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Meeting Cable's 10G Challenge Without Lots More Fiber

Alan Breznick
7/22/2019
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If you thought that the new Full Duplex DOCSIS 3.1 spec offered the only way for cable operators to offer symmetrical 10-Gig speeds to subscribers, then think again.

There is another viable option for cablecos that can't or don't want to go through the trouble and expense of installing fiber much deeper in their networks, getting rid of all the amplifiers and adopting the brand-new Full Duplex spec. Instead of taking this expensive, difficult route, cable providers could reach the 10G promised land by employing Ultra Wide Band (UWB) modulation over their existing HFC networks.

Indeed, UWB modulation teamed with time-division multiple access (TDMA) capability shows great promise as an economical way to enhance existing HFC networks that are not well-suited for upgrades to the "Node+0" Fiber Deep architecture that Full Duplex DOCSIS currently requires. By tapping into the currently unused RF spectrum in the cable plant that sits above 1.8GHz, UWB could make 10G a reality without requiring huge fiber rebuilds.

That's because an Ultra Wide Band implementation could make this untapped spectrum viable in "Node + N" designs all the way up to the 3GHz frequency limit, thanks to its superior loss tolerance and modulation error ration (MER) performance. As a result, UWB, with TDMA's help, could provide a credible roadmap for gigabit speeds that exceeds even the FTTH-based PON platforms now available commercially for the residential broadband market.

Rather than go FTTH or even Fiber Deep, cable operators could take advantage of UWB's potential by pursuing a hybrid Distributed Access Architecture (DAA) strategy. In this nuanced DAA approach, the fiber demarcation point is determined by the network's data capacity over coax for each individual network segment. What this means is that the demarcation point may actually be different for each network segment, depending more on the capabilities of the coax link than the capabilities of the fiber link.

How does this proposed approach work? Frequency-differentiated PHY layers are essentially overlaid or inserted based on the most viable frequency for the demarcation point. This allows the HFC network to perform optimally at each segment for maximum results throughout the entire node architecture.

For instance, the lower the frequency goes, the shallower the PHY layer becomes because that layer must perform across a variety of passive and active network components. Higher frequencies are reserved for the more passive segments of the HFC network, where the high frequency signals can be more easily supported.

Antronix's Proposed Hybrid DAA Framework

TDMA technology comes into play here because it provides a great deal of flexibility that fixed upstream frequency plans cannot match.

Silicon support for UWB modulation should not be a major issue. Indeed, there appears to be plenty of runway for an Ultra Wide Band roadmap in future silicon revisions that will be capable of supporting 10 Gbit/s and higher speeds over segments of the coaxial network.

Can the UWB-based strategy keep delivering such top speeds when network traffic becomes congested with widely used, bandwidth-rich applications? Good question. Scalability will certainly be one of the central challenges for cable providers as far more aggregate capacity is required in the coming years, in addition to the faster rates of 10G.

To meet this expected tidal wave of bandwidth demand, high-density optics will have to evolve along with the capacity. Plus, remote modulation devices will need to be more prevalent and numerous than ever before. Think of extending Remote PHY to deeper and deeper points in the network, ultimately all the way to the tap. That day may come sooner than we expect.

Thus, Full Duplex DOCSIS is not necessarily the only answer for cable providers seeking to offer the blazing-fast network of the future. A coherent 10G roadmap should also include an RF modulation and frequency plan that can be proven out beyond 3GHz in a widely deployable hardware design that can be economical over time.

This blog is sponsored by Antronix.

— Alan Breznick, Cable/Video Practice Leader, Light Reading

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