December 14, 2011 – As cable industry strategists discuss the pros and cons of moving modulation and other functionalities now resident in hubs and headends into HFC nodes one company has voiced its intentions to deliver on the concept with the promise of radically reducing cable’s costs of operating over fiber.
Aurora Networks is developing what it calls a universal services “Remote QAM” for deployment in trials in the first quarter and commercial availability by the end of Q2. As described by John Dahlquist, vice president of marketing at Aurora, the “industry-first solution” addresses both the capital and operational challenges cable operators face as they continue to increase narrowcast traffic to support the growing demand for more sophisticated video and data services.
“We believe that positioning QAMs in the node will address a lot of issues that are complicating the migration to more narrowcast services and an all-IP infrastructure,” Dahlquist says. “Some people say they don’t know if they want to go that way. Others say it’s a natural evolution. We want to lead in this.”
One of the great benefits of moving QAMs to nodes in cable architecture would be the elimination of amplitude modulated (AM) or analog transmitters, the development of which made it possible for cable companies to use fiber to deliver their TV signals to remote nodes for conversion to RF over coax. Ever since the late ‘80s, vendors have been competing for the industry’s optical transport business by trying to outdo each other with technological innovations in AM optics.
But while Aurora’s technological skills in analog transmission have been fundamental to its success, it doesn’t want to be relying on those skills if the industry goes to a new mode of optical operations, Dahlquist says. “Analog transmitters are an important part of our business,” he notes. “We want to be in the lead if the analog transmitter is going away.”
Use of small form-factor pluggable (SFP) lasers to deliver digital signals without requiring modulation onto different carrier frequencies allows new QAM channels to be added without having to adjust the headend RF combining network or re-balance the HFC plant, Dahlquist says. And it cuts rack space consumed by ever more edge QAMs, relying instead on the Remote QAM’s ability to dynamically support the addition of more QAM channels with any mix of digital services within each QAM channel.
“This new approach eliminates the rats’ nest that comes with operating edge QAMs where you’re splitting signals into service groups from the digital input and then recombining them for modulation onto the fiber,” he says. “You can have legacy and digital services supported at the node QAM, with the dynamic capability of migrating to more IP digital video at whatever pace you want.”
Use of SFPs with the elimination of edge QAMs will also radically cut power consumption in the headend or hubs, he adds. “Plus you get improved signal quality, because you’re using SFPs and bypassing the signal loss and noise from the headend RF combining network and HFC-related conversion and amplification,” he says.
That a leader in the AM optics space rather than a QAM vendor not relying on that business would be introducing the first node QAM attests to the momentum building behind this idea. For example, in an E-PON over cable (EPoC) architecture as described on p. 8, an all-Ethernet transmission path from headend to node would not require amplitude modulation until the signal was translated to RF for transmission over coax links from the node.
In a paper discussing next-gen architectures for cable, Jeff Finkelstein, senior director of network architecture at Cox Communications, and Boris Brun, senior manager of technologies at Harmonic, Inc., suggest it’s time for operators to consider a remote-QAM component for the emerging solution for streamlining the transition to IP services at the headend known as Converged Cable Access Platform (CCAP).
In Brun’s and Finkelstein’s parlance, the new approach splits the MAC (media access control) mechanisms from the PHY (physical layer) in a departure from how things have always been done with cable’s DOCSIS broadband technology. “By removing analog elements from optical access, we believe there is the potential to run with higher order modulations than previously thought possible, given current HFC plant constraints,” the authors say.
They don’t speculate on the potential bandwidth gains resulting from using higher modulation rates on the coax, but the value of the solution as a way to overcome bandwidth challenges in the years ahead was the main point of the paper, which was presented at the SCTE Expo conference in Atlanta last month. As with the Aurora approach, Brun’s and Finkelstein’s proposal calls for co-existence of the new remote PHY modulation system with the current QAM infrastructure but with the understanding that as ever more content moves to IP, the legacy infrastructure would fade away.
Dahlquist, too, doesn’t speculate on potential bandwidth savings that might result from use of Aurora’s Remote QAM. In early deployments with existing MPEG-2 TV services delivered through the Remote QAM to set-top boxes locked on the traditional spectrum bands up to 750 or 860 MHz, there would be no bandwidth impact in those frequencies, but for TV services delivered in IP mode the spectrum on the coax above 860 MHz would be available with upgrades in elements on the coax, resulting in more bandwidth for narrowcast signals.
The initial Remote QAM product release will support 64 6 MHz channels delivered at 256 QAM over existing coax plant without requiring deeper fiber penetration. That equates to about 2.4 gigabits of throughput on an all-digital service feed. By 2013 the company hopes to increase the QAM channel count to 160, which would be sufficient to cover the full RF downstream spectrum up to 1 GHz.