Washington – CableLabs demonstrated downstream speeds of 6 Gigabits per second here using pre-production hardware from Broadcom that uses a new, more efficient channelization scheme that’s being baked into emerging DOCSIS 3.1 specifications.
The demo, conducted at the CableNet exhibit, relied on a prototype device from Broadcom that uses orthogonal frequency-division multiplexing (OFDM), an approach tagged for DOCSIS 3.1 that will enable cable to use existing spectrum more efficiently by packing tiny subcarriers into wide blocks of bandwidth and use higher levels of modulation.
The 3.1-pointing use of OFDM for the purpose of the demo this week pumped out 6 Gbps using 750MHz of bandwidth (six 250MHz-wide spectrum channels), according to Dan Rice, the senior vice president of access network technologies at CableLabs. Today, DOCSIS 3.0 networks use more limited, fixed channel spacing of 6MHz for North American DOCSIS networks and 8MHz in EuroDOCSIS environments.
From a bits per hertz perspective, the early generation hardware used for the demo produced about a 20% efficiency gain over DOCSIS 3.0 spectrum. Rice expects future, updated OFDM hardware to generate an additional 20% efficiency boost, which would produce about 7.2 Gbps.
To demonstrate comparable efficiencies, CableLabs also conducted a DOCSIS 3.0 that logically bolted together four new Broadcom modems that can each bond 32 6MHz-wide downstream channels over 768MHz of bandwidth. That experiment delivered almost 5 Gbps of downstream capacity.
DOCSIS 3.1 fits into a possible all-IP transition and delay the need for cable operators to pull fiber all the way to the home. Rice said the demo also showed that there’s still plenty of life left in DOCSIS 3.0.
But DOCSIS 3.1 development remains on a relatively fast pace, in large part because consensus has already been reached on which new technologies, such as OFDM, are going into the new specs. That means chipmakers can get to work before the specs are complete, and shorten the time it takes for them to spin final silicon.
Rice said drafts of the specs will be sent to vendors that have signed non-disclosure agreements within the next two months, with the final specs on track to be complete by the end of the year. MSOs are expected to start DOCSIS 3.1 trials next year, with commercially-ready D3.1 products coming online by by late 2014 or early 2015.
The initial wave of DOCSIS 3.1 modems are expected to be hybrids that also support DOCSIS 3.0 spectrum.
OFDM will allow operators to use spectrum in noisy, lower portions of the spectrum, where the upstream resides, or up above 1GHz, where downstream spectrum might face attenuation issues.
With OFDM, cable could use spectrum up to 1.2 GHz for DOCSIS 3.1, and yield another 200MHz of fresh capacity to eventually pursue downstream speeds of 10 Gbps.
Gains on the lower end of the spectrum, meanwhile, would push cable’s potential upstream capacity target to 2 Gbps. That upstream potential could only be reached if a U.S. operator executed a “high-split” and raised the current upstream bandwidth (5Mhz to 42 MHz) to 200MHz. A 1 Gig upstream path would require about 125 MHz of spectrum, Rice said.
But that’s a long term view. Top engineering and technology execs at Comcast, Time Warner Cable, Cablevision Systems and Cox Communications said the efficiency provided by OFDM and DOCSIS 3.1 could prolong the need to widen the current upstream bandwidth range for U.S. MSOs (5MHz to 42MHz) and avoid a “mid-split” that would raise the upstream to 85MHz or a “high-split” that would push the upstream up to 200MHz.
