for several years, it is a natural evolution of VDSL2. The emerging G.fast standard holds promise but is even more susceptible to crosstalk than VDSL2.

The very high frequencies that G.fast uses are at the root of the crosstalk challenges. VDSL2 uses up to 17 MHz of spectrum in outside plant applications. The G.fast standard will allow for 106 MHz and 212 MHz profiles, providing a significant increase in bandwidth. "At these frequencies, it is not uncommon to see crosstalk on a G.fast line that is similar in strength to the actual signal. One challenge is to create a compensating signal that eliminates crosstalk without exceeding the Power Spectral Density (PSD) mask. More advanced algorithms are required to compensate for these high crosstalk levels", according to an AlcaLu insider.

Through research at Bell Labs, Alcatel-Lucent identified a number of factors that increase the complexity of vectoring with G.fast. This complexity is driving new innovations that will result in Vectoring 2.0.

Based on Alcatel-Lucent's Techzine


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