DOCSIS 3.1: Engineers finding a way to continue using HFC

The cable industry is approaching its next generation DOCSIS 3.1 platform with the tenacity of a group of engineers who have been presented with a problem--ravenous demand for bandwidth--that they must solve using existing tools and infrastructure because it's frankly too expensive to abandon what's there today--hybrid fiber/coax--in favor of a straight fiber to the premises run.

"We know what our plant can do as we migrate it," said Robert Howald, fellow of the technical staff of Motorola Mobility, during a Thursday morning SCTE Cable Tec Expo panel, "Leaving the 'DOC': Where is DOCSIS Bound," adding that this migration might include pushing fiber deeper in the plant.

A variety of engineering trickery can be used to conserve enough bandwidth to reasonably deliver 10 Gbps downstream speeds and 1 Gbps upstream--as required by the DOCSIS 3.1 specification--over most of today's existing cable hybrid fiber/coax (HFC) plant. Among the solutions for service providers is Orthogonal Frequency-Division Multiplexing, which gives operators a "very granular ability to manipulate spectrum" and break the bandwidth-constricted 6 or 8 MHz channelization process, Howald said.

Quadrature Amplitude Modulation can be boosted from today's 256 QAM level to 4096 QAM and "the fact is we're close [to 1024 QAM] without even trying," said Howald.

Low Density Parity Check (LDPC) can be used to monitor the quality of the signals and, in a push or when needed, operators can explore the bandwidth in the fringes above 1 GHz plant limits, although, "when you go above 1 GHz we know very little about that bandwidth," cautioned Howald. "There's a lot we don't know about spectrum."

But, as fellow panelist Niki Pantelias, associate technical director at Broadcom, pointed out, there's a lot they do know about DOCSIS, "and there are more tools available… to make DOCSIS more modern and more efficient."

The final trick to delivering DOCSIS 3.1 is to have a smart gateway at the residence that receives all this newly configured data and transforms it into something that the growing plethora of residential devices can use.

"Any new gateway will be a point of entry [PoE] device," said Howald, calling that a "key assumption" of the new specifications.

That PoE is something that operators both want and need, said panel moderator Charlotte Field, senior vice president of infrastructure and operations for Comcast Nasdaq: CMCSA) Cable Communications.

The interface "probably decreases truck rolls," she said. "This isolates where the problem is."

As long as the problem is in the outside network, the home network, filled with Radio Shack-purchased splitters and 20-year-old coaxial cable and every kind of wireline and wireless connector, isn't covered.

The gateway demarcation point helps, said Pantelias, because it "creates a cleaner home environment," but that home environment is still the domain of WiFi or powerline or MoCa, and "the way MoCa operates is really different than the way DOCSIS operates," she conceded.

And anyway, Howald concluded, there is "a lot of work being done on home networking," so the problems in the home may solved by the time the signal reaches the home.

Related articles:
SCTE creates DOCSIS 3.1 working group
Next up, DOCSIS 3.1
Cable ops reveal game plan for DOCSIS 3.1

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