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DOCSIS

Setting the Stage for Docsis 3.1

4:10 PM -- There were any number of things that turned heads at Society of Cable Telecommunications Engineers (SCTE) Cable-Tec Expo last month, but the biggest attention-getter might have been the special session that pulled the covers back on the upcoming Docsis 3.1 spec.

In front of a standing-room only crowd, representatives of CableLabs , major MSOs and SCTE discussed what the new spec would mean for the industry and the steps operators need to take to accelerate deployment. (See Docsis 3.1 Set for a Spring Fling and Docsis 3.1 Targets 10-Gig Downstream.)

Once again, cable engineers are faced with the need to leverage the flexibility and the limits of HFC (hybrid/fiber coax) networks to create higher capacities, faster speeds and -- most important -- more satisfied customers. Docsis 3.1 promises to usher in a whole new era for HFC plant that includes significantly higher performance and greater cost effectiveness.

So what's all the excitement about? There are three key areas in which Docsis 3.1 signaling will be markedly different from its predecessors:

  • Using a higher order of modulation, for greater spectral efficiency, could conceivably add at least 25 percent more capacity and up to 50 percent more over the same HFC network. Note that the proposed DVB-C2 specification in Europe has been tested to support 4096 QAM downstream within existing cable networks.

  • A new modulation format, Orthogonal Frequency-Division Multiplexing (OFDM), that takes efficiency and robustness to new levels. OFDM enables sub-carriers to be squeezed directly against one another, eliminating the need to use valuable RF spectrum as guard bands. At the same time, the longer symbol durations of the sub-carriers make OFDM more capable of dealing with impulse and burst noise than are SC-QAM guard bands.

  • The use of Low Density Parity Check (LDPC) coding to improve noise immunity by several dB over current Reed-Solomon encoding at similar channel efficiency, or to provide greater channel efficiency at the same MER (modulation error ratio).


What does all this mean for cable engineers? Nothing that we haven't proven that we could do in the past. We'll need to tighten our networks further and eliminate ingress and impairments that can impact performance. And to deliver our ultimate objective -- 10Gbit/s downstream by 1Gbit/s upstream -- we'll need greater RF spectrum (1.2GHz to 1.5 GHz downstream, and 200MHz to 400 MHz upstream), but this is far less than would have been required without the other improvements in signaling.

To ensure that engineering teams are aligned with the timing and details of the Docsis 3.1 spec, SCTE has created an HFC Readiness for Higher Order Modulation working group. Under the leadership of Motorola Mobility Technical Fellow Jack Moran, a seasoned Docsis and RF plant engineer, the working group will be creating recommended practices documents that will complement updated SCTE measurement recommended practices and Docsis training. (See SCTE Rallies Around Docsis 3.1.)

Our special session on Docsis 3.1 was a big hit at SCTE Cable-Tec Expo. SCTE and CableLabs are working together to ensure that the real thing lives up to its advance billing.

— Daniel Howard, SVP, Engineering & CTO, Society of Cable Telecommunications Engineers (SCTE)

This is the latest installment of "Technically Speaking with SCTE," a monthly blog of interviews and columns to provide Light Reading Cable readers with timely updates on the SCTE's initiatives and activities.

Duh! 12/5/2012 | 5:17:32 PM
re: Setting the Stage for Docsis 3.1

LDPC = Low Density Parity Check (not Power).  AKA Gallager Codes, after their inventor, Bob Gallager.  That it is now practical to approach the Shannon Limit at these kinds of rates is a testament to Moore's Law.


Jack Moran is a terrific choice for chairman of the HFC Readyness working group.  Jack is an engineer's engineer, with decades of experience driving standards.   I doubt that anybody has more in-depth knowledge of the HFC physical media and transmission impairments.  He's definitely one of the good guys.


 

Jeff Baumgartner 12/5/2012 | 5:17:31 PM
re: Setting the Stage for Docsis 3.1

Yep, "parity," not "power"... thanks, should've caught that typo. JB

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