New HFC Return Path Solution Opens Way to Double Capacity

July 20, 2011 – Aurora Networks, building on the capabilities of its digital optical return technology, has introduced a means by which cable operators can double their upstream capacity by adding the 42-85 MHz portion of the RF spectrum to today’s 5-42 MHz return path.
 
While the current HFC upstream bandwidth allocation has stood the test of time with ever deeper extensions of fiber and node splitting to accommodate increasing levels of upstream traffic, new developments on the horizon point to the need for much greater capacity in the return path. With broadcast stations abandoning use of the 54-88 MHz spectrum for analog TV, the cable industry has begun looking at that segment as a relatively interference-free zone for upstream HFC communications.

Aurora’s move to introducing a means of accommodating this expansion on the optical side comes in response to new demand from international customers, says Aurora vice president of marketing John Dahlquist. “We’ve taken this step in response to immediate needs of our international customers for more upstream bandwidth, but we believe it will eventually be necessary for domestic customers as well,” he says.

Laptops and PCs have been the primary drivers behind higher bandwidth demand so far, with peer-to-peer traffic serving as the dominant factor and the sharing of personal media and use of Web-cams for video communications becoming ever stronger contributors. Industry studies have shown upstream traffic on the Internet is increasing at a rate of 30-50 percent annually worldwide, where data transmission over mobile devices are a growing contributor.

As previously reported (April 2010, p. 8), operators are increasingly concerned about the upstream impact of bringing smartphones and tablets onto the home network. And they also anticipate growing impact on traffic from emerging applications such as cloud computing, business collaboration and telemedicine.

The 85 MHz cutoff point for the new upstream expansion is determined by the need to avoid the possibility that FM radio signals leaking into the coaxial plant could cause clipping on return lasers. The expansion is proportionately less for European and Asian operators, who already use 5-65 MHz as the return path. In all cases where RF amplifiers are involved on the coaxial plant, the move to 5-85 MHz will require either elimination of the amplifiers with deeper fiber penetration or installation of new amps.

The attraction of the Aurora solution lies with the flexibility and cost effectiveness of its long-standing approach to delivering optical signals in the return path from HFC nodes, Dahlquist notes. Rather than modulating the RF amplitude-modulated (analog) signals onto the transmitters, the Aurora platform converts them to digital and multiplexes them together for transmission over a single wavelength.

Digitization avoids the distance sensitivities imposed by analog transmissions, which means the Aurora return solution can accommodate any link budget that can feasibly be used for architecting downstream paths, Dahlquist explains. “The beauty of digital return technology is the independence of RF loads and required laser performance,” he says. “Digital return provides operators with a cost-effective pathway to meet performance requirements that are currently not achieved by today’s upstream analog lasers.”

Operators deploying the Aurora upstream solution for transmission over the traditional 5-42 MHz or 5-65 MHz path will be well positioned for going to 5-85 MHz when Aurora releases the new return module for general availability this fall, he adds. That’s because the firm’s Universal Digital Return module uses a common platform for all band-splits along with a “personalization” module that configures the return to requirements for data transmission speeds, operational modes and other factors. Operators will be able to transition to 5-85 MHz by simply changing out the inexpensive personalization module, he says.

The ability to support a higher return bandwidth with elimination of RF amplifiers becomes another incentive to extending fiber deeper into the distribution network, Dahlquist notes. “We’re seeing our customers talking much more about upgrading with our Fiber Deep solution,” he says. “The ability to expand upstream capacity adds another incentive to the Fiber Deep option.”