ORLANDO -- SCTE Cable-Tec Expo -- The Docsis 3.1 platform will support capacities of at least 10Gbit/s downstream and 1Gbit/s upstream, a move that will certainly prolong the industry's need to deploy fiber all the way to the home.

That was one of the big takeaways here Thursday as engineers with CableLabs and some of the nation's biggest cable operators revealed significant details about Docsis 3.1 for the first time. (See Docsis 3.1 to Be Smarter, Faster & Cheaper and Diving Into Docsis 3.1.)

Docsis 3.1 will try to hit some other broad objectives, including cost reductions on a per-bit basis, the development of an effective migration path to the new platform, and assurance that 3.1 will work on existing hybrid fiber/coax (HFC) plant. Thursday's session didn't outline all the apps and services that might require 3.1, but support for much more IP video is certainly going to be among them.

CableLabs expects to complete the core Docsis 3.1 specifications in 2013 and anticipates seeing initial products as early as 2014, according to Matt Schmitt, director of Docsis specifications at CableLabs.

What's in Docsis 3.1?
To hit its capacity targets, the cable industry wants to increase its spectral efficiency by about 50 percent. As expected, the new specs will do away with 6MHz- and 8MHz-wide channel spacing and instead use smaller (20KHz-to-50KHz-wide) orthogonal frequency division multiplexing (OFDM) subcarriers; these can be bonded inside a block spectrum that could end up being about 200MHz wide. (See Docsis 3.1 Will Change Cable's Data Channels.)

OFDM will be matched up with low density parity-check (LDPC), a Forward Error Correction (FEC) scheme that takes up less bandwidth than the current Reed-Solomon approach. LDPC will let cable pump out more bits per hertz by utilizing higher orders of QAM modulation, including 1024 QAM and 4096 QAM in both the downstream and the upstream, Schmitt said. (256 QAM is typically used in today's cable downstream.)

To point out how much more efficient the new approach will be, Schmitt noted that it would take 780MHz of spectrum to get 5 Gbit/s using Docsis 3.0, but only 500MHz with Docsis 3.1.

The hope is that the move to OFDM will also open up the market to more chipset and system vendors and help to reduce costs. The Docsis 3.0 silicon market, for example, is dominated by Broadcom Corp. and Intel Corp., with STMicroelectronics NV just recently joining the fray. (See STMicro Takes On Broadcom, Intel in Docsis 3.0.)

Migrating to Docsis 3.1
The aim is to make Docsis 3.1 backwards compatible with Docsis 3.0 and 2.0. So, a 3.1 cable modem termination system (CMTS) will be required to support older modems. The first new modems are expected to be 3.1/3.0 hybrids capable of bonding at least 24 downstream channels and eight upstream channels -- essentially what's supported by the Intel Puma6 chip for Docsis 3.0. (See Intel's New Docsis 3.0 Chip Guns for 1-Gig .)

To avoid pricey forklift upgrades, the hope is that the new generation of Converged Cable Access Platform (CCAP) devices will support 3.1 with software upgrades.

Cable has tossed out the idea of doing a "top-split" that would put fresh upstream spectrum above the downstream spectrum, so it will keep things as they are, with the upstream spectrum operating below the upstream. But 3.1 does anticipate a wider upstream (maybe 200MHz or more) that would expand beyond the 5MHz-to-42MHz range used by most U.S. cable systems today.

The specs also consider the notion of expanding the downstream to about 1.2GHz. Most upgraded plant is built out to 750MHz, 860MHz or even 1GHz.

But that's all optional. The key thing is, "you don't have to change your plant to deploy Docsis 3.1," Schmitt said.

The first Docsis 3.1 products to emerge will be CPEs, predicted Jorge Salinger, VP of access architecture at Comcast Corp.. That would seed the market with 3.1 devices before the network is upgraded. Salinger also expects 3.1 downstream to be ready before its upstream counterpart.

He added that Comcast has begun to think about a second phase of its spectrum reclamation plan that would put space aside for 3.1 that could also help out with the operator's transition to IP video.

Light Reading Cable will have more coverage of Docsis 3.1 developments throughout the week.

— Jeff Baumgartner, Site Editor, Light Reading Cable