Reclaiming Analog Spectrum For The Future

Driven by the needs of today’s high-demand services, some operators face increased pressure to provide subscribers with greater upstream bandwidth capacities. To meet this need, many now are looking to implement a higher split return. While this once was considered to be an arduous process, using Fiber Deep and the recent digital shift, the process has been simplified.

This month is the second anniversary of the analog-to-digital transition, a plan that opened up new spectrum. While a good portion of this freed spectrum was dedicated to public-safety communications and to wireless services, spectrum in the 54 MHz-88 MHz band was left unoccupied. Operators can take advantage of this unmarked territory to increase their upstream capacity from the standard North American split of 5 MHz-42 MHz to 5 MHz-85 MHz through the deployment of digital-return technology and a Fiber Deep architecture.

And because the spectrum in these empty channels essentially is “wiped clean” of traffic, operators will benefit from a much smarter and easier return path process that provides a gain of at least 100 percent in the return path without losing bandwidth in the forward path.

Digital-return technology was developed as a tool for cable operators to counter and overcome the shortcomings and limitations found in analog return-path systems. It is the only practical solution for today’s operators to achieve the high link performance required by a fully loaded 5 MHz-85 MHz upstream pass band. The technology also supports a higher modulation scheme of 64-QAM (and the more efficient 256-QAM, when needed) required by DOCSIS upstream bonded-channel technology.

A key benefit of digital return is that the technology’s strenuous workload is undertaken by an analog-to-digital converter instead of by a laser. This is important, because the required increase in performance is not achieved cost-effectively with the upstream analog lasers found in the industry today. Digital return provides independence from transmitted RF load and required laser performance because the entire bandwidth’s RF load (whether it is one 6-megahertz channel or the full 80-megahertz passband) is digitized, with only a string of 1s and 0s left to be lased. Variations in loading and link distances are dealt with by network engineers.

“Digital-return technology was developed as a tool for cable operators to counter and overcome the shortcomings and limitations found in analog return-path systems. ”

Operators who use today’s advanced generation of digital-return technology have found Fiber Deep to be the optimal architecture for most network upgrades. Fiber Deep’s unique architecture eliminates the need for RF amplifiers, providing a huge cost-savings for operators transitioning their networks to accommodate greater upstream capacity per subscriber. A Fiber Deep architecture also allows increased network availability and improved network performance as well as digitized return transmission technologies to support the transport of both legacy upstream and future Ethernet-based services.

To gain full benefit of this newly freed spectrum with digital-return technology and Fiber Deep architectures, operators need to have proper downstream transmitters. These high-performance transmitters should cover the full spectrum while supporting the network’s evolution to full QAM capabilities, including a seamless migration to future Converged Multiservice Access Platform (CMAP) deployment. These transmitters also help support the process of spectrum reclamation, and they help operators as they utilize the full network spectrum for broadcast and narrowcast services.

As the industry continues to evolve and as technological advancements continue to flourish, operators will continue to find that the upstream capacity of legacy systems simply is not enough to meet the demands of today’s advanced services. By taking advantage of this unchartered territory with the proper tools outlined above, operators will discover a much easier path to conquer the upstream challenge.

John Dahlquist is vice president/Marketing at Aurora Networks. Contact him at [email protected].