Terabit DSL Copper Line Broadband Tech Begins Lab Test

Before it was only a mathematical model (here) but now, after three years, the idea of pushing broadband ISP speeds of up to 1 Terabit per second (1000000Mbps) along a traditional copper line by using previously unexploited “waveguide modes” is finally being turned into a practical lab test at Brown University (USA).

At present a lot of consumers in the UK still get their broadband using Digital Subscriber Line technologies like ADSL2+ and VDSL2 (FTTC), which send electrical signals down a tiny bit of twisted pair copper wire in order to deliver an internet connection into the home.

Stanford Professor and CEO of ASSIA, Dr John Cioffi, is one of those who helped to develop DSL and in 2017 he also proposed a new technology called Terabit DSL. However, unlike a normal DSL line, the TDSL solution adopts the radically different approach of using an existing copper wire as a mere “guide” (waveguide) to help direct a wireless broadband signal in the 100GHz+ millimeter Wave (mmW) band.

The original model predicted that this method could potentially deliver speeds of 1000Gbps (Gigabits per second) at distances of 100 metres, 100Gbps at 300 metres, 10Gbps at over 500 metres and possibly 1Gbps at 640-700 metres. Just for comparison, the best you could probably expect on an optimal hybrid fibre G.fast line at 300 metres, with the latest kit and amendments, is probably 500Mbps (or c.200-300Mbps on Openreach’s current setup).

The extra speed comes from the fact that above 100GHz you have a lot more spectrum frequency to play with (able to carry lots of data) and these signals can essentially “fit” between the copper wires. After that it would be possible to harness multiple-antenna style (MIMO) processing to transmit and receive the signals (modern WiFi and 5G networks also make use of MIMO).

Until now TDSL has only existed as an interesting mathematical model of what might be possible, but after a lot of work the idea is now being tested in a new lab at Brown University. “So far, the research results indicate successful transmission modes, even around bending pairs of wireless in the 200GHz range,” said a brief project update from ASSIA.

The fact that such speeds could be achieved, without needing to replace existing copper cables with expensive “full fibre” infrastructure, is a possible incentive for operators to explore the approach. “For example, upgrading each home with fibre to the home can cost $3000 to $4000 per home … [but TDSL] could reduce costs of building the high-speed access networks of the future by a factor of five to ten,” claimed ASSIA.

However there remains a big question mark over the real-world viability of using mmW spectrum in such a way, which is a band that can be easily disrupted (such signals usually don’t travel very far without a dense or powerful network to keep them stable). At the same time it could take years to turn TDSL into a viable commercial product and by then most of the UK will have hopefully already been upgraded to gigabit-capable FTTP.

The very fact that many countries, including the UK, are already planning to switch-off and remove their old copper networks means that TDSL may well arrive long after the main party has finished (it makes little economic sense to maintain FTTP and copper side-by-side). Nevertheless the work itself is fascinating and we’re curious to see how it develops. The following video from 2018 gives a good description of the new tech.