Amplifiers or SuperVector Could Boost UK FTTC Broadband Speeds and Reach

All the recent talk of BT’s plan to roll-out ultrafast G.fast broadband technology from 2016/17 (here and here), which could deliver speeds of up to 500Mbps to “most homes“, might be overlooking the fact that there’s still room to improve the existing ‘up to’ 80Mbps capable Fibre-to-the-Cabinet (FTTC / VDSL2) service via special amplifiers and other methods.

Most of our regular readers will probably already known about one of the incoming methods to help improve, or fix (depending upon your perspective), current FTTC performance – Vectoring – and that is already being trialled in a large number of UK areas (here). But there are others that are being considered and some could soon be set for trials of their own.

One of the better known options would be to increase the radio spectrum allocated on VDSL lines from 17MHz (Profile 17a) to 30MHz (Profile 30a), which would allow some lines to attain faster speeds. But this approach raises a lot of compatibility issues and so far BTOpenreach has shown little indication that they intend to pursue it.

Another potential direction might involve the adoption of so-called SuperVector technology, such as the one touted by Huawei (here) and a couple of other telecoms suppliers (e.g. Alcatel-Lucent’s VPlus). The SuperVector approach also works to cancel out crosstalk interference, but on top of that it would extend the spectrum from 17MHz to 35MHz, change the tone spacing to make it compatible with vectored 17MHz and use a new coding scheme called LDPC.

According to Huawei, trials have shown that their SuperVector prototype could achieve 400Mbps over 300 metres of copper (roughly two to three times better than normal VDSL2 Vectoring) and 100Mbps over 800 metres.

On the surface this sounds like a no brainer, except that right now SuperVector and similar approaches are, in the words of an Openreach source, “just a nice idea and some simulations“. Nobody has seen this stuff in the lab yet and the ITU would first need to set a standard. All of that takes time and by then we’ll be focusing on G.fast. In the meantime BTOpenreach would only officially say that their R&D teams are constantly looking at such technologies, but then that’s their job.

The next option, as hinted at by Thinkbroadband today, is to adopt something akin to the Actelis VDSL2 Broadband Amplifier (VBA). As the name suggest these bits of kit would be designed to amplify, alongside Vectoring, the existing VDSL2 signal so that FTTC services could push their performance to even more remote communities, with speeds of 25Mbps being suggested for premises that are as far away as 2.5km from their local street cabinet.

The VBA approach benefits from being highly backwards compatible with existing infrastructure, plus it could effectively plug many of the current rural broadband gaps (assuming the government’s Broadband Delivery UK scheme with BT completes its current FTTC deployment as required).

VBA Description

An automated, plug ‘n play device, the VBA is line powered from POTS current from the CO, features a low power draw, and can be flexibly placed at any convenient splice or termination point between the DSLAM and DSL modem.

The VBA is fully compatible with vectoring and additive to its performance gains, or can be used on a standalone basis to provide a significant boost to VDSL2 distance and bandwidth. Compatible with any vendor’s DSLAM or DSL modem equipment in the installed base, the VBA is also compatible for use on the same pair with POTS and ISDN services. Featuring a robust and reliable hardened design, should a VBA nonetheless fail for any reason, it simply removes itself from the loop and allows POTS, ISDN, and VDSL2 services (without the VBA’s added performance benefits) to continue to operate.

By increasing the speed and distance of VDSL2 services, the VBA effectively increases the size of a DSLAM’s customer serving area. Doing so without requiring a major CapEx investment changes the game for cost efficient broadband builds and rapid time to market

Interestingly TB’s article suggests that VBAs may be “considered” for trials in Q3 2015/2016, although it’s unclear whether this information has been extracted from either a prediction by Actelis or Openreach itself. Never the less such a solution does look promising and we’ve seen similar approaches taken in some areas with older ADSL2+ lines, so a precedent of sorts does exist.

At present though these are all just promising ideas and in the meantime Openreach will continue to focus on deploying vanilla FTTC and preparing Vectoring for areas that need it. Lest we not forget that the VDSL2 technology in FTTC is also being used via other deployment methods, such as a new form of Fibre-to-the-Basement (FTTB), Fibre-to-the-Remote-Node (FTTrN) and Wireless-to-the-Cabinet (WTTC); here are a few more details on those.

Suffice to say that hybrid fibre broadband isn’t going anywhere for a while and the technology has room to evolve in order to combat medium-term needs. But as always these things cost money and require trials before a direction can be defined. So until we see a firm plan then it’s all just interesting speculation.