40Gbps mmWave and full dupex DOCSIS take their place in 5G backhaul jigsaw

One of the key 5G challenges will be finding backhaul technologies which can deliver the capacity required by the new multi-gigabit RANs, while reaching far smaller cells in dense areas of the network, and remaining affordable to deploy or lease. Fiber will be ideal for most base stations, and densification is seen as a significant opportunity for cablecos and fiber-to-the-premise deployers to squeeze another revenue stream out fo their wholesale or retail connections. There are some non-fiber technologies, too, which will have a role to reach very small cells or to reduce cost – enhanced copper standards like next generation has been trialled by BT and others, for instance; while high capacity millimeter wave spectrum may give wireless backhaul a bigger role in 5G than it had in 4G.

The last of these options was showcased recently in a live trial conducted by Deutsche Telekom in Athens, Greece, working with Ericsson. The trial achieved data transmission at 40Gbps with latency below 100ms, said the operator, in E band spectrum (70/80 GHz).

The main downside of mmWave spectrum is its short range, under usual power restrictions, but that still makes it a strong contender for some small cells, which do not necessarily require full fiber speeds to every access point. Already, there are some architectures in which a master cell is backhauled by fiber, and other small cells are linked to it via a wireless mesh based on 60 GHz WiGig or a proprietary mmWave prptpcol. A similar approach can be used in virtualized small cell RANs, with radio heads linked to the centralized baseband over wireless.

In fact, DT’s trial system achieved a respectable distance of 1.2 kilometers for its 40Gbps transmission, which is four times the speed of commercially available wireless backhaul solutions, the operator said.

“A high performance transport connection will be key to support high data throughput and enhanced customer experience in next generation networks,” said Alex Choi, DT’s SVP for strategy & technology innovation. “While fiber is an important part of our portfolio, it is not the only option for backhaul. We have demonstrated fiber-like performance is also possible with wireless backhauling/Xhaul solutions.”

On the wireline front, the cable industry used the recent Consumer Electronics Show (CES) in Las Vegas to outline a 10Gbps cable future, with 5G backhaul and fronthaul among the applications in mind to supplement the core broadband use case. In setting out a roadmap, to start in 2020, the three organizations leading the effort – the Internet & Television Association, US R&D outfit CableLabs, and Cable Europe – even adopted a new branding, ‘10G’.

The foundations for 10G networks were mainly laid some time ago and these will not result in a single technology but a network comprising multiple technologies. “It’s the cable broadband technology platform that can handle more data from more devices, 10 times faster than today’s fastest cable broadband networks,” wrote CableLabs’ president and CEO, Phil McKinney.

The full list of these technologies includes:

  • 25G-PON (passive optical network) and 50G-PON
  • FDX (full duplex)
  • point-to-point coherent optics
  • DOCSIS 3.1, the latest release of the cable standard, along with FDX DOCSIS and low latency DOCSIS
  • Micronets
  • Various WiFi technologies, namely WiFi Easy Mesh, Passpoint, Vantage and WiFi PNM (proactive network maintenance)
  • Low latency mobile backhaul.

Full duplex DOCSIS is particularly hot in the cable world. It has a theoretical maximum of 10Gbps up and 10 Gbps down, with CableLabs describing it as “the ultimate technology to support the speed and latency requirements of current and emerging services over HFC networks”. But to achieve the spectral efficiency of almost 100% via full duplex requires a modem or gateway which can use all spectrum on the wire, and it’s unlikely any operator will ship one any time soon.

The project lists quite a line-up of cable darlings, spanning older technologies like the fiber standard 10G-PON, which was first ratified in 2009, progressing to developments in 50G-PON technology, as well as new kids on the block like Easy Mesh, the WiFi Alliance’s multi-access point standard, which launched in the middle of last year, and was developed in partnership with CableLabs.

Intel will play a critical role in FDX DOCSIS deployments, citing Comcast, Cox and Charter as three of its early 10G partners. Arris is also onboard the 10G project, having developed the underlying technologies going back “several years”, according to CEO Bruce McClelland. Its efforts have included spectrum expansion and utilization techniques for FDX DOCSIS and Ultra-High-Split with Extended Spectrum DOCSIS.

The 10G future is currently being built by cable operators in the US who offer broadband services to 85% of US homes – including Comcast, Charter, Cox, Mediacom, Midco and others – plus international operators, including Rogers, Shaw, Vodafone, Taiwan Broadband Communications, Telecom Argentina, Liberty Global and more.