ADTRAN and Deutsche Telekom Test cDTA Upgrade for G.fast Broadband

German telecoms giant Deutsche Telekom and ADTRAN, which supplies the kit being used in various broadband roll-outs around the world, have conducted lab trials of the new hybrid-fibre G.fast technology using the 212MHz and coordinated Dynamic Time Allocation (cDTA) upgrades.

At present most of the early G.fast deployments are only using up to 106MHz of spectrum, although the standard has long supported about double that and we’ve already seen several operators playing around with it. For example, Openreach’s (BT) recent Fibre-to-the-distribution-point (FTTdp) based test of pole mounted G.fast distribution points from NetComm Wireless made use of 212MHz to achieve Gigabit class speeds (here).

The downside of 212MHz is that in order to fully benefit you need to use a much shorter run of copper cable (i.e. the signal degrades faster over distance), hence why it works best with FTTdp rather than Openreach’s favoured deployment via extension pods on the side of existing PCP street cabinets. In short, 212MHz isn’t all that new.

The more interesting development here is that of coordinated Dynamic Time Allocation (cDTA). At present G.fast uses a form of half / full duplexing (i.e. the transmission of data in two directions, either asymmetrically or symmetrically) called Time Division Duplex (TDD).

cDTA is an enhancement to TDD that can allegedly improve the upstream performance of G.fast by up to “four to five times by dynamically balancing upstream and downstream capacity to match residential traffic patterns in real-time” (i.e. squeezing a bit more capacity out of the copper line for faster speeds). This sounds similar to the independent DTA (iDTA) method that already exists in the G.fast standard.

Jay Wilson, ADTRAN’s Senior VP, said:

“Operators in highly competitive, dense urban or urban environments are challenged to extend gigabit services due to the time and cost that can be associated with pure play FTTH techniques. With G.fast innovation, operators, such as DT, can significantly accelerate Gigabit Society goals by launching gigabit services over their existing infrastructure dramatically reducing subscriber disruption.”

Wilson believes that the advent of 212MHz and cDTA will “extract even greater overall performance from an operator’s existing assets” and he claims that in many scenarios it may also “eliminate the need for full FTTH for years.” At present Openreach aims to roll-out G.fast to 10 million UK premises by 2020 and the first non-pilot commercial deployments should begin before the end of this year.

However most or all of this initial roll-out is likely to use the street cabinet based approach and as such Openreach has had to cap the top download speed of their G.fast service to 330Mbps (50Mbps upload), although they have previously talked about pushing the top speed to 500Mbps by 2025 (we don’t yet know how much faster uploads could get but cDTA would certainly help).

Meanwhile the Government has been pushing for a lot more 1000Mbps+ FTTP/H and even Openreach are now consulting on a plan that could match the scale of G.fast’s proposed deployment (here), albeit at significantly greater cost and over a much longer period of deployment. Suffice to say that the balance of G.fast and FTTP/H plans in the UK are currently in some flux.