The next iteration of DOCSIS, version 3.1, is going to incorporate a new modulation scheme, along with more sophisticated forward error correction (FEC). It will support transmission speeds up to 10 Gbps downstream and 1 Gbps upstream, and it assumes operators will reallocate as much as 160 MHz of downstream bandwidth for use on the upstream.
DOCSIS 3.1 will rely on orthogonal frequency division multiplexing (OFDM), used in DSL, LTE, Wi-Fi and MoCA, among other technologies. It will also replace the commonly used Reed-Solomon FEC with far more efficient low-density parity check (LDPC) codes.
The plan is to complete the specification in 2013, so that equipment (most likely cable modems at first) will begin to be sold in 2014.
With the inclusion of two key technologies that are well-established but completely foreign to cable, there’s a good argument that the next version of DOCSIS ought to be designated 4.0. Perhaps calling it 3.1 is less threatening, however, and to be fair, the MSOs are insisting that 3.1 must be fully backward-compatible so that rollouts can be performed gradually and in steps.
DOCSIS 3.1 was introduced by Jeff Finkelstein, senior director of network architecture for Cox; Howard Pfeffer, senior vice president of broadband engineering and technology for Time Warner Cable; Jorge Salinger, vice president of access architecture for Comcast; and Matt Schmitt, director of DOCSIS specifications for CableLabs, each of whom has participated in every iteration of DOCSIS thus far.
Salinger, referring to his fellow panelists from the “DOCSIS 3.1 specification and standard development” session, said: “I don’t know that any of us thought we’d be doing it again. It’s exciting.”
The details of DOCSIS 3.1 were heavily telegraphed in a paper called “The mission is possible,” co-written by leading technologists at Arris, Cisco, Intel and Motorola and delivered earlier this year at The Cable Show (a serialized summary is available to Cable-Tec Expo attendees in CED’s Day 1 and Day 2 Show Dailies).
That paper presented almost every option under consideration and said LDPC error correction showed great promise, so use of that in DOCSIS 3.1 could have been expected. It said that continuing to use single carrier modulation was not going to be practical, and though several modulation schemes were considered, the virtues of OFDM in particular were extolled.
The authors of the paper said that denser modulation schemes would be inevitable. Many of their examples were of 1024-QAM, but they suggested that 4096-QAM be studied. The MSO panel at Cable-Tec Expo consistently speculated about going on to 4096-QAM.
As of The Cable Show, various spectrum splits were on the table, expanding the high end of the upstream band from 42 MHz, to as high as even 500 MHz. DOCSIS 3.1 will only go to 200 MHz.
To replace the spectrum lost to the upstream, the options were to expand beyond 1 GHz to as high as 1.7 GHz. DOCSIS 3.1 will top off at 1.1 GHz or 1.2 GHz.
At The Cable Show, the impression given was that downstream data rates of 2 Gbps were likely to be considered, but the MSOs said they want support in the 3.1 spec for up to 10 Gbps downstream and 1 Gbps upstream.
“We’re looking at 8, 10, even 12 bits per hertz,” Finkelstein said. “That’s an astounding number.”
The combination of new technologies is expected to lead not only to extraordinary transmission speeds, but also significantly reduced cost per bit, “otherwise, there’s no reason to do this,” Schmitt said.
That will be due in part because OFDM will enable MSOs to use their spectrum more efficiently. There is also the possibility that cable will be able to leverage economies of scale (as OFDM is widely used elsewhere), as well as leverage the innovation potential inherent in a larger vendor community.
The MSOs were adamant that any transition to 3.1 will be smooth, with backwards-compatibility with previous generations of DOCSIS assured. “This has to start with zero plant investment,” Schmitt noted.
Salinger said he expects that MSOs will install DOCSIS 3.1 CPE first, then implement 3.1 on the downstream, and then finally on the upstream.
The capabilities cable will have when 3.1 is fully deployed will be formidable. John Chapman, CTO of Cisco’s Cable Access Business Unit and a co-author of the paper, told CED he expects 3.1 may end up being the last iteration of DOCSIS.
The SCTE said that while CableLabs is helping to define the 3.1 spec, it is already working in parallel with its sister organization to develop training, certification and other support services. To that end, the SCTE has formed a Special Working Group to develop best practices and requirements to prepare HFC networks for higher-capacity signaling schemes, including DOCSIS 3.1.
Jack Moran, fellow of the technical staff for Motorola Mobility’s Home Business, has been named chair.